texts: Why do I have crosstalk in Arduino ADC, despite low source impedance?

texts:
I. THE CIRCUIT:

Below, an Arduino Due measures voltage signals from two parallel voltage-divider circuits:

We want the Due to accurately measure the voltages at the places where it makes contact with the voltage-dividers. However, we see significant crosstalk - changing the resistance in one channel changes the voltage in the other channel:

$$\textbf{TEST I} ~~(R1 = R2 = 10 MΩ):$$

$$\textbf{TEST II} ~~(R2 = 3.3 MΩ < R2 = 10 MΩ):$$

However, we can theoretically trace these effects to current leaking through the Due: the Due usually has an input impedance of around 10 kΩ, but we have under clocked it from 20 MHz to 1 MHz, which raises its input impedance to 266 kΩ. So the electrons in the voltage divider circuit will certainly prefer to enter the Arduino, rather than traverse the 1 MΩ placed in front of them.

II. THE FOLLOW-UP:

Below, we have made a tiny modification to our original circuit, in hopes of making the voltage channels truly independent: both signals are buffered by one ADA 4528-2 (a dual-channel op amp):

The op amp is not there to amplify the signal: it provides a gain of ~1.003. Instead, it is there to hide the high impedance of the circuit that we're trying to measure. Instead of an output impedance of 1 MΩ, the impedance is now <0.1 Ω:

so the electrons should stay in the circuit, and there should be no crosstalk at all. However, to my surprise, although there is some improvement, there is still noticeable crosstalk!:

$$\textbf{TEST I} ~~(R1 = R2 = 10 MΩ):$$

$$\textbf{TEST II} ~~(R2 = 3.3 MΩ < R2 = 10 MΩ):$$

The red channel should not "know" that the blue channel has increased resistance. However, its signal drops, when I have not made any changes to the red channel - What am I missing from my analysis (By the way, I'm using low-tolerance resistors <1%)?


texts: How to design a PID controller with no additional i) gain margin, ii) phase margin?

texts:
Given a system G(s), how do I design a controller C(s) such that no additional phase or gain margin is incurred? I would like to do this analytically

Surely I could go through the step of drawing a Nyquist plot of the CP(s) system and then tune the parameters one by one, but are there easier methods for which this can be done without going through the Nyquist or Bode plot?


texts: How to calculate R for an AC load on a 3-ph system

texts:
I'm trying to calculate the resistors in an AC dummy load for a 3-ph system.

A simplified schematic can be found below. The idea is to switch (with regular AC 1-ph contactors) some resistors on each phase, the middle point being the neutral point.

The generator has a line-to-line Voltage of 280V and we're trying to dissipate a maximum of 60kW.

I'm using the following formula : I = P/(sqrt(3)*U) = 60000/(sqrt(3)*280) = 123A

==> I'm trying to have 123A per phase in order to dissipate 60kW.

R=U/I = 2,276 Ohms
==> Am I correct in assuming I have to have a 20kW resistor of this value on each phase? (of course divided between several resistors in order to be able to reach intermediate power values via the contactors).

Thanks for the input!


texts:
I have been learning about transistors a lot lately. Following that I have managed to design a simple circuit that uses PNP transistor as a switch. Basically this is going to be a door alarm where if someone opens the door, alarm will sound. Reed switch will be the activator here which will interact with the magnet attached to the door.

simulate this circuit – Schematic created using CircuitLab

SW1 is a reed switch here.
Buzzer needs 30mA to operate

My question is do I need to add a resistor in series to the base of transistor in this circuit. I have observed almost in all transistor circuits that they add a resistor to limit the current flow.

If my understanding serves me right, in this circuit the emitter and base will be of same potential when reed switch is activated which will not allow any current to flow through the base terminal.

Did I got this right? Any advice is highly appreciated.


texts: Why is there no NOR with immediate value in MIPS? AKA NORI

texts:
One thing which got me thinking was the lack of NORI in MIPS. Is the argument similar to why there is no SUB for immediate values since it can be simulated with a different instruction? If so, how is it done?
Edit: I mean NOR with immediate values. Sorry about that!


texts:
I am working on a project that have to carry high amount of current (200A continuous). Therefore it is necessary to provide bus bars to the PCB, that would support passing it through circuit. I would like to pass finally version of this board into the assembly, but I am not sure how it is going with bus bars, that I would like place there.

Is it possible to mount bus bars to PCB in assembly?
Maybe there is any alternative solution instead of bus bars? Are you aware of any other, like specialized power PCB with local thicker copper? Of course - looking for low cost of service.
How about screwing bus bars to PCB instead of soldering? Would it work properly?


texts: Why earth ground connection does not leak current?

texts:
This seems like a question which has been asked multiple times on forums. I researched the problem but I still was unable to figure out the answer which I can at least intuitively understand. So in this simple circuit why is there no current leakage to earth? Assume that it is a true earth ground connection (a rod in the earth for example).

Update: I am giving researched answers below, but not as the only options. I am not satisfied with any of them, and give my explanation as to why. So I am hoping for either an elaboration or an alternative answer.

simulate this circuit – Schematic created using CircuitLab

The answers I have found:-

Here With only one connection to ground there is no circuit for the current to flow through. It can't flow "to" ground, because there is nowhere for it to flow to. There's no difference between ground and a wire dangling in the breeze. However for current to flow there must be potential difference. And because the ground and the battery return has the same potential - why would current prefer to flow specifically to the return point. Especially taken into account that earth can absorb all electrons generated by the battery (on contrary for example to just piece of wire).
Here The ground isn't a great conductor and while it is in parallel with the service, the amount of current returning through the ground is so small it is effectively zero - Firstly this answer implies that there's some leakage occurs which just depends on earth resistance. Also I do not understand which resistance is taken into account. Where it is measured? I think also the answer relates to the several connection of the circuit to the ground.

So anyone can give real physical explanation of this?


texts: Can I connect an inverter supply and AC mains supply in parallel?

texts: Consider a solar panel is used to charge a battery and the battery supply is fed to an inverter. When the mains AC supply goes off then the backup battery supply kicks in. Suppose I want to reduce my electricity bill, can I connect my solar power from the inverter, in parallel with the mains AC supply such that most of my load is supplied by the solar power? Are there any inverters with phase synchronization available?


texts: What can reduce overshoot and ringing on a simple square wave pulse generator?

texts:
I've built a simple RC and Schmitt-trigger-based square wave pulse generator. On the breadboard, it has some obvious unwanted qualities due to jumper length, the breadboard itself, etc.

Schematic and breadboard version:

And the waveform output:

In particular, the rising edge of the square wave has a substantial amount of overshoot (about 200mV over 500mV peak) and ringing. It is easy to make it worse, by physically touching R1. See edits for correct info.

In looking for solutions I've ran into terms like snubbers and dampening for RF circuits and things beyond my hobbyist pay grade.

Anindo suggests in an answer to a related question that one should use a 50Ω resistor for a load. I am measuring the output from the first Schmitt trigger (IC1D, at pin 2). The remaining triggers are used with 220Ω resistors to create an approximately 50Ω impedance, but I get almost identical results measuring at the output node.

This fast-edge pulse generator is purely for my own experimenting/education, so there is nothing critical about it. If I decide to make a soldered board of it, what sort of things can I do to ensure it's better than its breadboard cousin?

Edit:

I mistakenly was in AC coupled mode for the previous screenshots and measurements. Here are some more screens showing the signal at pin 1 and 2 of the IC (input triangle wave on 1, output square on 2). They are now DC coupled. The probes were always in X10 but the scope itself was in X1 (brand new scope, oops!). The overshoot however is still significant: on the output which is 0-5V, the overshoot (shown by the dashed white cursor lines) is 2.36V. Note that the overshoot on the input is only about 500mV. Is the input ripple due to the proximity of pins 1 and 2 on the breadboard?

Input (ch. 2/blue) on pin 1, and output (ch. 1/yellow) on pin 2:

Overshoot measured w/ DC Coupling:

Removing resistor R2 and measuring at pin 4 (IC1E output) did not yield any noticeable difference from the signal at pin 2.

I should mention that the original tutorial/video by W2AEW from where I got the information for this circuit also has some overshoot, but not to the degree I have. His circuit is soldered on a board which probably helps a lot.

Original author's (W2AEW) waveform (at node OUT) with maybe 500mV over 5V:

Original author's soldered version:

Edit 2:

Here's a picture of the overall setup including lead lengths to the PSU and scope:

Edit 3:

And finally, VCC (yellow) and the OUT node (blue) on the scope to show the coinciding ripple:


texts: Input and Output Resistance of an Amplifier

texts:
I attempted to find the input resistance by using the thevenin equivalent circuit. I shorted all the capacitors and changed the circuit  to its small signal equivalent.

I found Rb to be 13.33kOhms because it is the equivalent resistance of 120k and 15k.

I used the equation rπ = β × re and found re=(25mV/Ic)

I found re to be 4.537 ohms by using the relation

Ve=1/10 *Vcc. Ve= 1.2V
1.2=Ie *Re
Ie=1.2/Re === Ie=1.2/220 ===Ie=5.45mA

but Ie is approx = Ic,
so re=25mv/ 5.45mA = 4.537Ohms,
thus rπ = 4.537β.

Then I found Rin= [(13.33*10^3)*4.537β]/[13.33*10^3 + 4.537β]

But I have no idea where to start finding Rout


texts: Why it is required to write each byte with 0 before erase in NOR flash?

texts: It is written in some sites that for NOR flash, each byte has to be written with 0 before erase. Why it is required to write with 0 before erasing? Erasing the sector change each byte to 1.


texts: Digital timer rated for incandescent load only -- what would happen with a small motor load?

texts:
I have a small digital timer designed to replace a wall switch. As such, it runs on the 120VAC mains and has only a hot and a ground in (plus a switched hot out). Because it works without its own neutral wire, I assume it powers itself via passing a small amount of current through the load even when off.

Here is the manual: http://waterheatertimer.org/pdf/GE-15313-Manual.pdf

As you can see, it's rated for:

Incandescent (Tungsten): 5A/600W
Resistive: 15A/600W

The packaging specifically admonishes against using a CFL or LED load, and an inductive or motor rating is notably absent.

I was hoping to use this to control a small, "bathroom vent"-style fan until I noticed the rating. I'm going to get a different timer, but I still wonder what folks here think is the concern.

Would back-EMF damage the electronic guts when the fan turned off?
Would the (intentional) leakage current damage the fan?
Are they using a semiconductor switch that requires a zero-crossing to turn off and the inductive phase-lag messes with that?

Bonus question:

What is special about tungsten loads that warrants a much lower current rating than general resistive loads? Does it have something to do with filaments changing resistance as they heat?


texts:
I hava a tablet where I plug a PCB (with a microcontroller) on it. Because the tablet has only one USB port I have to connent and disconnect all the time the PCB, bacause I have to connect the computer with the tablet in order to transfer the Android program from the PC to the tablet. I designed a circuit with a relay with four contacts in order to avoid to disconnect and connect USB cables on tablet. I add one schottky diode on USB connector of the PC and one on the USB connector of the PCB so to avoid a short circuit between the two powers where in instance the VCC_1 contact of the relay will be stay close for some reason and the contact of the GND_2 will be open and as a result the VCC_1 will have different positive reference power. Please, tell me if this senario is wrong and the schottky diodes are not necessary or if the relay circuit needs something more.

I changed the USB micro connector to USB type A in order the tablet will be the slave.

Sample code of control USB ports - MIC2026-1YM - TS3USB221A:

Select(S)=0, OutputEnable(OE)=0
if (Second_Chip_FLB=0)
{
Switch off the D+ and D- at the port A sideside --> OutputEnable(OE)=1
Delay 500mS

First_Chip_ENA=0
Switch off the 5V at the port A
Delay 500mS
}

if (First_Chip_FLA=0)
{
Second_Chip_ENB=1
Switch on the 5V at the port B side

Delay 500mS
Switch on the D+ and D- at the port B side --> Select(S)=1, OutputEnable(OE)=0
}
else
{error}


texts: Need help in Altium polygon copper pour selects and deselects using arcs, angles, full circles

texts:
This is a follow up question of my previous question. I've done this board using AutoCAD and exported to DXF.

After that I used Altium designer to import the DXF file in which the outline turned out as shown in this pic.

Now I need to modify the outline to get the actual PCB board like this:

I have tried adding the polygon pour using full circle, arcs,lines but its pouring the copper all over including the gap tracks. So I'm confused and struggling to find a proper way to do this. Please help me guys.


texts: Transformer Going Up In Voltage Over Time

texts:
I have a transformer from a 1953 jukebox that seems to be increasing in voltage over time.  When I first got it, it was outputting 32V.  A week later it seemed steady at 38V, then 45V.  Now I just measured it and it's at 50V.
I see no visible signs of burning or excessive heat and I've not seen or smelled any smoke.
It is supposed to be a 115V => 32V (approx) transformer.
What is going on?  Do I need to throw this thing out?


texts: What the difference between a buck-boost converter and buck-boost controller?

texts:
I was looking for some buck boost power management IC for my circuit i have noticed that in Texas instruments website the buck - boost is categorized into 2 category converter and controller googling them only show results for converter. I have also noticed that the buck boost controller has a higher output current rating.

What is the difference between the two and which applications work best of either of them ?


texts: Battery charging with boost converter topology

texts: I'm designing a circuit for battery charging, which will make use of boost converter topology. I have determined the input/output voltage and current parameters for the circuit. If I put a resistor at the output with value of V_out/I_out, the simulation works just fine. My question is; how can I set the current, so that if I put a battery at the output when the circuit is built, the current would be same as the pre-defined output current value. Also, does the output current depend on the characteristic of the source? Like if the power value of source is constant but input current and voltage changable with PWM at the switch (like a pv panel), what would the output current depend on? Many thanks.


texts: Cheap and easy way to power MCU from Li-Ion, and keep it powered during charging

texts:
What is the cheap and easy way of powering MCU from Li-Ion battery, with automatic 3.3V regulator disconnect while charging, to properly charge the battery? I've came up with something like this:

Is it ok?


texts: Testing Power Supply Variac-Rectifier-Cap

texts:
I have built a power supply with the following order.
Variac-Full Wave Bridge Rectifier-Capacitor.

I get the input from the wall. I connected neutral and line to the rectifier. Not using the ground.

The multimeter shows a steady DC output.
However, I'd like to see the output with more details.

I build a really simple circuit with a resistor and an LED to test the power supply. Here is the problem! Everytime I connect the circuit to the scope the LED dies. I don't go beyond 40V out.

I tried to sketch what I have and what I am doing so far.

Any suggestions would help. Thanks in advance.


texts: What mechanism does a brushless motor use to generate electricity

texts: I have observed that when you spin the rotor of a motor, electricity is generated, but i don't understand how this applies a brushless motor that has its magnets as the rotor, all that is happening is that you are spinning the magnets, how does this generate electricity?


texts: Opamp precision PID loop without capacitors?

texts: I am wondering if it is possible to create a hybrid PID circuit using opamps with key components whose values are programmable. Programmable resistors - no problem. But capacitors?


texts: Led on for one minute eve if the switch is pressed for more than one minute?

texts: how to make a circuit that when press the switch the led is gonna stay on for one minute and than off even if the switch is still pressed for more than one minute


texts: Load capacitance for a microcontroller crystal?

texts:
I know there are lots of similar questions on here, but I've read many of them and am still a little confused.

I'm a student making a board similar to the Arduino Pro Micro, using a Atmega32U4 microcontroller. SparkFun's version shows the crystal circuit as this:

The above iamge shows 22pF capacitors being used, and I'm trying to determine what the load capacitance of the crystal should be.

I found the formula for the capacitors to be: CL = (C1 * C2) / (C1 + C2) + Cs

If I assume the stray capacitance is 5pF (seems to be a somewhat standard assumption) and use 22pF capacitors, then the above equation gives: CL = (22*22)/(22+22) + 5 = 16pF

So if I want to use 22pF capacitors in the circuit, I need a crystal with a load capacitance of 16pF, correct? Looking on Digi-Key, the closest I see is 18pF.

If using an approximate value for the crystal load capacitance (such as 18pF when 16pF is calculated) is unacceptable, then I could go in the other direction, first choosing the crystal and based on it's load capacitance calculate the required capacitors values.

For example, I see a crystal with 8pF load capacitance, so using the above equation I can calculate CL = 6pF. However, every single schematic I see for an Arduino or Atmega circuit shows 18pF, 20pF, or 22pF capacitors being used, which makes me question whether lower capacitor values such as 6pF are acceptable?


texts: MP3 Player, does volume affect power use?

texts:
When playing sound on a MP3 player to headphones, does the volume level affect how much power is used? Intuitively I think that high volume = high power consumption, and low volume = low power consumption, but that's just an assumption.

I know this is a very general question, as it will probably always depend (at some level) on the specific device.

Would the answer change depending on what was plugged into the MP3 Player? (Nothing/Earplugs/Large headphones/AC powered stereo through AUX)


texts:
I can see this as being 50/50 between here and Eng.SE, so I decided to ask here as it deals with the PCI Express standard.

I'm attempting to create a library of PCI Express card edge footprints in Altium Designer, but I'm running into two dilemmas as to how the Card Electromechanical Specification lays out the the card edge dimensions. The image below is a snippet of the mechanical spec:

The two issues I'm having are:

The length (or, I suppose, height) of the normal-size pins are not specified. I was able to infer based on the height of the PRSNT2# pin and the difference in distance between edge of pin to edge of card that the normal pin should be 4.20mm high - is that correct?
The distance of B12 to the key centerline is specified as 1.50mm, but not the distance in the other direction, that of B11 to the centerline. I'm a little uncomfortable making the assumption that the two are the same and that the pitch between the pins is 3.00mm - can anyone confirm (or deny) this?


texts: Automatically connecting LiPo batteries in series (for charging)

texts:
I have a battery charger capable of balance charging up to 10 cells in series (10S), but most of the batteries I use are somewhere between 1 and 4 cells.  I have plenty of experience charging the batteries in parallel, but I'd rather charge them in series.  Doing so allows my charger to report out to me details on the health of each individual battery, rather than some aggregate across them all.

Connecting the batteries in series is pretty trivial: connect + on one battery to - on another, make a balance lead tap between each battery and at the ends.  The net result looks something like

Balance:   |  |   |   |...|
Batteries: -C1+-C2+-C3+...+
Charge:    -              +

The problem is that charging / discharging batteries doesn't actually happen over the balance lead but instead over the charge wires.  As a result, I either hard wire the plugs to always charge the same number of batteries or I have to manually adjust which battery the + charge lead goes to.

I've tested this out with a 5x 2S battery rig, but I'd rather have a solution that didn't require I adjust the + terminal each time.

Is there some way I could rig up a simple circuit to detect the presence of a cell and use that to switch where the + lead is hooked up to?  For example, in the below diagram, could I use some form of a transistor in a SPDT setup for each of the |---| lines below?

-C1+-C2+-C3+-C4+
|  |   |   |   |
|  |       |---|
|      |-----|
|  |------|
-     +


texts: Arduino - Pulses get unstable when updating PWM duty-cycle

texts:
I'm trying to obtain stable pulse trains when adjusting the duty cycles wth an Arduino Uno board. In my actual project I need to use 4 adjustable PWM output pins at a fixed 25kHz frequency to control four pwm controlled DC motors.

But to point the issue easier I want to ask my question with an easy setup and with an easy short code.

Lets say the goal is to vary PWM duty-cycle of pulses with a fixed frequency. A potentiometer can be used to vary the input voltage at A3 pin which than is scaled to duty cycle of PWM pin 9. The simple setup is illustrated below:

To explain the issue in a clear way, I would like to show you couple of simple codes and short video records from the scope screen.

Here is the code which adjusts the duty-cycles from potentimeter readings at A3:

void setup()
{
pinMode(9, OUTPUT);
}

void loop()
{
  int val = analogRead(A3); //read the value from the potentiometer
  float volt =(5.0 * val) / 1023; //convert the value to voltage
  val = 255 * (volt / 5); //scale the voltage for pwm duty-cycle
  analogWrite(9, val);

}

And with this code uploaded to the uC, below is the video record for the output:

https://www.youtube.com/watch?v=0ZOHCazAqfM

As you see on the scope, the pulses are flickering. They are not stable. By the way the issue is not related to the poti output since I also tried fixed 3.3V pin out with an int cast. It seems to me it happens each time analogWrite updates.

And here is another code where analogRead and analogWrite functions are still continuously active in the loop. The only difference this time the analogWrite has a fixed value here as 24:

void setup()
{
pinMode(9, OUTPUT);
}

void loop()
{
  int val = analogRead(A3); //read the value from the potentiometer
  float volt =(5.0 * val) / 1023; //convert the value to voltage
  val = 255 * (volt / 5); //scale the voltage for pwm duty-cycle
  analogWrite(9, 24);

}

And now with this one uploaded, below is the video record for the new output:

https://www.youtube.com/watch?v=yv2umE11mcI

As you see on the scope, the pulses are extremely stable.

I need to control the DC motors with a high precision. Before this uC way, I made a simple analog circuit with 555 and a comparator but for some extra features I needed to use a uC.

But now I noticed this issue and spent too many hours to see if other libraries would have a better solution. I couldn't find any. I found the following video from a guy who wrote a library: https://www.youtube.com/watch?v=9JXGIeM3BSI but the same issue occurs with his library as well.

Is this a known issue and is there a workaround? And I would be very glad if I can find a solution or any suggestions.

Edit:

The problem was the Arduino being supplied by laptop's USB output. I checked the potentiometer and 3.3V pins with AC coupling and here is what I got:

Arduino ADC is 10 bit which is 5000/1024 = 4.8mV. Which means it is sensitive for each 4.5mV. In my case power ripple was causing sometimes around 15mV difference.

I tried with a non-USB 9V power supply from Arduino's power barrel jack, the issue solved. Thanks to Anklon for his intuition.


texts: USB line noise in aircraft cockpit recordings

texts:
I'm a pilot and we have a comm setup that I need some help with because of noise. We have a USB cable that supplies power to one of our GoPro cameras mounted in the cockpit. When this cable is plugged into the Apple USB adapter (or any 110 USB adapter for USB A (male) to USB mini, we get a lot of "hum/noise" in the audio. When we disconnect the USB from power, it's a clean recording.

A link to the noise and video is here, if anyone would be willing to offer their opinion. We have tried USB shielded cables and ferrite filters that go around the cable. No luck. While we don't have to have the cable plugged in for power and the camera is designed to run on battery, we would like to see if we can filter out this noise. We are not sure if it's something in the camera or if it's the line picking up noise.


texts: Need help solving a problem with ac resonance circuits from my uni book

texts:
simulate this circuit – Schematic created using CircuitLab

Okay I have struggling with this problem for some time and I cant figure out how to solve it.

The circuit is in resonance!

I tried solving it like this:
P = (I1^2)*R1 + (I3^2)R2 = R(I1^2 + I3^2)

R = (P)/(I1^2 + I3^2)

Then I drew phasor diagram and found I3 like this:

I - I3 = sqrt(I1^2 - I2^2)

I3 = I - sqrt(I1^2 - I2^2)

Then I plugged it into the first equation and found R and then I calculated the voltage like this:

U = I3 * R

and then the rest was easy but I got the answers different than in the book.
The solutions in the book are C = 50uF and L = 2.5mL

Anyway I dont know which part of my reasoning is wrong. I suspect that its this part : P = (I1^2)*R1 + (I3^2)R2 = R(I1^2 + I3^2)
or the way I drew the phasor diagram:
(https://imgur.com/HZrbWWN)

So any help would be greatly appreciated.


texts:
In an LR circuit with an AC source (\$V=V_0\cos(\omega t)\$) we have that
$$I(t)=\frac{V_0}{\sqrt{R^2+(\omega L)^2}}cos(\omega t -\phi)$$
where \$\phi=\frac{\omega L}{R}\$. I find this formula rather intuitive. If the inductance \$L\$ is high then the system has a strong 'ability' to fight back against changes in the current thereby reducing the currents amplitude. Similarly, if the frequency \$\omega\$ is high, then there will always be a very high change in magnetic flux through the inductor and thus a large back emf will produced meaning the currents amplitude will ultimately be reduced.
But now if we hook up a simple RC circuit to the same AC source, we get the solution
$$I(t)=\frac{v_0}{\sqrt{R^2+(\frac{1}{\omega c})^2}}cos(\omega t+\phi)$$
where \$\phi = \frac{1}{R\omega C}\$. But now I do not find this formula intuitive at all. Why should the currents amplitude approach a maximum as we increase the frequency? In the case of the LR circuit, the current goes to zero and the reason is rather intuitive (It's because of the increasingly rapid changes in magnetic flux which generate an increasingly strong back emf) except for an RC circuit, I can't think of any reason why the amplitude approaches a maximum. Also, why would the currents amplitude approach a maximum value if the capacitance is extremely high but approach zero if the capacitance is extremely low?  And finally why is there a phase difference at all for a RC circuit? The phase delay in the LR circuit can easily be chalked up to the back emf but for an RC circuit there doesn't seem to be any immediately apparent reason for the phase difference.
Basically, I can't seem to come up with any reasonable explanation as to why the capacitive reactance (\$\frac{1}{\omega c}\$ ) takes the form that it does.
Any help on this would be most appreciated!


texts:
I am setting up a new electronics lab for embedded systems related work. We need four or five workbenches/workstations, a soldering station, enough storage space for all the essential electronics supplies, and maybe some other useful equipments. We already have quite some equipments available such as oscilloscopes, logic analyzers, large cabinets, etc. But we need a storage solution for all those electronics components.

I see there's already a SE question (Best way to get components for a new electronics lab). But that one is about getting components while I am thinking about the higher level things including lab layout, workbench design, flooring & lighting etc. I would like it to be a bright, modern, and safe lab environment.

I guess I need some professional help here. I could quickly google some lab outfitting companies and contact them directly. But I would like to hear some  recommendations from you, my fellow engineers. Thanks.

Update 1: this is for a commercial company. There will be multiple projects going on in this lab.

Update 2: To make this post less "opinion based", I would appreciate some suggestions on which firms offer this kind of consultant service. I don't have a lot of time to figure out all things myself. I just want some help to set up a good looking and functional lab quickly.


texts: Negative voltage across ground points under load

texts:
All,

I have a circuit with an Exar XRP7659 5v 1.5A regulator and a Torex XC6210B 3.3V LDO Regulator. I am using this circuit to charge USB devices at full current and have noticed that when the device is charging I get negative voltage from any two ground points on the breadboard.

It appears that this negative voltage is coming from the GND pin on the USB port, as I read the highest negative voltage there, but it's seen throughout the circuit. The result is that the LDO goes slightly under voltage to 2.8 - 3.1 volts. The LDO returns to 3.3v when the USB device is unplugged. The issue is not apparent when using a 5V 1.5A power source but this results in ~4.4V out of the 5V regulator, which is unacceptable. I am using (and have tried multiple) a 12V 1.25A DC input source.

What could cause this negative voltage and how do I resolve it?

Here's a schematic for my circuit


texts: Why is an electronic circuit system should be linear to use Fourier and Laplace transforms?

texts: What I understood is, if we need to analyze a data from a system(such as damped oscillation or an output of an electronic circuit), the system must act in linear fashion to employ Fourier and Laplace transform. Why is it like that? I thought any signal could be decomposed as sinusoid. I mean if one make data acquisition of a system why that data has to be obtained from a linear system to employ Fourier and Laplace transforms?


texts: External power to STM32F4 Discovery board

texts:
I've recently finished programming the STM32F429ZI DISC1 board. I'm fairly new to this and now want to move away from connecting it to the PC via USB and power it up via a power supply.

At present I have connected a 5V supply to the 5V pin. This seems to power the board fine in that the LCD screen comes on (blank white), the PWR LED(LD2) lights up. However my program fails to initialise and stays blank, the COM LED(LD1) also flashes red at 1hz approx.

Has anyone experience with powering this board or other STM32 boards without a USB connection? And if so which Pin did you connect to and with what voltage.


texts: Please tell me what will happen if the instrumentation amplifier is constructed as this circuit? As in this, two resistances R1 are grounded in between? What is the problem in this circuit?


texts: Can you make a CPU out of electronic components drawn by hand on paper?

texts:
I explored a lot of literature about paper-based electronics recently, and one particular paper caught my interest: “Handwritten Oxide Electronics on Paper” (DOI: 10.1002/admt.201700009) by Elvira Fortunato et al.
It explains a method to make transistors (FET) on a sheet of standard paper, using a Zinc Oxide (ZnO) based ink (applied by a calligraphy pen) as the channel, paper as the dielectric layer, and silver coating as the gate, source and drain (screen-printed).
They achieve the construction of an inverter, with 15V as Vdd, a 3.75Mohm resistor, Vin = 12V, Vout = 6V.

simulate this circuit – Schematic created using CircuitLab
It's not spectacular, but given the simplicity of the method, I wonder if such transistors could be used to make logic gates, and adder, and eventually a complete CPU (at least a design from the 70s with a few thousand transistors) entirely by hand or at least printed? Maybe on rolled-up or stacked-up sheets of paper?
Zinc Oxide only allows n-channel, enhancement type FET, which means the logic used for building gates would be NMOS (with somewhat big mega-omhs pullup resistors).
That's highly hypothetical, and I'm definitely not an expert in transistors. But if we could one day make biodegradable computers out of paper, with kitchen shelf ingredients, that'd be interesting, wouldn't it?
Note: On a later paper they achieve better efficiency, but using IGZO (Indium Gallium Zinc Oxide) instead, which is an industry standard, but way harder to make at home.
The specific design I had in mind
I'm considering building a paper-based CPU based on that fabrication method. I could print transistors (about 1cm2) on sheets, rolled up for each component (or a bunch of them), then clipped together using copper wire with tips bent in a paperclip shape.
Given a box of about 1 cubic meter, it would look like a bunch of scrolls clipped together.
Capacitors could be made using the old paper+oil+aluminum design.
Resistors are just a zigzag pattern using a pencil.
Would that work or am I missing a major difficulty?
About the size
Some people say that such a design would be huge, and thus impossible to carry electricity around without fatal losses.
It seems, according to the illustrations in the scientific paper, that the transistors could be made about 1cm2 in size (maybe less if printed with a really high resolution printer).
For a 2000 transistors design, that would mean 50×40cm, which seems fairly acceptable.
About power distribution and signal loss
Did big (room-sized) computers just used a lot of current? How did they handle carying current over long distances?
Is there a way to prevent signal loss?


texts: Connecting resistor in LED parallel circuit

texts:
I connect 3 LED in parallel with a two AA battery source 1.2V each. As i searched in the web i realized that it is not correct to connect them without a resistor as they may get damaged.

How mane ohms will the resistor need to be?
I think to put one resistor  for all the LEDs like this:


texts: design a modular system, choosing bus and backplane

texts:
Our team has developed a several controller boards for our current Projects for over three years. With little modifications we have used this board in several projects so far. Its structure is as follows:

As you see almost all peripherals are connected to FPGA and The data bus between FPGA and CPU is a parallel bus (16 data line,12 addr line)based on FSMC-FPGA is like an SRAM for MCU-

Now we have decided to upgrade it to a modular system, here is system sketch:

At the moment we are investigating about buses and Backplanes and trying to choose one.

EDIT
here are some of our requirement:

we need one/two CPU slots(s)and modular peripherals on a multipoint Bus.
all nodes can send/recv data to/from the CPU slot(s)
CPU shall assess other slots like memory blocks (FPGAs on the slots act as memory for the CPU slot).
the communication speed of between CPU and peripherals Must be at least 25Mbit/s.
it would be better to have hot-swap capability but it is not essential now
we do not need communications between peripheral slots

questions:

what are possible or recommended choices for "Bus Drivers and Receivers" for our system? as far as i know here are some:

Backplane Transceiver Logic (BTL) e.g. SN74FB1651
General-Purpose Interface Logic  e.g. 74ALVT162245DL
Gunning Transceiver Logic Plus (GTLP) e.g. SN74GTLPH32912
VME64 e.g. SN74VMEH22501A

what are possible or recommended choices for "Data Link (node-to-node validity and integrity of the transmission)" for system? as far as i know here are some:

PCI/CompactPCI

Is there any application note,sample or reference design for
a parallel communication (add/data bus) over backplane on a uC?
Is there a Bus controller to Transceive our current parallel data over backplane on each slots so that we don't care about the bus or packplane :)


texts: Inverter Output Signal (Filter Input Signal) becomes distorted when LC Low pass filter is connected. Need Help please

texts:
I have built an AC/DC pure sine wave inverter (SPWM). My inverter is a full H-Bridge NMOS (IRF630) setup and the gate is being driven by a 4N37 optocoupler. My input DC signal is 12VDC and this signal is also being used for my optocoupler to fire the gate of my high and low side mosfets. The output of my inverter is the following (Rl=100ohm)

I have designed a low pass LC filter using L=68mH (Inductor 686C) and C=42uF to give me a cut-off frequency of approx. 94Hz. When I connect my filter to the output of my mosfets and connect a 100 ohm load I get the following output waveform.[![Figure 2: Inverter output of Filter][2]][2] I am assuming the the flat spot in my output AC waveform is due to the duty cycle imperfection approaching 100% duty cycle because of the switches not being ideal switches. Now when I connect my probe to check my input signal to my LC Filter expecting it to be similar to the of Figure 1. My oscilloscope now shows that the input signal is now greatly distorted.[![Figure 4: Close up of transients][4]][4] It seems to show that the inverter output response has become underdamped when connected to the LC filter. Is this happening due to impedance mismatch between my load and my source? If so how does impedance mismatch lead to an underdamped response? What is a possible approach to creating a matching circuit if this is the case? If not the case, what else is causing this distortion to my input signal? Parasitics of Inductor? Poor Inductor material Selection?? Also, When I disconnect my load the output waveforms seem to be approximately the same.


texts: How to get 5V 4A from two 5V 2A chargers

texts:
I have two 5V 2A chargers. I want to get 5v 4A. Can I connect both in parallel like this?:

simulate this circuit – Schematic created using CircuitLab

Can I do it? Because in parallel connection voltage doesn't change, so 2A +2A = 4A


texts: Identifying the configuration of transisitors

texts:
I have been handed the diagram below, as part of an introduction to transistors.

I am having a hard time finding out what type of configuration it is, therefore making it even harder for me to find the voltages and current values.

My intuition says the base needs to have some power source.

My question lies in identifying the configuration of the transistor [Common: {Base,Emitter,Collector}]

It's worth noting I have a limited understanding of transistor circuits.

EDIT:
Would the circuit below , be a somewhat equivalent to the one above in terms of calculations, I am new to circuits especially ones that don't have the cells in them.

simulate this circuit – Schematic created using CircuitLab


texts:
I am trying to use IRF520 as a relay driver for ESP32, but by reason unknown it does not works. I have replaced it twice with a new ones, but yet it keep not working.
I have 3V on the ESP32 pin when the state is HIGH and 0V when the state is LOW.
I am using the circuit below:

Why the IRF520 never trigger the relay ?


texts: Relay: wetting contacts before using sub-wetting current

texts:
I'm considering using small signal relay for my application since I need to switch shunt resistors to measure currents from 1uA to 10mA (two shunts) with voltages from 0V to 5V.
Now, it's clear for me what and why wetting current is. The relay I'm considering is EE2-3NU surface mount small signal relay. It has a wetting current of 10uA and it wants minimum of 10mV for it.
The question is: Can I apply minimum wetting voltage and current to the relay and then proceed immediately with my sub-wetting currents? For example, the device boots, wets the contacts with fancy current/voltage (min 10uA and min 10mV in my case), and then it does my 1uA current thing (or, say, 5mV applied - I can set either). Will this work? How reliable is this approach?


texts: Packing register pairs on Lattice FPGA slice. How?

texts:
On my design (Lattice MachXO2 FPGA) I use a lot of registers set by a signal and reset by another (both synchronous with the clock), like this:

process(Clk)
  if rising_edge(Clk) then
    if set_condition = '1' then
      flag <= '1';
    elsif reset_condition = '1' then
      flag <= '0';
    end if;
  end if;
end process

This is synthesized into a register (flag) with its CE and D inputs driven by one LUT each. I also tried code like this:

process(Clk)
  if rising_edge(Clk) then
    o1 <= i1;
  end if;
end process;
i1 <= '1' when set_condition = '1' else
      '0' when reset_condition = '1' else o1;

This is synthesized into a register (flag) with its LSR being driven by the set signal and the D input being driven by one LUT as a feedback mux.
Since the FPGA is allocated by slices and each has two LUT4s and two registers, both implementations share a common problem (for me) in that they use the register control inputs, which are common to both. This prevents using the second register on a slice for another purpose, wasting it and causing my design to fail mapping for lack of slices (I have around 80% of registers used, 90% of LUT4s and 103% of slices).

To resolve this I tested a component-instatiated feedback mux solution that uses a single LUT to drive the input of the register, without using the CE or LSR inputs. To verify the solution I've tested with two registers (only one shown below), that should be packed on a single slice. But they are not, each register uses its own slice.

d1: FD1S3AX
  port map
  (
    CK => Clk,
    D => i1,
    Q => o1
  );
l1: LUT4
  generic map
  (
    INIT => b"1111_0010_0011_0010"
  )
  port map
  (
    A => High,
    B => En1,
    C => Dis1,
    D => o1,
    Z => i1
  );

I've since found a partial solution, by adding LOCATE commands to the LPF file. By doing so I can get two registers into the same slice but I have to name the slice, locking it into place on the FPGA fabric.

LOCATE COMP "d1" SITE "R3C40A";
LOCATE COMP "d2" SITE "R3C40A";
LOCATE COMP "i1" SITE "R3C40A";
LOCATE COMP "i2" SITE "R3C40A";

Since I don't want to P&R the entire design by hand is there a way to group pairs of LUTs and regs together on the same slice but allowing them to float across the entire device ?


texts:
I bought this relay (http://www.ebay.co.uk/itm/400972235163) and this LED DRL lights (http://www.ebay.co.uk/itm/400757922989).

The questions are:

Can I attach 2 led lights to this relay (as it only has one red and one black wire) ?
If (1) yes, can I splice that red and black wires to get 2 red and 2 black wires?
If (2) yes, can I just solder and protect the ends of two red wires to the one from the relay ( a same for black ) ?
If (3) yes, can I use this cable (http://www.ebay.co.uk/itm/321770426302) to extend everything? Relay says 12V 5A and mentioned cable says 12V 8A.

Image attached ( that's what I have in plan )... is that all right?


texts: Finding drain voltage for a resistor loaded CMOS inverter with 0V at input terminal

texts:
Introduction:
The following example is from the textbook Sedra/Smith Microelectronic Circuits. It is stated in the solution to this example that since both \$Q_n\$ and \$Q_p\$ are both matched and \$|V_{GS}|= 2.5V\$ then \$v_o\$ must be 0V, thus both transistors will be in the saturation region. It is this conclusion that I wanted to investigate. My overall question is why does \$v_o\$ have to be 0V?

Used Equations:

Saturation current equation for NMOS:

\$i_D = \frac{1}{2}k_n^\prime(\frac{W}{L})(V_{GS} - V_{tn})^2\$

Saturation current equation for PMOS:

\$i_D = \frac{1}{2}k_p^\prime(\frac{W}{L})(V_{SG} - V_{tp})^2\$

Condition for ON:

NMOS- \$V_{GS} \geq V_{tn}\$ PMOS- \$V_{SG} \geq V_{tp}\$

Condition for Saturation:

NMOS- \$V_{DS} \geq V_{GS} - V_{tn} \$ PMOS- \$V_{SD} \geq |V_{SG} - V_{tp}|\$

Condition for Triode:

NMOS-  \$V_{DS} < V_{GS} - V_{tn} \$ PMOS-  \$V_{SD} < |V_{SG} - V_{tp}|\$

Solution Method:

Since I already knew the answer to this problem then I was going to work backwards to prove that the only possible solution to this circuit is for both \$Q_n\$ and \$Q_p\$ to be in saturation. My method is to show that both the transistors can not be in triode\triode, triode\saturation, or saturation\triode.

Solution:

Since the saturation current equations for both transistors in saturation are independent of \$V_{DS}\$ and are perfectly matched then both transistors have the same current passing through them. In order for this to be true that means that no current is going through the resistor which results in \$v_o\$ being at 0V. Now the problem is tackling other operative modes for the transistors.

For triode\triode it can be found that for \$Q_n\$ to be in triode \$V_D < -1\$ and for \$Q_p\$ to be in triode \$V_D > 1\$. Since the drains of the transistors are connected then there is no V_D such that it can satisfy both inequalities at the same time. This means that triode\triode is not possible.

Now where I am stuck is showing that triode\saturation and saturation\triode also are not possible, but I have yet to find a way. This is the underlying question to my solution method.

Is there a simpler solution to this problem or is there a way to show that triode\saturation and saturation\triode are invalid?


texts: Arduino analog input from an amp that uses a reference pin?

texts:
I am currently using an instrumentation amp (AD623AN) that uses a reference pin. I want to connect the analog output from the amp to my Arduino Ethernet so that I can measure it. How do I wire it up so that I can measure the output in reference to the required reference pin?

Note: When I am finished, I will have three of these amps to wire into one Arduino, so please take that into account if that changes the wiring.


texts:
I am looking at this simplified schematic for a linear regulator. The way this works is the error amplifier drives the base of the power transistor through the current amp. This in turn varies Vce to eventually stabalize Vcc. ,

I am wondering how its possible for the error amplifier to be working in linear mode without feedback. Is this just a very simplified schematic that doesn't show the feedback involved? Or possibly could it be an op amp with small open loop gain?


texts: Does wire gauge significantly impact the charging rate of smartphones?

texts:
This article claims that wire gauge in USB cables significantly impacts the charging rate of smartphones:

  USB cables have a data wire and a charging wire within the cable
  itself. Most USB cables, probably over 99+% are 28/28. Buying after
  market micro USB cables will pretty much always result in getting
  cheap quality 28/28 cables and your device will barely break 500mah [sic]
  when it charges, maybe even less.

The misuse of units makes me skeptical of the claims made by the article. Furthermore, the length of cables should also impact the total resistance, and the article does not mention cable lengths at all.

Is the article correct in saying that increasing the wire gauge from 28 to 24 (which has ~40% the resistance) would allow the charging current to increase from 500mA to 2A?


texts: Capacitance decay of SMD ceramic capacitors

texts:
I want to use a 330nF X7R ceramic capacitor for an analog circuit.
Obviously the capacitance value is very important for the correct working of the circuit.

I haven't found on the datasheet if these kind of capacitors has an important capacitance decay during time. For example, does the capacitance decrease after 1000 hours of usage?


texts: LM338 is getting hot and stop working when we try to flow current more then 1A

texts:
I try to make a 30 V, 5 A power supply using LM338 (without heatsink) voltage regulator IC.

In my case the value of R1 is 100 Ω and R2 is 2.2 kΩ. then it gives 29.6 V as output.
when we connect a 10 Ω 10 W resistor, the current is exceeded 1 A, the IC gets hot within a few seconds output current and voltage become zero. (I think the IC thermally shuts down).
After cooling the IC when we reconnect power then we got no output voltage and no current, IC is also not getting hot.
we can't conclude why it's happening. Is Ic got damaged?
After that, we did one more experiment.
Constant Current Circuit as given in the datasheet.

In my case R1 = 10 Ω, 10 W and load is again 10 Ω 10 W.
Here again within few seconds no output voltage and current.


texts: Do we have a voltage drop across this ideal current source?

texts:
Additional info includes Vss=0V, Vdd=3V.
Also assume saturation (since we have Vd=Vg) and λn=0.
We also know the reference current but not the Resistor.
I know Vgs and thus Vds but I am looking to find Vs/Vd/Vg.
I am guessing that there is a voltage drop across the current source so it is not as straightforward as Vd=Vdd=Vg.

Can we calculate those voltages?


texts:
I have this top module

entity top is
Port
     (
              CLock : in  STD_LOGIC;
           LED : out STD_LOGIC_vector(3 downto 0);
              taster : in  std_logic_vector(3 downto 0);
              teste_led: out std_logic;
              i_led: out std_logic_vector (2 downto 0)
      );
end top;
architecture Behavioral of top is

component game
port    (
              LED1 : out  STD_LOGIC_VECTOR (3 downto 0);
           CLK : in  STD_LOGIC;
              winLed: out std_logic;
              switch: in std_logic_vector(3 downto 0);
              pointerLED: out std_logic_vector(2 downto 0)
        );
end component;
begin
game1:  game    port map(LED1 => LED, CLK => Clock, winLed => teste_led, Switch => taster , pointerLed => i_led);
end Behavioral;

which i cannot see why isn't working. I've tested the game module by it self, and it work as it should be, but when i add it to this top module, nothing happens on my FPGA, eventhoug i am not getting any errors or warning?? what Am i doing wrong.

NET "switch"        LOC = "G18";

    NET "taster<3>" LOC = "K17";
    NET "taster<2>" LOC = "K18";
    NET "taster<1>" LOC = "H18";
    NET "taster<0>" LOC = "G18";

    NET "teste_led"     LOC = "R4";

    NET "i_led<2>"          LOC = "F4";
    NET "i_led<1>"          LOC = "P15";
    NET "i_led<0>"          LOC = "E17";

    NET "LED<3>"        LOC = "K14";
    NET "LED<2>"        LOC = "K15";
    NET "LED<1>"        LOC = "J15";
    NET "LED<0>"        LOC = "J14";

    NET "CLock"         LOC = "B8";

I did it exactly like this
http://www.eng.auburn.edu/~strouce/class/elec4200/vhdhier.pdf
I am therefore very confused on what i've done wrong..
Complete code:
https://www.dropbox.com/s/mro1wmk2bjkigp1/randomnumber.rar


texts:
I'm having an issue with this PWM controller circuit. In this circuit the potentiometer comes with a on/off switch.

The way it should work is:
As the potentiometer resistance value varies the output voltage varies (with the help of a 555 timer chip). When the output voltage increases the red LED increases in intensity and the the green LED decreases in intensity.

The problem that is happening when test the PCB is that:

1- The circuit is always "ON" the switch circuit doesn't seem to work

2- The output voltage doesn't vary as I turn the potentiometer, it is always at full intensity

3- The red LED is always at full intensity, the green LED never turn on

This PCB has 12VDC input.

Q1 and Q2 are N-Channel Mosfet (https://octopart.com/buk7y08-40b%2C115-nxp+semiconductors-19677921)

Q3 is a PNP transistor (//octopart.com/bcx5316ta-diodes+inc.-13152586)

U1 is a 555 timer chip.

Is there a problem with the schematic? Or is it that something went wrong during the PCB design?

I'm a hobbyist so forgive any mistake or oversight. Any help would be appreciated

Thanks you,

Roni


texts: Figuring out if an led strip/matrix has a short or not with a multimeter

texts:
I am relatively new to electrical work, mostly stay on the software side of things. I recently soldered header pins onto a few led matrixes I have. They are 3 wire leds (power, data, ground). I'm trying to figure out if I shorted the connections when I soldered them before I plug them in (I see tiny gaps, but first time soldering a breadboard and easy to use too much!)

I have continuity through everything I should have continuity through - data to data, hot to hot, ground to ground, but I also have continuity from hot to ground.

Part of me things that makes sense since it should be a circuit, part of me thinks that it means I have hot and ground touching in the soldering somewhere.


texts:
I am servicing a truck rig. This is the system that reads the "turn light switch" and "windscreen wiper switch".

I would like to understand how the image plate 1 reads each position of the levers. On the lever there are 3 contacts that are indicated with blue arrows in image 2. When the lever of image 2 is placed and pressed on the printed circuit board of image 1 it is possible to read each position of the lever.

I wonder how this reading is made since the contacts indicated with the blue arrows are made of a nonconductive material.

I thought it might be a change of capacitance, since capacitance depends on the physical characteristic of the capacitor and so contacts could change that characteristic.

Has anyone seen this kind of position reading system and could opine?


texts: Assigning the different value to parameters in Generate block in Verilog

texts:
I want to instantiate a module having parameters using generate block. But I want to assign different values to parameter for different instantiation of the module.

For example:

  This is my module that I want to instantiate and it has parameters DATA_WIDTH & SIZE_WIDTH .

module gen_module (
     input clk,
     input rst );

     parameter [3:0] DATA_WIDTH = 1;
     parameter [3:0] SIZE_WIDTH = 2;

endmodule

  This is another module in which I am instantiating gen_module using generate statement. (But here I am using only one parameter value of D_WIDTH and S_WIDTH for all instantiation )

[It is working but with single value for all]

module top_module ();

    wire clk;
    wire rst;

    parameter N = 5;
    parameter [3:0] D_WIDTH = 7;
    parameter [3:0] S_WIDTH = 4;

    genvar j;

    generate
        for(j = 0; j <= N; j=j+1) begin : GEN_BLOCK
           gen_module #(.DATA_WIDTH(D_WIDTH), .SIZE_WIDTH(S_WIDTH)) i_gen_module (
             .clk (clk),
             .rst (rst)
          );

        end
    endgenerate
endmodule

But I want to do something like this statement. (As I know parameter array is not applicable in Verilog)

gen_module #(.DATA_WIDTH(D_WIDTH[j]), .SIZE_WIDTH(S_WIDTH[j])) i_gen_module (

Here I want to give different values to D_WIDTH[j] & S_WIDTH[j] and want to use them to assign to parameters (DATA_WIDTH & SIZE_WIDTH) in generate block.

[Here J will change with for loop]


texts:
I am designing a SMPS from TI http://www.ti.com/lit/df/tidrgc2/tidrgc2.pdf

We replaced the Mosfet fro schematic with STL11N65M5 that has a Coss of 18pf

So I am designing a RC snubber across it and I calculated at about 47pf (and use R of 50R). The overshoot and damping is not optimized.

So I am trying to increase the C to 330pf (with a 50R) but my Mosfet blows up. How to calculate the maximum capacitance of RC snubber that Mosfet can whitstand ? Is it in relation to C and R ?

(we already removed the ferrite beads question)


texts:
I'm not understanding the concept of L-Pad attenuator other than seeing it as another ordinary voltage divider to attenuate a voltage. Electronics-Tutorials: L-pad Attenuator gives the following description:

L-pad attenuators are commonly used in audio applications to reduce a
larger or more powerful signal while matching the impedance between
the source and load in provide maximum power transfer. However, if the
impedance of the source is different to the impedance of the load, the
L-pad attenuator can be made to match either impedance but not both.

I understand maximum power transfer occurs when input impedance matches  output impedance (or \$ Z_{in} = Z_{out} \$), and that \$ \text{dB} = 20log({V_{out} \over V_{in}}) \$.  In terms of impedance matching, looking into the attenuator from the left, \$ Z_{in} = (Z_L || R_2)+R_1  \$ and from the right, \$ Z_{out} = (Z_s + R_1) || R_2 \$ in series. Hence for the two impedances to match and if I'm given a voltage attenuation ratio, I'll have exactly the following two equations to solve for two unknown values of \$ R_1 \$ and \$ R_2 \$:

Matching input and output impedance: \$ (Z_L || R_2)+R_1 = (Z_s + R_1) || R_2  \$.
Voltage attenuation ratio(): \$ V_{out} = V_{in} \big({{R_2 || Z_L} \over {({R_2 || Z_L})+Z_S+R1}}\big) \$

Aren't these two equations all I need to match input and output impedance while achieving a specific attenuated voltage? Why are there these logarithmic equations with a 'K' value solving for \$ R_1 \$ and \$ R_2 \$? And what does it mean when they say

L-pad attenuator can be made to match either impedance but not both


texts: Why do DMMs have so low update/refresh rates?

texts: My DMMs ($50-$100 range) refresh the displayed value every ~250mecs. Are there technical reasons (limitations) for this, or is this just a UI thing?


texts: Could a 4 pole 3.5mm jack be used to power a RGB LED?

texts:
I'm hoping to make my LED pluggable into a jack of some kind. Could a 4 pole 3.5mm jack be used? Could each pole carry 3v-5v?

Here's the LED: http://www.tandyonline.co.uk/5mm-full-colour-rgb-led-common-cathode.html

Thanks


texts: Placing a net tie underneath another component without the DRC error?

texts:
I'm using Altium Designer 19 and I have a ton of Net Ties many of which I'd like to place underneath other components.  My net tie is just 2 6mil pads connected by a trace without any silkscreen or 3d bodies or courtyard or anything... and with the component type set to "net tie (no BOM)".  All is well.

However, putting these net ties ( which just looks like a "chunk of trace") under another component I get a DRC collision error.  I could ignore these errors, but that seems like bad practice and there are a lot of them.  Is there a way to update the library net tie component to tell it that it doesn't have any actual component body and shouldn't generate any collision errors?


texts: How to interface a thermal printer to an Arduino

texts:
I've a thermal printer which has TTL, RS232 & a four pin interface. I want to connect it to an Arduino and take printouts with it. It has the following pinouts:
RS232 & TTL

GND
TXD
RXD
DSR
DTR

Another Four Pins Interface

LED
FEED
ONLINE
GND

I've tried printing using the serial communication by sending serial print commands from the TX of the Arduino to the RXD of the printer but for some reason it did not work.
How can I connect it to an Arduino and write a program for it?
Datasheet Links
https://drive.google.com/file/d/1F7it7uGA20YBPsqsTllIjLz1V8hDCv9Y/view?usp=drivesdk
https://drive.google.com/file/d/1FKDVJOw3tqIYPo8PN1DfwKDOgMbw3mg6/view?usp=drivesdk


texts: This is a picture of a Common Emitter Voltage Divider bias and it is been modelled using a CCCS and a diode resistance using the r_e model. Now my doubt is that I get problem in finding the input impedance/current and output impedance/current for the above model. How should I approach and how should I think and apply which techniques? What should I do so that I don't need to memorize and model the transistor myself for different configurations?


texts: How to calculate the required torque or HP of single phase induction motor to carry a massive object?

texts:
I need to know the power of a motor in Hp required to move a vehicle of about 300 Kg. The vehicle is equipped with gear assembly and required to run at 20 to 25 Km/h. The electric motor that is i used in vehicle is single phase induction motor( 1440 rpm , 50HZ , 220V, IHP) . I want to to know how much HP of the motor will be required to carry a almost 400Kg kg with a person . ( 300kg of vehicle and 100 kg for two persons)

How can we calculate the required torque to move a massive object by means of gear assembly ?


texts: Avoiding global variables when using interrupts in embedded systems

texts:
Is there a good way of implementing communication between an ISR and the rest of the program for an embedded system which avoids global variables?

It seems that the general pattern is to have a global variable which is shared between the ISR and the rest of the program and used as a flag, but this use of global variables goes against the grain to me. I've included a simple example using avr-libc style ISRs:

volatile uint8_t flag;

int main() {
    ...

    if (flag == 1) {
        ...
    }
    ...
}

ISR(...) {
    ...
    flag = 1;
    ...
}

I can't see away around what is essentially a scoping issue; any variables accessible by both the ISR and the rest of the program must inherently be global, surely? Despite this, I've often seen people say things along the lines of "global variables are one way of implementing communication between ISRs and the rest of the program" (emphasis mine), which seems to imply that there are other methods; if there are other methods, what are they?


texts: PCB design of crystal/oscillator ok in this way?

texts:
I'm working on a 4-Layer PCB design for my quadrocopter. I'm using a STM32F407 and I need the 32 khz and 8 Mhz crystal.
Is the pcb design of my crystal OK?

My layer order:

Sig1
VDD
VSS
Sig2

(please draw your corrections in if possible)


texts: does SPI delay between functions affect the communication correctness

texts:
I'm using SPI to communicate with a CAN controller. to read a register for example on the controller, I have to follow those steps:

CS =  low
write command
write register address
read  result
CS = high

does the time between those function affect the communication correctness, I mean if I put a delay between them, will the result be false?? and does the master continuously generate the clock or just when sending data?

CS =  low
write command
__delay(5ms);
write register address
__delay(5ms);
read  result
CS = high


texts: voltage on Oscilloscope without signal applied

texts:
I am doing some measurement on Scope ( non-isolated) , my set up is like this
-Scope is connected to 230V line mains with only two pin plug ( Earth or ground not used)
-channel is connected with voltage probe
-None of probe is hooked to any measurement point yet.

I observer when I touched any probe positive lead, I saw some high voltage waveform on screen,

a) First case :- I am reading 240Vac peak to peak and 82 Vrms on scope also can see sine wave on screen . I was sitting on chair , any I wore shoes and my shoes touching to ground.

b) First case :- I am reading 170Vac peak to peak and 50 Vrms on scope also can see sine wave on screen . I was sitting on chair , any I lift my legs form ground.

Q1) Is everything is right with setup

Q2) is it true voltage , then why i am not getting shock by touching probe lead

Q3) Why voltage shown when I am touching the lead, does I am generating the voltage from my body.


texts: Regulated 3.3V from a Lithium-ion (or LiPo) battery

texts:
Background

I wish to power my circuit with a Lithium-ion or LiPo battery (likely a battery with around 1000 mAh capacity). These batteries have a voltage that goes from 4.2V to 2.7V typically during their discharge cycle.

My circuit (running at 3.3V) has a maximum current requirement of 400mA -- although I should state that this is only the peak draw occurring about 5% of the time; the circuit draws only about 5mA the remaining 95% of the time).

Question

What would be the best way to convert the (changing) output voltage of a Lithium-ion battery into the required 3.3V to power my circuit with up to the peak current draw of 400 mA? By "best way", I mean most efficient voltage conversion so as to make the best use of battery capacity.

The tricky part for me has been the fact that the Li-ion battery voltage will be both sometimes ABOVE and sometimes BELOW my required final voltage! If it were only one of those two, I would probably have just used either a LDO regulator or a boost IC like TPS61200, respectively.


texts: Physically, how does connecting a PCB to chassis ground reduce noise?

texts:
I realize this may seem to duplicate Should chassis ground be attached to digital ground? but the answers in that thread don't explain why one should connect the chassis to PCB ground, aside from obvious safety concerns which I understand.

My logic is this: if I have a PCB with sensitive analog circuitry, I should put it in a metal chassis and keep it insulated from my PCB. The chassis acts as a faraday cage, which keeps my PCB from outside EM noise, and also keeps noise from emanating from my (say) RF PCB. I see no reason to connect the two, if safety is not a concern. draeth's answer in the aforementioned link seems to agree with this.

However,  conventional wisdom from very knowledgeable people says a low impedance path to the metal chassis should be established to reduce noise and EMI.

Why should this be done? It seems like by connecting my ground to the chassis, one would expose their circuit to noise from the outside. And as well expose the outside to noise!


texts: TP4056 battery output (charging voltage) is not constant

texts:
I tried to design a charging circuit based on the TP4056 li-po chip. At a usb voltage of 5V, the battery charging output (Pin 5 of TP4056) 4.3V. This seems acceptable, but there seems to be no regulation in my circuit as the battery voltage will vary with the input voltage
VCC-Vbatt
4.50--3.87
4.75--4.12
5.00--4.34
5.25--4.61
5.50--4.82

Can anyone suggest what the problem is? I'm too reluctant to plug in my li-pos until I get safe readings from a multimeter. Schematic included below

IBATT connector is shorted for voltage tests.
I do not want to overcharge my batteries with a voltage too high. The TP40456 dosent seem to be doing its job properly.


texts: Finding the exterior dimensions of a USB type-c receptacle

texts: I'm going to be using this USB type-c receptacle for my project.  For this project, I need to make a cutout in my enclosure to make this receptacle fit.  I consulted the data sheet and found technical drawings I thought would make this a simple matter.  Unfortunately I was not able to decipher the drawings.  I looked quite hard and could not find the exterior shape of the receptacle including the radius on the corner bends.  My question is if this is a standard shape that I can find elsewhere or if I am just that bad at reading the diagram and that the exterior shape is described in the datasheet.


texts:
I am designing a simple AVR development board based on the ATmega1284-pu and was wondering if there was any reason to use the RESET pin on an ATmega chip to reset it? Why not just cut the power to the device and then turn it back on?

(The ATmega chip is DIP and I will remove the chip to program it so no need for RESET during programming)


texts: Which is better from a Controls perspective, a Stepper or Servo Motor?

texts:
I'm designing a system to control the knob on an Air/Oxygen blender based off readings from a Pulse Oximeter. The idea to use a stepper to control the knob/retrofit an existing blender came from here.

I went with a Stepper motor for the initial prototype mainly because it doesn't require an encoder, and the speed and precision is more than enough for my requirements. I understand the differences in operation, power consumption, torque, etc and the only real argument for a servo over a stepper I see is heat. However this hasn't been an issue while using the driver circuit I selected. I'm about to graduate with an EE degree and am still learning how to use what I've learned to makes these types of design decisions.


texts: Quantifying Eye Diagram for high-speed SERDES channel

texts:
I need help quantifying Eye Diagram. I have to quantify Eye Diagram at the end of my Thesis for my Serial Link channel. Viewing an Eye Diagram, I can say probably whether it is bad or good. But for the hypothesis or any conclusion qualitative analysis is not enough. I need to have quantitative analysis. I know what parameters are there like jitter, eye width, height, crossing level etc. etc. But how to say up to which value of parameters the eye diagram is good. like how can I decide that like 35% BER or "x" ps jitter is tolerable for the serial link (Though it depends on circuit & signaling techniques etc...)? Simply to ask what separates a good ee diagram from a bad one?

If you have any note or suggestion or anything regarding my specific question will be appreciated also.


texts: Sending battery info attached with GSM through SMS

texts:
I am writing a C code for receiving battery using GSM modem SIM 800E. I am using AtMega16 uC. Here I have used AT commands to get battery info.

void uart_send(unsigned char ch)     //Function to send via UART
{
    while(!(UCSRA &(1<<UDRE)));
    UDR=ch;
}

void bat()                         //Function to get battery info and send SMS via UART
{
    int x;
    char battery[16];
    UCSRB &= ~(1<<UDRIE);
    writecommand("AT+CBC");        //AT command to get battery status(My program stuck here)
    for(int x = 0;x<20;x++)        //Reading 20 characters by the response of AT+CBS
    {
        while(!(UCSRA & (1<<RXC)));
        battery[x] = UDR;
    }

    UCSRB |= (1<<RXCIE);

    for(int x=1;x<20;x++)          //sending 20 characters to UART
    {
       uart_send(*battery);
    }
}

int main()
{

    DDRB=0xff;                     //PORT as output port for LCD
    uart_init();                   //initializing UART
    _delay_ms(1000);
    writecommand("AT");
    writecommand("AT+CMGF=1");      //setting GSM to Text Mode
    writecommand("AT+CNMI=2,0,2,0,0");

    while(1)
    {
        bat();
        transmit("AT+CMGS=\"+9195xxxxxxxx\"\r");  //Sending SMS with values in UART buffer
        _delay_ms(10);
        uart_send(26);    // command to send SMS
}

When I run the code it stuck in the bat() function (at"AT+CBC") it displays the battery info on the LCD and terminal both but doesn't send it by sms and program doesn't proceed further. Please suggest me ways to get the info through SMS.

Edit

Regarding comments by Loongcat

I am receiving 20 characters after the comman "AT+CBC" then it should receive that. this is the loop for(int x = 0;x<20;x++)


texts:
I am working with building a digital scale (of sorts) and have a single load cell working connected to my microcontroller.

If I wish to use multiple load cells, can I simply connect their signal outputs together in series, then amplify that signal?
I do I need to collect the separate signals from each cell, amplify each one, then process each one, and sum them?

Thanks


texts: Starting (inrush) current of a resistor (heater)

texts:
We are going to purchase a 48kW electric drying oven.

As we know the AC motors have big starting current and a special starting equipment is needed - Star-delta, soft-starter, inverter and etc.

What is the situation with the simple resistors/heaters?

Is there a need for a special starting equipment? Or we can just connect them Direct-on-line. 16kW to each phase with a contactors?

Thank you in advance!


texts: RN41 Bluetooth module with MSP430 to Android device

texts: I have an RN-41 bluetooth module connected to an MSP430. I want to connect the RN-41 to an Android cellphone. Just by having power to the Bluetooth module, the cellphone finds the device. However, it is not able to make pairing the only documentation that I find about pairing on the RN-41 says that the default key for pairing should be 1234.  In any case the cellphone doesn't even ask for the pass key but shows an error saying that is not able to pair. Can anyone provide some guidance?


texts: AC output from the following buck-converter?

texts:
Will the output be 100% DC from this buck-converter? Or Am I missing a diode bridge?

simulate this circuit – Schematic created using CircuitLab

A friend pointed out that the buck-converter would output AC, I'm doubtful and maybe it's because the diode bridge is missing?


texts: When are we going to append the "j" term when analyzing ac circuits. When i say j term, im pertaining to opposition to current/impedance. In the image below, notice that Xl is not written as jXl. When are we going to use the j term and when are we not going to use it?


texts: I am making a project with 8051 which require a millis() function as like arduino, please suggest me how to implement it.


texts: Adding a transistor to cut the power makes automagically any device more power friendly?

texts: I'm currently designing a device that will be powered by batteries, I'm planning to make the MCU sleep and only wake up a few times a day to read sensor values and go to sleep again, one of the sensors is a GPS, It will be used once a day only a for a few seconds (not every time the device wakes up), the GPS I want to use can be put to standby mode but won't be more efficent to just cut de power with a transistor controlled by the MCU and only power it when is going to be used (very rarely) than using the software based power saving features of the device? I guess I'm missing something here because if it was the case the device would probably include this feature from the factory.


texts: Edge triggering seems to me leaving every circuit in an inconsistent state?

texts:
I was informed on this forum that edge triggering could be a solution for multiple propagation in a circuit with feedback (the output wired back to the input).

But to me edge triggering seems to leave a circuit in a completely inconsistent state.
Look at this one (one-element JK flip flop ripple counter).

Let the clock input be edge-triggering signal and look at the first NAND field at J when all inputs at J are high but the clock. At the moment the clock gets high the propagation starts. The edge lasts for a nanosecond so it will probably end before the value propagates through the NAND.
Anyway, a nanosecond-long low signal will travel through the output of the first NAND, preceded and followed by long intervals of high signal. That composition will get to the the second upper NAND and the NAND will change values accordingly, further branch-wired to another NAND plus an input, and it all looks like a great example of an inconsistent state of a circuit to me - who knows what is going to happen there?

I don't get properly something about edge triggering. What is that?
Thank you for the time!


texts: Can I swap TX+ and TX- (and RX+ and RX- ) using ethernet magnetics?

texts:
I am building ethernet connectors and a switch into a product. There is a requirement to include PoE which I haven't done before. This has required the use of a new magnetics chip to expose the two centre taps.

The new magnetics chip has a different pin ordering to the one used previously, so as in the below image, there is a crossover introduced in the routing:

I believe that the transformers in the magnetics are symmetric. I'm therefore hoping that I can simply swap the connections to the + / - (p/n) pins of the magnetics:

(This would apply to both the TX and the RX pairs)

This is what the datasheet for the magnetics (Bel Fuse S558-5500-25-F) shows:

The centre tap is - I believe - genuinely in the centre and to my understanding the dots indicate that the coils are the same polarity.

Does anyone have any reason not to make the swap I intend to improve my routing?

The alternative would be to put the magnetics on the underside of the PCB, but this introduces unwanted layer changes, and potentially an interference issue. That or I find different magnetics.


texts: Why does rectification of a digital signal double the frequency content?

texts:
I'm performing envelope detection in the digital domain. This consists of rectifying the signal (i.e. taking the absolute value) and low pass filtering it to extract the slower varying envelope signal. I've heard that rectification doubles the frequency content in the original signal, therefore this information has to be taken into account when designing the digital low pass filter.

I would like to understand the mechanism in which rectification doubles the frequency content of the original signal.


texts: Naming and grouping individual pins with the ATXMEGA

texts:
I am new to using atxmega chips (atxmega128a1 specifically) so sorry if my question is not worded in a "professional" way!
So far in order to set or clear a pin I use the following programming in C:

PORTA.OUTSET = PIN1_bm;
PORTA.OUTCLR = PIN1_bm;

The problem with this for me, is that the individual pin definition is on the right hand side of the "=" sign. I would like to be able to set a pin individually in this fashion:

PA0 = 1;

This would be useful to me as I have many individual pins on different ports that need to be "virtually grouped" in the code as they are doing related functions.
For example I have four motor "enable" pins set on different pins of 4 separate ports. Currently if i want to turn them on simultaneously I have to do this:

PORTE.OUTSET = PIN5_bm;
PORTH.OUTSET = PIN0_bm;
PORTJ.OUTSET = PIN3_bm;
PORTK.OUTSET = PIN6_bm;

I want to keep my naming conventions and port names clear and easy to read such that I can group these outputs into some sort of structure and simply write:

Motor1_Enable = 1;

How can I manipulate C to do this for me???
Hope this is clear! Thankyou!


texts: Very sensitive dim led indicator detector

texts:
Background: My car aircon recirculation button often turns off by itself. This happens when the aircon is cold enough. Problem is. When it turns off and the indicator light disappears, the pollution outside gets into my car and I can smell the pollution and my pm2.5 monitor registers 20x higher.

I need to build a very sensitive dim led indicator detector to trigger a buzzer if the light turns off below.

What kind of photon detector can I fit into the almost 2 inches round button so if it detects the light is turns on it will sound a buzzer alerting one to it?


texts: Is the datasheet of the AVR ATmega32 wrong?

texts:
I'm currently using an ATmega32 to keep time, so I carefully read the datasheet and configured the Timer 1 to generate an interrupt each second.

According to the following formula on the datasheet, using a 16 MHz clock, a prescaler of 256, and OCR1A = 31249, I should get a frequency of 1 Hz in CTC mode:

\$  f_{OCnA} = \frac{f_{clk\_I/O}}{2\: \cdot \: N \cdot \: (1 \: + \: OCRnA)} \$

This formula is available on page 99 of the ATmega32 datasheet.

I've configured Timer 1 as follows:

TCCR1A = 0;
TCCR1B = (1<<WGM12)|(1<<CS12);
OCR1A = 31249;
TIMSK = (1<<OCIE1A);

Here is the interrupt code

ISR(TIMER1_COMPA_vect){
    sec++;
}

Then, I use an LCD to continuously print the value of sec, and I get a timing of 0.5 seconds. In other words, for each second that passes, the timer generates two interrupts.

At first I thought maybe I got the fuses wrong, but that doesn't seem to be the case, as delays work just fine. Anyway, here's how I configured the fuses:

-U lfuse:w:0xff:m -U hfuse:w:0x99:m

I have absolutely no idea of what's going on, I've double checked everything, tried another ATmega32, tried another 16 MHz crystal oscillator, and I still get the same result.

Is the datasheet wrong, or am I missing something here?


texts: USART between Atmega16 and Beaglebone black

texts:
I'm working on a project which involves me to send data from AVR atmega16 microcontroller to a beaglebone black.

I had written a code for the atmega USART but when connected, the beaglebone black didn't receive any data. So I tried using an arduino uno to see what's going wrong. The USART interface between the arduino and beaglebone black worked perfectly but while connected to the atmega, the same problem kept occurring. I then tried doing USART between the atmega and arduino and the arduino didn't receive any data. The Baud rates are same on all the devices and I've even connected all of them to a common ground.

I'm using PySerial on the beaglebone black to receive the data. I'm posting the USART library I'm using for the atmega.

Can anyone please help me and tell me where I'm going wrong?

#define USART_BAUDRATE 9600 //Baud rate value
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)

void usart_init()
{
UCSRB |= (1 << RXEN) | (1 << TXEN); //Turn on the transmission and reception circuitry
UCSRC |= (1 << URSEL) | (1<<USBS) | (1 << UCSZ0) | (1 << UCSZ1);
// Use 8-bit character sizes

UBRRL = BAUD_PRESCALE;
// Load lower 8-bits of the baud rate value into the low byte of the UBRR register
UBRRH = (BAUD_PRESCALE >> 8); // Load upper 8-bits of the baud rate value..
// into the high byte of the UBRR register
}

unsigned int usart_getch()
{
while ((UCSRA & (1 << RXC)) == 0);
// Do nothing until data has been received and is ready to be read from UDR
return(UDR); // return the byte
}

void usart_putch(unsigned char send)
{
while ((UCSRA & (1 << UDRE)) == 0); // Do nothing until UDR is ready..
// for more data to be written to it
UDR = send; // Send the byte
}


texts: Do any SMT components require hand soldering due to heat limitations?

texts:
It has been claimed on another board that some SMT components cannot be used in an automated production line (i.e. reflow or wave soldering) because they cannot withstand the heat/temperature. Hand soldering is used to avoid these problems.

An example given where this was the case was film capacitors. Capacitors are often the component which limits the maximum temperature and time at high temperature, but I haven't seen any that preclude the use of reflow soldering.

I haven't encountered a single SMT component that cannot be used in an automated soldering process in the past. Some require care i.e. the temperature profile must be carefully chosen and times at high temperature limited. Some components do not support the use of lead free solder (in terms of maximum temperature), but these are becoming rare.

I suspect that requiring hand soldering is either due to:

Limitations in the equipment i.e. the reflow oven cannot deliver heat
quickly enough to meet the requirements.
Poor design i.e. it hasn't
been designed with reflow in mind and large and small components
cannot be soldered at the same time.
A few very special components
require special treatment and it is easier to hand solder than change
manufacturing processes.
Small scale production where hand soldering doesn't cause costs to explode.

I also feel it might be incorrect to assume that hand soldering results in lower temperatures, but that is not the core question here.

I don't think it would ever be an inherent limit in an SMT component - they pretty much came about to support automated manufacture.

Thoughts?


texts: How do digital function generators generate precise frequencies?

texts:
I was designing an electronic circuit that requires precise frequency control when I realized how much I don't know about the frequency synthesis itself.
For example, when I take my low-end 2-channel arbitrary waveform generator, I'm able to set one of the channels to a sinewave with a frequency of 6.00000000 MHz and the other one to 5.99999999 MHz. When I multiply those two signals and filter out the higher frequency what I get is a precise sine signal with a frequency of 10 millihertz. So the period difference between the two waveforms should be the astonishing 278 attoseconds. That would require a 3.6 PHz of bandwidth just to distinguish the difference over one period! And yet my AWG is able to generate any frequency from 0 to 6MHz with 10mHz precision and with the thermal and phase drift accuracy of a crystal oscillator. (I've checked with an oscilloscope and the frequency is stable up to a 6-digit precision, can't check any further).
So it happens to be beyond my understanding how this can be accomplished (especially under $60). Using frequency division/multiplication would be unthinkable at that bandwidth and any VCO I know of has far more jitter and will eventually drift too much.
Am I missing something? Does any of you engineers know what's happening inside such cheap digital generators?


texts: Inverter on npn-transistors - how does it work?

texts:
From Inverter (logic gate) article on Wikipedia:

(source: afiskon.ru)
Could you please explain how does it work? Is it OK to connect an emitter like this (see the left transistor)? In this answer inverter has only one transistor:

(source: afiskon.ru)
What are pros and cons of these two inverter implementations?


texts: I came across an 'N20' motor, and I don't know what that means. As far as I can tell (and please correct me if I'm wrong), N20 is the SKU of the motor. What is the SKU?


texts: What RF transmitter and receiver to buy for long range

texts:
I have 3 main questions that I want to know. I mostly worked with computer science but recently I got an arduino to play around with. I also extracted some motors from an old rc quadcopter that i had. I figured that with these parts, I could build my own arduino quadcopter as a learning project. Anyway, I did some research on RF transmitters and receivers, but there were many types, and I wasnt sure which one to get. Which leads to my questions

Does power determine range?
There are many transmitters with varying degrees of power, and it seems pretty consistent that more wattage = longer range. I was wondering if this is in fact the case, and I should be looking for a transmitter with higher power intake.
Does 2.4 ghz go through objects?
I was reading about most RC transmitters switching to 2.4 ghz because there is less interference, but i also read that you need line of sight. But then looking up line of sight, it turns out that you only need radio line of sight, which looks more like an elipse than a straight line. So I was wondering if 2.4 ghz will work for me, since I eventually want to fly it where I cannot see it, and control it with an FP camera.
What gives me channels?
https://m.ebay.com/itm/1-pair-of-RF-433Mhz-Transmitter-and-Receiver-Module-Kit-for-Arduino-Raspberry-Pi-/311858165335
This module for example has on the receiver 3 terminals, VCC, GND, and data. Does this mean it only has 1 channel? Does this mean that I can only control 1 function (ie. Rotation, forward/backward) with this module?

So in summary, i was hoping someone could point me to a decent transmitter and receiver combo with 1000m range and multiple channels. Not looking for prebuilt, just the circuits. Hope everything made sense and thanks


texts: Using a digital ammeter to loop power a pressure gauge

texts:
I'm trying to set up a digital pressure gauge which gives out a 4-20mA signal and needs to be loop powered. Rather than buying a digital pressure meter, I'm thinking of purchasing a 12-30 VDC power supply, which I'll connect through a digital ammeter in series with the power supply. I have the calibration files to relate output current to pressure.

Does this seem like a reasonable approach? What would be the benefit of purchasing a dedicated digital pressure display: wouldn't that require more steps of calibration (from gauge -> current and current -> display)?

Thanks
Tom


texts: How do I determine my burden resistor for my current sensor?

texts:
So I've got a -12v +12v ADC input limit and I've got a 200 turns ratio current transformer.
My input Max current is 30A which is stepped down to 150mA. How do I determine the right burden resistor so I get a -+12V input for my ADC, also do I need a regulator and filtering for this circuit.

Cheers


texts:
I'm designing relay optocoupler driver for PIC microcontroller and i'm bit confused. In the internet there are lot of relay optocoupler driver schmeatics where current limitter resistor value 1-10k. Why is it too big? According to the datasheet PCF817 forward voltage 1.2V and forward current 20mA. Indicator led has 2.1-2.5V forward voltage and 20mA forward current. So we have: 5V-2.2V-1.2V = 2.6V. To get 20mA current we need 2.6V/20mA = 130 Ohm resistor.
If current limitter resistor value 1k then current will be 2.6V/1000Ohm = 2.6mA it's to small current for led.


texts: Case fan making humming noise when used with potentiometer

texts:
simulate this circuit – Schematic created using CircuitLab
When I turn on the circuit above, when the potentiometer is not at minimum or full speed, the fan makes a high-pitched whining sound, but the speed still changes. How do I prevent the whining?


texts: Safe temperature for desoldering SMD components w/ hot-air rework gun?

texts:
What is a reasonably safe temperature to use for desoldering SMD components using a hot-air rework gun? I have a new-to-me rework station from Xytronic and the documentation clearly assumes you know what you're doing… It tells you what temperature range the gun is capable of, but has nothing to say about where you should be setting it.

Also, I was surprised by how little air pressure the unit generates even when the AIR setting is set to max (99). Is this normal?

My one test so far was to desolder a random surface-mount IC package from a piece of electronic salvage I had lying around (kept for exactly this purpose). I tried to step up the temperature slowly, but I got all the way to 400 degrees Celsius before the chip seemed to suddenly be floating free. I never did see any visible change in the solder… (But perhaps that's just my eyesight.)

I am concerned that at that temperature any component that I can get off a board might be damaged by the heat.


texts: What are the exact semantics of "ENDIR IRPAUSE" command?

texts:
Consider the following SVF file snippet.

ENDIR IRPAUSE;
SIR 10 TDI (002);

Once the data have been shifted into the instruction register, should the state machine go

IRSHIFT->IREXIT1->IRPAUSE

without going through IRUPDATE? Or should it go

IRSHIFT->IREXIT1->IRPAUSE->IREXIT2->IRUPDATE
->DRSELECT->IRSELECT->IRCAPTURE->IREXIT1->IRPAUSE

as if STATE IRSELECT was issued?


texts: Doesn't a curve tracer harm modern circuits?

texts:
I've read about a thing called a "curve tracer" that you can use to compare known good circuits with bad circuits.
It consists of an AC voltage with a resistor that sweeps from -5 to +5V (or similar) and reads the voltage and current going to the component to plot a XY graph. The resulting graph will be the "signature" of the component.
Below is the basic circuit that makes this work:

And here are some example graphs:

Image source (both)
This is all nice, neat and easy to build, but my question is:
While you can hook up a simple LED or capacitor and get a nice graph out of it, won't any modern IC be damaged if you put -5V (AC) through its VCC rail, even if low current, considering that most ICs have a very low reverse voltage maximum rating.
I saw a couple of videos of people testing and making whole databases from a single board, but isn't that playing russian roulette, in a way? In the motto of: "Let's put AC through until something breaks?"
EDIT: There are some commercial devices that rely on this principle, for example the "UCE-CT220S". Of course it's much more sophisticated, but it still relies on passing AC through a component that could be sensible.
Thanks for any help in advance!


texts: How should I make an ECAD schematic for my RFID chip?

texts:
I want to integrate a sensor component with an RFID chip.
From the answers I have from this question. I decided I need to contact a PCBA house. I need to draw an ECAD schematic for the PCBA house (never done this before) .
These are the components:

RFID Chip;  (Datasheet)
Sensor (TFT transistor)
Capacitor

I want to connect a 1uF capacitor between VGS of the Transistor. Connect Source and Drain to VDD, VOUT. And Connect the antenna to the antenna pads.
Below is how i think i should draw the schematic:

simulate this circuit – Schematic created using CircuitLab
How should i make an ECAD schematic so that it is clear to the PCBA house what i am looking to do?
What is the correct way of making the ECAD shematic so that it is clear to the PCBA house what I am looking to do ?
EDIT From Voltage Spike's answer:
I have modified the schematic so that it matches FIgure 3: pin configuration for SOT886 (from datsheet of RFID SLES1203_1213). I have connected the transitor, Capacitor, and antenna. At this point would it be clear for a PCBA house what i am askinf for ?

simulate this circuit


texts: CSB batteries Constant Current Discharge Characteristics

texts:
I'm comparing batteries for use in UPSes and during my tests I was consulting the datasheets of 2 manufacturers. The datasheet from SunLight is crystal clear but CSB's datasheet is using terminology that I haven't seen anywhere else and googling didn't help. Here's the table from the later regarding discharge time:

Does anybody understand anything from this table? What is F.V/Time? What are the numbers of the table correspond to?


texts: Do PCB routing vias require soldermask expansion?

texts:
Most recommendations I've come across regarding solder mask expansion state that it is required so that misalignment between the copper pad and the solder mask opening do not interfere with the solder connection to a mounted component.

However, nearly every default recommendation I've seen for PCB design rules includes solder mask expansions for routing vias.  Tented vias are possible, but used for specific cases and not by default.

Can anyone explain why soldermask expansion on default routing vias shouldn't be zero?  If the soldermask overlaps the copper by a small amount, why does that matter?

EDIT:  To clarify, in my CAD package, an expansion of "zero" means that the copper pad and the soldermask opening have the SAME dimension.  It doesn't mean that the soldermask opening is non-existent.  To tent a via in my CAD package, I would need to either check the appropriate box or use a negative solder mask opening value.


texts: How variable is a typical U.S. 110V outlet current?

texts:
How much does the power vary in a typical U.S. wall outlet over time?

Note: lightning spikes are an obvious event that seem like will surely cause a massive power spike, hence "surge" protectors.


texts:
I was looking to survey some microgrids and I couldn't get the following information.
Are the microgrids commissioned in Alaska DC, AC or a hybrid topology? And is the transmission system used just the traditional AC or LVDC/MVDC?
Any help will be appreciated.


texts: I have an old Nokia phone charger with 5.6 V output, so I tried to adjust it to 12 V. By changing the Zener diode though I manged to do that, but I can't understand its circuit (I replaced the 9v1 with 16v Zener). I would really appreciate any help to understand it. I already understand most of the circuit, but the feedback and switching action isn't clear.


texts: Resetting two CD4017 counters simultaneously, only one resets

texts:
I am working on a simple 24-hour clock based on the CD4017. To reset when the clock reaches the 24th hour, two diodes are used to produce an "and" logic when the 2 digit and 4 digit LEDs receive a high output from the CD4017. The output from these diodes are connected to the reset pins of both CD4017 chips.

What I have found happens in practice is that the U-H10 chip resets as expected, but the U-H01 chip does not. I imagine this could be due to a delay in the signal due to differences in trace lengths (maybe 10-20mm) and or placements somehow creating a tiny RC effect. (One has more vias than the other.) I tried adding a small cap, shorting resistors R138 and R6, as well as removing R18 (on an etched PCB, not a breadboard.) I also checked the reset (pin 15) of U-H01 and it does not APPEAR to be shorted to ground.

Has anyone else faced a similar problem? Ideas?

NOTE For those unfamiliar with the CD4017, the reset is high, not low. From the TI datasheet "A high RESET signal clears the counter to its zero count." Therefore a monostable circuit that is waiting for a falling edge voltage to trigger will not work in this application without using an inverter.


texts: Pulldown resistor on output pin, how does output still work?

texts:
On a part I'm working with, it says that you can configure the part to operate in a particular mode by "strapping" a particular pin to ground. That is, it wants you to use a pulldown resistor to pull it to ground. From what I understand, when this part starts up, the pins are inputs, so the pin gets pulled down, which tells the part to be in X mode. I believe microcontrollers are like this as well, where all pins are inputs when it starts up or after it resets.

What confuses me is that after the part starts up, this is an output. It's basically connected to ground through this resistor. How could there still be an output if it's basically tied to ground?

Let's say it's supposed to output a signal to, I dunno, a microcontroller. Whenever it outputs, wouldn't that current all go to ground and not end up at the microcontroller?

Thanks for the help!


texts:
I am trying to implement V/F control for 3 phase ACIM using STM32F407 MCU. I am using 6 Complementary outputs of its Adv. Timer 1, Center aligned 256-points PWM waveform. The DC Bus voltage is 600 VDC.

One thing that I am confused about is that since I will be connecting the 3 outputs of the 3-phase Full bridge directly to my ACIM so do i need to generate the 3-Phase -Neutral PWM outputs or 3-Line-Line PWM outputs from the MCU?