texts: Unkown DC offset of an isolation amplifier circuit design

texts:
I am designing an isolation amplifier that consists of the following blocks:

A comparator which produces a PWM signal
A coupling capacitor that achieves galvanic isolation
A voltage follower that acts like a buffer
A 2nd order LPF with cutoff frequency at ~20 kHz

At the output, the output signal can recover the input waveform with a slight phase shift. However the output signal also introduces an unkown DC offset (~1.85V). I have plotted the voltage waveforms at different nodes and found out that there is a DC offset at the buffer input. I think it is this DC offset at the buffer input that causes the DC offset at the output. But I have no idea what circuit component introduces such DC offset in my circuit.
I have attached my schematic as well as my simulation waveforms. I am designing my circuit using LTSpice and AD8513 as my opamps. Greatly appreciated if I can have any advice or help regarding this issue and how to improve my circuit design.

Thank you for any advice in advance.


texts:
I have an image sensor problem and I am looking everywhere to identify the problem but couldn't. Attached is the problem I observe. As you can see there are several horizontal lines in the image.

So far, I have checked power, clocks and all seems in order. Appreciate any ideas you may have. (If I get a test image from sensor-diagonal tiles etc-, all seems to be good. So, I am assuming it is not communication with the sensor. Sensor datasheet is here)

I am not looking for a specific answer but more of a direction and/or ideas. Somebody with the right experience could know where to look.

Apparently this type of problems can be observed in other sensors. See the link.

I have realized, I missed out one critical information, if I reduce the clock frequency of the sensor the problem disappears. So there is a clock frequency dependency. However I do not suspect read out since if I set the test pattern, regardless of frequency all is good.

Imager Power Supply Noise figures

Analog Supply

Digital Supply

UPDATE

After further testing, I figured the problem is same in every frame. Previously, I was wrong. Here is the 4 images from different times. Images are stiched together, all 480x752


texts:
The circuit is the following and i think this RC filter is used for anti debounce purposes but i'm not sure. Is it to prevent the optocoupler and the indicator LED from being "damaged" by the debounce effect of the switch?

And the circuit doesn't connect to any microcontroller so is that RC filter really necessary in this case?


texts: STM32 CAN bus Rx interrupt only triggers in loopback mode

texts:
I'm designing the CAN interface for a STM32F042C4T6 to be able to receive and send messages. I've tested my code and everything seems to work perfectly fine in loopback mode. However, when I hook up two STM32's together (with CAN transceivers on both ends as middle men) with one of them transmitting and the other receiving, the STM32 that's supposed to be receiving never enters the receive interrupt. I am sure that the correct CAN message is being sent using my Digilent Analog Discovery board that is able to receive digital CAN, and I probed the CAN Rx pin on the STM32 that is receiving and the message is correct. When I saw this, I thought there might be something wrong with my GPIO initialization code, but it looks like it should work fine. This is it :

//GPIO setup for CAN Tx and Rx
RCC->AHBENR |= RCC_AHBENR_GPIOBEN; //Enable the GPIOB clock
GPIOB->AFR[1] |= (0b0100 << GPIO_AFRH_AFSEL8_Pos) | (0b0100 << GPIO_AFRH_AFSEL9_Pos); //Set PB8 and PB9 to AF4 for CAN
GPIOB->OTYPER &= ~(GPIO_OTYPER_OT_8 | GPIO_OTYPER_OT_9); //Set PB8 and PB9 to push pull
GPIOB->OSPEEDR |= (0b01 << GPIO_OSPEEDR_OSPEEDR8_Pos) | (0b01 << GPIO_OSPEEDR_OSPEEDR9_Pos); //Set PB8 and PB9 to medium speed
GPIOB->MODER |= (0b10 << GPIO_MODER_MODER8_Pos) | (0b10 << GPIO_MODER_MODER9_Pos); //Set PB8 and PB9 to alternate function mode

Another thing that I think might be wrong is that the CAN transceiver outputs 5V digital signals and this is a 3.3V microcontroller, STM32F042C4T6, but I checked, and it is stated in the documentation that these pins are 5V tolerant I/O, which means it should be fine right?

Another thing that I think is very unlikely to be wrong, but still a possibility because I can't really think of anything else is that maybe one the STM32s that is transmitting is sending data out at possibly 1 kHz different than the other STM32 that is receiving, and the CAN message is interpreted incorrectly. However, the bit timing register for both MCU's is the exact same so this is also unlikely.

Does anyone have any ideas as what I could be doing wrong here? If you need for me to post any code I would be glad too, as this is quite important.


texts: Drop 12v supply to 6v to power a water pump

texts: I have a submersible water pump that requires 2.5-6V. I want to power it from a 2A, 12V supply. I assume that's powerful enough, but the pump doesn't specify its current. How can I determine the current required, in order to find the right resistor to drop 6V?


texts:
I'm drawing my own CAD library for the ATXMEGA*-E5 devices.
At page 69 (Seztion 35.2 32Z) there is the drawing of the package 32Z (5x5mm 32-lead VQFN).

I cannot find any information about the connection of the exposed pad. Searching "pad" in the whole document return nothing.

Is there a way to understand if it's connected to GND? I think if it was mandatory to connect it externally it should be written... Perhaps is there for thermal reasons only?


texts:
I am hoping someone can help me with a circuit idea I have. I am wanting to build a door sensor with a reed switch and an esp8266. I was thinking to keep it low power when the Reed switch closes the circuit it could provide power to the ESP 8266 while charging a capacitor and when the door shuts the capacitor will be charged and will dissipate its energy to the 8266 keeping it on a little longer to finish sending a message to my raspberry pi that the door was opened.

I am assuming this is a fairly basic circuit but I am a beginner and could not really find anything online about doing this. So if someone could help with I'm sure the basic design and the size of capacitor I will need q store enough power to keep the ESP 8266 on for the quarter of a second or so.


texts: Need help for pointing out, source follower circuit with current source, designing NMOS

texts:
I'm not sure did I solve this problem right.
I made \$ r_{o2} \$ , which is resistance looking at Q2 drain.
So I can get
$$ g_{m,Q3} = 1.8m(A/V) $$
from
$$A_v = \frac{r_{o2} || r_{o3}}{1/g_m + (r_{o2} || r_{o3})}$$
and I could get W/L by
$$ g_{m,Q3} = \sqrt{2I_D \mu C_{ox}(W/L)} $$
then
$$ (W/L)_{Q3} = 16.2 $$
And I can find out \$ V_{GS} = 0.8V , V_{GS} = V_{DS}\$ at Q1
so
$$I_{REF} = 1/2 \mu C_{ox}(W/L)_{Q1}(V_{GS}-V_T)^2(1+ \lambda V_{DS})$$
then I get
$$ (W/L)_{Q1} = 20.576 $$
and I can guess (W/L){Q2} = (W/L){Q1} because their \$V_{GS}, V_{DS}\$ is same.
I know in Q2
$$g_m = \frac{2I_D}{V_{GS}-V_T} = \mu C_{ox}(W/L)(V_{GS}-V_T) $$
But this equation is not true when I substitute my values. What's the problem?


texts: Incorrect operation of the Allegro A3941 driver

texts:
I use the Allegro A3941 driver in these modes:

At very low duty cycle (<10%)PWM motor consumes 0.05 A and produces a squeak. If you increase the PWM duty cycle of the PWM to 10% the squeak disappears the motor to spin at the same speed and consumes a current of 0.01 A. The PWM frequency is 84 kHz.

My circuit:

My PCB:

Sometimes the driver burns out for no apparent reason.

Where could I have made a mistake that causes the driver to burn out?

I do not understand this, because I believe that all the large current flows through the transistors, not through the driver. And, what causes the squeak?


texts: Why does an infinitely decreasing resistance infinitely increase current?

texts:
So I have been mulling over Ohm's law for hours today. It makes sense to me that the current gets bigger as voltage rises, since the voltage is supplying more electrons and current is the number of electrons flowing. However, I'm confused by the theory that as resistance drops, current increases, even when voltage stays constant. Such as:

$$V/R = I$$
$$\frac{1V}{0.0001 \Omega} = 10,000,000 mA!!$$

That's a big current from such a small voltage!

My mental picture of a current is more electrons flowing. Electrons are supplied by the voltage, right? If we start off with a small voltage, say 1V, but infinitely decrease the resistance, we'll get a bigger and bigger current. How can this be? Isn't current the number of electrons flowing? With fewer electrons (because of less voltage), how can less resistance infinitely increase the current?


texts: Altium Designer - PCB import components offset

texts:
Does anyone know why is Altium importing some of the components to the PcbDoc in this manner?
I've checked each of the imported component pick-point and it is in the center of the footprint.


texts:
I'm trying to construct an 8-Bit Program Counter, in Logisim. It currently has functions LOAD, which makes the 8-Bit input (A0-A7) appear at the output (S0-S7) on the clock pulse:

Loading 1 as input:

1 successfully loaded/stored:

When LOAD is high, A0-A7 is run through the full adder, which technically is used - it just adds 0, so therefore doesn't affect the output.

Now I'm trying to implement an INC (increment) also, which when high will basically just add 1, but take the current register value as the input, rather than A0-A7. Here is the logic flowing in the simulation, which is exactly what I want (I've circled the value going into the register, which is 2 - perfect):

However, now when I try to store this value in the register by pulsing the clock - I get an 'oscillation detected' error in Logisim:

This is the first time I've tried to build this, so is there something intrinsically wrong with my implementation, or am I missing something small which should make it perform as expected?


texts:
I have been recently been collecting parts from various machines that I'm quite sure have micro-controllers. My question is this: is it possible to take the micro-controller and reprogram it (to be somewhat similar to an arduino, and at least Arduino IDE compatible) with only some to very little hassle? Would I need to remove it from its current circuit board and rebuild around the specific micro-controller? How feasible is all this?

Note: I know this is very vague, and was hoping only to get a very generalized answer.


texts: How do I calculate the required value for a pull-down resistor in a PWM circuit?

texts:
I'm using 74HC595 with SoftPWM to control some LED's.

When the 74HC595 is off, its outputting about 0.57v, enough to turn my LED's on somewhat.

How do I work out the value of the pull-down resistor (R1), so that the LED is completely off when meant to be, but also able to reach maximum brightness.


texts: How are logic gates created electronically?

texts:
So we have AND, NOT, NAND, NOR, OR gates, but how are they created electronically/electrically?

For example, what makes NOT gate reverse the value?


texts: Is a special charger required for Li-ION battery packs with a BMS?

texts:
I am replacing the lead acid batteries in an electric scooter and a kids electric motorcycle, in addition to building a 48V eBike battery pack.

The (3) units require 24v, 36v & 48v respectively so I'm building 14.8v battery packs that I can wire in series for each of them and will be using a 4S 40A battery monitoring system (BMS) on each battery module (see: https://www.amazon.com/gp/product/B07RPW8MM6/)

Can I put these 14.8V packs in series & use the scooter's existing 24V charger & the electric motorcycle (Razor MX650) 36V charger to charge them?

Or do I still need a special Lithium aware battery charger for each?


texts:
So I have a circuit like this:

With the output equation as: \$ V_{out} = -(\frac{R_2}{R_1})\frac{s}{s+\frac{1}{R_1C}} V_{in} \$

So the question is to derive the time-domain equation in terms of the input and also to show that the circuit performs the function of a differentiator.

So here's my work:
\[ V_{out} = -(\frac{R_2}{R_1})\frac{s}{s+\frac{1}{R_1C}} V_{in} \]
\[ \mathcal{L^{-1}}(V_{out}) = -(R_2C)\mathcal{L^{-1}}(\frac{s}{sR_1C+1} V_{in}) \]
If we assume that \$R_1=0\$ then we have
\[ \mathcal{L^{-1}}(V_{out}) = -(R_2C)\mathcal{L^{-1}}(s V_{in}) \]
The \$sV_{in}\$ implies a differentiator since \$ \mathcal{L^{-1}}(s) = \delta'(t) \$

But I'm pretty sure that is either totally wrong or mostly wrong. Where am I going wrong on this derivation for the time-domain equation?


texts: Given a pull-up network, draw the complimentary pull-down network (CMOS gates)

texts:
this is for my computer organization class (I am a CS major), but I figured this post belongs better here than on stackoverflow.

I am asked to draw out the complimentary pull down network for the given pull-up network (see picture).

So far, I have been determining the pull-down networks by replacing the series compositions with parallel compositions (and vice versa), and replacing the transistors with n-transistors. However, I am confused, because in the picture of the pull-down, it looks like A and D are in series, but it also looks like (A and D) is in parallel with (B and E).

For the complimentary pull-down network, how do I make A in parallel with D, while making (A and D) in series with (B and E)??


texts: Meaning of single trim for BAND-GAP circuits

texts:
I have to design an accurate voltage reference using BJT transistors. In order to design a voltage reference (a band-gap) a PTAT and a CTAT have to be summed up to cancel the temperature dependency.

What does it mean to trim the reference?

What is the meaning of The spread of Vbe can be corrected by a single room temperature trim?

Why is it precise to trim only at the room temperature?


texts: What do you call the dynamic range of a variable gain amp?

texts:
Dynamic range is the ratio of the largest signal a system can process to the noise floor of that system.

If the system has variable gain, though, then you could interpret this two ways:

Fixed gain case: Dynamic range = (biggest signal at some gain x / noise floor at same gain x)
Variable gain case: Dynamic range = (biggest signal at minimum gain / noise floor at maximum gain)

I'd generally assume definition 1 for an electronic circuit, where you're picking the best gain to minimize noise while maximizing signal and then measuring both at the same gain.  However, when people say the human ear has a dynamic range of 140 dB, they're using definition 2, since the human ear has variable gain.  Likewise for human eye.

When measuring mic preamps or ADCs with variable gain stages, I could use either definition.

Questions:

If the term "dynamic range" really only applies to one of these cases, is there a name for the other thing?
If the term "dynamic range" can ambiguously refer to both cases, are there unambiguous terms for each case?

Example using the term "SNR":

  Human Ear Range (Instantaneous) 85
  Human Ear range (Total) 120

Definitions of dynamic range based on filtering out a -60 dB tone imply that the gain is fixed:

  The EIAJ standard measurement for dynamic range is done by reading THD+N at an input amplitude of –60dB ...  inverting the polarity of the THD+N reading, and adding 60dB.


texts: Trimmer pot to fixed resistor conversion

texts:
Sorry for the simplicity of this question but I've been struggling on this circuit for a while.

In the schematic link below you'll see a trimmer pot and I simply want to replace it with one/two fixed resistors.

I'm under the impression it will be two resistor to form a voltage divider, but still struggling to achieve this.

Following the schematic that states the 10k pot should be tuned to ~7.8k how would the circuit be rewritten to include fixed resistors?

http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Kits/UhOh-v11_corrected.pdf

Thanks for any help.


texts: How do I use a phototransistor for a line follow robot?

texts: I'm building a line follow robot for a competition in 2 months and I'm using Arduino but I have no idea how to find the line (what sensors needed). I did some research and discovered that if I can use a photo transistor and red LED to detect the line. I wanted to know would this set-up work? Will the data received be fast and accurate?


texts: For a bandpass transfer function, are there two gain bandwidth products?

texts: Every example I have come across shows the gain bandwidth product used only for low pass transfer functions, but I never see it used for bandpass or in fact high pass transfer functions. Why is this?


texts: Provide opAmp supply voltage using charge pump

texts:
I have low power (USB 5V, up to 500mA) available on a microcontroller board I am developing. Because the voltages I am going to measure (1.2-2.3V) using the MCU are not filling the ADC's range (0-3.3V), an opAmp seems suitable to scale it appropriately.

Case is, an opAmp needs not just a positive, but also a negative supply voltage to work properly. The opAmp I am looking at currently is the AD8027. So to provide its supply voltage this IC seems quite nice (judging by all its features, such as low-dropout-regulators): LM27762. But running TIs simulation web-software (Webench Power Designer), I am not getting the expected value of +3.3 and -3.3 Volt, when supplying it with the 3.3V of the microcontroller. It's more at a stable +3.1 and -2.9 Volt with attached load.

So my question is, how much will this degrade performance and quality? Will this still work to some degree? Are there better solutions to this kind of problem? Can I even trust the simulation?

Thanks in advance!


texts: How do FLIR cameras work with multiple spectral image acquisition?

texts:
I am looking to buy a FLIR camera, but it is hard to get in contact with the company. I wonder if somebody already used, or has knowledge about my question, which FLIR cameras can capture images in infrared, thermal and visible spectra (RGB)?
And, how does that acquisition work? I've noticed that for many cases the datasheet, manuals and Youtube, come short on this information. Is there a GUI to choose, do I need a software specifically, or are they fused altogether? Also, on the same note, I would like to know the same things for the LEPTON 3.0 - 3.5 module.


texts: What does reverse diode on NPN symbol indicate?

texts:
Update: A diode in this position is (at least sometimes) referred to as an anti-parallel diode. This term brings up a lot more results on search.

I've been scavenging parts from compact fluorescent (CFL) bulb ballasts just for the sheer joy of getting something for free. Plus, I'm all into inductors just now and there are some nice little specimens in there yearning to be rewound and repurposed :)

One of the parts I'm finding is a 200V NPN power transistor in a TO-220 package, the 3DD4126PL (marked D4126PL). There's a datasheet for it here if anyone is interested.

The schematic symbol for it in the datasheet includes a reverse diode symbol, like a MOSFET does:

Unless it's escaped me for quite a while now, an NPN BJT doesn't naturally have a built-in body diode the way a MOSFET does, does it?

Can anyone explain what this added bit in the symbol means? Is a bypass diode added as an extra in this case, perhaps because it's meant for high-ish voltage operation in a fluorescent ballast (albeit a pint-sized one)?


texts:
I want to convert unregulated 10-14V DC to 5V DC and 12V DC regulated(constant) supply;This is a buck step down regulated voltage supply IC it outputs the voltage that I require. Is this IC all I need? Or there will be some more components needed?

Will this IC have:

Under-voltage and short-circuit protection.
Thermal shutdown prevents damage from overheating.
Reverse-voltage protection.

I have seen buck step down regulators which have many more components, than just a IC. For example this: http://www.pololu.com/product/2110. What is the use of other components, Are all the other components used to provide the above mentioned 3 points?


texts:
I'm trying to store data from an analog sensor using an openLog board. I'd like for the openLog to transmit its data using an XBee, should another XBee come into range.

I'd love to be able to do this without an additional microcontroller, by using the ADC in the XBee to convert the analog signal into a serial out that the openLog will store. It needs to be able to do this without transmitting at the same time.

Any help would be greatly appreciated - I'm a total novice at this sort of thing!


texts: Sonar HC-SR04 analog output. Multipoint Sonar Radar

texts:
Im working on replicating the work found on Ultrasonic Radar; Multi-Point.
It bypasses the echo out on HC-SR04 and enables full analog output to Arduino ADC. The results are quite good but unlike the project described on the website, anything further than cca 20 cm is noise.
Any ideas why?

used
4.6k ohm resistor
2x 4.7nF capacitors

Thanks,


texts: Simulating a microphone with a microcontroller?

texts:
I'm trying to use a microcontroller to replace where a microphone would normally be connected (to a radio module) to feed a sine wave into the radio module.  I can produce a sine wave (I think) but it will be between 0-3.3v.  How can I make it acceptable as what a microphone would be?  I'm guessing I need a series capacitor to block the DC component, but is that enough?  And if so, how do I choose the right capacitor for this use case?

(The radio module is a DRA818V and the MCU is an STM32L0, if that helps any.)


texts: 4 layer board stack-up and some question related to power layer

texts:
I've got some questions regarding my stack-up and power layer, which is layer 3 on my PCB.

But before I ask my question I will describe my PCB.
Most components are SMD parts (capacitors etc.).

Top layer is used to route almost all signals which is required for SMD components.
Top and bottom layer is not filled with ground polygon, because I already got 2nd layer which is my reference plane.
OFC top layer uses some polygons and vias to connect SMD parts to 2nd layer, but I'm not using via stitching and free space is not filled with ground.

Bottom layer is pretty empty, I can place some parts there (but I could use top layer as well), if there will be some traces it will be power traces or non critical signals like enable, sense etc.

My question is if I've got whole power supply how to use power inner layer?
Should I split it to VCC and VEE only (I've got bipolar power supply), or should I split it even further?

My power supply look like this :

Full bridge rectifier -> CRC -> LC - LDO -> LOAD.
I also got some comparators a front of LDO to control startup and UV/OV state.

As you might see from picture below this is not so advanced circuit.
Almost whole top layer is empty (for now) and whole bottom is free for routing.
So I'm little confused how to use 3rd layer which will be usefull for connecting other parts which will be included on same PCB later (aprox. 10 opamps and some other analog muxes etc.).

I've got few ideas described below :

I will use TOP plane to route power directly do LDO input then whole third layer will be used as VCC and/or VEE plane,
whole third layer will be used for power routing (including LDO input and output) and TOP layer will be used when it's required to connect SMD parts,
third layer will be used as a ground plane and whole power will be routed using top and bottom plane.

I think my picture is rather easy to understand :)
BTW I'm not using bottom and top for ground because I don't to make many cutouts and splits, after that I will still need to place many vias to connect planes together to avoid making antennas.

If you got some question feel free to ask :)
Have a nice day.


texts: Limit KiCAD track selection to current layer

texts:
When I do the track selection in KiCAD and click Select -> Connected Tracks it also selects tracks connected through vias on the back of the board.

I only want to select tracks on the current layer. Is there a good way to do this?


texts: What would cause DC bus voltage on my VFD when the disconnect is off

texts: 125 hp 480 vac HMax VFD. Controlling a pump motor. Motor is not spinning and line to the VFD is disconnected.  I was putting the output wires back on the VFD, when moving the second one into place, the cable lug brushed against the DC bus terminal and sparked.  I thought that was strange.  I went ahead and measured the voltage and there was 10VDC on the bus terminals.  When the motor leads are connected, the DC bus will charge. the most voltage I read was 20VDC.  When I disconnect the output wires the bus bleeds off.  I checked for AC and DC voltage on the wires and there was none. The VFD is installed in an MCC.  There is another VFD beside it same size controlling another pump.  When it (the other vfd) is running that is when the DC bus gets a charge going to it.  When it (the other vfd) is not running it does not charge the bus.  The motor wires both exit the MCC on the bottom into their own conduit, and run parallel underground to their respective motors.  Any thoughts on why the DC bus is charging, and how I could stop it from happening?  Would a filter on the output of the other VFD help.  Would transients or noise from the other VFD be causing it?


texts: Why are Switching Signals Used for DC-AC converter

texts:
I have noticed that oftentimes an NE555 timer circuit is used to generate AC switching signals, which allow a DC to AC rectifier to convert a DC voltage to AC voltage. This AC voltage can be used for electromagnetic induction. Why isn't a signal from the NE555 timer used instead for induction? Why can we not treat the NE555 timer as a DC to AC converter? What makes the Ne555 timer + DC to AC converter better?
Here is a related picture (although it doesn't use a NE555 timer, but something else to create switching signals). The switching signals are AC so why bother using a DC to AC converter for induction when we have the switching signals?


texts: When biasing an AC Transistor amplifier circuit, does it bias the AC current/voltage by shifting the output wave up, or does it actually amplify it and change the amplitude of the output wave?


texts: How frequency effects on screening effect in ac power transmission. I know that at 0 frequency that means in DC there is nothing like screen effect but as the frequency increase screening effect also increase. But my question is how. Is there perfect equation. I am an undergraduate student so that's out of my current syllabus sorry.


texts: I couldn't understand the purpose of the varying Vee.


texts: Reading a transducer sensitivity from its datasheet

texts:
How can I calculate the sensitivity of this transducer? I also read at a text "The sensitivity is typically rated in terms of mV/g or pC/g, it is valid only at one frequency, conventionally at 100 Hz."

But in the datasheet only the range is given lets say for +-0.1G version if I map it  to +-7.5V. So how is the sensitivity calculated?

But my actual question is if we calculate the sensitivity it is not indicated at which frequency it is valid. How can we conclude on that by looking at datasheet at least in terms of error?


texts:
I have the following circuit and I want to reduce the current consumption to the lowest possible.
Basically, I have a series voltage regulator whose output is connected to a transistor to switch on the OpAmp using the micro-controller(uC).

Prior to connecting 11V (from emitter of Q1) to R3 , I get \$120\mu A\$; but once the 11V is given to R3, the current shoots up to \$1.2mA\$ even before triggering the base of Q2. Where does the current leak and How do I reduce the current?

I Found a similar question, in which they mentioned that the \$V_{BE}\$ of Q1 increases by \$V_{CE}\$ of Q2. Do I need to alter R2 for that?

Thanks for the help!


texts:
I recently came across a symbol like this on a PCB: (forgive the use of Paint)

The component was marked as being 0.1 (symbol).

You can just make it out in the centre of this photo:

It's a capacitor, so I'm guessing it's perhaps measuring farads, but surely then an F would have been used... What is it measuring?


texts:
At the university we have seen this circuit as a Phase Modulator:

simulate this circuit – Schematic created using CircuitLab

where \$m(t)\$ is the message at audio frequency and \$v_p(t)\$ is the carrier at radio frequency.

The idea is that \$m(t)\$ change the value of \$g_m\$, modulating the phase of \$v_p(t)\$.

The proposed small signal linear circuit is this:

simulate this circuit

The first thing I do not understand is how the bypass capacity for \$ m (t)\$ is a short-circuit at audio frequencies and an open-circuit at radio frequency, as can be seen from the proposed small signal scheme.
Also why do you think the prof used this model for JFET? It is an extremely approximate model for very low frequencies, it is not good especially if I work at slightly higher carrying frequencies.

\$g_m\$ depends on \$ m(t) \$, so it is a function of time.
In the frequency domain then \$ g_m \$ is a function of \$ \omega \$ and i cannot consider it as a number, which has been done both on the book and the prof, obtaining the following expression (approx):

$$\frac{v_{out}\left( \omega  \right)}{v_{p}\left( \omega  \right)}=\frac{1-\frac{g_{m}}{j\omega {C}}}{1+\frac{g_{m}}{j\omega {C}}} $$

How can this analysis be correct even if in this case \$ g_m=g_m(t) \$?

Thank you.

PS: Sorry if my English is not very well.


texts:
Here is the schematic:

I got a little problem in electronics: it involves simple things but I can't figure it out (and found no other circuit that was the same configuration).

At t < 0 ms, both switches are open.

The problem is the following : when t = 0 ms, the switch I is closed and the switch II is open. Then I need to make an equivalent circuit when one DC source is in series with A and B (from UAB = UTH), to find the value V0 and calculate the exponential equation for the voltage of the capacitor.

Do we remove the branch that is open to calculate UTH or do we keep it? In short, is Uth (when t = 0ms) equal to 0V or 10V?

The question is here: if we close the switch I, and if V1 is equal to 10V, the equation for the capacitor being equal to \$V_1 + (V_0 - V_1) \times e^{(-t/TAU)}\$ will be equal to 10V constant, which doesn't seem logical since we added one resistance in the circuit!

But if V1 is equal to 0V, it would not be logical since the capacitor is in series with the 10V DC...

Can you please guide me in the right direction or tell me what I did wrong?


texts:
I'm looking to build a power supply that can continuously create pulses of at least 200 V (no more than 300 V). These 200 V pulses must have a pulse width of 0.4 uS. Each pulse should have a rise rate of 1.5 kV/uS, with the rise rate referring to the part of the leading edge of the pulse between 25% and 75% of the pulse amplitude.

As this is a trigger for the thyratron, the rep rate is not terribly important, although having at least 5 Hz would be preferable.

Any advice for how I could get started down this road would be greatly appreciated.

EDIT: The supply must have an impedance between 50-100 ohms

EDIT2: It's okay if the rise rate is a bit faster (i.e. 2 kV/uS), most Mosfets are much faster than 1.5. It's simply that this is being used for an old thyratron.

EDIT3: The 0.4 uS is also the minimum pulse width, it's okay to go a bit over.


texts: How can I convert a VGA signal to work with an old CRT monitor

texts:
I'm wondering if it's possible to convert a VGA signal to use as an input to an old CRT monitor (which I believe is monochrome), and if so how I'd go about doing this? The monitor has a 6 pin DIN input (see photos below) and I'm fairly sure I need to do more than just find an appropriate adapter cable to make this work.

The monitor is a Ferguson 3MM02G5, and the eventual goal is to be able to use a Raspberry Pi to drive the video signal (HDMI -> VGA -> Monitor).

Any help much appreciated!


texts: What is this wall-to-PCB connector called?

texts:
I'm trying to create my first device involving AC mains. It is a wall mounted energy meter. Essentially, it goes between the outlet and whatever device you want to measure and I'd like to have the final version housed in a neat enclosure. In essence, something like this but more basic:

Two questions arise:

What is the component called that will allow me to plug the prongs into the socket and feed that straight into a PCB? I'm aware there's PCB connectors, but there's so many and can't seem to nail what I'm looking for. Fortunately, I had a dead phone charger which I opened and managed to take a picture of exactly what I need:

It seems to be two pieces: the actual prongs that go into the socket and then a metal structure soldered on to the PCB and making contact with the small end of the prongs. Can anybody point me in the right direction? I'm looking for the same thing but with European prongs.

I'm not too sure how the new "socket" that my device would have works. In other words, how exactly do I plug something into my device and connect those terminals through to the wall? Is there another specific connector for this, or can I just connect the thing I'm interested in measuring to the wall through two lines in the actual PCB board? I'm probably making this more complicated than it is and I apologize, I just don't know the vocabulary.

Hope I can get some assistance!


texts: Can we produce more negative voltage from a less negative voltage source? (say -8 volts from -3 volts supply)

texts:
I was thinking about the concept of negative voltage when I came across this question. I understand that negative voltage means voltage below a certain threshold, say ground. So, can we use simple voltage division to produce even more negative voltages from an already generated negative voltage?

Forgive me if I'm off target here.


texts:
I'm connecting the N76E003AT20 microcontroller to an RF module. The N76E003AT20 has 4 SPI pins: SPCLK, MISO, MOSI and SS. The module also has 4 SPI pins which are SCLK, SDIO, CSB and FCSB as shown in the table:

I understand that I have to connect SCLK and SPCLK. Do I connect SDIO to both MISO and MOSI? How about CSB and FCSB?


texts: Are watts usually measured in watt-hours?

texts: Pardon me, I'm a total newb to electronics. My question is, when a device is measured in watts, such as a 60-watt light bulb, is this ALWAYS supposed to be assumed to be watt-hours, i.e. 60 watts per hour?


texts: Where do you put the inverter? Near the battery or near the load?

texts:
Where do you put the inverter to minimize power loss on a stand alone solar setup?
I'm using DC 12V as power on devices but I notice resistance on wires when running long lengths. AC is better on long distance, so I was thinking of converting to AC then just convert again to DC.
I'm just using typical 12V devices and lights.


texts: Bluetooth low energy paired vs unpaired communication

texts:
I am looking to seamlessly connect multiple slaves to one bluetooth low energy master, however I do not want to go through the process of pairing each individual device. The pairing process takes too long and I don't want to manually do it if I have 100+ devices; however, one side effect of unpaired seems to be the lack of security between devices.

I have been doing A LOT of research into this to see if this is even viable and I can't seem to find a clear understanding. At first I was under the impression that 'Just Works' was a form of unpaired communication but I believe this is incorrect. It seems that 'Just work' is actually paired. If this is the case it might solve my second question on how one might go about securing such communication. Though the documentation I have read says that it is a legacy method and the security support for it might be poor.

I have found this link Is Bluetooth Communication Possible Without Pairing?. Which seems to conclude that unpaired is possible however this is through traditional bluetooth communication protocols. And it is a little unclear to me how this is different from pairing.

It seems that one side effect of unpaired communication might be the lack of security between devices. They wouldn't be able to set up the right keys to securely communicate.

Tl;dr - What would a paired bluetooth low energy connection look like vs an unpaired bluetooth low energy connection?

A few of the several links/documentation I've viewed:

https://blog.bluetooth.com/bluetooth-pairing-part-1-pairing-feature-exchange
https://blog.bluetooth.com/bluetooth-pairing-part-2-key-generation-methods
https://blog.bluetooth.com/bluetooth-pairing-passkey-entry
https://blog.bluetooth.com/bluetooth-pairing-part-4
https://blog.bluetooth.com/bluetooth-pairing-part-5-legacy-pairing-out-of-band

Thanks


texts:
In the datasheet for TPS54202H as an example the manufacturer recommends this layout.

What about the white area on the picture, is it necessary to pour it with ground? Top and bottom?
Where to place the terminals for GND-IN and GND-OUT wires?


texts: Getting Clock/Time information from PC to an STM32F4

texts:
Assume I connect a microcontroller board (like an STM32F4) to a PC via USB. Is there anything in the USB communication protocol that contains host clock data? In other words, can I sync the microcontroller to the PC clock just by hooking up to USB?

If that's not possible, could you suggest some clever minimal-effort way to get the clock info from PC to the STM32F4?

I guess I could always write some software to run on the PC in the background and provide that info to the STM32F4, and I'll do that if I must, but I'd like to avoid that.

I could also use a network shield and have the STM32F4 query the PC over the network, but I'd like to keep cost and complexity down by not using any extra shields.

I could also have the STM32F4 run its own clock base, but that's not an option - it must be synced to this particular PC down to the second, even if the PC itself is out of sync with NTP.

By the way the Synchronisation is on the Microsecond level.

EDIT :

I found this for Arduino Board : http://playground.arduino.cc/Code/DateTime


texts: Using an AC rated light switch for switching DC logic level voltage

texts: Would it be safe and within electrical code to switch logic level DC voltage using a standard AC light switch? I know high power DC lines can create arcing with a switch of that style but low power should not.


texts:
I'm designing a 8-layer PCB stack up. I have two choices as below:

Layer   STACKUP 1    Layer   STACKUP 2   Question related
=========================================================
  1     SIGNAL         1     SIGNAL
  2     GROUND         2     GROUND
  3     SIGNAL         3     SIGNAL
       / / / / /            / / / / /
  4     SIGNAL         4     SIGNAL
  5     POWER          5     POWER
       / / / / /       6     SIGNAL          X
  6     SIGNAL              / / / / /        X
  7     GROUND         7     GROUND          X
  8     SIGNAL         8     SIGNAL          X

The / / / / / means there is a relative wider distance (around 0.5mm). The difference of the two choice is the reference plane of L6, closer to PWR plane 5, or closer to GND plane 7. Because I have many power rails, I have to split the PWR plane. So, for continuous transimision impedance, I think may L6 goes closer to L7 will be better than go closer to PWR plane, right?


texts: Can I power two linear DC regulators, each running a motor, from a single 12v source?

texts:
simulate this circuit – Schematic created using CircuitLab

I am building a twin air pump for a pond, powered by a 50W PV system with charge controller connected to a DIY fused DC consumer unit. I have a project box with two switches - each switch goes to a pre-made (fan controller) LM317 linear adjustable voltage regulator, each going to a simple DC motor. The idea is to have each pump independently switched and adjustable but running off one 12V output from the consumer unit - because it will be attached to a single timer.

When tested on separate outputs on the consumer unit, they worked fine, but when I forked them at the point of entry into the project box (before the switches of course) they worked erratically for a few seconds during adjustment. After a while the potentiometers 'died open' allowing full speed only. There was no visible sign of damage to each circuit board however.

I've now obtained another pair of these regulator circuits - but before risking them again is there a best practice method of protection here? My initial thoughts were a diode on each (+) between where the line forks and the switch and/or diodes on the line between each regulator and motor. I have 1N4001 silicon diodes and SB560 Schottky diodes available. Are diodes enough or is there something else needed here?

Parts used:

2x Mini toggle SPST switches. Rated 5A @ 125VAC / 2A @ 250VAC.

2x RF-370 Mini motor pump. Rated 12V. Suited 5V-12V. Rated current 250mA

2x DC Linear Converter LM317 Down Voltage Regulator Board 'XH-M137 v5'. Adjustable: 3V-15V. Input: 3.25V-15V. Output: 1.25V-13V. Output current: 5-1500mA. This consists of the 12v +- input, 2 5-band resistors (can't read them against the blue), 1 zero ohm resistor, 2 tiny brown disc capacitors labelled '102', the LM317T chip & heatsink, a B10K pot, tiny red LED, and 2 fan outputs (1 goes to +- wires for the motor, the other is a 3 pin socket for a PC fan which is not used). Schematic at http://img01.cp.aliimg.com/imgextra/i2/199304554/T2mq7tXkdXXXXXXXXX_!!199304554.jpg

My solar setup outputs around 12V and can deliver up to around 3A. The output this pump unit will be connected to is protected with a 1A blade fuse.

.

UPDATE 26/05/17: Having now blown these LMs- I've obtained a couple of 1803BK PWM controllers instead which appear to be better quality than the LM317s. I'm unable to get a schematic of these but I can tell you the spec (the large cap says 25v 100uF and the pot is 100K ohm if that helps):

Model: 1803BK - Ver2.0 201505
Input 1.8V-15VDC
Max output: 30W
Max output current: 2A
Self-recovery fuse (2A)
Duty cycle 0-100% (built in switch)

The updated question now is, should I still apply the advice given below (1N4001 diode and 1000uF capacitor per controller) for this new setup? Also, as I have switches before the controllers, is it safe to leave them turned up before switching on - or would the sudden jolt of voltage/drawn current be damaging? I really don't want to blow these somewhat cute 1803s.


texts:
I want to start a project and i'm clueless even after reading a lot.
I have an rf route with some rf components/equipments connected, analog signals going through (wired). My goal is to check the dB of the rf wave in a certain frequency and bandwidth and show it on a gui eventually in my computer.
I can check it in a spectrum analyzer but my goal is to show it on my computer.
I was thinking about connecting arduino microcontroller/power sensor in each point I want to check, in order to do this I need RF IN input and RF OUT output to continue the chain without breaking it. I also need to consider the attenuation comes with the microcontroller/sensor I connect.
After some more research, I found out I can convert the analog signal to digital with raspberrypi and then measure the voltage going in the computer with an rs232 cable. Then how can I convert it back to analog?
Is it necessary or there is an other way?
I need an advice how do I start with it?
-What components do I need, microcontroller/power sensor? And which one exactly is fitting my criteria?
-Where can I learn to code these specific components and rf waves?
Thanks in advance!!!


texts:
I have planned to build a circuit to display voltage and time value using PIC16F877A micro controller.To do this i tested the circuit using Proteus software as i attached here. It can display up to 5V.

my question is can i read up to 300V using this micro controller?(I planned to use LR8N3G voltage regulator to give input voltage to PIC).will it damage the PIC? If so how can I read high voltage from this?


texts: Control an UART protocol with FreeRTOS or Interrupts

texts: I am trying to develop an UART protocol to allow communication between two boards Master_Board and Slave_Board. Master_Board shall send commands over UART to Slave_Board and the latter shall answer. The thing is commands are with different priorities and some commands need to be executed in time. For example if the Master_board send "GET_VALUE" to Analysis_Board, the latter shall send values to Master_board for 20 seconds. If something bad happens while receiving data, Master_board shall send "ABORT" to Analysis board. The latter shall stop sending values even if the 20 seconds are not reached. I think there are 2 ways to do so. implement the UART protocol to be managed by interrupts or RTOS. Which way is better in my case? Which way is easier to handle and guarantees the best performance?


texts: Incompatibility between 5v processor and 12v source

texts:
L,H on the diagram below represent processor pins in LOW/HIGH states. LOW is 0v, HIGH -- 5V. Difference in voltage levels (5V vs 12V) leads to problems -- current flows on paths where it shouldn't. If I set the HIGH level to 12V, pins at the top of the diagram select the LED group and pins on the bottom the LED column, as expected.

How do I solve this incompatibility? One idea I have is to use multiple transistors at the top and at the bottom, but it requires 6 additional parts. Is there a more efficient solution?


texts: DC to DC power supply Virtual Ground circuit dillema

texts:
I am trying to power a circuit with two op-amps that require multiple voltages. The voltage requirements are -14v, +14v, ground/24+. I am trying to power this circuit from a 12vdc power supply.

I am using a 14vdc to 24dc boost module to obtain 28v and a rail splitter circuit to create a virtual ground for the -14v and +14v and its working. I am using 24v from the dc to dc boost to supply the board for the 24vdc requirment.

The problem I am having is the input/output negative(common) from the power supply through the DC TO DC board connects to the virtual ground circuit input and output 14v-. This rail cannot connect to the negative ground common, this is my problem.

So my logic is to isolate the dc to dc input from the output and this will in turn eliminate the -14v from being connected to the 12v negative ground common?

I think this will work but how can I achieve this? I already have the dc to dc board and the virtual ground board. Is there a simple electrical circuit I can make to add isolation or a whole other idea that doesnt require me to have to use a dc to dc board that has isolated negative input/output?

Any suggestion would be greatly appreciated, thank you.

Newbie


texts: Selecting pwm frequency for speed control of a dc motor?

texts:
I am using L298 motor driver to drive motors (12v , 900mA),I am using PWM to control motor speed but the problem is

1.When I set PWM frequency to 100 Hz motor work with jerks no noise at all.

2.When I set PWM frequency to 500 Hz motor work with little jerks and little noise.

3.When I set PWM frequency to 1000 Hz motor work with noise and no jerks at all.

4.When I set PWM frequency to 20 kHz motor dosen't work at all.

what should I do?


texts: Can this thing be built? Circuit to Increase 12vdc Rise Time Circuit (car-lighting)

texts:
I'm not a professional electronics engineer.  Just an auto-enthusiast.
I have no where to turn to ask if something like this old patent can be built by someone who knows electronics.
Does the info in the patent give precise directions to build this device or is there circuit info omitted to prevent it from being built?
THIS IS RELEVANT ONLY for cars that use non-LED brake-lights: any 2000's and older/vintage or classic cars that used incandescent bulbs, that are also retrofitted with hi-output incandescent bulbs which would increase the lag-time in bulb luminosity.
Here's the Patent and all the info, and I would appreciate your professional expertise if this can be built based on the info/schematics and description:
It's called a "Vehicle Stop Lamp System"
Inventors:  Michael J. Flannagan & Michael Sivak
Patent#  4,791,399
Date:  Dec. 13, 1988
https://pdfpiw.uspto.gov/.piw?PageNum=0&docid=04791399
Thanks,
Chris


texts:
The image below shows how a Filterless Class-D amplifier works:

The way I understand it: Vout(minus) is just the mirror image of the Vout(plus) but there was a certain phase shift(time delay?) between them that when these two signals are taken as input to a comparator, the Vout(diff) will be the result.
How much of what I said is wrong? Im confused on how this amplifier knows how much degree of time delay there is between Vout+ and Vout- so that the Vout(diff) will SURELY be high when Vin is at the upper half of sine wave and low when Vin is at the lower half of sine wave. I thought that if the input frequency is changed, there will be some kind of overlap between Vout+ and Vout-.
Source:https://www.eetimes.com/filter-free-design-helps-class-d-audio-amplifier-implementations/


texts:
In the PLL it is said that Capture range is the frequency from which the PLL starts functioning and Locked range is the frequency where the output of VCO is equal to that of reference oscillator frequency.
If that is the case why  the Locked range is greater than Capture range?
My doubt is it shouldn't get locked as it crosses capture range because it stops functioning as PLL.


texts: I have a common 12V led strip (SMD5630) connected to my car battery directly. I have noticed that it gets really hot after a couple of minutes so I'd like to reduce the current it takes (now it's 1A) to get less heat, longer lifespan and less power consumption (of course in exchange of some brightness). How to do it properly?


texts:
Just recently, I was watching a video where the presenter used a current divider formula (I think he called it the "G" rule) to calculate the current flowing throw a resistor on a circuit with two resistors in parallel.

Basically, given two resistor in parallel as follows:

simulate this circuit – Schematic created using CircuitLab

The current divider formula he was using to calculate the current flowing through R2 was something like this:

I2 = ( (1/R2)/(1/R2 + 1/R1) ) * ITotal

In case it helps, the link to the part of the video were he uses the rule is here:

https://www.youtube.com/watch?v=cF2XmaG2-Cw#t=411

I am pretty new to all these so I was hoping that someone could tell me how this current divider formula is derived (proof of the formula)?

Thanks.


texts: Does a turbine experience a countering electromagnetic force while it induces a voltage?

texts: I am assuming yes, because of the law of conservation of energy. A certain amount of energy is required to turn a turbine. So if we want a turbine to spin as well as induce a voltage, then more energy will be required to do so. I suspect the turning of the turbine is impeded by an emf, which requires more energy to push through, compared to a situation where we were just looking to spin a turbine without wanting to induce a voltage.


texts: Function of RC circuit in a bistable multivibrator using op-amp

texts:
What is the purpose of the RC circuit in a bistable multivibrator?

Can't we obtain the same result, if the trigger input is supplied directly (bypassing the RC circuit)?


texts:
We know that Apple's Arm A4 Chip that powered the iPhone 4 had approx 1.6 GFLOPs of processing power.
In the second generation of Apple's Airpods - there is a custom chip called the Apple H1.
My question is: Do we know the processing power (in GFLOPs) of Apple's H1 chip?


texts:
I was reading that for high frequency switching applications with
 semiconductors, the ratio of the electron to hole mobility should be high.

Why is it so? Is it a necessary condition always? Or just one of many possible
 ones?

As per my basic understanding, for high switching applications, taking the
 simplest case of a diode, the reverse recovery time should be dependent on the
 time the minority carriers in each side of the junction take to return to the
 opposite side on application of a reverse bias from a forward-biased state.
 Now, a scenario like that would ideally want both the mobility of electrons and
 holes to be high.

What I inferred from this condition is also that this necessitates that the
 difference between the electron mobility and the hole mobility should be high
 enough for the ratio to be appreciable.

Any insight on this would be helpful.


texts: I was looking at the traces of a computer's mother board and noticed that some traces appear excessively long and zig-zaggy(Really couldn't think of a better term). I am wondering why the designer would have added all the extra turns. Is this just a way to fill the empty spaces? Or just this have a purpose such as increasing inductance/capacitance or for EMI? I am aware that there are probably different rules for different things, but is there a semi-generic reason for this? I can't figure out what the little "bumps" in the trace would be necessary for. It should be noted that the traces in the picture connect 2 RAM sticks to the main processor.


texts: Reliability of the Arduino platform for industrial use

texts:
I'm no electrical engineer (just mechanical) but I would like to apply some of my hobbyist experience to my job and implement various automated systems in an industrial (manufacturing) environment.

Traditionally, automation in the industrial setting consists of either engineered systems or PLCs. Engineered systems are too expensive and PLCs lack flexibility (and they can get pretty expensive as well).

I would like to replace traditional PLCs with more flexible, powerful, and cheaper Arduinos but I'm concerned about the Arduino's reliability. PLCs evolved in the industrial setting and are thus very rugged and reliable but how does the Arduino platform compare?

Assuming that proper measures are taken to protect the Arduino from mechanical and electrical damage, how reliable is the platform? Would you trust it to replace a traditional PLC that controls say a machine's safety interlock system to prevent people from getting too close to a machine in operation?

Edit: What about non safety critical systems? For example, introducing intelligence into say a fixture which a PLC would not be capable of?


texts: What options do I have to combine and format 18 600Mbps ADC serial streams over QSFP+?

texts: The 18 serial streams are not encoded or scrambled. The idea is to multiplex them onto one or more encoded serial streams at higher rates for onwards transmission over optical fiber.


texts: Aluminum foil under anti-static discharge mat

texts: I have an anti-static-discharge mat similar to the one in this question. Like the OP in that question I doubt the mat's effectiveness, mostly because my ohmmeter measures an open circuit across small distances on it. Would I be wise to place the mat on aluminum foil and to ground the foil? Is it enough to ground the foil to the ground pin of an electrical outlet?


texts: How can a constant secondary side current cause a primary current to flow in a transformer?

texts:
This is a question which was originally asked by my power electronics professor but left unanswered.

Suppose you are given the following system (kindly borrowed from this question)

Suppose that:

The inductance L is so big that the load current is practically constant (remove Vx and think of the load as an ideal current source).
The diodes are ideal.
The voltage source is a secondary side of an ideal transformer (no leakage reactance no resistance and no magnetizing current).

As you can see, the secondary current is a square wave. How can a square wave (i.e. a constant current on a half period basis) cause a primary current in the transformer to flow?

My answer is the following:

We can see the secondary current as a Fourier series, that is as an infinite sum of sinewaves. This  means that, at least on the transformer part of the circuit which is linear, we can apply the superposition principle and therefore obtain a lot of AC circuits to be solved and then combined. It's the fundamental frequency and the harmonics which are causing primary current to flow. If it were pure DC it wouldn't work.

In reality of course, the transformer has a leakage reactance which will smooth out the edges of the square wave, providing a (perhaps more evident) time varying current on both its sides.


texts: What do the white and green colours on the earth leakage CB denote?

texts:
I've come  across two 4 pole earth leakage circuit breakers, one with the all green lever and another with white levers for phases and green for neutral. Is there any special meaning to this?

I've attached pictures to illustrate exactly which devices I'm referring to.


texts: Is a self-locking relay the same thing as a latching relay?

texts:
This self-locking/inching WiFi relay can be configured to work in self-lock mode, in either NO or NC mode.

I’m not sure if self-locking means the same thing as latching. Wikipedia says:

  A latching relay maintains either contact position indefinitely without power applied to the coil. The advantage is that one coil consumes power only for an instant while the relay is being switched, and the relay contacts retain this setting across a power outage.

The device above has a SRD-05VDC-SL-C 5V Relay component, and I saw a video where someone took one apart and it appears to have a copper coil which leads me to beleive this is using an electromagnetic current to close/open the contacts.

What happens if the coil is charged and then power is removed from the relay?  Wouldn’t the contacts drop?  If so, then how could the relay maintain the current state?

BTW this relay specifically states it is latching and uses the same component, so maybe my understanding of how the SRD-05VDC-SL-C 5V works is incorrect.


texts: Can I detect when my HRS-2 Series Solid State Relay is energized?

texts:
I am using a HRS-2 Series solid state relay. I am trying to determine whether I can use a simple continuity logger to determine when this relay is activated. I've attached the circuit from the data sheet below.

The idea is that I'd attach continuity leads between the trigger leads 1 and 2. The input circuit would already be wired up so that when power is applied to the input circuit I would hope it would be able to see that power was applied with my data logger on the trigger circuit 3 and 4. In practice however I'm not seeing any continuity between terminals 1 and 2 when the relays are turned on. These are dry contacts as of right now with no voltage going across 1-2.


texts: Can I run a liquid-pump motor below its specified operating voltage range?

texts:
The liquid-pump/motor is a miniature one from ebay with its operating voltage rated as "6-12V".

Even at 6V (the minimum of that specified range), it's pumping liquid too fast for my requirement.

Will there be any problem if I instead supply just 1 V or 2 V (assume long-term usage) so as to reduce the pumping power?

If that is not the recommended approach to reduce the pump's motor speed, what other method should I use?

I'd like to avoid using a different pump, because this one has dimensions just small enough for my application.


texts: Blown computers and tablets due to blackouts and brownouts

texts:
We have experienced a lot of blackouts and brownouts where voltage was once measured at 135V (nominal 240V). Computers and tablets were working and plugged in before we had a blackout and dead after the power came back on.

It happened on different occasions. I need to claim damage from insurance but the assessor cannot pick up any burn marks that proves damage, but all units are dead. how can I prove to my insurance that damage was due to blackout or brownout? Please help with some advice.


texts:
I have a question conserning some strange values I get when sampling a rotary potentiometer using an STM32F103CB MCU.
The circuit is as follows: Potentiometer(powered @+5V from a custom PCB) -> Voltage divider(0-5V to 0-3V3) -> OpAmp(OPA4344) -> MCU. On the MCU side the ADC is run in DMA and the result is sent to another device using CAN BUS. When observing the readings on the second board is where the strange behaviour is noticed. The potentiometer is placed inside a steering column so I know that there are equal degrees around the center, but if lets say at 0 degrees the pot reads 1750mV, the two equal distances read 10mV and 4995mV instead of 10mV and ~3500mV as someone might expect.
Any ideas what may cause this behaviour ?
Note: I checked with a multimeter the potentiometer and I observe the same readings I mentioned +/-60mV.
Note 2: In the second board, prior to displaying the data, I multiply by 4995/4095 to scale the readings from the 12-bit ADC values to mV.
Edit: The potentiometer is a B10K rotary potentiometer and its power and ground come from the PCB.


texts: How is Phase Shift of an Op-Amp calculated using Polar Coordinates

texts:
I have a textbook (Op-Amp: Characteristics & Applications by Robert G. Irvine, 1981) and its Frequency response chapter started by discussing the Internal LP filters between the Input Differential Amplifier stage, the Voltage Level Shifting Stage, and the Push-Pull Output Stage.

It explains that the Capacitor will create a -45 degree phase shift at it's corner frequency (where attenuation is -3dB). and corner frequency is 1/(2*pi()RC).

It says that if the Frequency on the input of the Op-Amp is much less than the pole Frequency then the phase shift is negligible but uses the equation:

RC=159,000-ohms*0.1uF=15.9-milliSeconds,

pole F: 1/(2*pi()*.0159)-1/0.1=10-Hertz

When F=0.1-Hz Vout/Vin=10/(10+j(0.1))= 1 @ -0.57-degrees
When F=10-Hz Vout/Vin=10/(10+j(10))= 10/(14.141 @ +45 Degrees) = 0.707 @ -45-degrees
When F=1,000-Hz Vout/Vin=10/(10+j(1000))= 10/(1000.05 @ +89.43 Degrees) = 0.01 @ -89.43-degrees
When F=10,000-Hz Vout/Vin=10/(10+j(10,000))= 0.001 @ -89.94-degrees

I can use Euler's formula to transpose Polar coordinates to rectangular, but the textbook doesn't give any explanation as to how, say, "10+j10" becomes 14.141 @ -45-degrees.

or how does "10+j1000" become 1000.01 @ +89.43 degrees?

Basically how do you calculate phase shift due to a a capacitor as a function of it's frequency in polar and rectangular coordinates?


texts:
I'm trying to understand the real-world construction of 1950's radar correlators. The articles on the topic I have seen so far are jargon-filled explanations with no real-world examples. Does anyone know of a better introduction?

Looking over the ones I've found, it appears that the basic idea is that you have a bunch of tunable bandpass filters connected to a series of delays so that each filter receives a small amount of the signal sampled over a short time slot.

The system is first set up by feeding through the sample signal, which in the case of radar I assume is simply an attenuated version of the transmission. This results in the filters being set to a series of values. Then you take the receiver's output and send it in and measure the output, then change all filters up or down by the same amount and repeat looking for the maximum output.

Is that basically it? If so, how do you send the received sample back through the filter network again? Is there some sort of storage loop like a delay line? I'm really curious how they built the Winkle system in the UK, if anyone knows how they did it electronically I'd love to hear.

UPDATE: Adding links:
http://www.radartutorial.eu/10.processing/sp54.en.html
http://www.radartutorial.eu/10.processing/Matched%20Filter.en.html
https://en.wikipedia.org/wiki/Matched_filter
http://ee.eng.usm.my/eeacad/mandeep/EEE436/chp%203.pdf


texts: Altium : How to connect pads of an F antenna

texts:
I'm designing a reverse F antenna. It is connected to ground and the antenna line.

It is built of several place fill with small overlaps.
To do this, I declared the component as a net tie. The package exposes 2 ground pads and one antenna pad (called 0 on the pictures).

Now I'm facing an issue while placing it on the pcb :

I designed a ground plane around the antenna line and set the clearance rule
for this net in order to get the correct impedance.

Problems :

The ground plane is poured against the ground plane of the antenna.

I tried to connect the ground plane and the ground pins of the antenna but
I'm not allowed to do this. I suspect that altium assumes that there the whole antenna is connected to antenna line and therefore does not allow to reach the ground pad.

Do you have any idea on how to solve this issue ?


texts: Disabling the lane change signal feature of a 2014, 2015, 2016, 2017 Corolla

texts:
I'm not an engineer or auto mechanic, but I know what a diode is, and I know I need one for my application.

A little background (forgive me).  I own a driving school, with a fleet of Toyota Corollas.  Like many modern cars, these are equipped with a "lane change turn signal feature"... That is, if you move the signal switch only part-way, it will continue to blink 3 times after you release it.  This confuses the heck out of our students, who attempt to cancel a signal but if they move it a little too far they see it still blinking, try to move it the other way, then the other way, etc.  I dislike the feature myself as it's never proper to blink only 3 times.  So, I'd like to disable the feature.

To figure things out, I bought a used turn signal switch matching this model and put it on my multi-meter.  So I know which pins are connected as the switch arm is moved.  As shown in my graphic, the car sees a connection to GROUND when the switch is moved either left or right, BEFORE it "clicks in".  Then when it "clicks into position", it sees another connection... just one wire representing both sides.  When the turn signal is turned off after this wire shows a closed circuit, it does NOT keep blinking.

So I'd like the switch to "lie" to the car, telling it that it's "fully clicked" whenever it's moved at all.  I don't want to tear the switch apart or even remove it since it's inside the steering column, but the cable is easy to access. It seems I need to add two diodes, shown below in brown.

I've got room to put pretty much any diode between spliced wires, but the only diodes I've worked with are tiny ones on circuit boards.

Any suggestions for where I can find a diode and be reasonably confident it will work?  I know almost nothing about diode specs.  (Or is my theory completely flawed somehow?)


texts: How can I convert a very high positive DC voltage to negative DC voltage

texts: I have a high voltage power supply which can power up to 30 kV with respect to ground. However, for my experiment (something like the one used in photocopier machines) I need a high negative DC supply. So how can I convert a positive let's say 20kV into -20kV. I'm a material scientist with a limited knowledge about electrical and electronics machines.


texts: VHDL ieee.numeric_std: Division by zero defined?

texts:
As the title says, I'd like to know if the behavior of a zero division in ieee.numeric_std is somehow defined. If one does

signal a, b : unsigned (width1_g-1 downto 0);
signal c    : unsigned (width2_g-1 downto 0);

div_proc : process (clk_i)
begin
    if rising_edge(clk_i) then
        c <= a / b;
    end if;
end process;

for example, what will be the outcome of c?


texts: Why does this three phase induction motor have two kW ratings?

texts:
I came accross a three phase induction motor with two kW ratings written on its nameplate against the two frequencies 50Hz and 60Hz.

Does the kW rating increase with frequency?
Shouldn't the kW rating depend upon the design of the motor?
Why does current rating change, too?


texts: How are ultrasonic bursts generated electronically?

texts:
I'm curious how the ultrasonic sensors generate bursts from pulse trains electronically. Here is a plot about how a burst look like?

I couldn't find any illustrative explanation about it.


texts: How can Erlang C values be greater than one?

texts:
Here is an Erlang C plot I did myself. The x-axis represents the total traffic while the y-axis represents the probability. Each line represents a different total number of channels.

As you can see, the graph has probabilities greater than one. How can this be even possible?


texts:
I'd like to measure the force that a human leg impacts on a knee brace during normal gait. I have a problem in finding a suitable sensor for the job...

The leg (and hence the brace) are not flat at their contact surface and it seems FSRs change their response dramatically when bent... and load cells seem quite bulky and also have the same restriction.

I looked at more exotic solutions, e.g. Creating my own sensor out of Velostat (http://www.robotshop.com/uk/pressure-sensitive-conductive-sheet-velostat-linqstat.html) but my concern is it won't be accurate or reliable.

Can strain sensors give me low creep and good repeatability?


texts: Nitrile and touch screens. What is the distance required from your finger to the screen to make it work?

texts: I am working for a safety company and we need to certify how we can use some nitrile gloves with touch screen, I read that your finger needs to be at .5mm to the touch screen to make it work. So depending on the thickness of the glove this could work or not. Any expert on this?


texts: Converting a three-wire system's "EMC filtering configuration" to a two-wire one

texts:
I'm designing a board which has -48V input.
For the power module, I'm considering using KSTW010A0A Barracuda from GE(DOSA compliant 1/16 brick, Isolated DC-DC Converter)

In the datasheet, there is this figure which shows suggested configuration for EMC filtering:

The problem is:this configuration is intended for three-wire system where there is Vin- & Vin+. But my system is a two-wire one.
So my question is how to use this configuration for my design.

I guess the Y-caps will be removed and the choke will be replaced by an inductor? How much caps values will affect by this change? what is the value of new inductor?

Thank you

PS1:
In the first place I draw my schematic just like the configuration and obviously it's wrong!


texts: Can an inductor be substituted for a coil

texts:
I am designing this FM receiver circuit.

I have a few questions related to the circuit.

Buying coil in my locality is a  little expensive. So would it be alright to substitute an inductor in its place? If yes, would it be alright to use a 0.2 micro-henry inductor? And also what should be the capacitance range of the variable capacitor if this is done?
Would it make a vast difference if I use a different transistor? I prefer using 2N3904 because it is more cheaper.
Can the LM386 be replaced by an ordinary class A transistor audio amplifier? Would it affect the audio signal?


texts: I have completed my schematic and PCB design and made a design rule check (DRC). I have realized a concept as LVS - Layout vs Schematic. Can i do it in Altium Designer or does it already done by DRC? If you share ideas i will be happy. Thank you so much.


texts:
I'm currently trying to design an Uninterruptible Power Supply for my microcontroller (Raspberry Pi 3 Model B). I've read from the documentation that the microcontroller requires 5V and the amperage drawn by it will be dependent on the peripherals I use.

Under normal conditions the microcontroller will be powered with the 5V microUSB that it comes with but in the event of a power outage or the cord getting pulled out I want to use rechargeable Lithium-Ion Batteries as a backup power supply. I'd also like the circuit to be capable of charging the rechargeable lithium-ion batteries, with a way of preventing overcharging to the lithium-ion batteries.

I also want my microcontroller to be portable so that way I can use it outside. So I wanted to use a solar panel to provide power to the circuit, but in times where the solar panel is not providing enough power I wanted the rechargeable lithium-Ion batteries to supply the necessary power to the microcontroller. I'd also like the solar panel to recharge the lithium-ion batteries when the solar panel has excess power to give out that isn't necessary to the microcontroller. Again, the circuit needs to be capable of preventing overcharging to the lithium-ion batteries.

I've looked around and seen some others doing something similar but I haven't found anything that gives me a concrete explanation or schematic that I understand.

My attempt:
(Note the 5V is the microUSB or Solar Panel and the 4V supply is the rechargeable lithium-ion batteries.) I understand the values aren't correct and that a DC-DC Boost converter might be required... I also need something in place to make sure that when the batteries are fully charged that reverse polarity does not occur, correct?

Any help is appreciated!

This is when the 5VmicroUSB or the Solar panel is connected, notice it is 'charging' the Rechargeable Lithium-Ion Batteries (Idk how to model rechargeable lithium-ion batteries

This is when the 5V microUSB is disconnect, and then the lithium-ion batteries immediately start providing power to the microcontroller


texts: what is the simplest set up for detecting ions?

texts:
I try to detect a flow of positive charged ions. These ions produce an electrical current in the order of 10^-12 Ampers. My question is that, what is the simplest set up for detecting these ions?

Charged particles traveling in vacuum and hitting a metal box, When an ion hits the metal box, its charge is neutralized by an electron jumping from the metal on to the ion . That leaves a space amongst the electrons in the metal, and the electrons in the wire shuffle along to fill it.


texts: Is it OK to use internal pull-down as part of voltage divider?

texts:
There is a NUD3160 relay driver on the board that I need to set ON at power-up. According to datasheet, it has internal 100k pull-down and 2V threshold voltage. So, if I add external 910k pull-up to 24V power line it should form a voltage divider sufficient to open the driver.

What bothers me though, is how reliable the datasheet is, especially in the long run. Technically, the manufacturer does not have to use these exact values, as long as the electrical characteristics remain the same.

I don't know if this question is "opinion-based" or not, but what would you recommend?

Update

After reading all the comments and answers I've come to the conclusion that relying on internal workings of the driver was a bad idea. So, here is what I am going to do:

Add second resistor to get normal external divider;
Adjust divider to produce around 5V gate voltage. This will ensure full opening of the driver and will reverse-bias diode so that this circuit would not load 3.3V power control signal coming from TC7PZ17 buffer (see full circuit here).
Use lower values so that driver's input impedance won't matter much, but not too low to draw much current; Something like 24k + 8.2k seems to be a good compromise, wasting only 0.8mA / 0.01W per node.

Critique?


texts:
I am having issues understanding the Per-Unit System calculation. I don't come from an exact power engineering background so I hope my question is not too stupid.

For the calculation of base impedance and current, I found it using the two giving base values.
Ib=500/4=125A , Zb=4k/125=32 ohms

For the per-unit value of the resistor: I divided the actual value (400) by the base impedance (32) and the value is 12.5 p.u.

For the part asking about the resulting current if connected this bus to the ground am not sure if I do understand it fully. I found the current by dividing the base voltage (4k) by the per-unit resistance (12.5) so >> I=4k/12.5 = 50 p.u.

for the remaining two parts I am confused with the frequency given how to use it.  I could only found the actual inductance by using the base impedance so >> L(actual)=L(p.u) * Zb = 0.1 * 32 = 3.2 H.
Not sure and feel like I am missing something. Also, I tried to look for material to understand how to solve the remaining two parts but I couldn't find any useful material.

I hope someone could help explain this to me. I would appreciate it.


texts: I am building a IoT device using Raspberry Pi Compute module 4, Using usbboot, we can read eMMC as a flash device with which we can read and write the eMMC from any computer. Is there any way we can disable this functionality.


texts: Initial voltages of capacitors using mesh currents analysis

texts:
simulate this circuit – Schematic created using CircuitLab

The book I'm reading is noting that I should recognize the initial voltage across the \$C_1\$ capacitor is \$10 V\$ but I can't see why this is.  I see that by setting up the mesh equations for \$i_2\$ I would get:

\$-4\frac{di_1}{dt}\ + 4 \frac{di_2}{d_t} + \frac{1}{8} \int^t_{t_0}i_2dt' + 5i_2 + v_{C_1}(t_0) = 0\$

Could someone explain to my how \$10V\$ is derived?


texts: Resistive Touchscreen Stands in Midway of the ADC in standby

texts:
In a resistive touchscreen I am trying to read x-y position. The schematics is as followed. The code works fine and when I press a point, it reads correct position well but the problem is in standby ( when no touch ).
The ADC shows the middle of the screen both for x and y instead of reading zero ( around 512 in a 10 bit ADC reading ).
I set a parallel 4.7 k resistor from X1 and Y1 to ground and the result is better ( it reads around 20 in standby) but I have not seen such design anywhere and dont know which value of the resistor is the best if this is the solution.
There is a good tutorial on resistive touchscreens by ATMEL here. In page 4, there is a table about the settings. I couldn't understand what Hi-Z stands for and I think the main result of my problem goes to that pull-up/int in the table for standby , but I couldn't find any sample code for setting a pull-up/int . What is that? should I clear SFIOR register PUD before reading and turning it off during the scan?

Schematics without resistor:

Schematics with resistor:


texts: Power produced and internal resistance of solar cell vs distance from light source

texts:
Solar cell can be modeled (rudimentally) as a DC voltage generator \$Vp\$ with internal resistance \$Rp\$.
Consider a solar cell  at a distance \$d\$ from a (constant) light source.

What kind of relation is there really between produced power \$P=\frac{V_p^2}{R_p}\$ and \$d\$?

I found on different sites that it should be \$P \propto 1/d^2\$ since the light power incident on the cell \$P_{inc}\$ is proportional to \$1/d^2\$. I'm ok with that but since \$P\$ is not the power incident on the cell but the produced power, it is related to \$P_{inc}\$ by the efficiency \$\eta\$, that is \$P=\eta P_{inc}\$.

Therefore \$P \propto 1/d^2\$ implies that \$\eta\$ does not depend on \$d\$! And that seems strange: is \$\eta\$ really a constant tipically?

Moreover, while it is clear that \$V_p\$ varies with distance, is it the same for \$R_p\$? Does \$R_p\$ also change with distance from light source?


texts: Printing variable characters to UART does not work, constants work fine

texts:
I have a rather strange issue with XC8 on a PIC18F27K40 microcontroller. On a PIC16F1778 it works. I have defined:

void uart_putch(unsigned char byte) {
    while (!PIR3bits.TX1IF);
    TX1REG = byte;
}

When, in my main loop, I call uart_putch('a');, this works fine. However, when I define const char c = 'a'; and call uart_putch(c);, it does not work. It prints something, though not an a - I think they are 0x00 characters, which I get from hexdump -x /dev/ttyUSB0. This is not an issue with the serial port on my computer; I looked with a scope and the signal is different (left works, right does not):

The code is simple:

void main(void) {
    init(); // Sets up ports and UART control registers
    while (1) {
        uart_putch('a'); // or c
    }
}

What does not work either is using any of the string functions (puts, printf, etc.), which I think is related - so in this question I made a minimal working example with characters.

The generated assembly when I use a variable c has:

_c:
    db  low(061h)
    global __end_of_c

_main:
    ; ...
    movlw   low((_c))
    movwf   tblptrl
    if  1   ;There is more than 1 active tblptr byte
    movlw   high((_c))
    movwf   tblptrh
    endif
    if  1   ;There are 3 active tblptr bytes
    movlw   low highword((_c))
    movwf   tblptru
    endif
    tblrd   *
    movf    tablat,w
    call    _putch

And with a constant it has in the _main block:

    movlw   (061h)&0ffh
    call    _putch

I'm using MPLAB XC8 C Compiler V1.41 (Jan 24 2017), with part support version 1.41.

The relevant parts of my Makefile:

CC:=xc8
CFLAGS:=-I. --chip=18F27K40 -Q -Wall

SRC:=main.c uart.c
DEP:=uart.h
PRS:=$(subst .c,.p1,$(SRC))
OBJ:=main.hex

all: $(OBJ)

$(OBJ): $(PRS)
    $(CC) $(CFLAGS) $^

$(PRS): %.p1: %.c $(DEP)
    $(CC) $(CFLAGS) -o$@ --pass1 $<

Any help to get this working would be very much appreciated.


texts: Circuit to find difference, in binary, between most significant and least significant 1

texts:
If A = 1100, and B = 1010, I want to find the positional difference between the first 1 from the left on A, and first 1 from the right on B. In this case the answer would be 10.

In other words, the circuit would find how many times i need to shift B to left, to allign its rightmost 1 to A's leftmost 1.

How could such a circuit be created? Preferably in the best O time?

I could do it with a logic table, but that seems rather tideous for a 32 bit circuit. My example was just 4 bit for simplicity. I am implementing this in logism - a digital logic simulator.


texts: Why capacitor value should be greater than gate capacitance of gate of NMOS in Bootstrap topology?

texts: In case of buck converter when NMOS is used as high side driver then bootstrap circuit is used to keep gate voltages higher. While designing that bootstrap circuit, the value of capacitor is recommended to be 10 time greater than capacitance of gate of transistor. What's the reason behind this?


texts: Mutual capacitance pads of footprint component

texts:
I've a 0402 footprint and i would like to evaluate the stray (mutual) capacitance between the two pads.

What i know are

l*m : pad size
w   : thickness of the pads
d   : distance between pad
h   : distance between pad and GND layer.

Actually i'm a bit confused about how to evaluate this stray capacitance. How can i take into a account the fact that i've both air on one side and FR4 on the other?

The only formula i've found on internet is:

C= e0*eFr4*L*w/d

Can you give me further information about the calculation?

Thanks in advance for the consideration.


texts: FFT analysis of summed signal in LTSpice

texts: I know that simulating FFT analysis of current/voltage across a single element via LTSpice is quite straightforward.   I have simulated the summation of three distinct currents in the time domain. I'd like to perform an FFT analysis of the summed signal in its current incarnation (just as it is). Can anyone suggest to me how to compute the FFT analysis of the summed signal?


texts: Protecting unpowered op-amp, or how can I use 12V to switch 3.3V?

texts:
I'm designing a Eurorack synthesizer module which includes an MCU, DAC (TI DAC8565), and TL074 op-amp for scaling and buffering the DAC output.
In normal operation the module will operate from a +/-12V supply and use voltage regulators to get 5V and 3.3V for the digital components of the circuit.
During development, however, the module will be disconnected from the +/-12V supply and the MCU and DAC will be powered via USB. A diode protects the 5V regulator against the reverse voltage in this case.
My concern is that the DAC will be outputting 0-2.5V to one input of the op-amp, and a 1V reference voltage derived from the 3.3V will be going to the other input, and these are outside the op-amp's absolute maxima when the supply is 0V.
I'm considering two options to deal with this:

Add diodes from the 5V rail to the 12V, and from ground to the -12V, so that when the +/-12 rails aren't directly powered, the op-amp gets a few volts of supply, so it can handle the DAC output. I don't care if the op-amp functions correctly here, I just don't want it damaged.

Hold the /RST line of the DAC low while the +12 is unpowered, and derive the 1V reference from the +12 instead of the +3.3, so the op-amp inputs are at 0V if there's no supply.

For implementing option 2, I see a bunch of questions here about how to switch 12V from a 3V control signal, but I want to do the opposite. The circuit given in this answer does the trick in simulation, but I note that when the control line is high, the transistor would be reverse-biased to the tune of around 8V, which seems bad. Is there a standard way of switching a low voltage with a high voltage, non-inverting?
And a final question, is it generally true that the absolute maximum voltage figures for an op-amp, given relative to supply voltage, hold true down to zero supply voltage? Will a couple of volts on the input of an unpowered op-amp damage it?


texts: Multimeter current measurement: internal resistance or input impedance specification

texts:
As the internal resistance (or input impedance) of a multimeter influences the circuit you are measuring, and therefore influences the accuracy of your measurement, it would make sense to me to if this internal resistance were mentioned somewhere in the multimeter spec sheet.
When multimeters used physical d'Arsonval movement "galvanometer" where a typical industry standard developed around 50 µA for full-scale deflection, that was all the user needed to know.  Regardless of current range, 50µA would flow through the galvanometer and the remainder through the shunt resistors.
For example, when measuring DC current through a low resistance load, a couple of Ohms internal resistance can make a big difference, so it would be helpful to know at least its order of magnitude.
However, although some manufacturers (e.g. Fluke) specify the input impedance for voltage measurements, I have not been able to find similar specifications for the current measurement part (e.g. the ammeter internal resistance or shunt resistor values for different measurement ranges).
I know how to measure the ammeter resistance using a load in series and resistors (or decade box) in parallel with the multimeter, but I don't understand why manufacturers do not provide these values in their spec sheets.
Does anyone know? Am I missing something obvious? Am I looking at the wrong specification perhaps?
As electronic DMMs replaced d'Arsonval galvanometer, it took time for  the industry to determine how to represent the equivalent effect.  Eventually they settled on the term 'burden voltage' to convey equivalent information.


texts:
As far as my understanding, wiegand device should be connected to wiegand controller so they can communicate in wiegand protocol which is 2 parity bit and the 24 data bit (the Standard wiegand 26).

So let's take an EM4200 card as my example. EM card with 40 bit id. Let's say it's ID is 1234567890(hex) or in binary:
0001 0010 0011 0100 0101 0110 0111 1000 1001 0000

Using a wiegand EM Reader, it transmit 123456, or the 3 byte
0001 0010 0011 0100 0101 0110

This would only equal to 24, so where is the 2 missing parity bit?

Same goes with UHF card. But with HID card, there is really  a slot for parity bit on its memory structure.

Someone please share your idea.

Thank you.


texts: Completing a circuit, how is the necessary voltage determined?

texts: When you have some device, like a TV, why is there a necessary Voltage-or current for that matter. Whenever I see circuits, it always says to find the current from the voltage and resistance given, so presumably with any battery there should be a current. Why do some things require bigger current and bigger voltages? And how would one calculate the voltage required? Furthermore, even with some deemed insufficient Voltage, there would always be a current, so I don't know why a device wouldn't work.


texts: SMP, NUMA, local memory - limits on numer of processors

texts:
I consider what are limits on number of processor in following models of shared memory:
a. each processor has only own local memory.
b. SMP
c. NUMA

I can't see any limits.  Am I wrong ?


texts: FreeRTOS causes SYSTICKACT (HardFault) exception

texts: I generated a basic project with CubeMX for STM32F4. After compiling and having successful run, I added FreeRTOS manually. Unfortunately, all the time I'm getting HardFault exception with SYSTICKACT bit in SCB->SHCSR set to 1. What wrong I've done while adding FreeRTOS?


texts:
I am going to Purchase LM7805 for 5V supply for my school project and I now know how to connect it. Now I want to know that will excess current damage my circuit?
As per datasheet output current is 1.5A. Can you tell that will my IC work on it? ICs are -: 7404,7432,7438. And how do I know what is max current limit for a certain IC? Is that is related to iol and Ioh?


texts:
The item below is one of two components of an old (c 1950?) electric chisel.  (The other part is a reciprocating solenoid.)  The name tag on this part says "Electric Converter", with a 6 amp rating.  Inside the case are 10 thin disks, separated by plastic-looking spacers.

The output socket has 4 pins: frame ground; 'neutral' (connects to one AC input line); and two which (unloaded) each measure 120 Vac relative to the 'neutral'.  The latter two do not show continuity to any other pins, or to each other.  No DC, at least on my DVM.

I'm wondering if this is a dual half-wave selenium rectifier (Wikipedia).  However, if the 10 disks are the "plates" described there, the 20v reverse voltage per plate rating seems marginal.

Questions:

Any idea what it is?
If it is a rectifier, it's broken, yes?  (AC on the output)
If it is a selenium rectifier, is the 20v per plate Vrev not a problem?
If it is selenium, would that material's properties (e.g., current-limiting (per wikipedia)) be advantageous in this application (large switching inductive load), compared to a diode-based rectifier with a similar power rating?

EDIT: The output cord from this device feeds the solenoid section of this tool.  The nameplate on that says 120 V, 60 cy [hz].  So, not a rectifier.

Size: 6" long, 4" diameter

Disks & spacers:


texts: I have a flashlight with a strobe mode and need to know how to slow down the strobe on it. Please tell me if I should add a resistor or vary the power source to slow and NOT dim the strobe light.


texts:
I have connected by lithium-ion battery to a tp4056 IC charger with builtin circuit protection(shown below).

Which means the circuit will automatically disconnect the load when the battery voltage goes below 2,4V. My problem is when the battery goes below 2,4V the IC disconnects the load from the battery, but then the voltage picks up to around 3,2V and then reconnects the load. When the load gets connected again the voltage drops back below 2,4V and then disconnects the load. So basically when the battery drops below 2,4V the first time my load then keeps on reconnecting to the battery via the TP4056 IC. Hence I want to design a switch that when the battery drops below 2,4V initailly the swtich closes and disconnects my load. BUT when the battery voltage increases after disconnecting the switch must remain closed. How do I design such a switch? and the charger IC is connected to a 5V boost then to my load to give my logic part of the switch

initially: output=5V

voltage drops below 2.4: output=0V

voltage goes back up: output=0V


texts: Can problems arise from mixing 2.5mm pin pitch components with 2.54mm through-hole protoboards?

texts:
I am new to electronics and from what I understand, most protoboards seem to be standardized on a 2.54mm (0.1") pin pitch. I am also aware that there are through-hole components which are manufactured at a 2.5mm pin pitch, namely JST connectors.

Note:

  Connector confusion on the internet:

  In recent years, it is preferred to use millimeter (mm) instead of inches for pin-to-pin
  pitch distance. Note: Some 2.50 mm parts are incorrectly sold on the
  internet as 2.54 mm (0.100 in), and the 1.25 mm parts as 1.27 mm
  (0.050 in).

I have some JST-XH connectors which fit just fine in a protoboard advertised as having 2.54" pitch spacing and does not feel tight at all; tested on a connector with 8 pins to maximize error.

Should I take any special precaution when mixing 2.5mm specced parts on 2.54mm protoboards or should I expect them all to fit as my JST connector does?


texts: Is there any difference between a track made from 2oz copper, or one plated to 2oz

texts: Is there a difference in reliability if I start with  a copper clad board with 2oz copper vs starting with 1oz and letting them plate up to 2oz?   Intuitively I would say no but someone put the idea in my head that somehow the plating layer could de-laminate.  Has anyone had any experience with that.


texts:
I am trying to perform a software reset of my STM32F2. (Reference manual available here.) The relevant page of the reference manual (page 80) gives little information. Basically, the SYSRESETREQ bit of the Application Interrupt and Reset Control Register must be set.

Now this page explains that to be able to modify the SYSRESETREQ, a specific "key" needs to be written to the VECTKEY bits.

Neither document explains where this Application Interrupt and Reset Control Register is. What is its address, and how can I access it?


texts: Does an ATMEGA328P need a crystal oscillator while using ISP?

texts:
I tried to burn the Arduino bootloader to an ATMEGA328P on my custom PCB but it failed. I want to know if it is possible that my crystal might be broken and causing problems.
While using ISP it seems like SPI uses the clock signal from the master (programmer) so the target MCU has no need for the crystal to do ISP.


texts: LTSpice error with V() function, .......... when referencing net within a subckt (V(subCktName.NetName))

texts:
I've converted an IBIS model to a SPICE model using microCap, and am trying to simulate that subckt with LTSpice.

Using LTspice, I get an error with the subckt in the library.

"u1:g1: Unknown circuit node: "u1:xvkdr.vkdr" requested in behavioural source"

It cannot understand the V() function used in this way "V(XVKDR.VKDR)"
Which is referencing a specific voltage net (VKDR) within the subckt (XVKDR).

Here is the LTspice project with .lib

LTSpice project

Thank you


texts: how to overcome the slow pace of my simulink model?

texts:
I have run the solver profiler to debug where my simulink model stuck and take very long time to simulate. I found out it is the diode model that I model as following:

It runs fast on its own. However, in the big simulink model it sticks for 30 min. I tried a simple function block ans shows same result.


texts:
I am trying to make LED in MSP430G2 Launchpad keep blinking / off with button like Switch example (http://www.arduino.cc/en/Tutorial/Switch) in Arduino/Energia but I seem to miss something stupid and i don't know what...

const int buttonPin = PUSH2;     // the number of the pushbutton pin
const int ledPin =  GREEN_LED;   // the number of the LED pin

int state = HIGH;      // the current state of the output pin
int reading;           // the current reading from the input pin
int previous = LOW;    // the previous reading from the input pin

// the follow variables are long's because the time, measured in miliseconds,
// will quickly become a bigger number than can be stored in an int.
long time = 0;         // the last time the output pin was toggled
long debounce = 200;   // the debounce time, increase if the output flickers

void setup()
{
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT);
}

void loop()
{
  reading = digitalRead(buttonPin);

  // if the input just went from LOW and HIGH and we've waited long enough
  // to ignore any noise on the circuit, toggle the output pin and remember
  // the time
  if (reading == HIGH && previous == LOW && millis() - time > debounce) {
    if (state == HIGH){
      state = LOW;
    }
    else {
      state = HIGH;
      digitalWrite(ledPin, HIGH);
      delay(100);
      digitalWrite(ledPin, LOW);
      delay(100);
    }

    time = millis();
  }

  digitalWrite(ledPin, state);

  previous = reading;
}

It blinks once when i press the button.
I know that this

digitalWrite(ledPin, HIGH);

or state part messes up.
Any help?
Thank you.


texts: References for writing spice model code?

texts:
I'm currently looking into building my own spice models from datasheet specs to ensure accuracy. Are there any references for this sort of thing? I've looked around online and haven't found anything great.

I'm wanting to build things up to the complexity of an op amp.

Thanks in advanced.


texts: What is the synchronous speed of single phase induction machine from 2 phases of 3 phase machine in parallel?

texts:
If I take all three windings of a three phase induction machine and put them in series, it acts as a single phase induction machine with three times the number of poles. This scheme is used to perform zero sequence braking. The synchronous speed of the single phase machine is then 1/3 of the synchronous speed of the original three phase machine (due to the higher pole number).

My question is, if I take two or three windings of a three phase induction machine, and put them in parallel with each other, will this also operate as a single-phase induction machine, and what will the pole number and synchronous speed of the resulting machine be?


texts: What design testing can I do before fabbing a PCB?

texts:
I'm an EE graduate who enjoyed the first taste of designing and fabricating hardware. My first board was a really low speed microcontroller board using mostly DIP and through-hole components, like something straight out of the 80s. It's very easy to translate to a PCB from a breadboard using these packages, but they are large and cost per square inch is very high for single-digit run project boards. To cut down on costs I designed a board using solely SMT components which was far more compact (as well as complex) than any other previous board I've made. I'd like to verify as much as possible that my designs work before spinning a board so I don't waste my limited budget (and have to delay for the new boards).

What verification practices should I use, besides making a breadboard facsimile, when making a (low speed) PCB? Up until now I've just made sure everything was routed, passed DRC and ERC and hoped the board works. I feel like there's more I should do.