texts:
I have been trying to figure out the "right" way to size pads for surface mount components, and I have found some conflicting wisdom floating around the internets.

Lets say I have this hypothetical part that requires two square pads, the centers of which are 15 units apart, and the edge that are 5 units on edge.

This SO post suggests that I should have my copper be the exact size of the pads, and the mask be slightly oversize to account for shrinkage and/or misalignment.  This seems somewhat reasonable, as relative shift/shrink/misalignment can be tolerated.  Under this scenario I might want the the masks to be 6x6 holes with the same center-to-center spacing as the underlying copper.

Conversley, in a different scenario if you were to  oversize the copper to 6x6, you would gain the same tolerance to misalignment,and additionally some extra adhesion holding the pads down.  This approach is suggested in some BGA/QFN packages I have been looking at.  (Example 1) (Example 2) (Example 3)

I realize that there isn't really a "Correct" answer, but what motivates one arrangement verses the other?


texts: Understanding voltage isolation using resistors (555 Timer)

texts:
As I understand, resistors limit current. I also think that resistors allow all voltage to pass through them, but now I am confused. Apparently, the 555 timer in mono stable mode has its output high once the trigger goes low until the voltage on its threshold is 2/3 of the voltage in vcc (stabilized by control). What I don't understand is why the 555 timer only is looking at the voltage given off by C1, and why the voltage coming through R1 from VCC doesn't trigger the threshold itself.

Why is the threshold not activated by the voltage coming through R1? Is the capacitor a 'short circuit,' so it bypasses the threshold?

--edit--
Why does the voltage between VCC and ground not trigger the threshold?


texts: Should an NCP3420 Draw Minimal Current with Only VCC and GND

texts:
I am trying to make a Buck Driver (More Info). While Building up the circuit and testing it seems to draw too much current. The NCP3420 was getting warm.

NCP3420 Datasheet

After Removing it and only connecting the VCC and GND to my bench power supply set to 8v 70ma it goes into cc-mode at about 5.1v. Is it broken?

Also is this the correct orientation?


texts:
I am looking for small size(preferably pcb mount) wifi antenna that is directional, more specifically half sphere coverage area. The product I build stays on the ground and I like utilized antenna that is always looking up.

I looked at several ceramic antenna datasheets but could not see one that fits. What type of antenna I should look at?

UPDATE

Based on the response, I thought I should define the problem differently. I have a working product where there is a wifi on top of the product and there are sensitive analogue circuits below the wifi antenna/module. I occasionally get spikes in my analogue circuit (analog has very high gain, about 5M times) when the module is receiving data (TX is fine). Currently, I slapped a EMI absorber on top of my analog stuff and shipped the product, unfortunately this also reduces my wifi coverage/signal by about 10db. In the next version of the product, I like to replace my omnidirectional antenna with a more directional one and avoid signal loss. Hence the question of perfect half sphere of antenna. Now that I know that is not possible, either I need an antenna that has  a cone shape coverage or more shielding on Analog which I really like to avoid.


texts: Using Piecewise functions for LTSpice behavioural voltages

texts: I'm currently designing an analog signal conditioning circuitry for a sensor in SPICE, but I have little time so instead of creating a macro model for that sensor, I will be using behavioral voltages to mimic the sensor voltage output for that sensor. The only problem is, the calibration curves that I have are two equations (for two different sensing ranges) and I need them combined as one behavioral voltage, which means I'll need to input a piece-wise function.


texts: Do different frequencies have different capabilities?

texts: I read that google was planning on purchasing a spectrum from the Fcc and they were going to use it to transfer data. I was wondering if the value of the frequency affects the data that is being transfered (ex. Higher the frequency the more data you can send)?


texts: How do I amplify a 0-100mV signal to an ADC with a range from 0 to a specific reference voltage?

texts:
Ignoring the issue of noise, I want to amplify a "static" 0-100mV DC signal to the range of the ATmega328P's 10-bit ADC using a specific voltage reference. Let's assume this reference is 4.096V and call it AREF. This gives me 4mV steps and I need a gain of 40.96.

From what I understand so far, an in-amp such as the AD623 could work for this. It has an input range from 150mV below Vs- (GND in my case) to to 1.5V below the positive rail (which is 3.5V in my case, with a 5V Vcc.) My problem is that the the output voltage range on a single supply has a minimum of 10mV. That means that the ADC will see 0V, 4mV and 8mV all as "0." How can this be avoided?

I can only amplify by about 1.22 times more before hitting the rails on the output, so I don't see how a voltage divider on the output would help...

As far as I know, there's no way to raise the ATmega328P ADC's bottom voltage without doing something like differential ADC, which I read requires calibration that sounds relatively difficult.


texts: Connect two computers with USB using two FTDI chips

texts:
I have a very specific problem. I need to communicate between two computers (Intel NUC and a Jetson TX2, both running linux to be specific). I cannot use wireless, and the ethernet ports are occupied by other devices. I need a very simple low bandwidth communication between those two computers.

So my plan is to make a small pcb with two FT232RL chips, and connect them like this:
Computer 1 -> USB -> FT232RL <=> FT232RL <- USB <- Computer 2.
I assume that this would work like a serial port between the computers.

Will this work? Is this a good solution, or is there something better?


texts: I am using a cap discharge welder to weld Stainless steel to a mild steel galv plate.  I know this should not work but I have managed to get the parts to "stick" enough so I can bowl feed them to a final assembly.  My question is how do I measure the resistance between the electrodes so I can accurately track the differences between the parts. I am getting differing results when welding because the parts are different in their density so the resistance will differ between the electrodes.  I can us a scope for the voltage but not sure a multi meter will be accurate enough to give significant results.


texts: Splitting the voltage from a lipo battery to 5 outputs

texts:
So I'm a bit confused and hopefully I explain my question well.
Let's say I have a LiPo battery at 20v and I need to supply power to 5 different components. My initial thought is just to just create a voltage rail type of thing and have 5 wires coming out of that.

Is that a good idea or is there a better way to do this?
How do I calculate the voltage and current that would be given to each component?

Below is an idea of my voltage rail. Just a simple wire that expands to 5 other wires to connect to my components.


texts: A delta function like response for voltage in to voltage out

texts:
I was wondering if anyone knew of a simple circuit design that would output "high" only for a certain voltage (within a small degree of error).

Thanks in advance!


texts: Cutoff frequency of passive RC integrator used to measure magnetic flux density

texts:
Note: this is part of a larger question which I was asked to separate into subquestions.
Other subquestions: 1 and 2

I am using a passive RC integrator to measure the induced magnetic flux density in a toroidal transformer made of Nanoperm (additional datasheets here and here). This method is outlined here but involves using an op-amp integrator rather than a passive one. (I tried building the active one but it was giving me issues.)

The circuit diagram of my proposed circuit is given below:

simulate this circuit – Schematic created using CircuitLab

The signal generator is connected to an audio amplifier capable of driving large currents. I'm driving the transformer with sinusoidal signals at 50 Hz, 350 Hz, and 380 Hz, and I had initially set R2 to be 5 kOhms. According to comments on the previous larger question I had posted, this value of R2 is too small (cutoff frequency is too high). I increased R2 to 10 kOhms, 27 kOhms, and 37 kOhms. The table below  summarizes the cutoff frequencies and gains for input frequencies of 350 and 50 Hz, which were used in these experiments:

The first subplot in the two figures below show hysteresis loops measured at an input frequency of 50 Hz and 380 Hz for R2 = 37 kOhm. (I tried additional input frequencies and values of R2, and details of my complete experiment can be found in my original question.) Additionally, the raw voltages VM1 (V(R1)) and VM2 (V(C2)) are plotted in the second and third subplots, and the Fourier transform of V(C2) is plotted in the fourth subplot.

While my results look slightly better after changing R2, they still do not match the results reported on the datasheets. (Q1) It is unclear to me why we increase rather than decrease R2 because the cutoff frequency of the filter only gets smaller as we increase the resistance. If someone could clarify for me why this is helpful, I would appreciate it. (I understand that the higher the resistance, the lower the cutoff frequency; and the lower the cutoff frequency, the greater the window of integration since (1) the time constant gets larger and (2) a larger time constant implies a larger window over which the signal is smoothed, which is what is required for only lower frequencies to be passed. I'm just not sure why reducing the gain of the frequency of interest, which is much higher than the cutoffs tabulated below, is a good thing in this case.) (Q2) Furthermore, is it even reasonable to use any gain other than 1 unless we compensate for it when we calculate the field strength and/or flux density from the measured voltages?


texts: How to choose a output cap for a 5v buck converter

texts: I am designing a 5v buck converter as a side project, what kind of output capacitor should I choose?


texts: Questions about CNY70 Reflective Optical Sensor datasheet

texts:
I am using the CNY70 for a project, but i need information from the datasheet. In Figure 11, which i have added below, the relative collector current, \$I_{Crel}\$, is shown versus the displacement, s, for six different distances, d.

As i understand, d is a measure for the distance between the reflective sensors emitter and the reflective surface, as shown in the image in the upper right corner of fig. 11. But i can't seem to find a description of the displacement s. From the image, it seems as if the displacement s, is the distance from the center of the CNY70 to some surface perpendicular to the reflective surface. But that does not make any sense at all.

I hope I have provided enough information. Thanks in advance.
Sorry if i left something out, i am new here and in the field of electrical engineering.


texts:
I am trying to subtract one 8 bit number from another but I keep getting an error that "<=" is unexpected. The rest of it I am just AND-ing the 8th bit of each output. Can someone tell me what is wrong with my code?

module test(n1,n2,n3,z);

input [7:0] n1,n2,n3;

output [7:0] z;

wire [7:0] x1, x2;

x1 <= n1 - n2;

x2 <= n3 - n2;

and and1(z, x1[7],x2[7]);

endmodule


texts:
We have a project where we need to weigh product material for selling to customers. This is a project installed in Europe.

This is an industrial product line performing material manufacturing, preparation & packaging. At the final step of the packaging, the product is weight using a load cell scale, information is read by PLC and then the PLC produces a label which is printed out and then applied to the packaged product.

INTRODUCTION

Our general understanding is that: "In all commercial application where product is sold by weight, it is a legal requirement that weighing equipment must be verified as legal-for-trade".

To go through a legal-for-trade process, the weighing system has to be approved by an "approved qualifier".

To make sure to obtain that approval, care must be done to have proper certifiable components for a trade application. Components that detect tilting for instance or that verify standstill, etc.
If a trade approved unit undergoes any alteration or repair, it does require re-verification for the approval to remain valid.
One additionnal concerns is tampering, so that the "approved qualifier" can ensure no tampering happens.

PROBLEM AT HAND

The weighing electronics can be locked-down with a password set by approver or with a seal.

Given how the PLC is involved in the weighing loop (getting data and printing the label), the PLC software cannot be locked-down as it will prevent troubleshooting and adjustment of the entire manufacturing line. How can an "approved qualifier" ensures and certifies legal-for-trade of the system?

What are common strategies employed in such industrial legal-for-trade application?

Would it be required to have dedicated hardware from weighing to printer without involvment of the PLC in the loop? This would require interfacing multiple components from various manufacturers together, the most difficult beeing the interface between the weighing electronics and the label printer; that seems most likely to fail!

Is there something I am missing?


texts: How to select resistance to cancel offset output voltage due to bias current?

texts:
Consider the figure above how Rcomp was choosen. I know for simpler circuits
like inverting amplifier and ideal integrator how Rcomp was calculated but following same procedure (that's using superposition principle for Ip and In and then convert to Ibias and Ioffset) here gives a time variant equation of single time constant circuit I don't know how one can cancel offset due to Bias current in such equation.


texts: Does Analog Comparator mean Voltage Comparator?

texts:
I was asked to define what an Analog Comparator was.

After doing research, it seems to me that Analog Comparator is the same as a Voltage Comparator.

Is this true?


texts: Is it possible to implement a host on stm32 (without hardware support) with only the program code to write data to the USB flash drive? I did not find any information on the Internet on this issue. There is an implementation device, but not a host. I'm studying the usb specification for the answer, but I still do not understand well her.


texts: OpAmp Buffer configuration with max allowed output

texts:
I'm designing a circuit, and a section of it is as follows:

simulate this circuit – Schematic created using CircuitLab

What circuit can i use to allow OA1 to follow the Non-inverting input from 0 to 5V exactly, and anything above 5V in the input remains 5V on the output?

(i thought of using 2 resistors or a trimmer to reduce voltage on the input, but i have no use of the 5-10V range, and i want to use the full 0-5V range on the output)

(the 0-10V input is not available for redesign, the OA2 doesn't exists, but i placed it there to signify a high impedance circuit after the output.)

Note: I'm trying to be accurate, i could use a resistor+zener diode on the Output to limit to the closer commercial value for zeners eg. 5.6V, but there must be a better and more precise way to do this..


texts:
I have a THS3491 Op amp, and want to use non-inverting configuration.

Reading through the datasheet, all the specs are defined with \$R_L=100\Omega\$.
So, does this mean I have to attache \$ 49.9\Omega \$ resistor in SERIES with \$ 50\Omega\$ load (Oscilloscope, for example) to match impedance? Just like above image?
If I do that, then the output voltage will be halved, so I got worried about the maximum output I can get.
Reading again the datasheet, I found in the page 1, output voltage swing is \$28V_{p-p}\$ at \$\pm 16V \$ supply and \$R_L=100\Omega\$
(I am still not sure about the maximum voltage I can get. Is "output voltage swing" parameter I should be interested? or "input/output voltage range" parameter? (below table) )

If \$28V_{p-p}\$ is only output I could get with \$R_L=100\Omega\$, then at the end, the oscilloscope will read only \$14V_{p-p}\$. Is this correct?
In summary, I have three questions.

To use THS3491 op amp with noninverting configuration, do I have to put \$ 49.9\Omega \$ resistor in SERIES with \$ 50\Omega\$ load?

If I want to know maximum output voltage of THS3491 op amp, what is the parameter? "output voltage swing"? or "input/output voltage range"?

If I use \$ 49.9\Omega \$ resistor in SERIES with \$ 50\Omega\$-load oscilloscope, only \$14V_{p-p}\$ will be observed, is this correct?


texts: How to build a DC amplifier using opa552

texts: I am working on a project which requires me to amplify a dc supply volatge of 2v to 20v. I used the opa552 op amp with an input resistance of 100 ohms and a feedback resistance of 1k ohm (i.e., Rf/Rin = 10 is the gain). However I wasn't successful in getting the output of 20v with a single supply Vcc of 25v. The opa552  is designed to take supply voltages up to -30v to +30v. Basically am looking to amplify a dc supply voltage range of 0-5v to 0-30v. Please help


texts:
I need to control a Half H-Bridge circuit to move a DC motor on both clkwise and ctrclkwise directions. I've tested the following circuit:

It worked as it was supposed to: when the digital input signal (OUT_COM (L)) is LOW, Q5 and M5 are off but M6 is on, so there is GND in the pin OUT_COM (H), which is connected to one of the motor's pin; when the input is HIGH, Q5 and M5 are on while M6 is off, so there is VCC in the output. It works fine when the input is HIGH and the ID current in M5 is just a bit bigger then the current that the motor drains (around 100mA). The problem happens when the input is LOW, because while the M6 ID current is normal (100mA), the ID current in M5 (that was suppost to be 0 at this moment) goes pretty high to around 400mA. I think this is happenning because M5 might not be fully off when the input is LOW because R20 is to big (10k), although I'm not sure if thats the reason because the gate current should be tiny, causing a low voltage drop in the resistor.
Does someone know if R20 is the problem or if there is any other issue in the circuit?
UPDATE
R20 was the problem. Because of the current drained by the mosfet's gates, the voltage drop in R20 is to high for deactivating M5 when the input is off, so it stays on and the source is shorted.


texts: What does it mean by, "No voltage is applied"?

texts:
I've a very basic query.
If a question says, "no voltage is applied to the circuit" does it mean the battery is replaced by short-circuit (since, no voltage => 0V) or by an open-circuit (literally, no battery is connected across the terminals of the circuit)?


texts: Replace fixed to variable potentiometer on DC regulator

texts:
I recently bought a DC regulator (power supply and tester.)
It is a 15V and 2A power supply with voltage fixed to 1.5V, 3.6V, 4.8V, 6.0V, 7.2V direct output of the sub-grade and the current is adjustable from 0.6 to 2A. It also has potentiometers for fine voltage and coarse voltage, but I do not get any difference when it is connected to a multimeter. I rotated the coarse and fine potentiometers but the output didn't change, not even when I connect it to other electronics.
Is it possible to change the potentiometer from fixed to variable?


texts: Can a voltage regulator work below minimum Vin?

texts: I am have a bluetooth speaker that is powered by a single 18650 battery. It can only handle 6V input to the PCB. I want to add one or two more 18650's. I have a bunch of different voltage regulator IC's that are transistor shaped. I was thinking of using a LM7805 regulator to cut the voltage down to 5.0V. It says that the minimum voltage input voltage is 5V and maximum is 18V. If I were to use this, would it shut off as soon as the total voltage of the batteries drops below 5V?


texts:
I'm designing a custom current limiting circuit designed for electric bikes and small electric vehicles. It's purpose is to limit battery current to "dumb" motor controllers so that you can maximize life cycle of your battery. My problem is the moment any output, such as the heater circuit, charger circuit, or especially the main output circuit is active they send EMI throughout the entire circuit. This of course cause a lot of problems such as PLL out of lock on my micro and noise on my analog inputs. I've tried isolating parts of the circuit, and adding 0.1uF low ESR, low ESL caps all around the circuit with little to no improvement. I've tried using a crude snubber on my mosefets with no change in the amount of switching noise in the system. I've tried adding a 100 ohm resistor to the bootstrap input of my mosfet driver and that helped a tiny bit.
My question is, what else could I try to solve this. I know my board layout is far from ideal, but I didn't think it would be that big of a problem. Like I said before, I've tried isolating parts of the 5V rail with no change in the amount of noise showing up. The voltage spikes are about 250ns rise time, the same as my gate rise time, and the amplitude is about 0.2V, enough to trip the PLL out of lock system in the micro. (dsPIC30F3011) I can connect my scope probe's ground in a loop and place it next to the circuit and it picks it up with some ringing at about 2.6mhz
KiCad schematics and board layout can be found on my github. https://github.com/RingingResonance/EV-Battery-Controller/blob/master/BTMSv3.zip


texts: Mechanical Switch with electronic trigger/gate

texts:
There are any part in market that consists in a mechanical Switch which can be turn ON or OFF by a person, and by a electronic? Something like a real switch with a tiny servo inside to push on or off?
My main porpouse is to avoid relay that consume some current and mosfet as well.
Need to deal good amount of current in AC


texts:
i found Rth to be 4kohms but i cannot seem to figure out Vth
i short circuited the voltages sources and open circuited the current source to get Rth.


texts: What is the underlying mechanism behind RO or WO and WR registers?

texts:
In embedded systems you have read only and write only registers. How are the two type distinguished in the produced netlist?

How one builds a flop which you can only write to and not read from?


texts: Why does this transformer have an additional winding on the side of the core?

texts:
This photograph is of a wire feed welder. This unit consists of a step-down transformer with a bunch of taps on the primary side. It is fed from 115 Volt 60 hz supply. The switch on the left allows the selection of the tap on the primary side.

The output side is an unusual arrangement. The device on the right appears to be two SCRs, connected to the AC output of the transformer. The trigger wires lead back to the circuit board on the left side. One output of the SCR arrangement leads to the ground clamp, but the other leads to an additional winding on the core of the transformer. This then passes through an under-rated relay and out to the wire feed apparatus.

What purpose does this additional winding serve? Unlike some transformers used in welders, this one has no shunts in the core to cause leakage inductance. My guess is that the SCR arrangment is used to vary the output of the duty cycle to provide a Constant-Voltage power source for wire feed welding. What I can't understand is why this additional winding is needed on the core of the transformer. Some welders use an additional inductor on the output, but that only applies to DC welders. Also, it is usually isolated from the main transformer core.


texts:
My ultimate goal is to measure how many Amps are drained from my battery UPS with an Arduino chip. The circuit should be ready for up to 1kW loads creating currents of about 50A.

Consider the following circuit:

Link to circuit simulator

In that circuit I have a 24 V battery (2 x 12V in series actually). The 0.6 Ohm resistor simulates a 1kW load.

I want to measure how many Amps flow in the circuit, by measuring the voltage drop over a 1 mOhm shunt.

In the linked example you can see that there is a 41.6 mV drop. That is way to little for Arduino, which measures 0-5V as a 10 bit number, so there are only 1024 steps between 0 and 5V.

I therefore plugged in an Op Amp with 1 mega Ohm and 10 kOhm resistors, which should give me a 100x amplification.

On the top voltmeter I do indeed see a 4.16V, so it seems to work.

I am just learning the basics of how Op Amps work and my question is:

Is this a valid approach? Is the Op Amp wired correctly?


texts: Principle of operation of a Panasonic e-bike torque sensor

texts:
Question: What is the principle of operation of the e-bike torsion sensor used in Panasonic drives from the early 2000s.
I have a ten year-old Kalkhoff bike with a Panasonic motor system. The system uses a torque sensor between the pedal crank and the chain wheel to detect the rider's input and in normal mode of operation it will match the rider's effort and so double the effective drive through the chain to the rear wheel. This gives a very natural control to the bike as there is no throttle, etc.
The electronics are dying so I have removed the control board and replaced it with a cheap JY01 based BLDC control board controlled by a 0 to 5 V analogue voltage from a potentiometer. I now want to generate the 0 - 5 V signal from the torque sensor.

Figure 1. The pedal crank is cyan, the chain wheel drive is blue(-ish) and the connection between the two is the pink torsion tube containing some engraved stripes (marked "indicator"). The torsion tube is connected to the crank at the left end and to the chain ring at the right end. The torsion sensor coils are used to monitor the deflection of the indicator. Image source: Kalkhoff USA.

Figure 2. The indicator (right) and the dual coil (left). Image source: flecc.

Figure 3. The torsion sensor coils are 75 &Omega and share a common terminal. Image source: flecc.

simulate this circuit – Schematic created using CircuitLab
Figure 4. (Left) Test circuit for oscilloscope and (right) circuit used by RoboDurden on his OpenEBike hack. (Lots of shaky videos.) He gets enough of a change in DC level to detect torque.
I've hooked up a squarewave generator as shown in Figure 4 (left). The 75 Ω coil pulls the voltage down to about 2 V and I can get a 100 mV or so on the secondary. Monitoring both on the oscilloscope I am unable to detect any change in signal amplitude, phase relative to the source or shape when applying torque manually on the bench. (I lock the chainwheel and apply as much body weight as I can to the crank.)
Does anyone know the principle of operation of the indicator / torsion sensor coil arrangement? I've never come across anything quite like it so I'm at a loss to know how to debug the arrangement which is the first step in the design of a circuit to monitor the torque.
Mine looks like a heavy foil etched with a pattern similar to that of Figure 1 but with each of the stripes broken into three shorter segments. I'll get a better photo when I have it apart this weekend.

Update 1.

Figure 5. Close up of the Panasonic indicator. Notice that it appears to be a label stuck to the shaft with a small gap on the "join". The slots seem to be cut right through the foil.
I have hooked up the original electronics to measure the voltages used on the coils. It seems to be a 12 V, 16 kHz squarewave (all positive) but I can't detect any change in phase or voltage on either coil using my oscilloscope. One possibility I have considered is that the indicator label has come unstuck and is sliding on the shaft. Inspection suggests that this is not the case. More tomorrow ...
Meanwhile Marko Buršič appears to have correctly identified the system as a torductor and the comments below suggest that the principal of operation is magnetorestricion.


texts:
Ok so I am revising some transistors and I came across using BJT as a switch, so I decided to design a simple circuit to control an LED. I want someone to kindly check the steps that I followed and offer any suggestion, corrections or improvements that can be made.

The LED needs 20mA for full brightness and at that current has a forward voltage drop of 2.0V. The transistor I am using, 2N3904 has a saturation voltage of 0.2V. Also, I am using a 5V supply. So the collector resistor comes out to be Rc=(5-2-0.2)/(20*10^-3) = 140Ohm.

Now the minimum Hfe specified on the datasheet of the 2N3904 is 30, so I used that to find the base current as Ib = 20/30 = 666uA. Assuming Vbe of 0.7 volt, the base resistor can be found to be Rb = 6456Ohm. I can use the closest 6.2k.

Below is a schematic of the circuit I made in proteus, along with the simulated values of collector current and voltage.


texts:
I would like to make a switch which will be able to switch on/off 12-60V low current devices using nRF52840, optocoupler and mosfet.

I found this schematic and my idea was just to adjust R1 because voltage of GPIO of nRF52840 is 3.3v. I realized that source current of GPIO might not be enough to run optocoupler so I decided to look for low input current optocoupler. I found VO618A and my questions is would it be fine if I just switch PS2801 with VO618A and adjust R1? (I don’t have many experience with electrical engineering experience so any guidance/help is welcomed)


texts: 1200 Baud Rate UART at a 9kHz clock speed

texts:
I just did the math and with the internal clock of the ATMega328.  The lowest clock frequency that you could use to have a 1200 Baud rate is 9.6kHz.

Unfortunately I need to be under 9kHz.

Is there any micro that can drive a 1200 Baud rate at 9.000kHz?


texts:
I am currently working on a project with LoRaWAN technology using STM32F103C8T6 microcontroller. For LoRa I am using SPI in Full-Duplex Master mode (spi1 specifically) and in CubeIDE when you activate SPI1, automatically pins PA5, PA6 and PA7 are activated (ver1):

However, PCB is designed and printed and those pins are unfortunately busy. Because, before it was planned to use other SPI1 pins (PB3, PB4, PB5) (ver2):

So, when I use ver1, all is good, LoRa connects to server and sends data without a problem. However, when I use ver2, it does not work at all. I debugged to find where is problem and found out that, SPI read fails (when version of LoRa is read, it returns 0). Thus, ASSERT fires and code is stuck in infinite loop. I could not find any reference of difference of SPI pins in the internet.

Can anyone explain the difference of these pins? And is it possible to use ver2? Thanks beforehand.

P.S. I am using HAL Library + LMIC library (for LoRa) and the configuration of SPI are the same for both ver1 and ver2. Here is code of configuration, if needed:

void MX_SPI1_Init(void)
{

  hspi1.Instance = SPI1;
  hspi1.Init.Mode = SPI_MODE_MASTER;
  hspi1.Init.Direction = SPI_DIRECTION_2LINES;
  hspi1.Init.DataSize = SPI_DATASIZE_8BIT;
  hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
  hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;
  hspi1.Init.NSS = SPI_NSS_SOFT;
  hspi1.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_64;
  hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
  hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
  hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
  hspi1.Init.CRCPolynomial = 10;
  if (HAL_SPI_Init(&hspi1) != HAL_OK)
  {
    Error_Handler();
  }

}


texts:
I'm trying to build an LED chaser circuit using a 555 timer and a 4017 counter. I've built the circuit successfully on a breadboard, but now that I tried to create a soldered version it just does not work.

On my breadboard version I can observe the clock signal coming out of pin 3 just by measuring the voltage there and I see a proper oscillation. On my soldered circuit there is 0V respective to ground, and no oscillation.

I compared the voltage on all pins of the 555 in my working and my non-working circuit, and the difference I found is that I see no voltage on pins 2,6 and 7 to ground.

How can I identify the problem now? Could I have damaged the resistor, the potentiometer or the capacitors by causing too much heat during soldering (I use sockets for the ICs, so they can't be affected by the soldering)? If that is a possible problem how would I check if a component is damaged?

I checked the soldering joints and resoldered any that looked suspicious. Should I resolder every connection, or is there a way to locate the potential bad soldering joints?

This is the schematic of my circuit, pin 3 goes to the 4017 timer which I omitted from the diagram.

simulate this circuit – Schematic created using CircuitLab


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I want to check whether I understand correctly:

Real-time means an action always performs in a specified amount of time and is never late for deadline - an upper bound, and sometimes a lower bound as well. If a system is real time, its execution time must always be deterministic.
To achieve real-time behavior, both hardware and software must be designed to satisfy the above constraint. Not all hardware comonents are real time, for example, the internet, and a real-time network is a network in which every node and connection behaves in real-time. Are there any other examples of non-realtime hardware?
When a hardware component is real-time, software that controls the hardware must be designed to do so. For this reason, we have to use low level language like assembly and C (i.e add instruction always takes 1 ms) to have tight control of execution time of every instruction.
We can achieve real-time behavior on non-realtime OS like Linux if we write software as if we are writing a realtime software: we can control the execution time of software. However, because desktop OS is non-deterministic (for flexibility), even if we run software designed for realtime execution in it, there's no guarantee that the software executes in realtime. In this situation, we call the software soft-realtimme.

Do I understand correctly?


texts: Entry level books/magazines/software/websites for a beginner

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A bit of background: I have a masters in engineering, mostly electronics. That was years ago however, and I've been working in finance since college. I've learned a great deal of programming as a part of my job, but when I was a kid, I always thought I'd one day learn how the insides of electronics worked. These days though, the easiest form of "designing something cool to play with" is done by programming, so I never really got into electronics design.

I do recall I made a radio back in Uni, and we designed a simple CPU using Cadence as well. Of course I'm not fresh on the details of how that works, though I believe I still have my semiconductor physics books somewhere.

What are some interesting projects I can start with building? What kind of books/magazines/software/websites do you guys recommend? What kind of tools would I need?

My partners and I are going to be building a car later this year. I was wondering if that's the kind of thing people on this board get involved in? What about things that interface with a computer? Home equipment?


texts: I am looking for a latching relay motor start and stop circuit

texts: I have some past electronics education but have not used in over 30 years.  I am trying to make  a circuit which uses two normally open tact switches and a dpdt single coil latching relay.  I have a circuit that one button is forward and the second reverses the motor.  When I wired it up it would start in one direction and stop with the press of the second switch,  which actually works great for my need.  The problem is I cannot find the mistake I made when wiring it that allowed it to stop instead of reversing.  I actually want to replicate the mistake (I have tried to trace the circuit and cannot find the problem, but it works just right for my device), or find a similar circuit that will allow me to push one button,  the motor starts and continues until the second switch is pressed and then stops. Any suggestions would be helpful as my knowledge is very rusty and I thought the circuit I had would work.  I am on a tight constraint as a client has decided on an electrical or electronic configuration for a project that originally was supposed to be manual. Greatly appreciate any help.


texts: Power Latching Relay off/on in response to 12V ignition and 1 second ground pulse

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I have the following sample schematic of a 12 volt automotive circuit to trigger about 60 seconds of power output to a latching relay on output pin 3 of the 555 Timer chip.

The schematic below is a just a sample and not the final circuit.  The 12 volt automotive battery is driving the circuit.  It requires 2 different types of input to the 555 Timer.

Inputs:

1) 1 second ground pulse coming from various Viper alarm outputs.  It is a floating Viper model-5906V (-) 200mA 1 second OUTPUT. (This input should turn the relay on for 60 seconds, once it sees ground.)

2) Turning the 12 volt ignition on should turn on the relay (set) and leave on as long as the ignition is on.

3) Turning the 12 volt ignition off should trigger the 555 Timer.  After 60 seconds the relay should turn off (reset).

4) Ideally if the ignition turns off and it has been 50 seconds (relay is still ON) and then the Viper alarm sends a 1 second ground pulse on the input, it should wait 60 seconds from the last input received.  I am not sure this is possible however without adding a 2nd 555 Timer to the mix.

The 555 Timer needs to be configured to turn on (set) the 12V Hella Latch Relay (Hella 933364027), specs are here: http://hellahd.com/index.php/default/electrics/relays/micro-iso-relays/electrics-product-12/ , when either of the above inputs are triggered.  The relay should turn off (reset) after the 60 second Timer output expires, this should expire 60 seconds after the last ground pulse from the alarm trigger, or 60 seconds after the ignition is turned off, whichever is later.

The circuit is used to supply power thru the latching relay to power assessories after the ignition is off for 60 seconds, with a provision to allow for remote controlled activation via the alarm's 1 second ground pulse.

Need assitance in getting the outputs to fire the latching relay contacts briefly with the above timing.  Currently the output signal to the Set (pin 1) contact is working but when I try to use that to power a transistor as in the example to the Reset (pin 2) it does not turn the transistor on.

How does this circuit need to be modified to set and reset the latching relay?


texts: Can 8051 pins work as inputs or outputs at the same time in a program?

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I have confusion in assigning ports as input or outputs in 8051 microcontroller.

As I have done programming with atmel atmega16 and variants we clearly have DDR registers to assign ports as inputs or outputs but not both in same program(or it might be both since I dont know if it can).

If it can be both(i/p and o/p) how would the microcontroller does this?

In a program while interfacing a 16x2 LCD with 8051 the P1.0 is used as input to find the value as busy flag and is used as an output pin when sending commands and data.

Please provide explanations.

Thakyou


texts: Would an audio signal be degraded by adding a 0.45 ohm resistor?

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I have a pair of expensive in-ear monitors (earbuds). Each side utilizes six balanced-armature drivers and a passive crossover.

The right side is quieter than the left side. The headphone wires are detachable, so measuring across the mini coaxial port where the headphones connect to the cable, the right side's internal resistance is 15.60 ohms while the left side is 15.16 ohms. This imbalance in impedance might explain the imbalance in volume between each side. In Windows and Android software I can choose to increase the volume of the quieter right side. I have to increase the software's volume slider by 6dB in order for both sides to feel balanced.

Normal headphones have matching impedance on both sides. Something inside the right side is causing an increase in impedance and all the solder joints still seem solid, so I think the issue may be something internal to one of the six drivers. The 6dB difference is simply what the audio-control software in Windows and Android say I need. It is not actually the difference measured at the audio ports of the headphones.

You can see photos here:

Photos of Internals

Would I be able to take a headphone cable and on the left side solder a 0.45 ohm resistor inline to balance out the impedance of both sides, and thus fix the volume balance issue?

Would adding a resistor affect the quality of the analog signal reaching the drivers? Would it change the phase or timing of the signal, causing weird imbalances in the music coming out of the headphones?


texts:
I'm controlling a 12v RGB LED strip from an Arduino Mega following the tutorial here

I'm controlling with 3 pots via the Mega's ADC >> PWM value written out using analogWrite(LED_PIN) & everything works fine or so I thought!

In addition I have 3 servo motors that are also controlled by another 3 pots these also worked well when tested without the LED driver attached. As soon as I wire up the LED driver there is a crazy amount of noise generated that feeds back into the servo control that manifests as random jittering of the servos.

I have tried putting a number of different capacitors (basically whatever I could find in the cupboard) across the 12v - ground rails. Which do seem to filter out the higher harmonics of the noise but to get the noise (and the servo jitter) to disappear I lose servo response to their control pots.

I've also tried a couple of moving average algorithms in software whilst they do have an effect they by no means filter out enough of the noise.

So is there a way of filtering out this noise without compromising the servo control?


texts: A low latency wireless communication link

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At this moment I'm working on a wireless charging system where feebback (error for PI controllers) is being send by the nrf24l01 modules. I have implemented 2kHz communication link.
Can anyone suggest any modules where I can send 6-8 bytes with low latency and with the packets frequency 5-10kHz (200us delay) or more?
I was playing with WiFi and BlueTooth but with a the structure of protocol I can not make transmittion with a fixed period.


texts: Why does this circuit keep killing my 555 timers?

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I have a 555 timer set up in a standard monostable oscillator configuration. Nothing fancy, no modifications whatsoever. I'm driving it with about 12V. If I trigger the 555 with the ground directly, everything works as planned. However. if I connect the collector of a transistor to pin 2, the emitter of that transistor to ground, and the base to a positive pulse, the 555 triggers, but then it quickly overheats and dies.

Of note, the circuit triggered by the number 3 pin is an RC circuit where C=940uf and R=10k, and when the timer switches off, pin 3 drains this fairly large capacitor. However, with a 9V battery, there's no overheating, and no dead chip. The overheating only happens with 12V, which I'm getting from a hobby power supply normally used for a train. My meter reads ~11.5V on the supply.

Why is my 555 chip overheating and burning out? Everything looks within specs, and it doesn't happen if I use a 9V battery.


texts: Resonant Circuits do all capacitors count towards resonant frequency?

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I am trying to design a variable frequency oscillator for use in a superheterodyne FM receiver and have been reading First Steps in Radio (http://www.arrl.org/first-steps-in-radio). In this example a varactor diode (D1) is being used as a variable-voltage capacitor to vary the resonant frequency of the circuit. I am having trouble understanding which capacitors in the overall circuit would be used in the resonance equation.

Of course C1 and D1 would be included but what about C2? or C3. The same goes for calculating the bandwidth using the following equation.

What resistances do I use.

Any sources to help me in understanding circuit design and to answer questions like these would be useful.


texts: What frequency is Ferrite Bead reactance usually given at?

texts:
I've noticed on schematics at work, when I was at uni, and on datasheets that Ferrite Beads usually (90% of the time) are only given with their designator (FB? or L?), then the reactance (XOhms) and the current rating (1.5A for example).

However, their reactance is obviously a function of frequency (and ideally, it would always be stated "XOhms @ 100MHz" etc.). However, this isn't really the case.

So I was wondering, from any super experienced Electronic Engineers, what frequency for a Ferrite Bead is the reactance "typically" (rule of thumb) given at?


texts: Low voltage GPU decoupling capacitor longevity

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Recently noticed my GPU card (Nvidia 1060) made more coil noise (electrical noise, noise level proportional to frame rate) than usual. I discovered that directly behind the GPU chip one of 2 big 470uF, 2 volt capacitors had broken off. I just received 3 replacements (EEF-HX0E471R4).
But it got me thinking about the noise I heard and the remaining capacitor. Should I change the other capacitor also?
The voltage ripple must be bigger with the loss of capacitance, but can the system be designed such that a loss of capacitance can start a domino like degradation of the rest of the capacitors? (I am an EE, and of course I have to overthink it, but I have little experience with ~2 GHz digital design)


texts: A weird question about the cutoff point of an RC low pass filter

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I have read the linked explanation about the RC low pass filter circuit and understood most of it. I understand the relation between the time constant RC to 1/(2*pi*f_c). I understand it means there is a trade off between the size of the time constant and the capacitor cutoff frequency point. I understand this point determines the "Phase shift" size etc. But to be honest, nothing of it is making sense. I'll try to state a question here that should help me clarify "what did I miss here..."

So, my question is:

  The Bode diagram shows the capacitor properties for each frequency. i.e the relation Vout/Vin (log of it times 20 but this doesn't matter to me here..).
  But, if I apply a step function say at time t_0. Then, at this exact time, all frequencies are given. So, at this exact time, the capacitor should have all the properties of all frequencies. So Vout/Vin should get an infinite number of values at the exact time t_0. So, How does this make sense? Shouldn't the capacitor have one behavior for each point of time?

I really hope my question is making any sense for you.

Thanks!


texts: How to calibrate current transformer such as SCT-013 without having to actually generate the actual current?

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I have a current transformer like this one but is rated at lower Ampere rating (30A/1V). I would like verify how accurate its reading is. I will be using it read the current consumption on a 220V mains line

Is there some way to verify its reading without actually having to generate the Ampere on a line. I do not own an AC bench supply that can generate that amount of power. Even the lowest rating that I can buy for this transformer is 10A that is still a lot of power to generate.

I hope that going further after changing the burden resistor built in, I will be able to confirm the reading is accurate to at least 1%. All equipment I have access to is a DC bench power supply, multimeter, digital oscilloscope, and a function generator. Is there some way to validate its reading?


texts:
I'm working with a colleague to digitally control an old peristaltic pump using a digital potentiometer. The existing pump controller has a mechanical potentiometer and we are trying to replace it with an MCP4131-103.

Can anyone lend some insight on the types of questions we should be asking before doing a direct replacement? We have already burned a couple and I suspect we are wiring it incorrectly or using an under-rated IC. One measurement we already have is that the voltage across the A-B of the mechanical pot during operation is about 10V (from ground, I think I measured -40V on A and -50V on B, if that matters). Is that too much for this IC? Can anyone provide some pointers on how to proceed? Is there a better way to replace a mechanical pot than with a digital pot to allow for programmatic control?

Thanks in advance for the help provided. If I need to provide clearer details, please tell me some measurements/observations I can make about the current setup.


texts: FCC vs CENELEC-B band for IoT application using PLC

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I have done some research on the topic but I have not found any conclusive evidence. I want to design a system where I use the existing cabling inside a building to communicate with various IOT devices using PLC.

I need to make a choice between these two frequency bands; the preferred constraint is distance and robustness (as low noise as possible). Do power lines have a high impedance at higher or low frequencies.

CENELEC-B ranges from 98.44kHz to 121.88kHz
and FCC ranges from 154.68kHz to 487.50kHz

Any help is apresisted.

Bonous question and answer:

For G3 (not prime) how many sub-carriers are CENELEC-B and in the FCC band.

CENELEC-B has 16 sub-carriers and FCC has 72 sub-carriers.


texts: Digital out, output low voltage, no load

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I'm controlling a home-built current regulator, using a PIC microcontroller (PIC12F1572).

The regulator is implemented using an op-amp and mosfet, and works well. The input to the regulator is a voltage 0V to 0.25V, with zero corresponding to 0A and 0.25V corresponding to 0.5A.

I'm thinking of controlling the current regulator directly from the PIC, by having a resistor based voltage divider connected to an output pin on the PIC, to yield between ~0V and 0.25V.

According to the datasheet for the PIC, the output low is guaranteed to be at most 0.6V. With my voltage divider, this means ~0.03V to the current regulator, or approx 60mA out.

However, I want it to be able to shut off completely.

The output low quoted in the datasheet is valid at 8mA, so when (practically) unloaded, it should give lower voltage.

Do I dare assume that the output low voltage will always be very close to zero in practice under these conditions? Or am I inviting trouble?


texts:
As I have to make driver for this matrix module, I have a big problem finding its schematic or datasheet. There are many similar modules on the internet, they are made in China. I'm making driver on our hardware engineer assumption, and its going very slow.

Anyone have any documents or worked with this type of modules?

Here is a picture:


texts: Voltage controlled switch always closed in simulation

texts:
simulate this circuit – Schematic created using CircuitLab

I have made the above (useless) schematic in LTspice. This after running into issues with a full schematic. The idea is to let e pulse train pass to the 2nd voltage controlled switch if and only if the Condensator connected to the positive input of SW1 reaches at least a voltage of 1.5V

However, this did not seem to work so in a test case I connected SW1 both the positive and negative input to ground. (Which to my knowledge should make SW1 always open). I have just a few days of experience with LTspice so it might be that I'm missing something. I have however googled and this seemed to be the right way to do it.

The full schematic in LTspice is given below

This results in next simulation:

Does anybody know what I'm doing wrong? S1(SW2) is the MYSW and S2(SW1) is the UCSW. I can't seem to get it to work even if I change Vt to 15V.


texts: What does worst-case gate capacitance mean in a MOS transistor?

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I have searched the statement; MOS worst-case gate capacitance in various forms but no avail.

Keep in mind I'm a student. The course I am taking has no reference material. With note slides with pictures and formulas.

The only "formulas" that are provided for gate capacitance are:

There is no text on what does a worst case gate capacitance per unit area means. Yet there is a homework question on it. There was no mention of it in class.

What does it mean? And how do you judge it is worst-case?


texts: Measured my PCB with Handheld LCR Meter - can you tell me anything?

texts:
This is a 5x4cm 8-layer PCB. It has 2 sets of dedicated VCC/GND planes plus ground plane polygons on top and bottom. It is not high speed. The top digital speed is 1Mhz SPI. It has 3 micros running on their internal oscillators. However, I have noise (spikes, overshoot and undershoot) on my i2c clock and data lines running them at only 100kHz -to different parts. Do you see anything unusual in these numbers? Are these normal and expected for a design like this? The numbers are simple ground/vcc measurements. I am reading about power integrity. I have no dc-dc converters, but the board is powered externally.

C 100Hz  12uF

Z 100Hz  135ohms -74

L 100kHz 1.7uH 15 degrees

Z 100kHz 0.9ohms 90 degrees

DCR 60kohm

It looks normal to me, maybe good. Maybe not enough bypass. I didn't measure DC though.


texts: How to solve for current given resistor value for LED circuit?

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So I have the following LED circuit:

I know how to find the forward voltage and current from the datasheet of the LED and how to then solve for the appropriate value of \$R\$.

However, what I really want to do is fix the resistor value at \$R=100\$ (I'm just picking a resistor value that exists in a kit I have) and solve for \$I_F\$:

The only way I can currently think of to solve this is:

$$V_F+V_R=V_{CC}-V_{OL}$$
$$V_F+I_FR=V_{CC}-V_{OL}$$
$$V_F+100I_F=4.3$$

I found \$(V_F,I_F)=\{(2.3, 20), (2.8,15)\}\$ to be 2 arbitrary solutions to the equation. Then I graphed a line on the VI plot to determine all possible solutions to the equation. Finally I found the intersection of the line and the VI plot to determine what was the true solution to the equation is.

From this it looks like \$V_F=2.1\$ and \$I_F=22\$.

However, this was a lot of work for such a basic circuit. Is there an easier way to solve for or at least nicely estimate what \$I_F\$ would be given \$R\$? The value of the current matters a lot to me because I need to make sure I don't fry my microcontroller!


texts: 13-bit Latch Pedal Sustain IC M147 - Old Datasheet Questions

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My questions are as follows:

F1 is the way out for an applier?

If the outputs are 1 ', 2', 4 ', 8' and 16', what kind of filters are these?

Acronyms TS and TP, what are they?

It is the first time that I have seen these acronyms and this expression on the filters without a practical explanation. I want to put this pedal to work using this old IC since it was made especially for organs, as it says in the datasheet.

Full datasheet in pdf: M147B1.


texts:
I looking for a drive for my sensorless bldc motor for a project of mine.

1)Will I be able to drive my motor with ESC(electronic speed controllers) used to RC hobbyist powered by Smps.

2)what are the parameters should I look for if the ESC are compatible

This is the specification of the bldc motor I have.
-Motor type: BLDC sensor less motor
-No. of poles: 4
-Nominal Input Power : 160 W
-Nominal Voltage  : 24VDC
-Nominal Speed : 6000 rpm
-Max input Power : 176 W (max)
-Max voltage : 30 VDC
-Nominal Current : 6.3 Amps (approx)
-Max current : 8 Amps


texts: Why isn't my SysTick_Handler() being called in my LPCxpresso C++ Project?

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I have created a C++ project for an LPC1227 using LPCExpresso 6.1.0.  The project, up until now, builds and runs fine.  I have not made any changes to cr_startup_lpc12xx.cpp.

I would like to add a SysTick_Handler().  In my main.cpp I have added a method:

void SysTick_Handler(void)
{
    timerCounter++;  // these variables are all declared globally in main.cpp
    timer_10ms_tick = true;
    if ((timerCounter % 10) == 0)  //every 100ms
    {
        timer_100ms_tick = true;
    }
    if ((timerCounter % 100) == 0)  //every 1000ms
    {
        timer_1000ms_tick = true;
    }
}

I have also add the following line in my main() method:

SysTick_Config(12000000/100);

When I run my code via debug, the interrupt is firing, but it is getting stuck in the default SysTick_Handler() that is inside of cr_startup_lpc12xx.cpp (which is just an infinite while loop).   If I delete the default SysTick_Handler from cr_startup_lpc12xx.cpp, my program hard faults.

I have looked at the Blinky example (which is C, not C++) and it adds a new handler into main.cpp without deleting the handler from the startup file.

Can anyone suggest why my overriding handler is not being called?  Is this a C++ difference?


texts:
Hey all.
in a typical design of a capacitive sensor for level measurements, compensation capacitors are added as a reference. I struggle to understand why we need a reference capacitance to measure the level of the liquid in a tank, shouldn't only the main capacitor be enough for this job? like we calculate the equivalent parallel capacitance and then we figure out the level of the water.
and here, can we do our measurements using DC voltage ? or we need an AC voltage for this application to keep our circuit flowing?
Thanks ahead.


texts: Need RF advice (NFC antenna VS GND pour)

texts:
I'm currently working on a design who involve a NFC chip (ST24DV) who need to be on the board as it's used to communicate with a smartphone.
Here is the picture of the antenna:

There is a LED on the right (yellow circle) I can't move due to mechanical compatibility.
When this board is alone, I have no problem communicating with the NFC chip with my smartphone.
But this board is supposed to be connected through wires to satellite boards who share the same GND.
When these other boards are connected, impossible to detect the NFC chip with my smartphone.
I would like to know if someone have advices about how to overcome this difficulty. Maybe by pushing cooper pour away... but the LED need to stay here.
Another thing is I can't move the antenna too much because it need to be in front of an opening in a case.
Thank you for reading.


texts:
Is there an effective way to directly measure the gate capacitance of a power MOSFET, like say the IRF530N?

The way my circuit is behaving would indicate that the effective gate capacitance is perhaps double or more of the value quoted in the datasheet, which would be throwing off my op-amp stability by lowering the frequency of the op-amp \$R_O\$+\$C_{iss}\$ pole.

Here's the circuit schematic in case that's a help, but I'm really just interested in the general case of a test fixture I can wire up, pop an arbitrary TO-220 MOSFET in there and calculate the effective capacitance from a scope trace or something like that.

Is there a practical way to make a useful measurement of MOSFET input capacitance on the bench?

Outcome Report

Both the answers provided key insights. In retrospect, I think the short answer to my direct question would be: "How do I measure gate capacitance? At many different combinations of gate and drain voltages!" :)

Which represents the big insight for me: A MOSFET does not have a single capacitance. I think you need at least two charts to make a decent start at describing the ranges, and there is at least one condition where the capacitance can be way more than the quoted \$C_{iss}\$ value.

Regarding my circuit, I made some improvements by switching out the IRF530N with an IRFZ24N having less than half the quoted \$C_{iss}\$ value. But while that overcame the first instability, the following tests it enabled showed full-out oscillation at higher currents.

My conclusion is that I need to add a driver stage between the op-amp and the MOSFET, presenting a very low effective resistance to the MOSFET input capacitance and driving the pole it creates up well past the 0dB frequency of the op-amp. Not mentioned in the original post is that I require pretty decent speed, say 1µs step response, so applying heavy-handed compensation to the op-amp to achieve stability is not a viable option; it would simply sacrifice too much bandwidth.


texts: What is the purpose of the op-amp feedback circuit?

texts:
This is an existing circuit of buck regulator circuit I have been reviewing with.(Here I have not mentioned the part number of the due to the confidentiality issue)

Following is the screenshot of the feedback resistor design.

Reference voltage of the buck regulator is 1 V and output is designed for 3.3 V . Feedback regulator resistors (51 kΩ , 22.1 kΩ) combination design I have reviewed and verified the values.

Opamp feedback path and its functions are confusing sections for me.
Following is my understanding, current feedback across the 100 Ω resistor is taken across to the amplifier input and voltage output comes in parallel with the feedback path ( 22.1 kΩ) through a buffer.

Can anyone suggest the purpose of the opamp-feedback circuit? And what could be possible output voltages at the buffer (op-amp) output.


texts:
In 2013 the California Independent System Operator (CAISO) published this image, dubbed it "the duck curve", and took the internet by storm (or, at least the part of the internet that tracks trends in renewable electricity generation):

Here's an explanation of the duck curve from Wikipedia:

  [The] curve comes from the Net Load ("the difference between expected load and anticipated electricity production from the range of renewable energy sources"). In certain times of the year (namely Spring and Summer), the curves create a “belly” appearance in the midday that then drastically increases portraying an “arch” similar to the neck of a duck, consequently the name “The Duck Chart.”

Essentially, solar production causes a reduction in net demand in the mid-day (the belly). Later, sunset coincides with increased demand, causing a sharp ramp in demand (the neck).

This image generated lots of interest and people are still talking about it today -- lots of search results in the past year are still showing the same image.

But the most recent actual data on the chart is from 2013, and the duck shape was created by the projected net load curves from 2014 through 2020.

I tried to find some recent data from CAISO to see where things stand. To do this, I assume I'll need hourly historical demand and solar production data, in order to calculate net load.

CAISO's OASIS tool includes historical load data, but as far as I could tell solar data is only included lumped with wind, and only goes back to 2016.

Has someone published an updated version of this chart? If not, where can I find historical hourly solar generation to reproduce it myself?


texts: Bandgap References - What's the need for a PTAT voltage if we can invert a CTAT?

texts:
I was reading up on bandgap references. I noticed that a CTAT voltage can be simply produced by taking the Vbe voltage of a BJT.

However, when generating the PTAT voltage, most books seem to mention that you need two bipolar transistors operating at unequal current densities, then the difference between their base-emitter voltages is PTAT.

My question is, if we have an easy way of generating a CTAT, why do we need a PTAT? Can we simply not just generate another CTAT and invert it by plugging it into the inverting input of an differential amplifier? Why isn't that good enough?


texts:
I have a circuit that I believe will work, but I was hoping someone could double check?

Original schematic

In my circuit, I use a MOSFET, a photo-interrupter, a CVCC, several resistors, a battery, and an LED.

The load has a resistance about 2.525Ω

Assuming that the CVCC is required, would my circuit work?

Also, the purpose of this circuit is switching. When the photo-interrupter beam is intact, the load gets no current. When the beam is broken, the load gets current. Or, that's the idea here.

Changed freewheeling diode to Shottky diode as suggested.

Current Schematic:


texts: Why is modifying (by adding extra gates) clock inputs undesirable?

texts:
I am taking a course in digital electronics at university. I am second year mechanical engineering student, but I felt like it was important to understand some electronics. The lecturer in one of the slides, when talking about making a binary synchronous counter out of T-flip flops, said

  It is undesirable to modify clock inputs

I don't understand why this is the case. I have thought about it for a bit, and I can only think of the propagation delay affecting the frequency!? But surely for nMOS and pMOS it's < a few nano seconds. If you only have a few MHz clock the difference is not even worth thinking about.

Can anyone explain why this is undesirable / correct me if I'm wrong.


texts: Similar circuit not working because of wire

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I've setup a series circuit with an LED and a 1kohm resistor. If I plug the led positive end (longer end) directly to the power positive rail, it lights up.

But if I connect the led positive end to the positive rail with a wire, it does not light up. This looks exactly like the same circuit to me. Nothing has changed other than now there is a wire. What's going on?


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How can i turn a DPST button in to a DPDT?
I've replaced all the stock rocker switches in UTV, got all 14 of them done except for one all to Push Buttons. The push buttons are SPDT, "on/on" NC and NO, rated to 5 A. (billetautomotivebuttions.com 22mm)
To get the light to engage with the button, you wire the positive or negative switching, and run it through the light. It works fine for 12 V relays and normal functions, and for the rest of the button locations.
I ran in to an issue. There is a button that goes to the ECU, it is a over ride function,
negating the rev limiter to a higher preset, for launch control. This was a kit they had, and as an oversight, the stock rocker was a DPDT switch to achieve this.
It has a 3.3 V to the switch (override),
a common GND back to the ECU,
and the other lead is 12 V (normal), a same common GND back to the ECU.
I can wire this with one of the NC and NO contacts,
and I can get the function to engage on the cluster correctly, on and off no problem, but I can not get the light to engage when on.
If i wire the indicator led to the loop, a few things happen,

If I wire the light after engagement, I get override and a faint light, (3.3 V instead of 12 V).

In that same setup, if I engage and disengage the button, the light will come on but cancels out and doesn't engage the override function.

If I wire it to ACC, or the other lead, I can get a light on when off, or light on all the time scenario (duh - right? lol).

So I figured I would try a small 3 V trigger relay, so I can get it to engage the relay when the circuit is connected, and engage the indicator light.
Well they all use the same GND ultimately, and I get a light on all the time scenario :(
And they don't make a DPDT button like the other ones to match the panel.
I am getting frustrated because other than the light, the rest of this install is complete, and I'm a few weeks behind.
Any ideas?
(They do not make a DPDT button to match the rest in the cluster ...)
Thank you.
Ultimately trying to figure how I should wire the image in the lower right corner? Or if there is a better way to achieve this desired outcome?


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I want to find the total resistance between A and B.
This is a HOTS mcq, which has the following options:

A: 45\$\Omega\$
B: 15\$\Omega\$
C: 5\$\Omega\$
D: 22.5\$\Omega\$

A book says that the answer is 5\$\Omega\$ as R1, R2 and R3 are parallel. But I cannot understand how can they be parallel? Our science teacher said that R1, R2 and R3 are in a series, so he said that total resistance R=45\$\Omega\$.
The book that says that the answer is 5\$\Omega\$, does not have the method to find it out.

I tried that:

All are in series :- 45\$\Omega\$
15\$\Omega\$ is parallel with 15+15+15\$\Omega\$ and with one more 15\$\Omega\$, which would turn into : 45/7\$\Omega\$, which is not possible.
R3 is parallel with R1 and R2, as well as in a series with R2.
R1 is parallel with R2 and R3, as well as in a series with R2 and R3. But then I cannot determine the method to get the answer.

So I am confused between 5\$\Omega\$ and 45\$\Omega\$. I think as the book says, the answer must be 5\$\Omega\$, but what is the method?


texts: What is the simplest way to make a small low power and low price circuit that flashes LED's

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I am wanting to make a small handheld circuit that could flash anywhere between 4-6 leds in a programmed order. It has to be as small as possible and use very little energy. I am trying to make these cheap enough that I can make a lot.

I was thinking about using one of the AVR series mcu.

Size wise I was thinking of having it run on triple A'S.  I am open to suggestions.

Edit I am looking for DIP MCUs not smd.


texts: How to hide part names and values in EAGLE via ULP script

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I am trying to automate the generation of different assembly versions of an EAGLE PCB layout. For this I need to hide components names and values. It seems to be impossible to get hold of the NAME and VALUE by use of the ATTRIBUTE command, since they seem to be protected:

CHANGE DISPLAY OFF; ATTRIBUTE DC101 NAME

Result:

Reserved attribute name: 'NAME'

So the question is: How can I select a name or value text in the board and hide or move to an other layer by using commands?


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Reading through a Vishay datasheet of a NTC, I found the guide to devise the temperature error:

I don't understand why the errors of X and Y, for the non-approximated formula, were multiplied instead of summed. I am sure it is a silly thing that I forgot.


texts: can i run 70 LED (3 volts) on two 4V and 1.2AH batteries ?

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i need to run 70 3V LED lights on 2 Small 4V 1.2AH batteries. LEDs are attached to a long piece of wire in a parallel way. i mean if one goes off rest keep running.
Should i attach batteries in series or parallel to current the circuit ?
Also can you give estimated time for how long the lights will keep running ?


texts: Why is opamp slew rate specified at unity gain?

texts: Is there some reason besides convention to add the "at unity gain" qualifier? Does adding or omitting it communicate something about the component? Are the opamps which have a slew rate that varies with gain?


texts: DC power supply with DC input either polarity?

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I'm wondering if a power supply can be constructed that accepts a DC input of either polarity. Can a rectifier be built that converts both possible inputs into a DC power supply of the expected polarity? What would its size, cost and efficiency be?

Basically I am wondering why (if this is possible) the world of DC power supplies isn't a lot simpler. Whenever I'm looking for exactly the right wall wart in a box full of them I wish everything just accepted 100-240VAC.


texts: How do I make a simple bidirectional current limiter

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I want to connect two separate batteries together and let the highest voltage one charge the lower one not exceeding the desired current. I expect it to be a solid state solution without the need for programmable parts. I was looking for something in the range 1A-10A. It does not need to be adjustable, although I would like to make a 1A one and a 10A one, for example. The voltage difference  would be 4v maximum. I would like it to continue to work down to diode voltages.  When balanced it would need to draw only a low current maximum. Say < 1mA. Obviously resistors would do this job. I was hoping for a solution that would maintain a higher current as the voltages converged, would be more efficient and would not get too hot. Efficiency is not a deal breaker.

The following site suggests back to back JFETs but I cannot find any more references to such a circuit and its not clear to me what the typical components I could use and the magnitude of the current when limited. http://unitedsic.com/sic-jfets/

Would it be possible to use back to back constant current source circuits made from linear voltage regulators?

The aim is to get the batteries into a "storage" state where they are nether fully charged or discharged. At the moment I am charging the fully discharged batteries from a separate supply and discharging the unused fully charged batteries to a load. I can charge a discharged battery using a charged one. However to charger boosts the voltage so it can over discharge the battery I am using as a supply. The charger does not protect against this. It would be nice just to balance all the batteries. The final voltage is likely to be within the storage range.


texts: RC transmitter and receiver for Raspberry Pi possible?

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I've got a pet project in which I'm trying to write/build a self learning autopilot for my rc plane. I've got a Raspberry Pi with an IMU and a pitot tube in the plane and it can now control the servos of the plane. So far so good.

I'm now thinking about connectivity. I want to be able to send commands in json from my laptop to the Raspberry Pi in the plane. I got it working over wifi, but that means I need to take my router outside when I go flying. Plus the range of the wifi is not very good (I tested it outside and it comes to about 50 meters).

Conventional rc transmitters and receivers have way better ranges (up to 1000 meters) than my wifi from the router does, so I'm wondering how I can leverage that technology. I see plenty of rc receivers around to buy, but they all work with a number of channels, instead of a data link over which you can send arbitrary data/json. I searched around for things like "raspberry pi rc receiver" and "USB rc receiver" but apart from some tips on how to turn your raspi into a transmitter to an rc car (for which I don't know the range), I can't find anything about longer range receivers for the pi, or rc transmitters to attach to my laptop with which I can just send and receive arbitrary json.

Does anybody know whether there are any simple modules which I can attach to my raspi and laptop to send json with this rc technology to and from the pi over a range of at least 200 meters? All tips are welcome!


texts: What is the reason that Bus resistance is normally small

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I have seen typical bus resistance as few ohms. For example on MAChX02 1200 ZE board the bus that connects FTDI chip and the FPGA has only around 11 Ohm resistance.

Is there any specific reason for keeping bus  resistance small?

Thanks in advance


texts: Altium PCB: what do these patterns on traces and vias mean?

texts: I was just checking a PCB design, and found these box-patterns on some of the nets. What do they mean?


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Is there a basic passive GPS reference antenna design that would be considered fair-use or "free to use" that can be placed on a PCB as a strip antenna or patch antenna?   I'm looking not to violate copyrights of an antenna design on a project I eventually might want to sell.
Thanks


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simulate this circuit – Schematic created using CircuitLab

In the circuit above, what is R2 doing?  I've not seen this before.  The only thing I can think is it is current limiting for D1 if there were some transient backfed from Vout.

Ideas?


texts: turn level-based input to edge-triggered input

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I'm trying to figure out with the most minimal part count how to convert an input of a digital IC to an edge-triggered input.

I am using the 82C55 IC and the input on it I want to make negative edge-triggered is the WR input. This is because I want to control both WR and the clock of an external latch (74HC574) with only one GPIO pin of a microcontroller.

I am able to pull this off by using a multivibrator (CD4538) and connecting the output of it to WR but the thing with that is I have to add a capacitor and resistor to create my own timing.

Is there a simpler way to convert a level-based input (where an output happens based on what level the input is at) to an edge-triggered input without introducing unnecessary long timings (which could happen with my multivibrator approach) and without using too many extra parts?


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I heard from a colleague that typical PLC serve as an interface between a the signals and, for want of a better word, a PC. The connection, being typically done with ethernet, and the PC runs some Codesys, or Labview applications.

This was the way the application could be changed while running, which is one of main advantage of PLC for debugging and maintenance.

However, looking at one example, like this one, I can see the Ethernet ports, but I can't find any precise information about that topic.

Looking around, I found that a remote PC can be used as a server and thus the PLC would communicate with it, typically via Ethernet. But it is not a must.

Can someone clarify that trivial point for me? Must or must not a PLC be connected with an external PC to run the application. And if it's not, can we still change the code on-line?

For the background, I have to decide on using a PLC or a µC-based solution, and up to a few days ago I ignored the existence of PLCs.

I should add that I have read the question: Why use PLC instead of microcontroller?, but unless I missed it, it does not answer that specific question.


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I want to make a cut in the via like this image:

I'm using Altium to develop.
I was recommended to make the via "castellation" but I can't find how to make this via in the center of the board.
Does someone know more about "castellation" and can help me make this via with cut in the center of the board?
I'm making a six-axis sensor.
They have three vias with cuts, to result in six signals to read. It doesn't exactly have to be done by "castellation", but castellation was the only way I found.


texts: Can I use Op-Amps to drive a ultrasonic piezo transducer at 200kHz

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I’ll admit I’m not the most knowledgeable guy when it comes to electronic circuits, so I thought I’d ask before breaking anything.
I’m looking to drive a piezo transducer using a 200kHz sine wave. The transducers should have a relatively low impedance of around 150Ohms. While searching on the web I only found complicated amplifier circuits or expensive piezo amplifiers. I’m wondering if it’s possible to do this using simple op-amps.
My first question is if I could just hook up a function generator and an oscilloscope to find/check the resonance frequency. (Look for the maximum voltage on the oscilloscope and a 90° phase to the current). I know that piezo transducer can have high voltage spikes, that might damage the function generator?
Next, I’d like to amplify the sine signal to about 60Vpp. The simplest way I could think of, was to use two parallel 30V op-amps, one having an inverted sine signal. Thus, the transducer would have 60Vpp. The current needed would be around 400mA, so taking two cheap op-amps with a 250mA output should do the job? I calculated slew rate of 38V/us and a bandwidth of 6MHz, which shouldn’t be a problem when looking for op-amps. Is this setup possible, or am I missing something important about piezo transducers?


texts: Modding a charger into a power supply + charger?

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I am making a handheld radio telescope which needs 13-18v to power and currently runs off 2 9V batteries. However it eats power like mad, drains them so hard that it actually needs to be recalibrated every 10 seconds. Now I am looking for a way to give it a stable power supply and more importantly to make it rechargable.

Now I was wondering if it would be possible (and smart) to take appart one of these chargers and wire it in with a swich. one position would make the device run off the batteries and the other side would charge the batteries and run the divice on power (which comes from the plugged in cord)

http://www.ebay.com/itm/2-x-9V-BTY-300mAh-Ni-mH-Rechargeable-Battery-PPS-18650-16340-14500-GTL-Charger-/200925157778?pt=US_Rechargeable_Batteries&hash=item2ec8129992

Alternatively, if that is a really bad idea for some reason, what about making it run on a laptop power supply? (19V but should also work) I got some BNC connectors, so I could swich the head and make it work off of that. It would not be rechargable, but atleast I could use a long cable.


texts: Why is there a constant -1A current through the voltage source at resonance?

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Below circuit is at resonance. Shouldn't the circuit offer infinite impedance to the voltage source ? I thought, then the current through the source would be 0A. But the simulation shows that the circuit draws a constant current of -1A. Why is this so ?

simulate this circuit – Schematic created using CircuitLab

EDIT : As suggested, with 0.1 ohm resistor in series with the inductor, the current slowly dies out


texts: Lighting up old vacuum tubes and making them turn on/off

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I know there were older posts about lighting up old vacuum tubes but I would also like to turn them on and off. I am a complete newbie with no real electronic  experience here so please bear with me.

I bought an old cabinet full of brand new but very old tubes that I would like to use/light up as decorative items. Some gave great information on how to light them up, thanks so much, but I would also like to program the lights to go on/off in an interesting way.

I know Amazon sells simple kits that you can create these kinds of things (at least I think they would.) But also what would you all recommend if this was my goal with these tubes? Again complete electrical newbie but very much appreciate any tips, tricks or insights on this project.

Here is a possible Amazon product that I might be able to use.


texts: Use multiple batteries in series vs Using a boost converter

texts:
I have encountered a circuit that totally confuses me:

I have a simple LED flash light that came with my electric bicycle. The flash light is designed to work with a range of 24V-36V so it can be powered by the bicycle's battery which is a 32V battery. As I assumed there is a circuit inside the flashlight which reduces the voltage to a voltage suitable for the LED

With the help of a voltmeter I got the following data:

When I power the flashlight with 24V the current measured is 36.7mA (around 0.9mW) and the output voltage of the step-down converter (the input of the LED) is 2.9V
When I power the flashlight with 30V the current measured is 30.4mA (also around 0.9mW) and the output voltage of the step-down converter (the input of the LED) is 2.7V

Let's say I want to power this flashlight with alkaline battery and not from the bicycle's battery. I know I can get a flashlight that receives a much lower input voltage or connect the battery directly to the LED but for the sake of the question, let's say I will use the same flashlight as it is and will feed it with 24V

I have 2 options as I see it:

The absolutly not reasonable option is to use (24 / 1.5 = ) 16 alkaline batteries in parallel to reach 24V (which will then be stepped-down and light the LED)
Use a step-up (boost) converter to reach to 24V from the input of a single alkaline battery of 1.5V

My question is how will putting a lot of batteries in parallel will make a difference opposed to stepping up a single battery. The capacity should not change because as I know when connecting batteries in parallel the capacity stays the same and you only get a higher voltage.

The second question is let's say I use a single alkaline battery with a boost converter: For how long can this battery will be able to power the LED? How can I calculate that?

I probably missing something in my understanding of connecting batteries in parallel...


texts: What is this port called? I want to guess it is for video

texts:
What is this port called?

If this is off topic, please direct me to the appropriate place for my question

Looks equal in thickness to micro, slightly more narrow resulting in a more squared shape.


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I want to use the motor of an electric vehicle as a brake. It is a 36V ~27A motor.
I looked up 500W+ resistors and they are quite pricey, I figured the cheapest alternative would be 100W resistors in parallel.

simulate this circuit – Schematic created using CircuitLab
This is my slightly complicated schematic, I couldn't find a motor symbol, excuse the ignorance.
I don't need to reverse the motor so for the drive I'm just going to use a bunch of MOSFETs (yes I will use MOSFET driver ICs). PWM1 controls the amount of drive current while PWM2 controls the amound of braking, it will only be one or the other never both. I would probably need to add a few more P channel MOSFETS in parallel but I'll think about it later.
So anyway getting back to the problem, in order to achieve 27A of braking current I need a 36V/27A = 1.3 Ohm load. I will order ten 12 Ohm 100W resistors and wire them in parallel this should give me a resistance of about that and still leave some headroom for the resistors because we all know they probably can't live up to what's said on ebay (or at least for long).
What will happen if the resistance is lower than that? The vehicle is moving and is generating plenty of mechanical rotation on the motor shaft, we apply PWM2 100%. I suspect the motor is going to generate more than the rated 27A? If my assumption is correct then why is that? I mean it is clear that the torque on the motor shaft from the vehicle's inertia will be greater than what is required to generate 27A but why does that not just limit the amount of braking torque that the motor can apply?


texts: Simplest automatic gain control circuit with BJT + op-amp

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I'm trying to implement a simple automatic gain control to my amplifier circuit. What I'm amplifying is a small signal from a superregen receiver. Without the transistor and the passive components with no values marked (aka a basic amplifier), when I tune the radio, I sometimes hear it oscillate which gives me the indication that I'm in need of an agc. I want to eventually detect the output on an LED.

But for now, what I want to do is set an output limit so that if the input is too high, I won't hear oscillations.

Could this circuit I have posted be usable as a decent agc? If so, how can I calculate the proper values for C2, C1, R3 and R1?


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I have a fixed wire and an electromagnet next to each other, and would like to induce continuous \$\epsilon\$ from the change of \$B\$ or \$A\$.
Currently I'm focusing on changing the magnetic field, causing it to increase then decrease and so on(repeatedly) , however, not sure of the outcome of the induced \$\epsilon\$ given Faraday's law:

$$\epsilon = \frac{\phi}{\Delta t} = \frac{\Delta (BA)}{\Delta t}$$

If the magnetic field is decreasing say from \$1Tesla\$ to \$0.5Tesla\$ it's is a negative induced -\$\epsilon\$, and when its increasing from \$0.5Tesla\$ to \$1Tesla\$ that is a positive induced +\$\epsilon\$.

This seems to induce AC current? Due to the -V to +V and vice versa.

How can this be converted into DC where there is only +V?

Also, changing the area is another option and seems to give out the same results.


texts: Simplifying boolean equations with K-map

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My professor told me that I could arrive at the simplified solution using the K-map, which I guess I did, however it does not seem correct.
The equation and corresponding solution are shown in the pictures below.
My simplification steps were:

ABCD' + A(B' + C' + D') + (A'B'C'D') -> used two De Morgan's rules

A(B' + C' + D') = AB'CD + AB'CD' + ABC'D + ABC'D' + ABC'D +ABC'D' + AB'C'D + AB'C'D' + ABCD' + ABC'D + AB'CD' + AB'C'D' (opened up the brackets using the identity)

Draw the K-map and arrived at this simplified equation: A + AB + B'C'D' (the drawing is attached down below)

Obviously, this is incorrect, could someone help me pointing on the mistake I did and also helping to find simplification without K-map?


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tl;dr For minimal signal loss: a longer cable is better than solid obstructions. Right?

I would like to enhance (the non-existing) phone signal indoors and have been thinking of connecting an external antenna to one inside. Basically:

cell phone <-> whip antenna <-> RG-58 cable <-> aerial

So I was thinking where to place the indoors antenna. Should I try to minimize cable length or obstructions? I might have found a conclusion by researching for this question, but I would still like to verify my thinking.

As RG-58 has about a loss of 0.3 dB/m at 960 MHz (GSM), and a 15m cable run would mean about 4.8 db loss according to this online calculator, or about 1/3 (1W in gives 0.3W).

On the other hand, solid wood dampens the signal by 5-12 db. That means even a 2m stretch of cable to minimize loss would be for nothing if I had an additional timber frame or door for the signal to pass through.

Is my thinking correct?

P.S. Follow-up question on using 75 ohm vs 50 ohm cable here


texts: LED that emits light in different direction

texts: Is there such a thing as an LED that emits its light horizontally ("to the side") when mounted on a PCB instead of the ususal "up" direction? If so, what are these called, and do they use the same standardized footprints as normal LEDs (1206, 0805, etc.)?


texts: What to use as a ground in a plastic, mobile container

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I'm building a basic stereo system, using a car stereo and speakers, inside a large plastic box.

The stereo requires grounding, but the box is entirely plastic, so there is no metal chassis, and it needs to be portable, so I cannot connect it to an external ground/earth.

What should I use as a ground?


texts: Where is the correct place for a body pad of a TO220 linear regulator in Eagle

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In my two-layer pcb design I have an LM317 with a TO220 package. I took the generic TO220 package from the default "linear" Eagle library which does not have a polygon copper pad under the body of the part. However, since the body is connected internally to pin 2 (middle pin) which is the regulator output, the current design would short output to ground (top layer, red).

But I am not really sure where to put the polygon under the part body. If I manually put it to the top layer of the board itself, this does not seem like a robust solution because on the next board I will have to remember again in order not to short supply voltage.

On the other hand, if I put the polygon on the pad layer (green) of the package of the part, it is going to be on the bottom pcb side as well where I probably want to place other traces (like for the design below, blue).

And finally if I put the polygon on the top layer of the package, I won't be able to place the part on the bottom side of the board, if I ever wanted to (or at least the polygon will be on the wrong side then). Edit: I was wrongly assuming that the top layer would stay the top layer when the part is mirrored (placed on the bottom of the board). On the contrary, it is going to become the bottom layer (quite logical...). So placing the pad on the top layer inside the package (like it is the default for SMD parts) is my solution.

So what is the right way of placing the poylgon under the regulator body?


texts: Can I use a transistor as a switch to close a pin to GND?

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I need to short an external pin to another external pin (gnd). Link to Nikon D90 pinout.

I want to control this with an Arduino, can I use a transistor for this? (e.g. BC548)


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I was doing a report for my lab in VISIR simulator, but I get a strange output for a RL circuit.
The goal, is obtain a frequency to fit the permanent regime in a half of input period, therefore, for a RL circuit where R = 2200 ohms and L = 820 μH, the right  input frequency would be a number about f = 268 KHz, in accordance with goal the frequency must be f= 1/(10*Tal). so the expected outpout should be:

But I'm getting this:

Could someone explain to me where I'm getting wrong?

the circuit image is following below:


texts: How do LEDs slowly degrade in normal use?

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As I understand it, an LED normally has a service life of perhaps 25 years with output that decays exponentially as a function  of time and current.

What causes the degradation?  I'm guessing that the current is slowly moving atoms around in the lattice, but what exactly happens?


texts:
I am using the PIC16F876 to program an AD9833. I am using the RA2 pin for FSYNC, RA3 pin for SCLK and RA4 pin for SDATA. I have used ADCON1 = 0x07 to set all the A ports as digital and PORTA = 0x00 to set all the ports as outputs.

The problem is that the RA4 pin is not responding to commands. I know this is a special pin but I think it can be used as a digital I/O.

Can someone tell me what I am missing? I assume there is another register write which enables RA4 as a standard digital I/O but I can't seem to find it.


texts:
I witnessed an impressive explosion of a lead acid battery when my collegue started an internal combustion engine connected with the battery without disconnecting the charger from the battery first.

What is the reason that charging the battery while using it caused its destructiion?


texts: Will using a wallpowered usb cable to power a beaglebone black provide more power than on USB to computer?

texts: I couldn't find anything about this specific situation, but will it work, and are there any side effects that could damage it? Also, will it treat the USB as a computer?


texts: Is PFC compulsory for AC/DC converters 75W and above?

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I’m reading the user guide for a Microchip reference design of a 300W AC/DC converter.  Section 1.2 starts with these requirements:

  A conventional SMPS must implement PFC if it draws more than 75 watts from the AC Mains. The PFC circuitry draws input current in phase with the input voltage, and the Total Harmonic Distortion (THD) of the input current should be less than 5% at full load. [emphasis by me]

What drives these requirements (in addition to efficiency)?  Are these requirements driven by a standard or a regulation?  If so, what's the driver behind the regulation?

Any insight or reference is appreciated!


texts: 6x UV-leds in parallel turning on and off when they should be on all the time

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I have 6x UV-leds in parallel driven by a 6V source. The problem I have is that they glow for a little while, then they
are completely off for a little while, then glows and then they are off completely. They all do this simulatneously.
My question is what could cause such a behaviour?

What I have done so far

I have very limited knowledge in electronics, but these are my thoughts so far:

Possible problem #1: I read in another question that LEDs are "current oriented" instead of being "voltage oriented" and that there needs to be a
circuit controlling the current. Due to the fact that my circuit does not take this account in at all, this could be the problem.
If that was the problem, wouldn't the circuit behave in another way?

Possible problem #2: Since the circuit behaves like someone is turning on and off a lightswitch and then leaving it off, I thought about that
there was a loose component or two components touching each other creating a short. But I have checked the solders closely and there seems
to be no problem with them. (I was very thorough when soldering. I used flux and made sure each solder had good contact with the board.)

Possible problem #3: The LEDs are rated for 3.3 V @ 20 mA, maybe since I'm supplying 6 V with a 330 Ohm resistor resulting in 18 mA they behave this way?
I thought as long as the current was close to 20mA they would be fine.

Possible problem #4: I have an error in the layout of my circuit.

Background

Here is the schematics and information about the components:

B1 = 6 V
R1 = 330 Ohm
LED1 = 3.3 V @ 20 mA

When testing the circuit I used a DC power supply with voltages 3.3, 5 and 6 with the same behavior.

Image of the circuit after soldering:


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The title says it all:
What does this Mosfet Symbol mean (two diodes facing each other at Vgs)? I know its an N-MOS, but I don't understand the meaning/purpose of the two diodes.

Part: AO7404

Datasheet Link: http://www.aosmd.com/res/data_sheets/AO7404.pdf

Picture of the symbol (highlighted part):


texts: Can I directly interface to 5V I2C devices with an STM32 running on 1.8V?

texts: STM32 I/O pins are 5V-tolerant. I2C devices use open-drain outputs. I currently see no problem with operating an I2C bus with 5V devices from a 1.8V STM32 (with pullups to 5V). Is my understanding correct?


texts: Estimated cost savings by going from a 2 layer to a single layer pcb?

texts:
I've been tasked with minimizing cost of an existing design by taking it from a 2 layer board to a single layer board.

I've never made a single layer board so I am unfamiliar with pricing. I tried using Sunstone online quote to get an estimate for a 3"x2.5" single layer board with 15,000 units, but there doesn't seem to be a difference between 2 layer and single layer.

2 Layer estimate cost

Single Layer estimate cost

Both work out to being $2.10.

So it seems that I am missing something because the price did not change. Either I don't have enough volume, or this estimate tool is not that great at estimating.

Everything is on hold until Jan because of the holidays, but I was hoping to get a start on this during next week. But I want to know beforehand if my efforts are "worth" it.

Question: How much (approximately), can one expect to save by going from a 2 layer board, to a single layer board ? Assume board shape and size (3" x 2.5") stays the same and the same number of boards fit into a panel. Or is this insufficient information here and I would just have to wait until the New Year to speak with a fab house ?


texts: phasor equation using Euler to rectangular

texts:
I am studying for a Bachelors in electrical engineering and have a question regarding phasors.
I have been presented with the question:

Find \$V_s\$ for \$V_1 + V_2\$ where
\$V_1 = \sqrt{2} \cdot 20\cdot cos(\omega t - 45)\$
\$V_2 = \sqrt{2} \cdot 10\cdot sin(\omega t + 60)\$

I can get the answer:
\$V_s = \sqrt{2} \cdot 29.77\cdot cos(\omega t - 40.01)\$
I'm not asking the question as a homework cheat! What I don't understand is:

Why the second phasor is been expressed as a sin function.
Why do I have to subtract 90 degrees from the angle to resolve the sin function to something workable in rectangular form?

Can anyone tell me why this is the case or point me to a good link that explains why?