texts:
I'm having trouble understanding how to route the signals out of the Molex 1054500101 Type-C USB connector - specifically the B1-B12 pins.

The distance between row A and row B is only 0.5mm, too small for me to put any vias in between. That leaves me with the option of routing the B row signals away from the board into the "pattern restricted area". However if this is a pattern restricted area doesn't this mean that I am not supposed to route any copper there? I'm confused as to how to get the B row signals into the PCB


texts: TPS92513 (LED Driver) - Question about varying the reference voltage

texts:
Datasheet for the part in question: http://www.ti.com/lit/ds/symlink/tps92513.pdf

So, on the pin description on page 3 it describes I_adj as:
Analog current adjust pin. The voltage applied to this pin will set the current sense (ISENSE pin) voltage. The range of the ADJ pin is 180 mV to 1.8 V and the corresponding ISENSE pin voltage is the IADJ pinvoltage divided by 6.

Okay, makes sense, U_Isense = U_Iadj/6.

Typical application just saturates it with the RC circuit, as internally, Isense has a 1.8V zener, Alright.

Now, I am looking to create a lighting application that's long lasting with variable light. Dimming through the PWM output dimms the output, well, with PWM, not regulating the current. As LEDs get more efficient at lower current, I'd like an option to also drive them with lower current. I require up to 1A through my string of LEDs, but they might be driven with 100mA or less. So I was thinking of being able to switch these around; having a circuit to cut the reference voltage in half, for when I'm driving the LEDs from 100-500mA. Would it be feasible to change the reference voltage during operation? As far as I can see, it goes into a comparator, so it would just adjust the output.


texts: What defines the sign of transistor rating values?

texts:
Here for example I have attached excerpts from two general purpose PNP transistor datasheets. One of them has negative values, other one positive.

I would like to understand what defines these values to be positive or negative.

P.S. Second one is for 2n3906.


texts: Difference between nominal speed and idle RPM of a DC generator

texts:
I am currently studying for a electrical engineering related exam and came across this problem.

What exactly is the difference between the nominal and idle RPM of a DC generator, and which one is higher?

To my understanding the nominal speed of the generator denotes the speed needed to match the power supply frequency (e.g. 50 Hz in Austria), if the generator is supposed to feed back into it.

When talking about a DC motor with shunt, I think understand the principle: Idle speed is reached when the rotor induces the same voltage in the stator as is applied to the rotor itself. Nominal speed is the RPM at which the motor delivers the nominal torque.
Here, idle speed is higher than nominal speed.

Are those assumptions correct?


texts: Are Bioimpedance sensor different from Biopotentials sensors?

texts:
I am building an portable health device , for which i am want ECG , GSR etc. then i came across 2 terms Bioimpedance and Biopotentials. Are these two same.
Also can any one say the applications of these ?


texts: How does a PLL recover the clock from digital data signals and what does recovery mean?

texts:
Is there an easy way to explain this process to a non-expert? I read many places but couldn't figure out.
I can understand the job of PLL which locks the output frequency to the fed back frequency hence can be used to increase the frequency of an oscillator stability.

But what is meant by clock recovery(wikipedia didnt help) and how does a PLL recover the clock from digital data signals (CDR)? Is there a easier way to explain this as a big picture?


texts: Why don't electronic thermometer "move back"?

texts:
I have noticed since a long time that electronic thermometers, which use a temperature sensor at their tip to measure temperature, only move forwards, i.e., their reading only increases as they measure the temperature.

Ideally, their reading increases until it reaches the actual temperature and then it stays still for a moment (waiting for further change) and finally gives the temperature (after a beep).

However, while the reading is increasing, if I immediately put the thermometer's tip at a cooler place (with temperature lower than current reading), the reading stops where it is and I get the beep.

My question is, why does the thermometer just stop when I reduce the temperature during the measurement? Why doesn't the reading descrease to the new, cooler temperature? Does it have to do anything with the temperature sensor?


texts: Meander coil shape for RFID/air transformer

texts:
I am trying to use meander shape coil on PCB for wireless power transfer, with no luck so far. The primary coil is meander shape on PCB, receiving coil is a loop of wire with a tuning cap. Both RLC circuits tuned for 740Khz.I would like to induce at least 0.5V at 1cm. I have successfully resonantly coupled secondary coil with THT drum coil I only have a problem with PCB coil.

Can I connect another inductor in series with primary coil to increase its inductance and will it affect electromagnetic field around PCB coil?
How to make electromagnetic field stronger on PCB coil other than increasing current?
When designing meander PCB coil is it better to make more turns, less spacing between them and thinner lines or wide lines and bigger spacing?
Does higher inductance mean bigger field surrounding coil?
Should Both RLC circuit be impedance matched and how crucial it is?

Edit: picture added, drum inductor added to increase inductance.


texts: Can ATmega88 be run at 3.3V with internal clock?

texts:
I want to use a few ATmega88s with Arduino bootloaders to act as I2C stepper drivers and temperature controllers that will interface with a Raspberry Pi. The thing is just that it seems the RPi interfaces with 3.3V so I therefore need to run the ATmega at 3.3V instead of 5V as to not damage the RPi without the need for a level shifter or will I be fine at 5V so long as the ATmegas act as slaves (I read something like that but I do not know if I it is the case)?

If I still need to use 3.3V would I be able to do so using the internal clock or will I have to use an external clock? Also, will I still be able to flash the bootloader on the ATmegas using an existing Arduino at the lower voltage (I have a feeling that it might interfere with communication speed but I am not sure if this is the case). If needed I could probably run the ATmega at 5V initially just to flash the bootloader but I am also not sure if that will work.

I know I am probably making life difficult for myself not using level shifters etc. but I want to use the bare minimum components for this project. Also, if the 3.3V affects communication, will it have an effect on my I2C interface?


texts:
The Wikipedia page on silicon-germanium states that AMD and IBM worked on a 65nm SiGe process. Unfortunately the source is no longer up and I cannot find more information about the 65nm SiGe process.

I know that TSMC provides access to 90nm SiGe process. Does a 65nm SiGe process exist?


texts: Goodday. I need info on this. If i connect say 3 x 12 volt 28amp batteries in parallel to increase the amp hour that makes it a big 12 volt battery and then connect 2 x 24 volt but lower in amps battery in series to make a 48 volt battery and conect these together to make  a 60 volt with the 1st one bigger amps, will it work. It will be for a electric scooter. All will be a gel batteries.


texts:
Can you give a circuit that would clean up noisy audio signal?

Basically, I have created a square wave from a software (Real Time Analyzer) at certain frequency to the audio jack port of the computer.

The output of the oscilloscope yields the signal as shown on the top part of the image above. The signal I created from the software is similar to the bottom part of the image. There is no problem with the software. My problem is how to clean the noisy signal from the audio jack? That is, how to make the output from the circuit created similar to the bottom part of the image?

I want to have a circuit that would clean the signal.


texts: I'm working on a guitar pedal distortion circuit and I've been experimenting with introducing diode clipping into the signal. My question is, how can I increase the influence this diode clipping has on the final sound? Right now it makes a very small change in the sound and i want to hear the diode clipping more.


texts: How to run a 0.05A fan with a 10A source?

texts:
I am constructing a circuit to drive a powerful LED that requires about 10 amps at 12V.  I also have a battery that happily supplies that.  For obvious reasons, that LED requires a cooling fan, and I've chosen one that takes 0.05 amps at 12V.  How can I run this fan with the existing circuit?

EDIT:

I will probably be using a boost converter to control the current. It will be boosting from ~10V to the 12V required for the LED. I will also be using it to dim the LED.

Specifications for the boost converter:

Input: 8.5-50V, 15A max
Output: 10-60V, 12A max


texts:
I made this scheme:

simulate this circuit – Schematic created using CircuitLab

Gain of this differential amplifier is constant and equal to 2. I would like to have possibility to substract variable voltage but this doesn't work. Is it any easy way to make this scheme work?


texts: A question about reverse polarity protection diode

texts:
Is the function of 1N4001 before the 5V regulator reverse polarity protection?

Is this a fine method? And I sometimes see 1N4148.
Can any diode(besides zener) be used for such function?


texts:
The total almanac data is transmitted in 25 navigation messages. Each navigation message takes at least 30 seconds to transmit. So, receiving the almanac data from the satellites takes at least 12.5 minutes, not taking Assisted GPS into account for the moment. If the signal was lost while receiving the message, the entire message has to be received again. This could double the time it takes to download the almanac data, depending on which navigation message is missing.

However, all the almanac data really does is give you a clue which satellites to look for. This information is not really worth the time and energy it needs when designing a low-power system. It requires you to keep track of the time, rough/last known location and almanac data.

Most GPS receivers nowadays include a lot of channels correlators, up to 256 from what I've seen. A satellite signal is repeated every millisecond and could be shifted by 1023 bits. Using a single channel per satellite, determining whether the satellite is in view or not could take one second, before it moves on to the next satellite. With 256 channels, determining whether the satellite is in view or not could only take 4 milliseconds.

Performing a sky search means that the receiver will process all the satellites and check if they are in view. This sounds more logical to me than downloading the almanac data to determine which satellite to look for. With as many as 256 channels, it would theoretically only take 100 milliseconds to know which satellites are in view and needs their ephemeris data downloaded from.

So the question here is: is downloading the almanac really necessary? Would it be better to skip downloading the almanac data when the amount of available energy is low? Especially when you want to avoid the need of having a RTC etc.

Edit:

I made a wrong assumption about the satellite signal decoding attempts, as pointed out by Dmitry.

However, the question remains if it would be feasible to ignore the almanac data. For instance, the datasheet of the Maestro A2035-H GPS module states that it has over 400,000 correlators. It consumes 40 mA while searching for visible satellites and 29 mA while tracking (getting the ephemeris data and calculating the position). It only takes 35 seconds to acquire a fix with a cold start, without a recent almanac or time and position estimate.

To me, it seems like it ignores the almanac like I suggested. Has the almanac still any use?


texts: Assembly language: Ampersand before a register

texts:
I'm trying to program the Programmable Realtime Units (PRU) on my Beaglebone Black in assembly language. Here is the instruction set, which comes in two flavors: pasm and clpru (I'm using pasm).

What does it mean when a register name has an ampersand (&) before it? For example:

// Copy 8 bytes from r2/r3 to the memory address r1+5
sbbo &r2, r1, 5, 8

How is this different than just

sbbo r2, r1, 5, 8

?


texts: Help using less pins controlling 8ch relay

texts:
I know this has been answered somewhere but can't find the solution online.

I have an 8ch 5v->120VAC relay controlled by arduino and need help using less digital pins. All channels need to be individually controlled on or off. Space is also an issue as it's on a shield. I've done this in class and reread this link) but am stuck on the coding.

The existing code has 8 variables for each relay's ON/OFF state. These would need to be passed directly to the relay (vs stepped/shifted one at a time like a chase pattern).

Chips on hand: 74HC595
Also have these if needed: (4051,4520,4514,4027,4099)


texts: I am trying to make a line follower robot using LM324 as comparator, but I cannot understand the theory or the explanation of this circuit. I also don't know how to calibrate it with the IRs.


texts:
I got a really strange result. I've build a full-bridge rectifier with a capacitor filter. And I used the following values \$\text{C}=500\cdot10^{-6}\$ and as a load \$\text{R}=1000\$. The maximum voltage of the sine input is \$230\sqrt{2}\$. Now when I measure the rms voltage across the resistor I measure around \$391.2611\$ but that is higher than \$230\sqrt{2}\$ so there must be something wrong. Or can it be this way?

the circuit looks like:

simulate this circuit – Schematic created using CircuitLab


texts:
I have an mbed project with firmware that controls some PwmOut switches. All works fine firmware opens and closes switches as expected. I tested this with a LED (and resistor).

Now my goal is that instead of a light coming on, a electric brush motor (with a simple +/-) 3v-5v should run. I understand that the PwmOut from the mbed will not provide enough current to run the motor.

Will I need a transistor that connects the PwmOut port with the motor?

If yes:

how do I know what type I need?
these three legged guys - how are they hooked up?


texts: Oscilloscope noise reduction when measuring IC voltage

texts:
I am trying to monitor the voltage of an IC. The supply voltage of the IC is 3.3V and clock frequency is 24MHz.

Here are some parameters for the channel used for measuring voltage:

vertical scale to 50 mV/div,
the offset to 150 mV,
and enable 20MHz BWL,
Sampling rate is 2Gs/S 200ms.

I get some samples. The shape looks like what I expect when observing by eye. However, when I use my computer to process the data (extract certain property from the waveform), I did not get what I expect. I doubt if there are too much noise in my set up. I mean the waveform looks right by eye, but have some problem when I do the accurate processing from the computer.

How do I determine how much noise I have? What are the ways I can try to reduce the noise in this experiment?

This is the oscilloscope waveform

This is the captured waveform plotted from my computer.


texts: Why is the transfer curve of a real MOS not perfectly quadratical?

texts:
I am a student and trying to understand the MOS transistor.
So I have simulated the transfer curve of a MOS in Cadence and done a parametric sweep for WL (500n, 1000n).
Here you can see the plot sqrt of the transfer curve Vgs/Id. (Level 1 Model)

If I change to a level 49 model in Cadence the curve is no longer quadratic. There are two effects I can see in the plot. First the curve rises exponentially/quadratic around the threshhold voltage and then it flattens out. Why is this so?


texts:
I have one doubt regarding SPI. I am very new to this module. I know that communication is initiated by asserting the CS(high to low) in SPI. And then in every clock based on polarity and phase the data is transmitted/sampled. My doubt is once data has been transferred and CS is asserted again(low to high), does the clock pulse still continues or clock pulse is only there till the communication is maintained.
The image shown is the waveform while trying to test SPI communication. The Master SPI shift register is of 16bits. I am transferring four 16 bits of data during the CS low period(i.e. when CS is enable). But during each clock I am getting 16 small incomplete waveform. I know this is wrong. Could someone give me the resolution or suggestion to rectify this.

I am expecting something like this, although it transfers two data of 8 bits each at 8 clock pulse, I want to transfer 4 data each at 16 bit clock pulse. When I increase my data buffer from 4 to 5, I get 5 square pulse, and each pulse having 16 jitters.

Please reply.


texts: Current mirror and differential amplifier

texts:
Hi,
In the attached figure, I am not sure how to formulate the relation between \$I_{ref}\$ and the DC currents through the four transistors \$Q_1-Q_4\$, given that \$I_{B1,2,3,4,5,6}\$ aren't neglected and that \$\alpha=0.98\$.
I found \$I_{ref}\$ to be \$1mA\$. Now, is \$I_{ref}=I_{c1}+I_{b1}+I_{b2}\$?


texts:
Currently, I have a board that powers 4 DC fans. A PWM signal is received from an external microcontroller to control the fan speeds. Unfortunately, the microcontroller sometimes fails to send the PWM signal, and I can not change it at this stage. When the PWM signal is not received the fans ramp up to maximum speed due to an internal pullup resistor in the fans. I want the fans to default at a speed anywhere between 20% and 50%.
I would like to make changes to this board by adding a default PWM signal which drives the fan speeds when no external PWM signal is received.
I have the following constraints and specifications:

All PWM signals have a frequency of 25kHz

I have 12V available to the board.

The board is tiny (the chosen components must be small and few).

The budget is low (the cheapest viable solution is prefered).

Below I have made a diagram of how I want to solve this problem. I have a few questions:

Is there a simpler way of solving this problem?

Is the 555 timer a good option for a PWM generator?

What logic level switch would be appropriate for a PWM signal?

How will I be able to convert a 25kHz frequency to 5V? (IC suggestions?)

Any advice, comments, critiques, component suggestions will be much appreciated.


texts: Understanding the Raspberry Pi 3's power input circuit

texts:
I am trying to understand the Raspberry Pi Model 3's power input circuit, as seen here:

However, I am stuck at the purpose/function of the centre subcircuit outlined in black.

What I have gathered so far is that the MOSFET - P channel enhancement type - is regulating the input power somehow based on the two PNP transistors, which are acting as some sort of current mirror.
As I understand, the current flowing from the right transistor's emitter to collector should be limited by the left transistor's emitter to collector current. This current is then split to the 47K resistor and the MOSFET's gate. The MOSFET will turn on when its gate voltage is ~-0.7V with respect to its source, so I can only imagine that when the voltage drop across the right transistor is ~0.7V, the MOSFET turns on. However, I do not understand how this effects the overall function of the subcircuit, nor the purpose of the 47K resistor (is it just an arbitrary value as a pull-down for the MOSFET gate?).

Additionally, the subcircuit is marked indicating it only allows (conventional) current flow from left to right, yet since a MOSFET's channel is bidirectional, should it not allow current to pass in reverse also?

So what is the function of the outlined subcircuit?


texts: Can't seem to add extra sheets to 4 page schematic design

texts:
I have an existing 4 page schematic I need to add an extra page too (see picture).  I can't figure out how to to add an additional page, how does one do this?

My version is Eagle 9.0.1 on Windows 10.

Thanks if anyone can help.


texts:
I have a motor controller board that handles 24v and up to 60a and can be varied via a mechanical pot of 100k ohms. I want to replace it with a digital pot like an MCP41100 and control it with an arduino.

Can I expect the motor circuit with the digital pot inserted to be isolated and separate from the arduino circuit with the control portion of the digital pot?

Bottom line is its not working and I'm trying figure out why.  Wondering if the two circuits are really one.


texts: Flash driver for 220V lamps according to the state of two switches

texts:
I am an absolute beginner in electronics.
I would like to actualize the simplest circuit capable to pilot small 220V lamps (in parallel), making them flashing according to the state of two switches and according to the following rules:

if both switch A and switch B are off, the lamps are off;
if switch A is on, the lamps are on;
if switch B is on, the lamps flash at about 1 Hz or little more, regardless to previous rules.

Lamps don't need more than 150 W in total.

It would be appreciated to have some explanation on how to vary the on/off cycle of flashing, remaining in the range about 1 Hz - 5 Hz.

Maybe what I need is a simple modification of this circuit, that satisfy switch B rule, but need to implement switch A functionality (to be always on, without flashing, ONLY IF A is off):

Many thanks!!


texts: An IC that would combine a counter and a decoder

texts:
I have a circuit that makes uses of a decoder to command the latch line of 8 latches.
To avoid spurious latching that could occur in transitions, I disable the decoder output while I change the input address.

I'd like (in order to work faster) to get rid of this mechanism. My input addresses are just counting (000 001 010 011 ... 111), so I was wondering if there was an IC that could fit my need, something like

8 output lines, with at most one line i reading 1
1 clock line which would do i = (i + 1) % 8 on an edge
1 reset line which would do i = 0 on an edge

Something like a synchronous counter + decoder without the transitional problem described above in one chip.

Does it exists ?


texts: Why can't my BJT common emitter trigger the pin interrupt of an MCU?

texts:
I'm trying to build a noise detector that gets triggered by pretty much all audible noises, provided that they are loud enough. The schematic design is as follows:

simulate this circuit – Schematic created using CircuitLab

At the out put, the oscilloscope reads the maximum reading of 3.3V (saturation or maybe it is called using some other term) , the maximum output possible when I clap my hand forcefully near the microphone. The MCU requires a 1.5 V input to consider logic HIGH. The above all happened when the entire circuit is on a breadboard and not in the MCU circuit, and as soon as I jacked the bjt circuit into the MCU circuit, the max voltage of the output (as seen on scilloscope) drops down to 1 volt, and the MCU simply doesn't get triggered, and I'm positive the MCU can be triggered properly because if I zap the interrupt pin with a  jumper cable attached to 3.3v source, the program will enter the interrupt handler.

This is quite confusing as I'm basically applying a circuit from a magazine that the author said would work.

My questions:

A. Why isn't a circuit capable of 3.3V output triggering the 1.5V requirement MCU? As I mentioned it probably has something to do with the voltage drop and I can only speculate it has something to do with the circuit not supplying enough current.

B. How do I do to solve this problem (not triggering)?


texts:
When I search for opamp-based voltage to current converters, I find scads of circuits with a transistor driver on the output of an opamp or variations on the Howland circuit.

I'm beginning to doubt my sanity -- it seems like the following would work just fine, as long as the device to be driven doesn't need to reference ground:

simulate this circuit – Schematic created using CircuitLab

Aside from the lack of ground reference and the other usual opamp caveats (stability in the feedback loop, maximum drive current and voltage), are there any things to watch out for using this configuration?


texts: Can oscillations happen even if negative feedback is present?

texts: By OPAMP book says that virtual short is applicable in OPAMP only if negative feedback is present an output is not oscillating.I don't get how oscillations can occur at output if the feedback is negative


texts: Carbon Brush Specific Resistivity and Wear

texts:
Kindly ask for knowledge share and support about Dc motor commutation principal.

I have a brush wear issue on a DC motor with brushes which I try to understand the reason. As I read in the literature, I see that sparking is an issue and could be solved by using higher brush material resistance, I did like this and used some increased specific resistivity having brushes, but I have lost some RPM at the same voltage in comparison to low resistive brushes.

Could you please explain me what is the physic behind that , why the RPM reduces if I use high resistive brushes ?

And generally why higher resistive brushes being exposed to lower sparking during commutation?

Thanks a lot.


texts: incorrect voltage applied, dev board still worked

texts: I took this guy from here - http://rlx.sk/en/accelerometer-gyro/3582-vibration-sensor-module-801s-er-sen801svs-.html and without noticing I have applied 3V3 instead of the advertised 5V to it. It also seemed to me it has worked fine. Can anyone tell me why it has still worked or if it makes any difference in this case ?


texts: Adding LFO Modulation to VCA in synthesizer

texts:
I just started sketching ideas to add LFO to VCA modulation in a device that already has a VCA circuit employed, but I’ve run into a snag… I can design a circuit to give proper modulation at full open VCA voltage, but as the signal voltage drops from 4.5v to 0v, the moduation signal falls and begins clipping the lower portion of the wave.

The first picture below is the stock circuit. 4.5V Key Down/0V key up (can be attack/release contoured) to 15k resistor feeding a 3906 transistor with base to ground. Collector to 10k resistor then to the input bias of a 3080 transconductance op amp. Voltage on the other side of the transistor before the 10k is -15V Key Up and -12V Key Down.

stock vca http://s.eeweb.com/members/patrick_edwards/discussions/2013/09/24/Screen-shot-2013-09-24-at-12.39.32-AM-1380002420.png!

Second picture is one my rough sketches. The LFO (1.6 to -1.6 swing) with a bias from the A/R voltage (which is fed through a buffer) feeds an amplifier that connects to the base of the transistor that was originally grounded. With this circuit I get a good modulation swing from ~-15V to ~-12V on the other side of the transistor at max A/R voltage, but as the 4.5 falls back to 0 the bottom begins to clip, as in picture three. I would like the amplitude to decrease steadily as the 4.5 falls to zero and then stop sending signal to base of transistor.

LFO added to VCA signal http://s.eeweb.com/members/patrick_edwards/discussions/2013/09/24/Screen-shot-2013-09-24-at-12.48.35-AM-1380002421.png!

Clipped LFO signal http://s.eeweb.com/members/patrick_edwards/discussions/2013/09/24/Screen-shot-2013-09-24-at-12.55.35-AM-1380002421.png!

I tried using biased transistors as variable resistors in the gain loop of the LFO amplifier but my knowledge of transistor switching and operation are not that great. If anybody out there could help it would be greatly appreciated.


texts: Maximum Vpp that doesn't change the output offset

texts:
I have a homework problem:

We have a non-inverting amplifier, \$G=+20V/V\$, which amplifies a perfect square wave, \$\overline{V_{IN}}=0.5V, \ V_{PP}=0.05V, \ f=50kHz\$. The output signal has offset equal to \$\overline{V_{OUT}}=10V\$. We also know that the smallest resistance value in this circuit is \$2k\Omega\$. What is the maximum \$V_{PP}\$ (peak peak input value) for this circuit, that will not change \$\overline{V_{OUT}}\$?
\$f_c=2MHz, \ f_{DP}=10HZ, \ SR=1V/\mu s, \ |V_{OUT(max)}|=13.5V\$

And, to be quite honest, I do not know what should I check and what will cause the change
EDIT:
The schematics:

And the smallest resistance will be \$R_r\$, i.e. the compensating resistor.
\$R_r=R_1 || R_2=2k\Omega \wedge R_2=19R_1\rightarrow R_1=2.11k\Omega, \ R_2=40k\Omega\$


texts: Simple Audio Amplifier Problem using BJTs

texts: Below is my constructed audio amp and graphs that corresponds to the voltage at the collector of Q1 and the emitter of Q2.  Everything works great until I add the capacitor to protect the speaker (8Ω).  Then for some reason the emitter voltage becomes cut off.  This is my first design so I am a newbie.  I expected the capacitor to just act like an open circuit at the high frequency..?


texts:
I'm playing around with different kind of 12 LED light sourcing. Normally I have used one of these 12 V power adapters (with EU plug). But I have got this idea of changing a halogen lamp with a home build LED lamp - so I need something safe that allows me to connect the 220 AC wires to some sort of light weight 12 V DC "converter" (I notice that most of the 12 DC power supplies are quite big and heavy).

Does such a solution exist ?


texts:
I have a circuit that I can't seem to understand how shrink down to one resistor.

This is similar to another problem i found on this form (Equivalent Resistance in a short circuit) however there wasn't much explanation as to how the answer was obtained. I was able to slightly redraw the circuit up to a certain point and couldn't procced.

If someone could please explain to me the process of solving these short circuit type of questions I would greatly appreciate it.


texts: Capacitor that stores one bit of information

texts:
I am a software developer (using high level languages like .NET,C,C++ etc) trying to understand how computers work at a lower level. I never studied any Electrical Engineering at university. I did GCSE Electronics.

I have experience using discrete capacitors and transistors to build circuits on breadboards and PCB's.

I am trying to understand how computers use capacitors to store information.  I understand the difference between SDRAM (flip flops) and DRAM (transistor/capacitor pair).

What do you call the capacitors in a computer that store one bit of information? (there are billions of these in a computer).  Every time I Google Capacitors or Capacitors in computers; Google returns information about discrete capacitors.


texts: What does Adafruit motorshield max amperage mean?

texts: On the Adafruit motorshield it says "1.2A per motor (3A max)." What exactly is this telling me, that the motors are drawing 1.2 amps from the battery?


texts: Resistance between non-inverting input of op-amp and voltage source

texts:
I encounter quite often this sort of problem in my textbook:

This is a classical non-inverting op-amp. However, I'm always perplexed with resistance R1 between voltage source and non-inverting input. Logically if there is a resistance, then there must be a voltage drop, then the real V(input) must be something like V(source) - V(R1). However, since the current in this branch is equal to 0, then V(R1) = 0. So, what is the point to draw this resistance (or a combination of different resistances which can give one Thévenin equivalent resistance) in numerous exercises? Is there some real world examples where R1 can play some role?


texts:
I have a 48 volts APC UPS (2200va/1980watts) attached to 4 65AH AGM batteries. A week ago after cleaning batteries and terminals, I accidentally put one battery in wrong direction. I turned the UPS on but it gave errors and showed red light and made a long beep noise. So I turned it off and noticed that one of the batteries was connected in wrong direction. I didnt have the tools near me, so 20 mins later I disconnected the 4th battery, put it in correct direction and turned it on. UPS turned on fine this time and has been running fine since.

But, Now the 4th battery voltage drops very fast down to 5-6 volts while other 3 are at 12.5 volts.

I would like to know, the batteries remained connected the wrong way for about 20 mins, what damage would this have caused to the 4th battery or may be all batteries.


texts: Safety Considerations for Wired Bathroom Cleaning Electric Brush

texts:
I've this Hurricane Spin Scrubber basically a battery operated surface cleaning brush. I love its convenience and effectiveness however I'm getting sick of the battery power limitation though, minutes of runtime and towards the end in limited runtime life with battery voltage dropping, brush's spinning actions slows, so really actual cleaning worthy power life is like 50-75% of the rated life. Battery also isn't easily accessible to keep hot swapping until job is done.
Multimeter measured 3-4 V DC and 4-5 A power being consumed by the motor coming from freshly charged unit's built-in battery. Motor isn't accessible to get its model # or read any labeled power specs hence the tapped power reading via multimeter.
I'm considering using low voltage power supply like this to hardwire power supply to the motor. Plug in the power supply brick outside bathroom away from any splattering water, use long tens of feet cable running from that power supply to the electric cleaning brush with adequate waterproof seal so water doesn't enter brush unit where power cable enters.
Is this too dangerous especially given wet environment of its application? I was considering adding in a 6A circuit breaker downstream of the power supply, haven't found any decent overvoltage protection yet. Worst case imaginations, over the time insulation of cable running from power supply to brush unit wares and my wet hands/body touch 5V DC 5A, is that unsafe, not worth pursuing? Any other improvement recommendations to safety or otherwise to solutions?


texts: I am having an issue with relays sticking

texts:
I use a DL205 PLC with a Do more CPU. This drives SPDT relays to control 90 degree motor operated valves. The valves are apollo motor actuated, which advertises 0.74amp starting/locked rotor current. I have confirmed this value with a clamp on ammeter.
The relays are automation direct 781-1C-120A 15A relays with 120VAC closing coils. During testing, I'm finding that some of the relays will randomly stick in the normally open position, preventing the valve from closing when the coil is de-energized. the relay will reset when mechanically agitated, but not otherwise. Voltage is correct, verified to 124VAC.

Has anyone seen anything similar to this?


texts: Where to get the core for an electromagnet?

texts: I understand that using a soft iron core or a ferrite core for an electromagnet increases the strength compared to an air-core. I'm going to be using DC current and want the core to be 5-8mm in diameter and roughly an inch in length. So where would I be able to find a soft iron core? I found this on Digikey and not sure if it's the right material.


texts:
I am designing a project that has around 50 or so outputs and around 20 or so inputs. I have designed a chainable breakout board for a standard '595 shift register for the outputs, and was planning on using a '165 or similar for the inputs. Because of board costs, I would love it if I could use the same breakout for both input and output. I could just set up one chain to be input and another chain to be output, but I would only need to have one type of board made. '595 and '165 do not seem to be compatible with that goal.

Is there any shift register that can operate as either PISO or SIPO depending on how you drive it. I would prefer something that I could read and write with SPI at a high speed at 3.3V logic and supply.


texts: Will be troubleshooting a motor, what precautions do I have to take?

texts:
I just purchased a secondhand portable band saw (corded) that just isn't reaching the maximum speed. I suspect that the speed circuitry is the culprit and not the motor as that is easier to sabotage.

So assuming that the maximum speed and power that the AC motor alone can achieve being connected directly to AC mains is what the circuitry will have at the maximum dial, can I simply connect the motor raw to the AC and bypass the circuitry? This is also assuming that the AC motor is singled phase AC. I've looked at the service parts manual (I haven't gotten to opening it yet) and it seems that there are only to wires going to the stator, I believe.

So how do I tell if it's safe to simply connect the raw AC mains to the motor itself? Could I simply measure the resistance and inductance of the motor and calculate the total impedance, to make sure it will not exceed 11A that the band saw is rated?

Also, do I have to worry about Back EMF? I have a bench grinder that is simply an Induction AC motor and I know it doesn't have a flyback diode. So do I NOT need a similar diode when running this test?

EDIT:

Come to think of it, the only 2 wires seem to be connected to the rotor, as there are brushes. So it could be a DC motor and it's controlled through PWM. I only have multimeters... So how do I test if it's PWM, especially if the PWM doesn't go negative?


texts:
Elec Eng student here, I've joined a project at my university's mechanical eng department who are building a rather large hybrid rocket. Unfortunately they've been having issues with the microcontroller (an atmega32) that's driving a hobby servo connected to the oxidizer valve. when testing in the lab everything works fine, but in two static tests in the field the valve closes shortly after opening. I suspect it's a power issue causing the MCU to randomly reset as they are running the MCU from a cheap switchmode 240VAC > 5VDC PSU with the only smoothing being a 100nF cap across the MCU! The problem I think is that in the lab they use normal mains but in the field it's powered by a generator..

If I can recreate the issue in the lab I'm going to look at beefing up the power-supply to the MCU, perhaps running from the 12VDC line into a linear reg (7805? ) with lots of input and output smoothing. what else could I do to make the power-supply bulletproof? common mode choke on the input? any suggestions or cool app-notes are welcome :P
I'm also considering a grounded metal box for the electronics to sit in as opposed to the current plastic one. good idea?


texts: If antennae work best at full, half or quarter wavelengths, why don't received signals at 1, 1/2 and 1/4 wavelengths interfere with each other?

texts:
How does a simple radio receiver-antenna differentiate between incoming wavelengths that are the same wavelength as the antenna, one-half and one-quarter?
Or would I just hear static unless I have a good changing-capacitance LC 'tank' tuner thingie?
(I am obviously still a beginner here... )


texts: How to overcome transistor heat in slayer exciter?

texts:
I build this circuit and it works but I have two problems. The major problem is that the transistor becomes very hot quickly. I burnt my transistor due to excessive heat. How can I get rid of the very high temperature of the transistor.

The second problem is that the circuit does not provide enough range. When I approach a florescent lamp, It does not light up. I brought a wire and modified its shape to be round (a circle). It looks like a coil that have one turn. I connected the high voltage terminal to one of the coil's terminals. The other terminal of the coil is not connected (open circuit). When I put the florescent lamp inside the coil it lights up. This is a very small range. I need a good range, something like 5 or 10 cm.
I need to know how to achieve a good wireless range? and What controls the range? Is it supply voltage, the base resistor or something else?

My supply voltage was 10 volts because I don't have a battery of 9 volts. The number of turns of the coil is 300 instead of 275.

Thank you,


texts:
I have been taking apart various consumer power supplies to try and understand their operation which is a most fulfilling use of a Sunday afternoon.

This transformer has two primary windings (see the four pins below the four surface mount resistors) I guess one for 110v and one for 230v. How does this circuit know which winding to use? I am guessing that its something to do with the network of diodes on the AC side?

AC at the bottom; DC at the top.


texts: Measure voltage using transistor with strange behaviour

texts:
I'm facing a problem that is completely strange for me.
This is simple, I build a small electronics device and in that one I just set up a voltage bridge divider to obtain battery voltage to be able to indicate what is the level of the battery.

Problem description

Behavior:
It works quite fine, means that when battery voltage is decreasing, it decreases on the input ADC on the MCU. The main problem, is that it discharges the battery same when the circuit is turned off.

What we tried:
OK, we have to find a system that permits to turn off the bridge divider when I turn off the circuit. That's why I simply added a transistor which is driven by the 3.3v regulator of the circuit:

When circuit is ON, 3.3v from the regulator drives a transistor BC547A (just for test) on the Base with a 10k resistor.
The transistor becomes "passing", and provide battery voltage to the bridge divider.
We read VBAT2 on the MCU, when system is powered

Strange behavior: But... this is not working, we observe that the transistor is acting like a regulator because it seems to be not "passing" enough to provide the voltage variation from the battery. This is the circuit that we are trying.

Schematic:

And when we measure variation at the input of the MCU, the transistor seems acting like a regulator O_o. It means that when battery voltage decreases slowly, voltage on the MCU input stay completely constant and stable.

Here are the measure that I've done:

The blue line is VBAT2 (the one that goes to the MCU), and the red one is the probe that is on the battery +.

The battery is a standard single cell lithium ion polymer, with battery voltage that move from 4.15 V (full charge) and 3.1 V (discharged).

Does someone can help me to solve this problem or explain to me why I observe this behavior?


texts:
when ldr is in dark, all voltage drop is across the ldr, so how does voltage at inverting input becomes negative when it is supposed to be 0V or (x)mV?

and when ldr is in light, all voltage drop is across resistor R1, so why voltage at inverting input is -7V?

note: i tried this on livewire simulator and got these values negative and -7V


texts: Combining two different voltages into one regulated voltage at higher amperage

texts:
The Commodore 64 user port has a +5V supply at 100mA and a 9VAC supply also at 100mA.  I need about 150mA from the port at 3.3 volts.

Is there a way I can use both supplies to get the amperage I need?

Can I rectify the 9VAC to DC and regulate it down to 3.3V, then regulate the 5V down as well with a second regulator and connect the two regulators in parallel?  Does that work like it might with battery cells?

Or is there a better way?


texts: Using solder paste instead of soldering wire for through-hole parts

texts:
I wonder if solder paste might work as a good substitute for soldering wire for through-hole soldering. I imagine that it could make soldering a bit easier in some cases, for example by providing a better contact between the part, the pad and the soldering iron for heat transfer.

Has anyone tried this and was it any more convenient than wire?


texts: ADC on a SAMD21 always gives zero values, except when using breakpoints in its interrupt

texts:
I started experimenting with the ADC on a SAMD21, and strangely, the result I get is always 0.

I initialized it like this (using the temperature sensor to get some values without external hardware):

SYSCTRL->VREF.bit.TSEN = 1;  // enable temperature sensor

GCLK->CLKCTRL.reg = GCLK_CLKCTRL_CLKEN | GCLK_CLKCTRL_GEN_GCLK2 | GCLK_CLKCTRL_ID_ADC;  // base clock GCLK2 = 1MHz
PM->APBCMASK.bit.ADC_ = 1; // Enable bus clock

ADC->REFCTRL.bit.REFSEL = ADC_REFCTRL_REFSEL_INT1V_Val;   // internal 1V reference
ADC->AVGCTRL.bit.SAMPLENUM = ADC_AVGCTRL_SAMPLENUM_4_Val; // average from 4 samples
ADC->SAMPCTRL.bit.SAMPLEN = 49; // for approx. 100 us/sample with a 4x prescaler on the 1MHz clock
ADC->CTRLB.bit.PRESCALER = ADC_CTRLB_PRESCALER_DIV4_Val;
ADC->CTRLB.bit.RESSEL = ADC_CTRLB_RESSEL_16BIT_Val;     // to support averaging
ADC->CTRLB.bit.FREERUN = 1;

ADC->INPUTCTRL.bit.MUXPOS = 0x18;  // temperature sensor

ADC->INTENSET.bit.RESRDY = 1;           // result ready interrupt

ADC->CTRLA.bit.ENABLE = 1;

NVIC_EnableIRQ( ADC_IRQn );

I checked that the clocks are working as they should, and made sure the ADC interrupts get regularly triggered, by toggling a portpin in the ADC interrupt.

After that, I tried reading some values.

volatile int debug_adc[201];
int debug_adc_c = 0;

void ADC_Handler()
{
    volatile int result = ADC->RESULT.bit.RESULT;

    debug_adc[debug_adc_c++] = result;
    if (debug_adc_c >= 200)
    {
        debug_adc_c = 0;
    }
}

I let it run for a while, and when I stop it, the array is full of zeroes, and the RESULT register in the I/O view is also zero.

However, if I place a breakpoint inside the interrupt handler, I see non-zero values, both in the array in the Watch screen and in the I/O view.

I don't touch the ADC anywhere else in my code. I also tried it without averaging (ADC->AVGCTRL.bit.SAMPLENUM = 0), nothing changed.

The datasheet recommends performing one manual conversion at the beginning, even if I use the freerunnig mode: ADC->SWTRIG.bit.START = 1;. I did it, but it didn't change anything.

Did I miss something obvious?


texts: Why place a diode in series with the LED in an optocoupler?

texts: Why add diode D7 in parallel with R20 on the LT4430 OPTO pin? Is there any reason excluding the diode and increasing R20 would be ill advised?


texts: Purpose of the Latch Enable (\$\overline{LE}\$) and Ripple Blanking (\$\overline{BI}\$) pins on 74HC4511

texts:
I am looking at the datasheet for the 74HC4511 (available here), and I am confused by the usage of two of the pins: Firstly, the "Latch Enable" pin (\$\overline{LE}\$), and secondly the "Ripple Blanking" pin (\$\overline{BI}\$).

Looking at the logic table for the IC gives states that if the Latch Enable, is high, and neither of the other two "special pins", \$\overline{BI}\$ and \$\overline{LT}\$ are active, then the output is dependent upon the BCD code applied during the transition of \$\overline{LE}\$ from low to high. Does this mean that it stores the BCD state and continues to output the corresponding 7-segment output (for instance if \$0001\$ was applied whilst \$\overline{LE}\$ was transitioning, and then was subsequently changed to \$0010\$, the 7-segment display would continue to display \$1\$ rather than \$2\$?).

I am more confused by the purpose of the Ripple Blanking input, it appears that this simply blanks the 7-segment display, but I do not know what the purpose of this would be, when you can simply set the BCD code to \$1111\$?)

Thanks in advance, and sorry if this is obvious!


texts: Are there types of standard coaxial cable with a propagation velocity of 0.9c? What would be the application?

texts:
Reading this answer I was surprised to hear that there are "excellent" kinds of coaxial cable with a propagation speed of 0.9c; 90% the speed of light.

The bargain basement number is about 2/3c, and coaxial cable with a faster propagation velocity would have to have a lower dielectric constant. Assuming \$v/c\$ scales as \$1/\sqrt{\mu_r \epsilon_r}\$ as it would in free space, that would mean the cable would have a relative dielectric constant of 1.2 for example.

Does this exist as a standard product? If so, are there applications where having "excellent cable" with such a high propagation velocity would be important? Or would it be a side-effect of other desirable properties of the dielectric?


texts: Trying to regulate 24V from 24-30V 3A input

texts:
I am trying to convert 24-30V input to 24V 3A regulated output. I tried using ti's 5A adjustable regulator LM338 but I faced heatsink problem which seems like impossible to keep cool while trying to supply that much. Do I have to buy a DC/DC converter or is there any other 'diy' way of doing it?

This regulator is going to be used for powering a water pump which requires 24V 3 Amps.

Heat dissipation calculation:

lm338 has a characteristic of 'Junction to Case, RθJC(top) 15.7°C/W'

The load will be dissipating 24v*3A=72 Watts of power, and the regulator will be dissipating (30v-24v)*3A = 18 Watts of power. So total is 90 Watts.

90*15.7= 1413°C seems too much isn't it?


texts:
I want to create a simple battery backup for my circuit.

This circuit is for battery charging

This is circuit battery switching, when power fails the switch-over would happen.
Am I on the right path of implementation.

Regards,

Chaitannya


texts: Want to output data on GPIOs in parallel, what is the delay between each pin?

texts:
I have the following setup to control 256 bi-polar stepper motors from a data stream via SPI.

I'm deciding between an MCU (teensy 3.6) or an FPGA.

Each motor (four wire) is driven by a driver that requires 2 GPIO's (A4988).

I use 32 16-bit shift registers to talk to the 256 drivers from around 36 GPIOs on the MCU/FPGA.

I want each motor to respond in unison when i issue commands, essentially they should be controlled in Parallel. An FPGA should do this well, but coding on one is not so trivial.

Using a Teensy 3.6 for the MCU approach, i would like to know how 'parallel' the control would be.

I.E. I have 32 Data lines going from 32 GPIOs to 32 16-bit Shift registers; I want to turn all steppers fully on in the same direction: how long is the latency between the command being output from GPIO 1 to GPIO 32?

Here is a block diagram to aid the setup.

I would probably go with the MCU approach if the latency is negligible, but i would like to know your thoughts. I would imagine any latency only being an issue since i bridge all other shift register control pins (latch, clock etc).

Thanks


texts: Is the series resistance of an analog ammeter the parallel equivalent of shunt resistor and resistance of galvanometer?

texts:
An analog ammeter is made by a galvanometer (with certain \$i_{max}\$ and resistance \$r\$), in parallel with a shunt resistor \$R_s\$ that depends upon the max scale chosen.

Nevertheless, when an ammeter is concerned, we talk about a series resistance of the ammeter. Is this series resistance simply the parallel equivalent of \$R_{s}\$ and \$r\$? that is

$$R_{series}=\frac{R_{s} r}{r+R_{s}}$$


texts:
In a distribution grid, what is the speed of

energy
signal

Is it strictly the same?

And how is synchronisation achieved? Is an electric grid essentially an orchestra where everyone is the chief and gives the beat to everyone?


texts: I2C - Cannot read temperature from TC74 with PIC16F887

texts:
The question was:
I want to read temperature from TC74 using I2C module of PIC16F887, however, in Proteus
simulation, I see noises in I2C Debugger Tool's output.

It told me that I had "Spurious SCL transition". Any other info about the question such as schematics, code and screenshot can be found in the older revisions.
The problem is fixed after adding a 4us delay after a restart condition as it is stated in the datasheet as:

START Condition Hold Time  -  Min: 4us
START Condition Setup Time(for repeated START Condition)  -  Min: 4us
STOP Condition Setup Time  -  Min: 4us

That means that we should always read the datasheet thoroughly first.
I am guessing that the reason people in the internet don't have any error when they don't obey those wait times is that their clock speed is low and they don't need to put a delay in the uC.
Working code and any other information of this post can be found in the older revisions of it. To see the final version of question before this shrinking, simply go to this page.


texts: How to use multiple input ports for internal ADC of PIC18F4550?

texts: Is it possible to use the setChannel() command to switch between the inputs for the internal ADC of PIC18F4550 at the end of each conversion, e.g. from AN0 to AN1 and back, or register initialisation is required for input switch?


texts: How is spread-spectrum implemented in low-duty cycle transmitters for 868/900Mhz, 2.4Ghz, etc

texts:
There are many point-to-point and mesh data communications modules available which operate in the 868/900Mhz and 2.4GHz bands.  I understand how frequency-hopping spread spectrum devices could work very efficiently in the presence of a nice uniform "time" signal.  Absent such a thing, though, how can transmitters and receivers efficiently find each other?  The only way I can see for transmitters to be found by receivers would be for them to precede any transmissions at particular frequency with a preamble that's long enough for a receiver to cycle through all available frequencies until it stumbles upon a frequency that's in use.  Under such constraints, increasing the number of channels used for a particular device's frequency hopping would increase the required preamble length.  Further, unless the preamble include a repeating data pattern to allow devices to reject early on transmissions that are not of interest to them, increasing the number of channels used for frequency hopping would increase interference among frequency hopping devices (since if two unrelated devices A and B attempt to transmit in the same range of frequencies, with A's transmission slightly preceding B's, a receiver that was interested in B's transmission might likely hear A's preamble, lock onto A's frequency, and thus not be scanning for other frequencies while B's preamble is being transmitted.

Am I misunderstanding things, or is the above how the various radio modules on the market actually work?

What would seem more sensible would be to have a small number of channels that were used to send "packet headers", where each packet header would then contain the number of a randomly-selected channel which would be used to hold packet data.  If the receiver only had to listen for a small number of channels, it could more quickly identify the preamble of a transmission, thus reducing the required length of a preamble (e.g. using four channels instead of 15 would probably allow a 2/3 reduction in preamble length).  Since only packet headers would be sent on the "introduction" channel, it would seem that contention there could be reduced.

If a receiver has to hear a four-byte preamble sequence to recognize a transmission, sending packets of 64 data bytes and 10 header bytes on 15 randomly-selected channels would require, for each packet, typing up a channel for 75+10+64 = 149 character times; divided among 15 channels that would be an average of 10 character times per channel.

If one were to use four "introduction" channels and 11 data channels, each transmission would require sending 20+10=30 bytes on the introduction channel, and 4+10+64=78 bytes on the other channel (figure most of the header wouldn't need to be retransmitted).  Utilization of the introduction channel would be 30 bytes/4 channels (7.5/channel), while the data channel utilization would be 78/11 (7.1/channel).  Does anyone know whether any devices do such a thing?


texts: Why 100nF capacitor between FT232R DTR pin and Atmega reset line is causing problems at boot?

texts:
I'm having issues with a 100nF capacitor between FT232R DTR and Atmega328p reset line  having too much capacitance between toggling the power on/off.

It causes the pc driver not to detect the FT232R (Unknown device).

If I press the reset button while the board is powered down or wait enough time, the capacitor will be discharged and it works then fine.

Schema between the DTR and Atmega reset Line:

             ATMEGA-RST
        100nF    |      10kOhm
DTR -----||------+------^v^v^----- VCC
                 |
                 +--RESET-SWT--GND

Could the problem be that the capacitor is not really 100nf but bigger thus taking more time to discharge after powering down the board?


texts: Component clearance for stencils and solder paste

texts:
I've never used stencils before, but now I'm going to have to (BGAs, lots of 0402 caps and resistors, etc).

How close together can the paste holes for say adjacent 0402 caps be for a stencil to work properly?

I tried calling my stencil manufacturer, and they basically said "I dunno, send us your board files and we'll let you know if it's too close"...

One person I know says 5 mils between paste holes, but that seems like an awfully awfully thin wall in the stencil.

What's a reasonable clearance value? Would that number be different for using a stencil by hand?  (vs. a more controlled automated unit)

EDIT: I'm currently aiming for a 10 mil clearance between paste holes. It appears that should be perfectly doable (since providers like Pololu say they can do approximately 0.5mm pitch, which works out to a ~10 mil gap between pads) However, what's a good clearance value assuming a nice laser cut metal stencil?


texts: Can Computer Motherboards Work Fine Even With A Damaged SMD Capacitor/Resistor?

texts:
I'm asking this because when I was replacing my laptop battery, I accidentally hit and broke/disconected one SMD capacitor off the board, then I turned my laptop on, it made some weird electrical noises while booting and apparently is working fine without the capacitor.

I'm worried because I'm overseas in the UK and I'm don't know how much they gonna charge me.


texts: Can anyone please explain how this Zener diode circuit works?

texts:
I am learning how a Zener diode works.

Can anyone please explain me how to analyze this circuit (with equation if possible)?

Thanks.


texts: A question about braking and deceleration of an AC motor

texts:
Here is an info about regeneration due to braking:

  Most of the time, in most applications, a variable frequency drive
  controls the motor by supplying it with energy which then powers the
  load. However, occasionally the energy flow will be in reverse, that
  is, from the load, through the motor, back to the drive. This will
  occur if the load is giving up energy, such as when a crane or
  elevator is lowering a load, or maybe when a conveyor is transporting
  material downhill. Regeneration, as it is called, will also take place
  if a high inertia load is decelerated; in this case, the energy stored
  in the rotating mass flows back through the motor to the drive. Fans
  often regenerate when slowed quickly.

I can understand first examples where a crane or an elevator is lowering a load it acts as a generator. But the info says this regeneration will take place if a high inertia load is decelerated. How can this happen in practice?

If I decelerate a motor does that mean I have to mechanically stall its shaft and it will cause regeneration? What can be an example to deceleration in this context? How does such braking happen so that it causes regeneration?


texts: I'm restoring an old vacuum tube radio, I removed all the bad capacitors, resistors and all 5 vacuum tubes and exchanged them with new ones. Finally, I installed the last two resistors in parallel, as per the schematics, but when I operated the radio both resistors became extremely hot so I put the radio off. Those resistors are installed in parallel and located between the main power transformer of the tube radio and the rectifier tube and their values are 270 ohms/2 watts and 330 ohms/2 watts, exactly as per schematics.  I've also done all the voltage checks and everything appears to be normal. What could be causing both resistors to heat-up?


texts: How do I measure very low frequency noise?

texts:
I'd like to measure low-level noise in the 1 Hz to 100 kHz range, for example at the output of a LDO.  For higher frequencies a spectrum analyzer would do the job, but most only go down to the MHz range.  I have access to an Agilent E7495A which goes down to 500kHz (kinda), and I have seen a few go down to 9kHz (Agilent E4411B), but I've never seen a 1 Hz analyzer.

TI for example has a whole video that describes how to measure LDO noise: https://training.ti.com/engineer-it-how-measure-ldo-noise-and-psrr  They show using some kind of analyzer, but what is it?

What is the usual type of instrument used for this?  Spectrum analyzer connected in a special way, audio analyzer, something else?


texts:
I made a sound amplifier and it requires a Capacitor, i removed the capacitor and my amplifier stopped working, what was amplifier doing in that circuit?
Why on removing it circuit stopped working.


texts:
When designing an output filter for a simple class-D amplifier I am unsure about sizing the components. Given:

cut off frequency of approximately 50kHz
the inductor DC resistance can be disregarded for this question
the load is 8Ω, for this discussion purely resistive
this architecture:

simulate this circuit – Schematic created using CircuitLab

The center frequency for the LC filter is:
$$f_c = \dfrac{1}{2\pi\sqrt{LC}}$$

Possible solutions include (but not limited to):

\begin{array}{|c||c|}\hline L & C \\
\hline
220\text{μH} & 47\text{nF}\\
22\text{μH} & 470\text{nF}\\
2.2\text{μH} & 4.7\text{μF}\\
220\text{nH} & 47\text{μF}\\
\hline
\end{array}

What are the proper design criteria for choosing a larger or smaller inductor / smaller or larger capacitor?


texts: What will be the effect of putting a single phase load on an open delta transformer secondary?

texts: Suppose I have an open delta transformer, 240 line to line secondary. I have a single phase constant power load I want to apply. I could apply it across either of the 'closed' phases and load that one phase. Presumably the two legs driving that phase on the primary will see all the load, completely ignoring the fact that the other transformer leg is present. But what happens if I load the 'open' phase? Will I see 240 volts still? Or something else? Will the load be distributed between all three legs on the primary side? Equally? What other effects can I expect?


texts:
I'm a total beginner with circuitry, but for thinking through a project for I want to build as a hobby some day, I'd need an "inverted relay."
A relay is, from my understanding this:
I have a main powerline that I either want on or off, and I want to control whether this is on or off by sending little bit of power through another powerline (i.e a control wire, e.g. controlled from a yes-no-switch). It's on when there is electricity in the control wire and off when not.
Now, I'd need something that breaks the current in the main line if it's set.
I can imagine that this very well exists, but through my lack of knowledge in this field I'm missing the correct terminology to google this properly.
So what's this name if such a component exists?


texts: Bench power supply - Inconsistent voltage output

texts:
It's been 3 years since I first bought my bench power supply, a Long wei LW-K3010D. This issue has reoccured to me a couple of months ago, but it usually "went away" when the PSU was switched on for a couple of minutes...
The issue:
When I use the voltage knob to adjust the voltage, the voltage goes up and down in a sort of crazy way. Let's say the voltage is 0V and I start turning the knob clock-wise. The voltage suddenly goes 12V, then 9, then maybe 15 and if I leave it for a bit goes down to 2V (for reference: it was supposed to go to 0.1-0.2V)
Could it just be a bad potentiometer?
Does anybody know what the heck has gone wrong so I can replace the part? I would be thankful if someone out there is able to give me some insight! Thanks so much!


texts:
simulate this circuit – Schematic created using CircuitLab

I am using a 5V 3A wall adapter. I have stripped the output end and connected it to a terminal block. I am rerouting the current to two places: a standard breadboard and the Raspberry Pi. When I use the multimeter to measure the current I see readings of 0 and then sudden spikes to 2A.

Why am I not seeing anything close to 3A? I am measuring the current directly from the adapter's PWR and GND wires. Please let me know if any additional info can help.

I also get PWR warning issues from the Raspberry Pi but I believe this may be a result of the fluctuating current readings OR the fact I am using 26 AWG cable (rated max 300 mA when the Pi needs 1A).


texts: Line-Neutral-Ground instrument to be plugged to a Line to Line power source

texts:
What are the problems that may occur when a Line-Neutral-Ground instrument is plugged to a Line to Line power source?

Any suggestions?


texts: Mixed Signal Grounding: Which approach will yield better isolation and analog performance?

texts:
I'm laying out a mixed signal PCB and I'm trying to decide between (1) separating the ground planes for the digital and analog/digital circuits completely [shown in top figure] or (2) keeping the two planes mostly separated [shown in the bottom figure]. The lines in the middle of the figure represent digital wires that carry data to and from the analog/mixed circuits.

I don't like (2) very much from a CAD perspective because then you can't have separate nets for AGND and DGND. Is there some reason not to go with (1), in terms of noise performance? Is there a better way to keep the digital noise away from my precious analog circuits?


texts:
I’m looking for a simple digital version of the functionality of a pull chain switch, but controlled by a tilt switch.
I want to put it into a book on my book case.  Tilt the book and the circuit latches and conducts.  Tilt the book again and it’s off.
I want to use the old tilt a book / Scooby Doo switch to turn on my fire place.  Currently it is a boring light switch.
Any ideas?
I can’t figure out a way to have the tilt switch activation toggle a flip-flop action. Maybe I could use a latching relay?...


texts: Developing a new System... confused between RFID or NFC.. just a few questions

texts:
I know NFC is the new in thing and it may go a long way specially w/ payment systems.

I'm new to this wireless tags thing.

I'm a PHP applications developer and I'm gona do a few applications like Daily Time Recording and Membership app for an establishment.. My requirements are simple.. rather relying on barcode on ID's , or magnetic strips, I wanted to employ RFID, or perhaps NFC for this system.

All I need at the moment is the secure ID of the tag to be combined w/ an entry / profile in MySQL and do my magic from PHP side. I don't need long range reading /writing capabilities like RFID.

Would like to know the following:

1) W/c is generally cheaper to implement? Cheaper readers? Cheaper tags?

2) Which is more secure based on the above? I was told NFC is more secure, but w/ people being able to read and write on tags using their phones, how secure is it really? I do not plan to store vital info on the NFC chip, or if I do ill probably use some encryption to jarble the text data 3) NFC tags can be set as READ ONLY.. how does that work? is that secure? reliable? 4) Is it easier to mimic the tag's id/serial vs rfid serial?

and lastly, not to ask you guys to shop for me, but more on to point me to the right direction.. is there a reader/writer that has API's built in so that i can interface w/ it immediately using PHP?


texts: What kind of magic is energizing the coils in this simple stepper motor driver?

texts:
Looking at this web page, i found a simple stepper motor driver circuit
https://www.electronicshub.org/stepper-motor-driver-circuit/

The problem is, i just can't understand how it can work when the diodes are reversed.
And even if they were not reversed, i still cannot see how any of the coils be energized when one of the pins on the CD4017 counter turns on.

At first i thought the circuit must be  flawed until i saw the video showing it does work, with the reversed diodes.
Video :
https://www.youtube.com/watch?v=ejvTG90kA0k


texts:
I need to measure pretty high currents (maximum 100A) flowing from one battery to another. I came up with a solution involving the measurement of the voltage drop across a shunt resistor. The supply I'm using for powering the circuit is isolated from such batteries. Since I'd rather use a single rail supply for the board, containing both analog conditioning system and microcontroller, I came up with the following schematic.

I chose a Rail-to-Rail output OpAmp (LT6232) in order to have its output ranging from 3.3V to 0V. The simulation has been carried out using LTSpice and its device models.

The output voltage (from how I designed the resistors) should follow the formula Vout = (Rf/R1)*(V2 - V1) + V_ref.

1) if Vbat1 = Vbat2 (current on the shunt 0A), I would measure 1.65V (correct!)

2) if Vbat1 < Vbat2 (i.e. Vbat2 = 12.15V and Vbat1 = 12V, current on the shunt 100A), I would measure ~3.3V (correct!)

3) if Vbat1 > Vbat2 (i.e. Vbat2 = 12V and Vbat1 = 12.15V, current on the shunt -100A), I should be measuring something around 0V, instead the simulation shows something slightly below 500mV.

What am I doing wrong? Thanks for helping.


texts: 5v/2.1A Power Bank batteries powering LED strip dropping output at 260mA

texts:
I am having an issue with powering a 30 x ws2812 RGB LED strip with a 5v/2.1A "power bank" battery.  The strip is controlled by an Arduino Pro Mini(-ish) clone (3.3v @ 16 MHz) (http://www.anarduino.com/mini/).  This Arduino clone does not have an on-board 3.3v regulator.  So, I am using an AMS1117-3.3 regulator module. (https://www.openimpulse.com/blog/products-page/product-category/ams1117-3-3v-voltage-regulator-module/.)  The unregulated 5v also supplies the LED strip.

When I use the power bank battery, The Arduino starts up,  But, when the LEDs come on to any significant brightness the regulated output drops to about 2.2v, and the Arduino stops.  I don't see this issue when I use a 5v/4A wall wart supply.  Note that with the wall wart, I am only drawing about 750mA.  When I use the battery, the Arduino is pulling about 260 mA--no where close the advertised 2.1A.  I have tried two different power bank batteries from different manufacturers with the same result.

One thought I had was that this was an inrush current issue--even though the capacitive load shouldn't really be that high.  Note that each LED presents about 15pF.  But, to test this, I modified the Arduino code to slowly turn on the LEDs--one at a time over the course of a few seconds.  Again the system halted (slower) at 260 mA.  If I only turn on about 10 LEDs, it works fine with the power bank battery.

So, this obviously appears to be a power/load issue.  But, I am still wondering, under what circumstances, will these power bank batteries provide anything close to 2.1A of output?  My understanding of these power bank batteries is they are basically Li batteries (3.7v) with a buck/boost regulator to bring them up to 5v.  Is there some weird load interaction between the power bank regulator and the AMS1117-3.3 that is causing the output voltage to drop?  Thoughts?  Ideas?


texts: MOSFET not turning OFF after first power ON

texts:
I have the following circuit wired up:

simulate this circuit – Schematic created using CircuitLab

Where 4 STP55NF06L MOSFETS are wired to 12V LED stripes, and one STP55NF06L MOSFET drain is wired to an ATX PSU green (PSU ON) wire.

System just plugged in. Arduino pulling "PSU" MOSFET gate LOW. PSU OFF.

Arduino pulling "PSU" MOSFET gate and "RED LED" MOSFET gate HIGH. Both PSU and RED LED turning ON accordingly.

Arduino pulling "PSU" MOSFET gate and "RED LED" MOSFET gate LOW (0.02V with FLUKE 106 multimeter). PSU and LEDs failing to turn off.

When the whole system is unplugged from mains:

MOSFETs Drain-Source resistance = 9Mohms.
MOSFETs Gate-Drain resistance = 9Kohms.

When the whole system is plugged to mains but no MOSFET has been turned on yet:

MOSFETs Drain-Source resistance = fluctuates every second between 3.5Kohms and Open Line.

When the whole system is plugged to mains, MOSFETs have been turned on before and now all the Gates are being pulled LOW:

MOSFETs Drain-Source resistance = Open Line. (But LEDs shining and PSU still ON in spite of "PSU" MOSFET gate pulled LOW)
Gate-Source voltage is 0.02V when LOW and 5.2V when HIGH.

I haven't managed to fix this myself in the last few days. There are many posts in the internet about MOSFETs not working properly but I don't understand why do MOSFETs work OK when the system is first plugged in and cease working once their gates have been turned HIGH at least once. I'd appreciate any suggestions. Please don't hesitate to ask me for any information I might have forgotten to post ! Thank you in advance.


texts: Touching MOSI on RJ45 connector cleans bus noise

texts:
I am using a STM32F767ZI-Nucleo development board from ST. i'm using it to communicate by SPI with a UM7 orientation sensor board. There a register to read in the FW version. Normally I only receive the right response about 66% of the time to what seems are good inputs (SCK, MOSI and SS lines). I used a wire to measure with the scope the MOSI line. When I accidentally touched the tip of this wire to the RJ45 connector casing of the dev board, all of a sudden 100% of my readings are now OK!

The RJ45 casing is not grounded otherwise there would be no readings, but the metal of it somehow changes my MOSI signal (no apparent change in scope). Since my team s developing an actual board, it would be nice to know what is going on here, so I can maybe replicate it in the board.

Any ideas? Thanks


texts: Multi channel Mosfet driver ghosting between channels (with suggested fix)

texts:
I´m pretty new to the forum (as you will see by my limited electronics knowledge) and I have a wierd problem when trying to control some automotive fans at variable speed. The fans each have an internal micro controller that you control with PWM by switching is signal wire (24V rails in the diagram) to ground at 90Hz. The small circuit I designed is just supposed to switch the 4 24V signal wires to ground at the same rate as the 4 TTL level PWM signals from my aquisition system(the signals are synchronous).

Here´s a diagram of the current setup:

This circuit is working perfectly when all the fans are running at the same speed(when all the PWM signals have the same duty cycle). But when I try to control the fans so they run at different speeds, they will not run at different speeds and instead all run at the speed corresponding to the highest duty cycle.

For the circuit depicted above, even though I only want the left MOSFET to be switched at a dutycycle of 50% while the others get a dutycycle of 10%, they all seem to be switched so they get a dutycycle of 50%.

After some thinking I realized my mistake, because even when the three lower duty cycle signals are low, the leftmost one (which is still high becasue higher duty cycle) will set the gate voltage of all the transistors to high through the ground rail (right?). As I see it, there´s two solutions to this.

The first one is that maybe there´s a grounding issue, as I didn´t ground my signal generator (Dewesoft Sirius STG-8) to the rest of the circuit. (before you say I should try this before asking, I have very limited access to the hardware mentioned because of high demand).

The other option is that my circuit is lacking, so I made a diagram for an improved version with resistors to protect the mosfets and diodes to hopefully prevent channels from controlling each other

Here´s a diagram:

Will it be enough to just ground my signal generator or should I start building the new circuit, and if I build a new circuit, is the one depicted in the diagram adequate?

Any help greatly appreciated!

EDIT WITH CLARIFICATIONS:

My circuit has NOTHING to do with switching the power to the fans, my circuit is only switching the signal wire to ground. When the signal wire is connected to ground, the fan ECU interprets it as a high PWM state, and the opposite is true for when the signal wire is not shorted to ground.

Every MOSFET has a separate TTL level PWM signal driving it.
Please keep the language as non technical as possible, my electronics background is limited!

Diagram one corrected:


texts: Why can't one battery power an infinite number of leds (or anything else)?

texts: If voltage is equal across parallel resistors, then why can't one battery supply power to a infinite number of leds, if they are all in parallel?


texts:
I heard someone said, using LDO is better than buck converter, but I don't know why.
Why is an LDO better to be used with op-amps than a buck converter?


texts:
I was hoping to use a Linear Comparator with a latch such as LT1016 as a trigger for the Register output clock for a 74HC590.

The 74HC590 is going to be cascaded with it's RCO going to several more 74HC590's on the 590's counter clock I am going to find (hopefully) an adjustable clock source so I can count the Time it takes between when a UltraSonic Transducer to receive a signal so I can calculate the velocity of the air in between them.

I was hoping to connect the comparator's output to it's Latch so I only catch the first pulse as I'm assuming their is going to be echos and whatnot after it first goes off.

Is a Linear Comparator the right tool for this situation?  I've seen other's that use a series of OPAMPS amplify the transducer's reception to something logic level (And I've ordered some as well to try) but this seems like a more straight forward way then trying to figure out the gain needed and the noise and whatnot, and with OPAMPS I'm going to need to figure out a way to stop them to keep the Register on the 590 from updating.


texts: Battery voltage isolated monitoring on Microcontroller

texts:
Is it safe to directly measure high capacity battery (100 Ah to 300 Ah) voltage with Microcontroller's Analog to Digital Converter (ADC)?
Would it be enough to use just a simple voltage divider to do this?

Battery voltage types to be measured are 2V and 12V.


texts: Is it possible to use 2 rotary encoders at once?

texts:
I'm working on this project: http://www.corsaclube.com.br/viewtopic.php?t=102183
I'm basically installing an iPad mini on the dash of my new car, but I'm facing a problem:
The iPad doesn't offer volume control when it's in Dock Mode and the head unit will be hidden behind the Tablet.
I was thinking in solder a second and identical rotary encoder as a "parasit" on the original one for the volume control, so I install that second one somewhere handy on the dash. The rotary encoder my head unity uses isn't optical, it's the "clicky" one (same feel of the scrolling wheel on some computer mouses, sorry for my ignorance)

Will it work? If not, how can I do that?


texts:
My LED TV is broken, so I disassembled it, and saw this weird thing on the power stage:

Above it, there are two 3 ohm resistors. (owners of the large drill holes in image) What could be the purpose of these? The only thing I came up with is that it is a clever use of solder to help the resistor from overheating. Is that the case here? How much of a difference - approximately - would they make?


texts:
I am new to Operational Amplifiers and I am trying to simulate a differential amplifier with a gain of 1.2, here it is:

As you can see I am using input voltages higher than VCC and according to datasheet the Common Mode Voltage Range is VCC-1.5V so the Operational Amplifier should work "ok" only with input voltages less than 28.5V am I right?

But on this simulation I am getting a correct output: (40-32)*1.2 = 9.6V. So I can put higher voltages than Vcc or simulation is wrong?


texts:
I've searched the forums but have not found what I'm looking for.
The problem at hand is that I have no idea how to successfully calculate the ripple over the load in this schematic:

simulate this circuit – Schematic created using CircuitLab

I know that Vripple = i / 2fC where i is the current over the load. But this is the ripple over/in R1. Not over the load.
So the question is, how do I calculate the voltage ripple on Rload? I thought some kind of voltage divider. When I attempt it I compare the values to the simulated values I get in Multisim. Not even close which makes me think that I have absolutely no clue where to start.

Some values that might be useful: Vpeak = 16.97 V, Voltage drop of 0.7 over each diode, zener voltage is 10 V. Everything else is given in the circuit above. Zener current in this circuit is (15.57-10)/180 = 31 mA

Thanks for any advice and pointers.

EDIT:
Is this it? I still have no idea how to calculate ripple though. The voltage over the capacitor will not change so it will always be 15.57 volts. More tips? I honestly have no idea what to do next. In my head everything in this value in this circuit changes based on the load which makes this so much harder to calculate.

simulate this circuit


texts:
Vs = 5V

R1 = 50k

R2 = 7k (adc internal resistor)

C2 = 120pF (adc internal capacitor)

I have a big output impedance as R1 at the output of the sensor and i want to connect it to ADC. But max allowed source impedance is 10 kohm therefore i thought to add C1 to decrease the needed charging time. But i can't figure out the exact timing analysis for this RC circuit. Therefore i can't decide the value of C1. Thanks in advance.

Edit: pic midrange mcu reference manual   In section 23.14 (Design Tips) For faster conversion putting C1 capacitor is advised but exact timing analysis is not given after adding C1.


texts: I need to build a circuit that adds two n-bit 2's complement numbers. the two numbers have to be stored in shift registers. The circuit should start with the least significant bits of each number and add each pair of bits using an adder. The sum bit from the adder will then be stored into one of the registers. WE need to use 2 shift registers, an adder and one dflipflop.


texts:
I'm working in an office with a Wi-Fi router, desktop, and a few cell phones making RF noise.

I have an 8 feet long by a 3-feet wide table, and I have an Aaronia BICOLOG 30100 + spectrum analyzer + comb generator (at calibrated EMC limits).

I'm getting too much ambient noise from my surroundings.

I was thinking of a giant cardboard box coated in aluminium foil inside and outside of the box, as a makeshift Faraday cage since I can calibrate my antenna readings off the comb generator.

I can put my DUT and antenna inside the cardboard box at the same time, and probably be within a few dbu/V of an actual reading since the comb generator is calibrated from a real chamber.

Has anyone come up with something better for a homemade Faraday cage?

Our office doesn't have space for a shielded chamber at the moment!


texts: Why is an op-amp necessary for photo detecting circuit generally?

texts:
I am trying to build a photodetecting circuit with a photodiode Hamamatsu Si PIN photodiode S6036
As I don't have much knowledge about circuit, I think a reverse voltage supply and a resistor are enough to build the circuit:

But, when I googled for a photodetecting circuit, the most examples are using op-amp. With a further search, I found that a such circuit is called transimpedance amplifier:

(source: wikimedia.org)
With my rough calculation, in the first figure, V_OUT across R will be I * R (Suppose that I is the current by a photodiode.) And in the second figure, V_OUT at the end of the op-amp will be I_P * R_F.
Both equations have the same form. Then, what reason makes TIA circuit si the widely used photodetecting circuit? TIA circuit can have higher gain? bandwidth? or stability?


texts: How to configure Multichannel ADC properly? Currently two different values stored in same variable

texts:
I want to use Multichannel ADC using the STM32F4 so I want to read two different AC signals on two different pins/channels. One AC signal value should be stored in ADCConvertedValue[0] and the other in ADCConvertedValue[1].

The problem is that both of the pins store their value in ADCConvertedValue[0]. I skipped the initialization code and put the important part below. Does someone see the problem?

  __IO uint16_t ADCConvertedValue[2];

  ADC_HandleTypeDef    AdcHandle;

  AdcHandle.Instance          = ADC2;
  AdcHandle.Init.ClockPrescaler        = ADC_CLOCKPRESCALER_PCLK_DIV4;
  AdcHandle.Init.Resolution            = ADC_RESOLUTION_12B;
  AdcHandle.Init.ScanConvMode          = ENABLE;
  AdcHandle.Init.ContinuousConvMode    = ENABLE;
  AdcHandle.Init.DiscontinuousConvMode = DISABLE;
  AdcHandle.Init.NbrOfDiscConversion   = 0;
  AdcHandle.Init.ExternalTrigConvEdge  = ADC_EXTERNALTRIGCONVEDGE_NONE;
  AdcHandle.Init.DataAlign             = ADC_DATAALIGN_RIGHT;
  AdcHandle.Init.NbrOfConversion       = 2;
  AdcHandle.Init.DMAContinuousRequests = ENABLE;
  AdcHandle.Init.EOCSelection          = EOC_SEQ_CONV;

  sConfig.Channel      = ADC_CHANNEL_1;
  sConfig.Rank         = 1;
  sConfig.SamplingTime = ADC_SAMPLETIME_480CYCLES;

  if (HAL_ADC_ConfigChannel(&AdcHandle, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

  sConfig.Channel      = ADC_CHANNEL_2;
  sConfig.Rank         = 2;

  if (HAL_ADC_ConfigChannel(&AdcHandle, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

 if(HAL_ADC_Start_DMA(&AdcHandle, (uint32_t*)&ADCConvertedValue, 2) != HAL_OK)
  {
    Error_Handler();
  }


texts: Is it normal to have SPI Clock with varying duty cycle?

texts:
I am working to get an SPI interfacing radio module on embedded Linux system. This particular module (RFM12B) is already ported onto Raspberry Pi. Now I am working on OMAP4 based systems.

I noticed that on Raspberry Pi, SPI Clock generates steady 50% duty cycle. On my OMAP4 boards, it varies between 2 or 3 values. The values in the screenshots are: 33.3%, 42.9%, 40.0%, and 42.9%. My logic analyzer is measuring at 16MHz, while the SPI clock run a little over 2MHz.

I am simply sending random text like below:

echo "HELLO!!" > /dev/spidev1.0

I am very puzzled because I think this might be causing buffer overflow and underruns - eventually getting CRC16 failure on the receiving end.


texts:
g

This is a picture of my Differentiator and Integrator combinded, in a working delta sigma modulator.

My question here is: Many other integrator and differntiators have the input signal on input 2. Opposite of what I have. And input 3 down to ground.

Will it have anything to say for the result ? Is my circut wrong ?


texts: Shielding from inductive charging in simple PCB

texts:
I am going to design a fairly simple binary LED wrist watch. For a cool feature and a good learning experience I want it to have wireless charging capabilities so I purchased this wireless charging set from adafruit link

Unfortunately this set comes with no documentation and I can't even find who made it.
I'm pretty new to wireless charging so I'm wondering what sort of shielding will I need to protect the other electronics on my board? I am thinking I'll put the coil on the bottom of the PCB and everything else on top. Will something as simple as a layer of aluminum foil do the trick?

I've done some research but everything I've read so far is pretty complex (and $$) for what I'd like to do for such a simple project.


texts: Realization of network function and positive real function

texts:
I just studied
'network realizibility theory' from 'Franklin F.kuo's ' book and it mainly talks about postive real functions from start to finish and to me what I understand that for a function to be realizable it should be a positive real function and as one of it's property suggest that poles and zeroes should be in Left half of plane .
But then how 'all pass filter' can be realized ? As it's zeroes are mirror image of poles about imaginary axis i.e if poles are in negative half then zeroes will be on right half of a plane and so it is not a positive real function then how does it's realization  possible?


texts:
Working on LoRa project with the RFM95W.  Most online resources like 1 and 2 suggest using a PCB since the module itself is quite small and hard to work with; but where's the fun (and learning) in that!

After soldering it looks like: (it isn't meant to be deployed, just testing it out on my workbench at the moment)

Please see photos:

And the back side:

To my untrained eye, they don't look like they would cause a short.

Googling brings up continuity testing, which would be proving the negative (no continuity means no shorting) but I am wondering if there's something better and what the procedure is like?

I do have this Multimeter.


texts: Method of generating a random binary number using gates

texts: I was wondering how a computer or any other device can generate random numbers. Is there a way to do this using only digital parts(non-programmable parts such as gates)? When I think of it, it seems like there has to be an "analog side" to generate random numbers. How can one make a multi-bit random number?


texts: How to convert device that uses OTG to communicate with Android device to Bluetooth?

texts:
We currently have a piece of hardware that uses an OTG cable to communicate with an  Android application. We are currently using USB Host to communicate with the Android device, but we hope to offer a Bluetooth feature for the project.

I was wondering, on the hardware aspect, how something like that could be achieved. We hope to connect to the Android device's Bluetooth. For that, I imagine we would need to build some circuitry that plugs into the external device and enables wireless communication.

I would appreciate any suggestions on how this can be done or resources to see. I have seen what some people do with wired mice, but they still have an OTG cable plugged into the Android device with a Bluetooth mouse dongle. We would like something that does not involve any wires connected to the phone.


texts: Protection and termination of an outdoor underground Ethernet cable

texts:
I have quite a quite long outdoor FTP Cat 5e Ethernet cable (just shorter than 90 meters) that will be used to connect 2 buildings, buried 1 meter underground.
As I understand, for a proper operation and reliability it has to be properly terminated, since this is a shielded cable, and since it is laid outdoors where it may be exposed to overvoltages and voltage surges from lightning strikes.
I have read a few similar questions, but none has quite specific answers, and have consulted electrical code book of my country, which suggests that underground cable runs don't need overvoltage protection, but it is referring to power lines, and does not take signal lines into consideration.
So, with that in mind I came up with a few schemes, and would like to know if my understanding and usage of them is correct:

Ethernet cable is terminated with regular unshielded connectors. As I understand, this is the worst case, as shielded Ethernet cable has to be terminated with shielded connectors. If it is not terminated, the shielding will pick up EMI from ground and from wire lines and decrease the performance.

Ethernet cable is terminated with shielded connectors, that connect to switches chassis, but since switches themselves are not grounded, it eliminates the possibility of ground loop, while aslo increasing performance, but it will not protect from lightning strikes.

Ethernet cable is terminated with shielded connectors on both ends, that are plugged into grounded surge protectors. As I understand, in this way the shielding is properly terminated and will protect the signal from interference and increase performance, it will also protect the equipment from surges, while also eliminating the ground loop, as in this case the current flows through the ground only in case of reaching breakdown voltage of protective equipment.

The same as 3, but the cable used to connect from Ethernet surge protector to switch is regular unshielded UTP, as there is no need for shielding.

As I understand, 3 and 4 are the proper way to connect outdoor Ethernet cable to the equipment. Am I correct?
Other connections that are, as I understand, are even worse, is grounding both switches (will result in ground loop), or terminating shielded cable with shielded connector only on one side (will make EMI and overvoltage worse).


texts: Pointer to an Memory Address of Flash Memory

texts:
I think that the following question is simple, but it is important for me to know.

I am working on microcontrollers. I have seen some code to access the data from the flash memory.

For example in order to read the contents of the 0xA010 address of the flash there is the following code:

           #define ADDRESS_TO_READ      0xA010

           uint8 *Read_Ptr = NULL;
           Read_Ptr = (uint8 *) ADDRESS_TO_READ;
           value = *Read_Ptr;

This is working fine. My question here is, since Read_Ptr is uint8, how is it storing the value 0xA010, which is a short value (16-bit Address)? How the read and write functions will occur in this memory, when the pointer is uint8?


texts:
I am accessing my SD card using SPI. But I've found this to be slow and I am also sad that when there is a faster protocol already supported by my SD card I am using a slower version.

Is there a C library that can be integrated to my C compiler which can be used to access my Sd much faster than SPI?


texts: Using built-in current limiting of an OpAmp to create a current source

texts:
I want to design a current source that can provide 2 different currents, 100mA and 1A using just a single power amplifier APEX MP38 which has a current limiting feature which is set by a resistor according to the following formula:

$${R_{limit}=\frac{0.7V}{I}}$$

The maximum load that current should drive is an almost-pure resistive load around 50 Ohms.

I will supply the opamp +Vs by 60V and -Vs will be connected to GND.

Almost all opamp based current sources that I see, except Howland Current Pump which is too complex for my case (because I only need positive currents) use a PFET at the output of the opamp. Since the opamp that I have is already been purchased I kind of have to use it for this case.

Lets say I choose R3 and R4 in such a way that in parallel they make a sense resistor to limit the current to 1A, and when only R3 is conducting the current will be limited to 100mA.

So the questions are:

Overall, do you think this is going to work?
Is using a switch (e.g. cold-switching a relay) to switch between
2 different sense resistors a wise idea? is it a misuse of the current limiting feature which I beleive is only should be used to define a SOA?
Having the -Vs connected to ground is OK or I need to provide the
negative rail of the opamp with some voltage to get out of common mode voltage range?
I want to use a 0-3V3 digital signal to turn on/off the output of
the opamp. What sort of gain will I need? Do I need to use another opamp in buffer mode at an earlier stage before the main opamp?
Do I need any capacitors in feedback or other paths (Of course the
supply bypass caps are going to be there!)

UPDATE
The load that I am talking about is a series of PCB traces that I want to see how do they perform under high-current stress. So it should be theoretically a resistive load with some small/negligible parasitic inductance/capacitance.


texts: Is it possible to move names and parts separately in board edit mode in Eagle?

texts:
Most factory-created PCBs I have seen has part names aligned very accurate, without any overlap, without placing under the SMD devices, and so on.

My question is - can I move part names separately from parts itself using Eagle (7.1.0 if that matters)? I know I can open library and edit related package, but

That would be too long for each part;
I'll end up with conflicts;

Also there is an option to create labels using Text tool and place them on tNames/bNames layer, but that is too long too. Is there a faster way to do it? Or, maybe my approach is not the best one? The only thing I care about is final result.


texts: Trouble Powering Microcontroller from Doorbell Transformer

texts:
I am working on a project that involves an IoT device, with a 3.3V microcontroller, powered from a doorbell transformer. In an earlier question, I was attempting to solve an issue with a bridge rectifier failing. One of the answers to that question involved a circuit similar to the one below. However, this circuit is not working correctly.

The doorbell transformer provides about 21V AC. My application requires that the doorbell still functions. The switch allows the transformer outputs to be shorted. This triggers a solenoid that rings the audible bell. To prevent the inductive kick from the solenoid from killing any of the other components, a bidirectional TVS (1) is used to suppress the voltage spike.

Because the MCU does not require much current, a half-wave rectifier (3) is used to convert the 21V AC from the doorbell transformer to about 13V DC. A capacitor is used to smooth the rectifier output (4). Finally, a switching voltage regulator (5) converts the rectified DC voltage to 3.3V to power the microcontroller.

In order to prevent a loss of power to the MCU when the doorbell button is pressed, a 6V zener diode (2) is used to allow power to be supplied to the switching regulator (or at least it is supposed to) while the button is pressed.

I've included links to all the datasheets below:

(1) Bidirectional TVS Diode

(2) Zener Diode

(3) Half-Wave Rectifier

(4) Capacitor

(5) Switching Regulator

I would greatly appreciate any insight into why this circuit fails to power the MCU. Thank you in advance for your help.