texts:
I am trying to wrap my mind around very small signals; what they mean, and how to amplify them.

For example, here is a screenshot from my cell phone. Notice the signal level received is -97dBm. Apparently, this is pretty standard for a cell phone signal.

So, by my calcs, -97dBm is approximately 0.1 picoWatt of power. That seems like a really small amount of power. And I mean really small!

I tend to think in terms of my college physics lab whereby we had 5v supplying 1A of current into a light bulb. Or something like this, from what I remember. When that power comes down from the receive antenna and into the amplifier, what does the amplifier "see"? A very small voltage potential? It just seems so small that I'm having a hard time grasping the concept.

Now, how does it get amplified? I was looking at some simple low noise amplifiers (LNA), NXP BGU7003, to make a simple circuit that amplifies the signal. I was planning on using the app note for this chip as an example.

Is there a discreet component way this is done? Where would I look to get more insight into the circuit design of something like this? Wouldn't a tiny power RF signal like this get "lost" in the noise of an LNA?

I'm just so perplexed by this. So any help/insight is most appreciated.

-brad w.


texts: The right way to have amplified speakers that mute when you plug in earphones

texts:
I am designing a handheld device that has an I2S DAC, small speakers, amplifiers (~2 watts), and an earphone jack. I'd love advice on the best way to hook these together. My goal is high quality audio for a broad number of configurations, including different types of earphones, without going nuts on complexity and cost.

Options I have explored:

Have the DAC output to an earphone jack with internal switches, when the earphones are present audio plays through them directly, otherwise the signal passes through the earphone jack switches to the amplifiers and then speakers. This is what I've been using so far. It works, but is it really okay to drive earphones from the DAC output directly? The speaker amps are always active which is wasteful and pick up some noise. Also potentially noisy during insertion.
The DAC feeds the amps directly, which connect to the earphones, or the speakers if earphones are not plugged in. Am I going to blow the earphones (or the user's eardrums) this way, or are earphones high enough impedance that the power delivered to them will be low? Will the brief shorting that occurs during insertion kill the amps? (I guess that depends on the amp)
Implement insertion detection (I've seen a few ways to do this with some pros and cons) and route audio to either the speaker amplifier, or the earphones (with or without their own amplifier). Would I need to switch the signal, or would it be okay to route the signal to both in parallel and simply disable the speaker amps when earphone insertion is detected?
Is there an integrated solution that can do this for me?

Thanks!

Relevant:

Mutually exclusive headphone and speaker

How does the phone detect if 3.5 mm jack circuit is closed?

How (not) to leave class-D amplifier's input hanging


texts:
I tested an amplifier on a circuit board with a network analyzer. It was tested under input power of -20dBm, which is well within the linear region.The amplifier uses SMA connectors.

The simulated return loss S22 is smooth, but S22 of the fabricated die shows ripples at round 7GHz. The red trace is from simulation, and blue trace is from measurement.

Do anyone have idea why it might happen? Probably something to do with the RF connectors?

Thanks!!


texts:
I am trying to replace the burned out fuse in my multimeter. It is very small with dimensions of 3.6mm X 10.25mm and has a rating of 600mA @ 250V.
I can't seem to find this fuse. I can find one with the same dimensions but it has a 1A rating and much larger ones with the same ratings.  Is there any reason why I shouldn't use a larger(physically) fuse in my multimeter? I'd have to make some modifications to the multimeter to accept it of course...(I'd only ever be using this multimeter for low power applications).


texts: How to increase veroboard's current capacity?

texts:
I want to solder below circuit into a veroboard. As I notice my motor will draw high current. Can I paste copper tape to handle the high current?

What others modifications should I do to make circuit better?
What value should I use for my resister?

My motor need to run for 2 hours at least.

Update:I solder on the strip board without servo motor. I run with my motor. It work. But connectors become hot.


texts: How to turn off a higher supply from a lower one?

texts:
I have a circuit powered by two 12V batteries in series (total of 24V). When switch A is ON, my circuit powers a regulator that outputs 5V to a board I'm using. I'd like to add a second switch (switch B), that taps onto the 12V of one of the batteries (the lower, so both 24V and 12V supplies would share the same ground).

How can I make a circuit such that when switch A is OFF and switch B is ON, it will drive 12V to my board, and when switch A is ON and switch B is ON or OFF, it will drive 5V to my board?

Note, my board has a regulator that takes up to 16V and regulates internally to 3.3V.

I need the 24V to drive motors, and the 12V circuit to drive lights. When I turn the switch to the 24V circuit (switch A) it powers an ESC (electronic speed controller) that provides 5V to my control board. At times, I would like to turn on just the circuit for the lights (switch B), without turning on the 24V circuit (switch A). But for that to work, I need the 12V circuit to power up the control board if the 24V circuit is off.

Note: my control board (not the ESC) that takes the 5V input has internally a regulator that can take from 3.3V up to 16V and regulates it internally to 3.3V.

So, in essence, what I'm trying to accomplish is that when switch B is ON and switch A is turned on, I'd like to ensure the power to my control board comes from the ESC's 5V. But if the 24V switch isn't on, I'd like the 12V switch to power the control board. Hence why I would need to turn the 12V off from a 5V supply.


texts: What should I get to desolder components from random boards

texts:
After failing trying to use my friends blow-torch to De-solder components from all these circuit boards and burning them badly and probably both of us getting lead poisoning and smelling the crap all day, I decided that I were to invest a bit of my money on de-soldering technology. I know Radio-Shack is a bit pricy, but I can bike to it and get free shipping therefore I don't want to get it online. I first heard about the de-soldering wick, but that runs out and I've heard it isn't the best. After a bit of internet surfing, two things popped up that seemed they may be suitable this and this.

The first one is a desoldering iron with a bulb. I would like to go for this because it is cheaper but I don't know if it will work very well (like it not sucking up any solder or me having to replace the bulb ALL of the time). It does look nice because of it's one-handed-ness but does it work? any experience with these? The second one was a de-soldering vacuum and it was a bit more pricy but may work better for my needs because of its spring-loaded pump.

So... Is the first one suitable for de-soldering a bunch of circuit boards, or should I get the vacuum?

Sorry if it is not "on topic"


texts:
I can't find an answer to this anywhere so I thought I'd ask around here.

I need a cable with 13 or more wires in it, preferably with a DB-15 or DB-25 connector, but I can't find one anywhere.  I grabbed some DB-25 serial cables but they only had 6 wires in them (not all pins are used), and I can't find a reliable way to discover how various cables are wired before I cut them in half and find out myself.

Anyone know a cheap source for 13+ wire cables?  Preferably thin and black.  I can also just get the cable and wire up D-sub terminals, but I wouldn't know where to start to look for this...

Any help or resources would be much appreciated, thanks.


texts:
I am setting up a audio delay circuit and i want to store the data on SRAM chip.

I am doing it with a 64khz clock and ideally i would like to write a word in every other pulse and read a word every other pulse so i'm reading and writing at 32khz - with a distance between the word addresses of course.

http://www.alliancememory.com/pdf/AS6C2016.pdf
this is the link to the datasheet...

I was wondering if anyone knows a clever way to alternate addresses with 2 different 16 bit binary counters? or maybe there is an easier way in general to fulfill this task?

Also there isn't a clock pin on this chip which is confusing... do i just oscillate the "chip enable" pin?


texts: Circuit to get a short at 0 volts and open at 3.3/5 volts using transistors

texts:
simulate this circuit – Schematic created using CircuitLab

This is the situation I am trying to solve. I am considering using a transistor, but am not 100% sure.

When I get a 0 volt input, the output needs to be a short circuit. When I get a high voltage input (i.e. 3.3 or 5 volts) the output should be an open circuit.

I can do this using an inverter and voltage controlled switch, but how can I do this with transistors? The csv voltage source is a pulse signal. Normally at 0 V, but will turn on momentarily.


texts: Find state space representation for a nonlinear circuit

texts:
The rectangular box in the diagram, through which \$i_2\$ goes through, has a nonlinear resistance:

\$i_2= 1/8 e_c^3\$, and
\$E_i(t)= 2+A\sin (t)\$.

The question is how to find the state space of this circuit by picking \$X_1 = e_c\$ , \$X_2= i_L\$?

I found \$ \dot{X}_1\$ depending on \$X_1\$ and the current \$i\$ from the source.
$$ \dot{X}_1 = \frac{1}{2} i + \frac{1}{16}X_1^3, $$
$$ \dot{X}_2 = \frac{1}{3} i + \frac{1}{3}X_2. $$

Is that correct?


texts: How to drive a 360 degree rotating servo from ESP8266

texts:
I am building a project in which I have hacked a servo motor to rotate continuously in either direction. This means that I need to cut power to the motor when not in use via the ESP. I need to drive this motor from a ESP8266 but I am having trouble in interfacing it. I have wired up the same as shown in the diagram. The issue I am facing is that in clockwise direction it works perfectly fine while in the anticlockwise direction it jitters and in unable to rotate. If I supply the power to the servo directly (and not via ESP) then all works fine in both directions. I measured the current it draws and I can see that in tries to draw much more current in the anticlockwise direction (~170mA) and maybe because of that it is not able to move. I tried replacing transistor BC548 with another transistor with higher Ic (~200mA) but I still get the same result. Then I put a 220uF cap across the motor and then it works fine although it still jitters for a sec or two. Although it works with the capacitor, I still feel there is something fundamental I am missing here.

Another point to note is I don't want to use a lot of components as the space where I will install this is small and so I am avoiding a relay (which is a lot simpler to wire though).

Can somebody pl guide me on this?

I think my code itself may not be relevant here, the only thing I would like to mention is that I am using myservo.write(180) for clockwise rotation and myservo.write(0) for anticlockwise.


texts: Are \$\frac{1}{4}\$watt 4x\$\Omega\$ Resistor and \$\frac{1}{2}\$watt x\$\Omega\$ Resistor equivalent?

texts:
We know Ohm`s law:
 $$\Omega = \frac{V}{I}$$
 $$W=\frac{A}{t} \space\space\space\space\space\space V = \frac{A}{q}  \space\space\space\space\space\space  I = \frac{q}{t} \space\space\space =>\space\space\space W= VI$$
 $$\Omega = \frac{W}{I^2}=\frac{V^2}{W} \space\space\space\space\space\space Right!$$

Lets say I have a  \$\frac{1}{2}\$watt x \$\Omega\$ resistor in a main circuit,
I need to know can I replace the soldered \$\frac{1}{2}\$watt x \$\Omega\$ resistor using another two \$\frac{1}{4}\$watt 2x \$\Omega\$ resistors in parallel or using single \$\frac{1}{4}\$watt 4x \$\Omega\$ resistor?

I think that if the power supply gives the same voltage before and after replacement across the resistor, then it will flow half current through new resistor and wattage requirement might be satisfied.
I mean if before replacement everything was working correctly and the original resistor was not burned, then the new \$\frac{1}{4}\$watt 4x \$\Omega\$ resistor also might work just fine!

Am I right? Is it possible to do? will any problem about voltage drop?
Is it possible to replace Anytime?


texts: Sensor to detect vehicle occupants from external viewpoint?

texts: Trying to solve for a project of mine. Thermal imaging (long wave infrared) sensors cannot pass through the metal skin/structure of a car, glass windows seem too reflective as well. I'm trying to find a safe, portable sensing technology that will allow me to tell if a car is occupied by one or more persons. False positives such as detecting a pet/animal in the car would be tolerable in this case.


texts: Pullup resistors value of STM32F103C8T6 GPIOs too weak, why not more flexible?

texts:
I'm trying to get a keypad to work, writing my own library (just because I want to learn it, and later use the keypad).

For the columns I need pullup resistors, and I initially selected the internal pull-up of the GPIOs of the STM32F103C86.

After quite some time debugging I found out it worked much better with 1K resistors, instead of the 50K internal pull-up resistors.

So since it matters much what the pull-up value is (at least for the keypad), I was wondering, why MCUs are just having one resistor value for pull up (or pull down) ?

Is it because the keypad is an exception (i.e. for most components a 'generic single value' pull-up is enough?

I think a resistor is one of the most simple components to add in a complicated MCU, so why not have more of them?

Just wondering, what the generic reason is (this question is similar for Arduino's and probably more MCUs).


texts: How do I wire a phone/AUX input into a car stereo?

texts:
My car came with a Blaupunkt 520 as the factory fit head unit. As it uses the on-steering-wheel controls, I don't really want to swap it out, but I do want to add the ability to plug a device into it such as a phone. The car had a CD stacker option, so my original idea was to find the inputs they would have used and add a 3.5mm jack.

After pulling the head unit out, I found the below sticker with the pin outs. Most I can figure out - FL, FR etc are the speakers, IGN is main power, 12V BATT is the memory, ILLUM is back-lighting and Earth is obvious. There are some there I'm trying to figure.

Using the information I have, does anyone know how to add an AUX input to this stereo head unit? I presume I need the TEL-AUX and maybe the TEL-MUTE. I have no idea what SDA, SCL, SDVC, MRQ, DIAG or SWC represent. I presume A-GND is an earth of some kind but not sure what specifically.

The first image shows the sticker on top of the head unit. The second is the receptacle in the car. You can see where some of the pins are not yet in use.


texts: Atmega 328 uart program: compiler error on undeclared variable on register name ending with "n"

texts:
I'm trying to get the atmega328 to communicate over serial port with my pc. I'm using hyperterminal to echo back the keyboard character entries. I'm using the max3232 chip to do the communicated with the computer.

When I try to compile it gives and error and says that the variables in this function are undeclared, but they aren't variables but data register assignments.

If I replace the 'n' char in the register assignments to a number it will compile and program but no info is displayed in hyperterminal.

What should the 'n' be set too?

My RX is on pin 2 and TX is on pin 3, if that helps. It is being programmed because I've done the blinky light programs.

unsigned char USARTReadChar( void )
{
   //Wait untill a data is available

   while(!(UCSRnA & (1<<RXCn)))
   {
      //Do nothing
   }

   //Now USART has got data from host
   //and is available is buffer

   return UDRn;
}

THE ENTIRE SOURCE CODE

#define FOSC 1843200 // Clock Speed
#define BAUD 9600
#define MYUBRR FOSC/16/BAUD-1

//This function is used to initialize the USART
//at a given UBRR value
void USARTInit(unsigned int ubrr)
{

   //Set Baud rate

    UBRR0H = (ubrr>>8);
    UBRR0L = ubrr;

   //Enable The receiver and transmitter
 UCSR0B = (1<<RXEN0)|(1<<TXEN0);
 // Set fram format: 8data 2stopBit
 UCSR0C = (1<<USBS0)|(3<<UCSZ00);

}

//This function is used to read the available data
//from USART. This function will wait untill data is
//available.
unsigned char USARTReadChar( void )
{
   //Wait untill a data is available

   while(!(UCSR0A & (1<<RXC0)))
   {
      //Do nothing
   }

   //Now USART has got data from host
   //and is available is buffer

   return UDR0;
}

//This fuction writes the given "data" to
//the USART which then transmit it via TX line
void USARTWriteChar(unsigned char data)
{
   //Wait untill the transmitter is ready

   while(!(UCSR0A & (1<<UDRE0)))
   {
      //Do nothing
          PORTD ^= 1 << PINB2;

   }

   //Now write the data to USART buffer

   UDR0 = data;
}

int main(void)
{
DDRB |= 1 << PINB2;

   //Varriable Declaration
   char data;

   USARTInit(MYUBRR);

  //Loop forever

   while(1)
   {
      //Read data
       data = USARTReadChar();

      /* Now send the same data but but surround it in
      square bracket. For example if user sent 'a' our
      system will echo back '[a]'.

      */

      USARTWriteChar('[');
      USARTWriteChar(data);
      USARTWriteChar(']');

  }
}


texts: LED Driver IC Current Setting and Switching Frequency

texts:
I have this Boost LED Driver IC and this IC is new to me. So, I require some help on how to set the current for my LED String of 300mA. 9LEDs with each forward voltage of 3V and forward current of 300mA.
Can someone help me on how the value of RVFB is calculated for a LED Forward current of 300mA? What equation should I use?
And what should I do with the ADIM pin and OVFB pin in this case?
For switching frequency, suppose I have a 51kohm resistor between FSW and ground, my switching frequency is 980kHz? What factors should I consider to select a correct switching frequency?
EDIT :

For the switching frequency calculation, I used the equation 4 on page 16.

Power LED Datasheet . My requirement is to drive 300mA through an LED String of 9 LEDs.

Can someone help me to calculate on what the input current for the LED Driver IC would be, the switching frequency, what to do with the ADIM & OVFB pin and RVFB value calculation?


texts:
In a large distribution grid, it is said that consumers and producers must be in balance; what that means physically, in correct (not simplistic) mathematical formulation, is not clear: perfect balance doesn't exist in nature and I'm fighting to understand how the out of balance system either stores and retrieves energy, and at what time scale the balancing done.

What are the short term energy flows?

When I turn on a light switch, power flows in the instant. Where is it taken from?

How much energy is present in the distribution network itself at any given time? Does it fluctuate?

Is there a good yet accessible description of the elasticity of the power system? Does it vibrate?


texts: Is there a standard component that can "save" a certain current or voltage and what is it's name?

texts:
What I am thinking about is something like this analog equivalent of a flipflop:

        ____________
1 °-----|---| A |---|-----° 2
3 °-----|----||-----|-----° 4
5 °-----|           |
        _____________
              |
             ___
              -

| A |: ampere meter
||: power source

The behaviour I'm looking for is that when a certain voltage is applied to pin 5 the current is measured between 1 and 2. This current should then be induced between 3 and 4.

Is it possible to do this in a purely non-digital manner?


texts: Wiring a power supply, arduino, and LED strip together?

texts:
I've been researching various websites on all of my questions and have found answers to many of them but I am also finding conflicting answers for some of them. I've read that electricity is something that is very dangerous when you are in contact with the main and that is what I think I am doing so I wanted to verify my setup and have all my questions answered so I can be safe while handling these.

My setup basically starts with an old wire that I found around the house. This is a standard 3 prong US plug which I'm assuming was from some laptop charger. What I've read online is that I want to cut the end off (the part circled in purple) and it'll have 3 wires which I will connect to the power supply. (If there are any cheap, fast, and safe alternatives that allow me to not cut the end off please let me know)

This is the power supply I've ordered. From what I've read I am assuming that when I cut the end off the wire I will reveal 3 wires, black, white, and green. Black goes into the L, white goes in N, and green goes into ground which is the one next to N with the lines. Now I can plug it in to test if it works and everything should be safe and I can unplug and cover that entire section with some black electrical tape.

After hooking up the wires I can hook the power supply to the arduino and LED strip. I read that I needed a common ground, but I don't know what that really means. I'm assuming I do since everything goes to the power supply which is grounded through the 3rd prong on the wire, but if I'm wrong please let me know. This is the arduino nano I am using. I'm going to use one of the V+ ports from the power supply and have a 20AWG wire run it to the 5v pin and then the V- is going to have a 20AWG wire ran to the GND pin. These will be soldered into place and then covered with electrical tape. Then there will be a 20AWG wire going from the D3 pin to the DATA pin of the WS2812 LED strip. Now from the power supply there are still unused V+ and V-. I will put a 20AWG wire into the V+ and it will be soldered into the 5v+ copper part of the LED strip and and GND of the LED strip will be connected to the V- of the power supply that is unused. Then I will wrap this with electrical tape.

Thank you for reading this and please let me know if this setup is safe. Also let me know if this has a common ground. If it does, does that mean V- and GND are essentially the same? Also is it safe for the arduino and my computer to plug the arduino into my computer via USB to upload code while its being powered by the power supply?

Sorry for the lengthy question, but thanks in advance for any answers!


texts: Voltage divider on optocoupler emitter output

texts:
I am trying to control a load switch from the GPIO pins of an STM32 which outputs 3.3V. They need to be isolated using the optocoupler shown.
The problem is that the isolated voltage supplied is 24V, but 5V maximum is needed to drive the load switch enable.
Will the voltage divider work the way I am intending to at the output? What is throwing me off is the pullup resistor in parallel. How does this look?
Lower current for little power dissipation is also of interest
My calculations so far:
MCU Sink current =25mA

Ic = (3.3V - 1.2V) / 1200ohm = 1.7mA
Opto CTR = 50%, Ic = 0.85mA
This is a safety switch, high switching speeds are not necessary.


texts: Speedup capacitor for compensating stray capacitance

texts:
I may be wrong here but I think C1 and C2 charge to different polarities, so when the output changes, C2 supplies the required charge(+ or -) to C1 quickly.

For example: If the output is \$+V_{sat}\$, the C1 can have +Q1 charge and C2 can have -Q2 charge. Then when the output changes to \$-V_{sat}\$, the C2 supplies negative charge to C1 quickly charging it to -Q1.

If I'm right so far, wouldn't this arrangement cause an issue as briefly ALL the output voltage may appear across R1 when the charge across C2 is \$0\$?


texts: How does ESR affect cutoff frequency calculations for capacitors?

texts:
I'm interested in estimating the cutoff frequency of a capacitor in a simple RC circuit. Since the capacitor and resistor are in series, can I simply add the ESR value to the resistor value?

For example, if the ESR is 0.5Ω and my load is 1kΩ, then is the R value in my calculation 1000.5Ω?

Is the ESR negligible in this case? Or is there a "Actually, in real practice..." addendum?


texts: Proteus, Ares, Isis - how to combine LYT and DSN?

texts: I have inherited some old files from a Proteus project, .DSN and .LYT files. Is there any way of combining them into a project file so new Gerbers can be generated etc?


texts:
I'm trying to build a latching switch connected to a door and would appreciate ideas.

The switch is connected to a microcontroller input pin, and I'd like it to operate as follows: When a person opens and closes the door, it latches on. It remains on until it is reset in software.

The basic idea is to time how long since the door was opened and closed again, and do something based on that. Once I have done this, I can reset the switch again. It does not matter if the door is opened or closed several times.

I'm not sure where to start, so any ideas welcome.


texts: Are there any disadvantages - apart from initial purchase cost - to over speccing a BLDC motor?

texts:
I am trying to find a BLDC servo motor for a pump. I have calculated the required speed, but while the manufacturer was good in getting back to me with the torque requirements, they did not give much detail. So, I only have a ballpark figure for worst-case the torque.

My instinct is to pick a motor with a much higher rated torque than quoted. My thinking goes that the higher torque rating basically means higher current carrying capacity, which means larger windings. If the motor is used up to its limits, it will work OK because its rated for them. If used well below its limits, the larger body will dissipate heat more efficiently, and the windings will have a lower resistance - so if anything it will use less power a smaller one operating at its limits.

So, rather than try to estimate the torque, I should just buy the largest motor that fits with my other constraints.

Have I assessed this correctly? Are there any downsides to oversizing a BLDC motor?

Related: Aside from cost, is there any disadvantage to using thicker wire than required?


texts:
I came across this question when reading about semiconductors, and found out I didn't really get the concept of electron volt with respect to voltage and electric field applied to an electron.

So the question is:

  What is the energy in "electron-volts" of an electron that has risen
  though a potential of 3V?

What is this question asking about?


texts: How does this flame ionization detector circuit work?

texts:
I'm working on a flame ionization detector (FID) which can read the ionized flame signal by micro controller ADC.

According to the following schematic, what is the cause of exciting 220 V phase and null in the circuit?

What happens if we don't insert phase and null in the circuit?


texts:
I'm looking for the correct way to connect a 4-pin oscillator to a PIC24F. I have seen diagrams like the one below, but it seems that this connection is only for crystals and not crystal oscillators.

I've also seen on various forums (such as: http://forum.allaboutcircuits.com/showthread.php?t=76570) that the correct connection for a 4-pin oscillator is VDD to one pin, VSS to one pin, and OUT to CLKIN on the PIC24F.

Here is a link to the datasheet of one oscillator that I've been looking at: http://www.mouser.com/ds/2/3/ASFLMB-24525.pdf

This datasheet states: "Note:Recommend using an approximately 0.01uF bypass capacitor between PIN 2 and 4"

So my questions are: is the the correct way to connect a 4-pin osciallator? Also, do I need the external capacitors as shown in the image below for this type of oscillator? Or should I only connect the one cap between pins 2 and 4 as the oscillator datasheet recommends?


texts: DC power supply is capping out at around 3amps and 3.1v for powering my electromagnet

texts: So i'm creating an electromagnet using copper wire that will be powered by a 9v source. My basys3 board will  output 3.3 volts which will switch on my mosfet which will then enable the external 9v power source provide current to my electromagnet. I'm using a Irl540 mosfet and here is my schematic with a 9 to 3.3 regulator(L78L33 part) to simulate the process. Right now the DC power supply in the lab im using is capping out with around 3.1 amps and 3.0v. Is there anything I can do to reach the 9v on my DC power supply that will be best for me other than strengthening my electromagnet with more copper coils?


texts: What is the purpose of the diode in the solenoid controlled valve circuit? (From what I read, without the diode, the MOSFET will break down but I don't know why)


texts: Charge on parralel cylindrical conductors with reverse current

texts:
Suppose one has two parralel cylindrical conductors with a distance \$d\$ and an radius of \$\rho\$ while \$\rho \ll d\$.
The currents through the conductors are reverse, but the absolute current is the same.
Now it is stated, that if the charge on one conductor is \$Q\$, due to the reverse currents, the charge on the other conductor would be \$-Q\$.
But how exactly can the current - provided that it is constant - influence the charge on the conductors, as the number of charge carriers (inside a fixed control volume around the conductor) stays the same?


texts: Is a metallic conductor within an electrostatic field necessarily subject to discharge?

texts:
Basically what I'm trying to determine is if the new RAM chips I received in the mail were potentially damaged from static electricity.

Late last night, tired and foggy, I built up a considerable amount of static electricity while fetching a mail envelope in a pair of flannel-type pajama bottoms. The envelope contained some RAM chips. After sitting down and opening the envelope, I set the unopened chips on my leg so that I could put away my trusty mail opener. While leaning forward to do so I could hear and feel some static crackling as the pant fabric stretched and rubbed against my leg in the vicinity of where I had placed the RAM chips.

The packaging isn't air tight by any means so I'm not sure if there is a possibility that the chips were exposed directly to the static field, and worse if any discharge into the chips could've resulted?

This leads back to my original question: does a static field continuously discharge into a metal conductor. That is, will a static field discharge into a (non-insulated) metal conductor if such a conductor simply resides within it, or must a certain threshold of distance (depending on charge/field strength and humidity) be crossed in order for the specific event/phenomena of ESD (electrostatic discharge) to occur (perceivable or not)?


texts: Determining results for the carry out and sum operations on 8-bit operands

texts:
The problems I'm trying to solve are these:

  Determine the values for the carry C8 C7 C6 C5 C4 C3 C2 C1, given
  A7 A6 A5 A4 A3 A2 A1 A0 = 0000 1011 and
  B7 B6 B5 B4 B3 B2 B1 B0 = 0110 1011.

Out of the possible solutions below, I picked the 2nd (marked with {}):

  0000 0000
{ 0000 1011 }
  1101 0000
  0010 1100

I chose number 2 because I carried addition 0000 1011 + 0110 1011 and the carry is 0000 1011.

Is my solution correct?

The other problem is this:

  Determine the values for the sum S7 S6 S5 S4 S3 S2 S1 S0, given
  A7 A6 A5 A4 A3 A2 A1 A0 = 0000 1100 and
  B7 B6 B5 B4 B3 B2 B1 B0 = 1111 1010.

  0011 0000
  1111 1010
  0110 0000
{ 0000 0110 }

I chose number 4 because I carried addition 0000 1100 + 1111 1010 and the sum is 0000 0110.

Are my solutions correct?


texts: Correct definition of transition in line coding

texts:
Hello I have following question and it says:

I basically cannot understand this solution.

My questions:

isn't it a sequence of 4 0s followed by 4 1s? (answer says 4 1s followed by 4 0s) since retangle below the middle line represent 0 in NRZ?
if you see the middle of those rectangle block, I think there is one transition (from what I learned, definition of transition is something that happens when there exists 0->1 or 1->0) at circled area shown in following picture:

But why is answer saying that there are no transitions?

Also above figure looks like polar NRZ but not NRZ. is that really correct drawing?

Thank you very much.


texts: Period or frequency counting circuit or IC, without using a microcontroller

texts:
The system I'm developing includes two pressure transducers that have three frequency outputs: reference, pressure and temperature.  That's six frequencies I need to measure.  The reference frequency is approximately 7.2 MHz, whilst the two signal frequencies are in the range 10 to 100 kHz.

I've got a Microchip dsPIC33E device on my main board, which I know can be configured (using the Input Capture peripheral modules) to do the job.  However, reading the pressure sensors is neither the main function of the micro nor the most time-critical, so I'm reluctant to burden it with this job as well.  For the same reason, I don't want to use an off-chip device with an i2c interface, as the separation between layers 1, 2 and 3 is not clean and the protocol overhead high in comparison with spi+dma or an adc.

Are there any relatively simple electronic solutions to the problem?

There are several IC devices available that have LCD driver outputs, but I've been unable to find anything (that's still in production) with a SPI interface.
I'd rather not use a second micro-controller, but might consider it if there really is no practical alternative.
An analogue solution could be acceptable, providing it is sufficiently accurate.
FPGA or CPLD solutions may have potential.

Further Information

The devices are Quartzdyne Frequency Output Pressure Transducers, which are to be deployed in an environment where the pressure and temperature can vary significantly over time.  Changes in either pressure or temperature can cause variation in the signal on both the pressure and temperature inputs.  The reference signal is provided as a control, as it is affected equally by both pressure and temperature variations.  Consequently, for best accuracy, all three frequencies have to be measured.  The device manufacturer provides mathematical functions for calculating the pressure and temperature from the three frequency measurements.

Resolution: A frequency error of +/- 0.01 Hz of the 7.2 MHz signal (or better) is desirable to achieve the best accuracy of the sensor.

Bandwidth: The pressure and temperature frequencies should be updated at 10 Hz.  If I use a period counting solution on a micro-controller, a gate time of 1 second (or longer) may be required.  But this could be achieved by accumulating consecutive counts over shorter periods in a circular buffer to create a longer 'virtual' gate time.


texts: I designed a oscillator circuit in proteus but oscilloscope not showing generated frequency of oscillator.As I am beginner in proteus it is bit difficult to understand the problem. Here is my circuit.


texts: What options can be used to deliver power to a distant PTC in this scenario?

texts:
As a part of a project, I need to supply 24V DC to the terminals of a PTC type heater. The heater will be outdoors 50 meters far away from the 24V DC power supply as shown below:

Without a long 50 meter cable, I made some tests with the heater applying 24V DC to its terminals and found out at the beginning the heater draws around 2.8A and then gradually it settles to around 1.8A. This also means the PTC resistance starts at 8.5 Ohm and with temperature increase by the time it settles to around 13.3 Ohm. So the electrical power supplied by the power supply starts from 67 Watt and settles at 44 Watt. And temperature settles around 60°C.

Now I need to supply 24V at the heater terminals. But since the resistance of the PTC is very low even I use a 20 AWG wire I will have significant amount of voltage drop at the heater terminals if I use a 24V DC supply and a 50 meters of cable.

I don't know the reason but I have been told that this PTC must be used with 24V DC supply. So I could come up with three options:

1-) I can bring 230V AC by a 50 meters of cable to the heater and place the DC power supply(in an enclosure) just next to the heater. But this is not safe since it will be outdoors.

2-) I can calculate the voltage drop for a given AWG to obtain 24V DC at the heater side. Then I can obtain 24V DC even though there is voltage drop at the cables. But I might come up with something like 36.7V and it will be cable length dependent.

3-) I also consider a DC/DC converter such as this one. So I can place the DC/DC converter just next to the heater and be sure it is around 24V always.

My questions are:

1-) Which options above would be a better practice for this scenario? Or is there a better workaround?

2-) What could be the reason to supply 24V DC for a PTC? What if it receives 12V DC wouldn't it still comes up to 60°C eventually? Im asking because I dont know why I'm told to use 24V.


texts: High voltage three phase transmission lines

texts:
The high voltage transmission lines in North America looks like this. If a three phase balanced circuit uses three voltage sources, would that mean that this pole in figure one is carrying the currents of 6 three phase voltage sources?

When I look at the transmission lines, some of them has only three "hands" (I do not know the exact term) like the one in figure two , and some of them six like the one in figure one. I always wonder what exactly is the reason behind it.

Another question that I have is that, if you count the cables in the picture, some "hands" have three cables and some have four cables attached to it. Why? The three cables make sense to me because that means the cables are carrying the current corresponding to three voltage sources that are 120 degrees out of phase from each other. But what about the ones with four cables?


texts: Is it a good idea to use a single heatsink for two IC's?

texts:
I am using a 7805 IC along with a diode bridge Br805D (bridge rectifier) IC on a general purpose PCB, with a 220V / 50Hz AC input.

Both the components tend to heat up really quick and I plan to set up a heat sink.

My question is: Is it correct to use a single heat sink / fan combination for both the ICs or should I separate heat sinks for both?

What are the potential concerns I should know about?


texts: Synchronous Counter to go through sequence 1,2,5,6,3,4,7,0

texts:
I have been working on a question which is:
Design a synchronous up-counter that goes through the sequence 1 2 5 6 3 4 7 0 and then repeats. Implement the counter using D flip-flops.

So Far I have the managed to work out the following:

Is this correct?

Would it be correct to use this truth table instead of the previous one?


texts: pymcuprog AvrCommandError: AVR response DAP command failed

texts:
I am trying to use pymcuprog with Atmel-ICE and a trivial ATtiny406 board. The Atmel-ICE and ATtiny406 board are working fine together in Atmel Studio. For Linux, I installed pymcuprog using pip3 with virtualenv, and created a udev rule for the Atmel-ICE. pymcuprog --help works, but pymcuprog ping is unhappy:
% pymcuprog ping
Connecting to anything possible
Traceback (most recent call last):
  File "/bin/pymcuprog", line 11, in <module>
    sys.exit(main())
  File "/research/attiny406/cloudsenvironment/lib/python3.5/site-packages/pymcuprog/pymcuprog.py", line 249, in main
    return pymcuprog_main.pymcuprog(arguments)
  File "/research/attiny406/cloudsenvironment/lib/python3.5/site-packages/pymcuprog/pymcuprog_main.py", line 53, in pymcuprog
    backend.connect_to_tool(toolconnection)
  File "/research/attiny406/cloudsenvironment/lib/python3.5/site-packages/pymcuprog/backend.py", line 162, in connect_to_tool
    self.housekeeper.start_session()
  File "/research/attiny406/cloudsenvironment/lib/python3.5/site-packages/pyedbglib/protocols/housekeepingprotocol.py", line 90, in start_session
    response = self.jtagice3_command_response(bytearray([self.CMD_HOUSEKEEPING_START_SESSION, self.CMD_VERSION0]))
  File "/research/attiny406/cloudsenvironment/lib/python3.5/site-packages/pyedbglib/protocols/jtagice3protocol.py", line 103, in jtagice3_command_response
    response = self.jtagice3_command_response_raw(command)
  File "/research/attiny406/cloudsenvironment/lib/python3.5/site-packages/pyedbglib/protocols/jtagice3protocol.py", line 93, in jtagice3_command_response_raw
    response = self.avr_command_response(packet)
  File "/research/attiny406/cloudsenvironment/lib/python3.5/site-packages/pyedbglib/protocols/avrcmsisdap.py", line 120, in avr_command_response
    fragment_info, _, response = self._avr_response_receive_fragment()
  File "/research/attiny406/cloudsenvironment/lib/python3.5/site-packages/pyedbglib/protocols/avrcmsisdap.py", line 130, in _avr_response_receive_fragment
    response = self._avr_response_receive_frame()
  File "/research/attiny406/cloudsenvironment/lib/python3.5/site-packages/pyedbglib/protocols/avrcmsisdap.py", line 61, in _avr_response_receive_frame
    raise AvrCommandError("AVR response DAP command failed; invalid token: 0x{:02X}".format(resp[0]))
pyedbglib.protocols.avrcmsisdap.AvrCommandError: AVR response DAP command failed; invalid token: 0x00


texts: How to find Rth (Thevenin Equivalent R) of this circuit

texts:
Suppose I find \$V_{th}\$ = 2 V. How to find \$R_{th}\$ seen from a,b?
My effort is short ab, and then in this case, 2//4 = 4/3. Note here that, the line across \$R_L\$ is a node (short ab). So the total current is
16/(5+4/3*2) = 2.087 A.
So I get Isc = 2.087 A. Note that \$I_{sc}\$ is the current flowing into the node when I short ab.
So \$R_{th}\$ = 2/2.087 \$\Omega\$.
Am I correct?


texts: Fault modelling stuck at fault for combinational circuit

texts:
A circuit has n inputs and n outputs. It is implemented only using AND, OR and NOT gates. Further, there are no fan-out branches. What is the number of s-a faults that remain after fault collapsing?

s-a means stuck at fault


texts: How can I wire two parts easily in Cadence OrCad?

texts:
I have two simple parts in OrCad layout. How can I wire these two parts easily, like from point 1 to point 2?
When the big red dot comes out, I click the left and then when I move the mouse to somewhere else, the dot disappears so that the two parts are not connected correctly and easily.
What should I do? There must be something wrong with this.
Point 1 of the first part cannot be easily snapped either.


texts:
I tried to set up my ATmega16 timer0 for fast PWM. I uset the code form this page:

ATmega16 Timer Fast PWM

It works, but the explanations on the page are not so good. Why is the dutycycle 25% if i set OCR0 to 64?


texts: Power requried for M-ary modulation schemes

texts: When we go for M-ary modulation schemes like QPSK etc, does the transmission power increase with M? Why?


texts: SPI: Receiving sets of bytes from master

texts:
I have SamC21 XPRO board as a SPI slave with program written using ASF and Arduino Uno as a dummy SPI master. I expect 3 bytes long values.
The master sets SS to LOW then sends three bytes and then sets SS back to HIGH then waits a while and repeats it forever. I also had to add small delays between setting signals otherwise the slave had problems with receiving.
The code of slave checks if a value is received in a loop. It uses spi_read_buffer_wait funtion for checking. But the problem is that it receives any three bytes long value, not just the one between edges SS LOW and SS HIGH. So when the slave misses a byte then it starts receiving nonsence. Is it possible to receive a multi-byte value defined by SS signal and discard buffer content when the value is not complete (or receive shorter value)? Otherwise it is like random number generator.
I also noticed when I change code to receive only two bytes then it works faster and delays are not necessary. Could it be related?
I am new to microcontrollers so the code is made from Example project. Code of slave is:
#include <asf.h>

/* SPI MUX define */

#define SPI_BUF_LENGTH 3
struct spi_module spi_slave_instance;

static uint8_t buffer_rx[SPI_BUF_LENGTH] = {0x00, 0x00, 0x00};

void configure_spi_slave(void)
{
    struct spi_config config_spi_slave;
    /* Configure, initialize and enable SERCOM SPI module */
    spi_get_config_defaults(&config_spi_slave);
    config_spi_slave.mode = SPI_MODE_SLAVE;
    config_spi_slave.mode_specific.slave.preload_enable = true;
    config_spi_slave.mode_specific.slave.frame_format = SPI_FRAME_FORMAT_SPI_FRAME;
    config_spi_slave.mux_setting = CONF_SLAVE_MUX_SETTING;

    config_spi_slave.pinmux_pad0 = CONF_SLAVE_PINMUX_PAD0;
    config_spi_slave.pinmux_pad1 = CONF_SLAVE_PINMUX_PAD1;
    config_spi_slave.pinmux_pad2 = CONF_SLAVE_PINMUX_PAD2;
    config_spi_slave.pinmux_pad3 = CONF_SLAVE_PINMUX_PAD3;

    spi_init(&spi_slave_instance, CONF_SLAVE_SPI_MODULE, &config_spi_slave);

    spi_enable(&spi_slave_instance);
}

static bool spi_read_data(uint8_t *buffer_rx) {
    return spi_read_buffer_wait(&spi_slave_instance, buffer_rx, SPI_BUF_LENGTH, 0x00) == STATUS_OK;
}

int main (void)
{
    system_init();
    configure_spi_slave();

    for (i = 0; i < SPI_BUF_LENGTH; ++i) {
        buffer_rx[i] = 0x00;
    }

    while (1) {
        if (spi_read_data(buffer_rx)) {
            /* Data Output here and clear buffer_rx again*/
        }
    }
}


texts: Accelerometer switch to trigger LED fade

texts:
I'm planning out a very simple circuit using an LED, capacitor, switch and a battery.

The Idea is that the LED is off until something "bumps into" the circuit. At this point it should light up and slowly dim out.

I could use a microcontroller, but it would be nicer to be able to solve it with just a large capacitor and something that can trigger it.

Is there such a thing as a switch that triggers (like a reed?) on impact?

I'm grateful for any other ideas or pointers on the circuit!


texts: Find admittance( G ) matrix of a resistive circuit

texts:
I am taking Signals And Systems class where I have to calculate the admittance parameter of a given circuit.
A given circuit for example:

This is tedious and calculating the parameters takes so long. I took last year a graph theory class where they pointed out graphs are used for solving electric circuit.

I have seen the following video on youtube:

https://www.youtube.com/watch?v=F8qiM3o0Jc0&list=PL_zr9aHBLF1cvVuhSH-4ps27AsSKXm2AQ

which kept me thinking maybe there is an algorithmic way to produce the right equations so then i can calculate all the required parameters.

Do you know if there is any algorithm or better(in other words logical)approach for a problem like this one?


texts:
I want build a furnace using firebricks and coiled nichrome wire. The dimensions of the furnace are 1×1×1 m. I need temperature inside the furnace to be 650°c. I have 220 VAC mains.

The furnace will be insulated with ceramic insulation plates and closed very well using a metal door. The heat can build up slowly.

It will used for drying Biomass and woods. The material will be placed into the cold furnace, then brought up to temperature for a time, then allowed to cool.

Now my questions are:

What is the suitable type and thickness for the nichrome wire?
What is the proper length of the coiled nichrome wire to get 650°c ?
If I will use electricity generator to supply the furnace with electricity , how many kilo watt the generator should generate to supply this furnace?
Thank you


texts: Why are electrons not pushed out from the conductor at an open circuit under the influence of a power source?

texts: Frequently, electric current is compared with water flow. For example, if I make a hole in a water tank, water will flow till the tank pressure and the atmospheric not become equal or the tank becomes empty. Why does this not happen with electricity?


texts: Combining DC power input from multiple erratic sources (solar / wind turbine)

texts:
My understanding level: I'm reasonably familiar with simple electrics and electronics - volts, amps, watts, simple circuits etc.
I'm thinking my question is either really simple, or complicated - but hoping it's simple.
So I have a 2400W inverter for converting battery to AC. The inverter will use grid power when battery is low. It will not feed excess energy back to the grid.
Batteries are currently 2 x 12V 100 Ah deep-cycle lead-acid connected in series. (The inverter takes 24V battery input). (I have another 2, but have not plugged them in yet because of concerns with plugging batteries in parallel.)
The inverter has a 600W solar charger which supplements the battery power - and the inverter will run off the solar / battery when the solar is generating power. The panels can nominally product 660W, but generally (so far) have been making 400W at best. (I'm just coming out of winter.) Excess solar is sent to the battery.
I have an Arduino, with voltmeter and ammeter electronics that I made to measure the solar output.
To this setup I wish to add a small (24V, 400W max) wind turbine. The turbine has a MPPT charge controller. My goal at this point is to feed this into the system, and at the same time measure the size, and time-of-day of the output, comparing that to solar, to determine whether I should invest in more solar or more wind.
Obviously I'd prefer not to just "dump" the wind power right now - I'd like to feed it into the system. My instinct is to simply plug the output from the turbine to the batteries, but I'm not sure this is electronically correct, and I'm hoping for circuit advice here.

Of course the batteries are not exactly 24V, but a bit more - ditto with the turbine. So how will that affect the inverter - and specifically would the inverter potentially "not notice" the battery was getting flat? (I don't want the battery to drop below about 60%).

I presume the MPPT would prevent the battery from driving the wind turbine as a motor - or should I add a diode to prevent that?

Am I even a little bit on the right track?
Electrically, my question I guess is as follows - given multiple power sources (battery, solar, wind) all with slightly different voltages, and different power outputs, can I combine them to create one "source" for the inverter? What would this circuit look like?
As an analogy if I was doing this with water I could combine rain-water with ground water with mains water into a single tank, which then aggregated those supplies into a single source for say my garden.


texts: Should one use resistors to protect an mbed when using it to simulate keyboard key presses

texts:
One can use mbed to act as USB Host or as a USB Device. One use of the latter is to have it emulate a USB Keyboard by sending normal key presses. The general page on using mbed as a USB Device is in their handbook here: https://mbed.org/handbook/USBDevice But looking at the photos of completed projects on that page, for example the one below, they do not use any resistors to protect the mbed from power errors coming over the USB connection.

Is that how one should do it? Would it be better to include protection and if so what would the amended schema/diagram be?


texts: An electronic component differentiating the current twice with respect to time

texts:
Say a AC voltage source, V,  provides current to a circuit with a resistor, R, and inductor, L. Then my equations to be solved, in terms of current will be:

$$ V - Ri - L\frac{di}{dt} = 0 $$

I would like to know if there is any electronic component (or an integrated circuit) such that the following operation is performed:

$$ V - Ri - L\frac{di}{dt} - \frac{d^2i}{dt^2}= 0 $$


texts: How does the differential cap at the input to an ADC/amplifier help reduce noise?

texts:
I often see differential amplifiers/ADCs with a conditioning circuit that looks like this:

I'm trying to figure out how Cdiff helps reduce noise/improve things.  So far as I can figure out it's basically there to help ease the tolerance mismatch on the two common mode capacitors.  In other words suppose that the two common mode caps have a tolerance of +/-20% -- that could ostensibly lead to a worst case scenario (C1 = .8C and C2 = 1.2C) with a large difference in cutoff frequencies for the common mode filters.  This would mean that for a certain range of frequencies (e.g. those between the two cutoff frequencies in particular) common mode nose at those frequencies would appear as differential noise.  Is the differential cap there to effectively reduce this effect?  If the differential cap is much larger than the common mode caps then all of a sudden the tolerances on the common mode caps would seem to have a reduced effect.

Is that it?  Is there any other way that differential capacitor helps reduce noise?


texts: SelectMap: Who drives the pins: FPGA or Microprocessor

texts:
I'm reading this application note regarding SelectMap image loading for my Spartan6. On page 2 I read:

  The device has properly powered up, but the internal configuration
  memory needs to be  reset. This portion of the configuration flow is
  signaled by PROGRAM going High and INIT going High

The wording "is signaled" is a little unclear to me. Is it the FPGA that drives PROGRAM and INIT high during the "Device Initialization" phase, or should it be the microprocessor?

Same goes for the "Configuration load" phase:

  The start of the configuration load phase is signaled by the INIT
  signal going High.

Is that the FPGA or the microprocessor that drives INIT high?


texts: Patch Antenna Inset Feed Past Exam Question

texts:
I'm trying to work out what 3.d) is meant to be.  I'm not entirely sure which part of the antenna it is referring to; I assume it's referring to width of the gap between the feed and the patch.  If this is the case, I have no idea what width one would want to make it.  I would've thought as small as possible to not perturb the antenna much.

As far as I can tell, the textbook we're using (Antenna Theory: Analysis And Design by Balanis) doesn't really talk about it, except for saying that it'll introduce some capacitance and perhaps shift the resonance by up to 1%.

The red numbers are the lecturer's answers.  I'm not really sure how he got 13.36mm for 3.c).  I believe the inset should be about 9mm based on:

$$R_{in}(y=y_0) = R_{in}(y=0) \cos^2\left(\frac{\pi}{L}y_0\right)$$
$$75=150\cos^2\left(\frac{\pi}{40.1\text{m}}y_0\right)$$
$$y_0 \approx 9\text{mm}$$

I really have no idea about part 3.d) though.

Could someone please point me in the right direction?


texts: Communicate through a VPN link using Arduino Uart WiFi Module

texts:
Following describes the configuration of the system and other details. The problem is mentioned after that. If the initial description is too much or not needed, please skip it.

I have a VPN (between two SIMs). One SIM is in a USB dongle, other one is in a WiFi Router. The dongle is connected to computer 'A', and another computer ('B') is wirelessly connected to the WiFi router which can access the dongle. VPN is between the router and the computer 'A' (dongle). As WiFi router lease 'B' a private IP, 'A' can't ping 'B'. But 'B' can ping 'A'. There is no any issue up to now.

I have created a socket based simple java network application (client - server pair). Client is running on 'B', server is running on 'A. Only client can send data to the server, other way is not possible. This part also is OK. Now I need to replace the computer 'B' with an Arduino. I need to send some data from Arduino to computer 'A' through the same network.

For this Arduino need a WiFi module to access router. I've this Usart WiFi module with the shield.It can successfully connect to the router, (i can ping it from a computer which is also connected to the router).

PROBLEM

Now the configuration is as below.

There's the (server) application running on computer 'A', which is listening on a given port (port 8090). How can I send some data (eg. some text "hello!"), from Arduino to the computer 'A'.

Please note the WiFi module I'm using, i found some examples for applications based on Arduino WiFi shield, but i can't apply them for my configuration (isn't it?).


texts:
I have here some capacitors (electrolytic, I assume), and I can not identify their capacitance. There are two numbers printed on it:
+15
+35V
So, I assume that it has 15 µF and holds till 35 V, is this correct?
Edit: Photo:

(The blue one in the middle)


texts: Inductive toroidal conductivity sensor doesn’t work with enclosure on toroidal inductor

texts:
I’m building a inductive conductivity sensor using the principle shown in this image.

I built a 4khz sine wave generator and connected it with the drive coil and look at the voltage across the pickup coil with an oscilloscope. When the coils are immersed in a liquid without any enclosure (toroidal inductors are in direct contact with the solution) I get a peak to peak voltage directly proportional to the conductivity of the solution.

The problem occurs when I enclose both the drive coil and pickup coil in a watertight enclosure, when I immerse them in the solution with the enclosure the voltage across the pickup coil stays at 10mV which is the same when it is in air.

I’m not sure why this is happening as the inductive method for determining conductivity is supposed to be contactless. It would be very helpful if someone could point me in the right direction.

EDIT: I got the image from this document https://www.emerson.com/documents/automation/application-data-theory-application-of-conductivity-en-68442.pdf

The coil specifications are as follows for both the drive coil and the pickup coil -
Number of turns: 50
Wire thickness: 22 gauge
Toroid Outer Diameter: 25mm
Toroid Inner Diameter: 15mm

The following image shows toroid enclosure structure.
The diameter of the plastic tubing is around 13mm. The toroids are very close to each other(could even be touching each other).


texts: How to use nRF24LE1 with Arduino and nRF24L01+

texts: I know nRF24LE1 has 8051 core and is compatible RF protocol with nRF24L01+. But are the nordic libraries compatible with Arduino libraries. Does anyone has used both these devices, please help me in finding compatible libraries. I want to connect some sensor to nRF24LE1 and send the readings to arduino.


texts: Impedence of 90° out of phase Capacitor and Inductor in parallel

texts: I'm curious as to what the equivalent impedance would be of these two elements. Mathematically it seems that they would have infinite impedance (meaning an open circuit), but this doesn't make any sense logically. If anyone could shed some light on this it would be much appreciated!


texts: Arm Debug Interface vs CoreSight infrastructure in Cortex-M

texts:
Both documents define standards for communicating with DAP.

The information seems contradictory.

Slide 4 of this presentation says Debug features of Cortex-M4 are compliant with ARMv7 debug architecrute (CoreSight based) which to me implies that CoreSight is some lower level on which arm debug architecture is build.

But Arm official website makes it look like CoreSight is actually build on top of Arm Debug Interface v6. Because the spec for ADI is included as part of CoreSight overview.

Different page on Arm official website says that CoreSight is based on The debug and trace architectures which to me implies that CoreSight is build on top of ADI.

The CoreSight white paper appears to mention the same things as Arm Debug Interface: DAP, SWJ-DP, etc. Which makes me thing that it is the same specification as Arm Debug Interface, but maybe just renamed, or the draft version.

But Arm Debug Interface v6 seems to imply that these are possibly compatible but different technologies:

  Compatibility between CoreSight and ARM debug interfaces:

  ADIv6 is compatible with the ARM CoreSight architecture:

  • ADIv6 can be used to access and control CoreSight-compatible components.

  • The ADIv6 specification does not require debug components to comply with the CoreSight architecture.

After looking at the above sources I just feel more confused :)

Question: How do they relate to each other? Is one of them an expansion of the other?


texts: How did smacking electron tube TVs help?

texts:
In old movies (or new movies playing in these times), I often see people smacking the top of electron tube TVs or screens. Somehow it seems to help to stabilize/sharpen the picture. But why?

Are there any reasons an electronic circuit could go from not working as expected to working as expected from a sharp mechanical jolt? What are the conditions that cause such an issue in the electronics? It would appear that the Atari ST suffered from a similar problem that could be fixed by performing what became known as the "Atari drop" (as discussed in this section on wikipedia) although this is described as being due to loose connections, are there any other failure modes that could be remedied in a similar manner, and why?


texts: I am very new to LED technology and still finding my way around voltages, strings and amps. My question is regarding "buck regulator", I've been told that they can be used as stand alone power supply's, is this true?. I already have a driver but it runs at 1.5A, whilst my chip requires only 1amp max, so would a buck regulator help to control the amperage?.


texts: Using CMOS Schmitt trigger inverters in quartz crystal oscillator circuit

texts:
In all sources I've seen about quartz crystal oscillators using CMOS inverters there's a note like this:

But why Schmitt inverter is needed? Won't classic 74HC04 work?


texts: High Frequency Excitation on Class D Amplifier

texts:
I'm building a discretized class D audio amplifier that's running at 250kHz that's designed to run on a single ended 80V supply. I was seeing very high amplitude, high frequency excitations on the output that actually damaged the driving FETs. I ran it on a lower voltage and saw them as well, here's the output of the FETs running on 20V (channel 2):

These seem to be at around 15MHz. I originally thought this was a bypassing problem, since I had no ceramic caps bypassing power, only about 3mF of electrolytics. Throwing a few uF value ceramic caps at the problem didn't seem to attenuate the excitations noticeably, should I just add a lot more ceramic caps?


texts:
I saw some sample and hold circuits from the Internet,and i find there will be a buffer in the output,so i want to ask what does that buffer do for the sample and hold,can i use two stage amplifier as that buffer?

The two stage amp schematic


texts: Can a single phase SMPS be converted to run from three phase?

texts:
If you have a switch-mode power supply that runs off 240 VAC single phase, is it possible to convert it so that it runs off 3P+N (415V phase-to-phase) by only changing the bridge rectifier?

I have been researching 3ph rectifier designs but most of them seem to focus on producing rectified output without using the neutral input, which would produce a voltage that is probably too high to feed into an SMPS designed for single-phase operation.

Is there a 3ph rectifier design that can be connected to a 3P+N supply, that will produce the same peak voltage as the single phase rectifier, and will allow the SMPS load to be shared equally amongst the three phases?  If so, what is its behaviour if one of the phases or the neutral is lost?


texts: Why are two pairs of a wheatstone bridge of opposite direction?

texts:
I wonder why are, e.g. when using a wheatstone bridge in combination with strain gauges, two of these SGs do have a positive k-factor and the other two a negative k-factor.
Gladly, there is already How does full wheatstone bridge with strain gauges work? so I can realize the equation - but I lack something like a physical meaning of that concept. Is it possible to understand it despite of just the final equation? Does it make sense due to "common sense" somehow which I'm not aware of?
And, btw, when these two pairs apparently behave counter-wise: Why is the resistance change not zero then in the end?
That is, when R1 is increasing because the SG is lengthening, and R2 is decreasing, because the SG is shortening, then there should be no change in resistance at all, or? And vice versa to the other pair.


texts:
I have this IR LED

IR LEDs emit when forward biased right? And we all know that the longer leg is positive.

When I forward-bias this LED it acts as an open circuit. And it emits when reverse biased!

Would you please help me sorting this out? If you want further explanation please let me know.


texts: Controlling speed and position of DC Motor

texts:
Is it possible perhaps with an Arduino to control the speed and number of revolutions on a brushless DC motor or a worm gear DC motor?

I'm asking because I know steppers and servos can do that but they make too much noise for my application.

I liked the DC motor as it was much quieter when being active.


texts: Does this Schottky provide MOSFET transient protection?

texts:
I'm studying the schematic for an electronic load available as a kit from Jameco:
http://www.jameco.com/Jameco/Products/ProdDS/2161107%20Schematic.pdf

There is a Schottky diode shunting the source-to-drain nodes of the MOSFET, D1 in this simplified schematic:

The kit instructions describe its purpose as: "used to protect the MOSFET from voltage transients".

I've searched and searched and can't find an explanation of how it would do that. I've found circuits that have a Schottky placed this way, but they do that for improved performance in switching power supplies and similar applications.

Would this diode do anything useful in this circuit or should I just leave it out?


texts: Reduce 2.503V regulated voltage by just about 3mV

texts:
I have a handful of REF192GP reference voltage sources. They are specified to produce a relatively precise 2.5V. Measuring each device I typically get a few mV higher than 2.5V, for example 2.503V. More generally, the datasheet specifies +-10mV for the "G Grade".
The reference voltage is used on one to eight (the number changes during operation) LM324 inputs, each having a 1MΩ pull-down resistor, so on the order of >= 100kΩ total load.
I would like to shave off just a few mV from that voltage so that I can get closer to the desired 2.5V. I am looking for a "clever" solution that is ideally simple to build with a few handy components (other than simply buying the more precise "F Grade" or "E Grade").
Example: A voltage divider on the order of a kΩ.
Pro: Adds around 2.5mA of load, which is comfortably below the 30mA specified in the datasheet.
Pro: The worst-case load of 100kΩ will drop the voltage only by a tiny fraction of a mV, which is more precise than I can measure anyways.
Contra: Potentiometers (even trim potentiometers) are difficult to set reliably to such extreme ratios.


texts:
I have searched a lot for simple ways to tranform high voltage to lower voltage, and I was settled on using transformers, but then I thought maybe a voltage divider could be ok.

Now I found these 25-35watt/250-350volt resistors that mounts to heatsink's, is it ok to use them for 230 > 110, 230 > 48v division etc, or would you see it as a hazard or issue to use resistors when dealing with higher voltage conversion? My power requirement is about 6watts on the current solution.

Thank you for your time
Kris


texts: A question on the response of an RC circuit and pole of its transfer function

texts:
Below is an excerpt from an introductory level book about poles and zeros:

The transfer function of the RC circuit system above for the output voltage is:

H(s) = s/(s+10)

The book claims that this system's response to e^-10t will be infinite because at s=-10 |H(s)| goes infinity.

So to check this out first I found the Laplace transform of an input  e^-10t as:

X(s) = 1/(s+10)

So the output Y(s) must be

Y(s) = X(s) * H(s) = s / (s+10)^2

And for the time domain I take the inverse Laplace transform of Y(s) and plot it in MATLAB as follows:

syms Y s t
warning off;

H = s ./ (s+10); %Transfer function for the RC circuit system
X=1./(s+10); %Laplace transform for the input e^-10t
Y=X.*H; %output

out = ilaplace(Y);

ezplot(out,[0,0.2])
xlabel('t [sec]')
ylabel('Vc [V]')
grid on;

Above plots are the response of this system to e^-10t for 0,2 and 2 seconds interval. According to these above plots the response starts from 1 and then damps to zero.

What is infinite here? I underlined the claim of the book in yellow above.
I don't see anything absurd or infinite in the response of this system for the e^-10t input. Where am I wrong here?


texts:
Following on an earlier question I am looking for a circuit where it powers from USB when it is available and uses the battery when USB is not plugged in.

I want voltage drop to be minimal, zero if possible. So using oring diodes is not possible. The mosfet power oring ICs mentioned in the answer are extremely expensive (4$ for 1K) although they have low voltage drop.

I am looking for a discrete solution where I can build with simple switches or even a cheap LDO. I didn't try to build it but I thought I could use the existence of the Vbus to do a simple switch to control LDO's one from VBus, the other from VBat.

UPDATE

Ideally zero drop is wanted however up to 100mV can be tolerated.
My system has 4 AA batteries, so there could be cases where the battery voltage is larger than 5V, that is why I focus on the existence of VBus. The small drop comes from the Operation voltage of one of the ICs, it needs to be 3.5V (min) and the larger voltage drop eats into the battery life. (i.e. 4 battery, 0.9 each, 3.6V, 100mV drop, I can squeeze the batteries). If there is a 0.7V drop, I can not use the full battery power. (I have to shut down the system at some point of time to ensure proper operation but batteries has still a lot of juice left)


texts: Linear power supply output voltage modification

texts:
I recently got this "made in china" linear power supply which converts 220VAC/50Hz to 15VDC/1A.
Please see attached photo.
Would be possible to do some modifications to it so I can get 5VDC instead?
Ideally the changes should not introduce additional noise, since I'd like to use this psu in a low-noise application.
Efficiency reduction is acceptable, as far as I can get 500mA at the output.
Thanks


texts: Calculating output impedance without measuring open-loop output voltage of a push-pull Class AB MOSFET Amplifier

texts:
So I am building and analyzing a Class AB / push-pull amplifier implemented with MOSFET as depicted in the following schematic:

R2 is the load. The input is an AC signal with 3V amplitude and 1KHz frequency. I am trying to determine output impedance and doing the usual way where I turn off the input signal and inject a test voltage to measure the current and then calculate impedance, I get around 150 \$\Omega\$. However, I am also trying to do it the way my professor suggested, which is what I'm having issues with.
He said to think of the load as a voltage divider and that I could measure the output impedance by just simply changing the load.
So that makes sense to me. After all, looking at the following image:

The load and the output impedance can be modelled as a voltage divider network.
I can put the amplifier under the same two known loads and solve both equations simultaneously and solve for \$Z_{out}\$. I can rewrite the equation for \$Z_{out}\$ using \$V_{L1}, V_{L2}, R_{L1}, R_{L2}\$ (voltage over load for the first and second load) without involving \$V_{out}\$.
This is where I'm stuck. Doing the above, I get:
\$V_{L1} = V_{out} \times {R_{L1} \over Z_{out} + R_{L1}} \Longrightarrow Z_{out} = V_{out} \times {R_{L1} \over V_{L1}} - R_{L1}  \$
and obviously the same is true for the second load:
\$ Z_{out} =  V_{out} \times {R_{L2} \over V_{L2}} - R_{L2}\$
Now, since the output impedance doesn't change regardless of the load, the two equations are equal:
\$ V_{out} \times {R_{L1} \over V_{L1}} - R_{L1} = V_{out} \times {R_{L2} \over V_{L2}} - R_{L2} \$ and so \$ V_{out} \$ cancels out on both sides.
However, I don't know where to go from here. I can't solve that equation cause there isn't enough information to solve it; I would need a second constraint because obviously that equation has an infinite number of solutions.
So I tried a different route:
\$ Z_{out} = V_{out} \times {R_{L2} \over V_{L2}} - R_{L2} \$
&&
\$ V_{out} = {(Z_{out} + R_{L1})V_{L1} \over R_{L1}} \$
Solving both of these together by replacing the \$ V_{out}\$ expression in the \$Z_{out}\$ equation I get:
\$ Z_{out} = { R_{L1}R_{L2}(V_{L1}-V_{L2}) \over R_{L1}V_{L2} - R_{L2}V_{L1} } \$
I tested this out with two loads and measured the voltages:
\$R_{L1} = 10k\Omega  \text{ & } V_{L1} = 5.9V\$
\$R_{L2} = 1k\Omega \text{ & } V_{L2} = 5.4V \$
Using the values above, I get \$ Z_{out} = 103.95 \Omega\$ which is close enough to the value I got with the original method.
But then I repeated the calculation with a different load:
\$R_{L1} = 1k\Omega  \text{ & } V_{L1} = 5.4V\$
\$R_{L2} = 100\Omega \text{ & } V_{L2} = 3.3V \$
and I got a different value \$Z_{out} = 76.09\Omega\$
So, I don't know where to go from here.
Is my derivation wrong?
What should I try next?
I'm not asking for anybody to do my homework, just for guidance
Thank you!
EDIT: Am I not supposed to repeat the calculations with such a low load? I retried with loads of 1k or higher and I get the same impedance of about 103. I'm thinking maybe since the load is so small that it's close to the output impedance, that's affecting the calculations. I've read that an effective damping factor is chosen so that \$ R_{load} >> R_{out}\$ so I do get the right result when I use a load that's much higher than the output impedance.


texts:
I am an experienced programmer (mostly C#), I also know how to get along with physical electrical circuits, but do not know anything about how to start the simple task of connecting a switch (12v or 220v, my choose) to a computer and controlling it through the code. It's just about switching on\off the light, so it's hard for me to believe I have to have very smart cards.

I know, this question is a duplicate of... but no! There is no place that explains in simple steps are required, only vague indications of electrical components.. I need something like: a. Materials required, b. technical steps (what to compose why)


texts: What formulas do I need to use to design a voltage regulator circuit for a zigbee radio?

texts:
I've written the code for my zigbee radios, but now I face the obstacle of getting them onto a carrier board to allow access to VCC, GND, TX, RX via a 4 wire connector.

The supply voltage is 3.712 DC and the module takes 2.1 to 3.6 volts.

I know I need to use a voltage regulator suited for this input/output voltage and that there needs to be capacitors on both sides, but I haven't been able to find a formula to figure it out.


texts: How does frequency affect the ability to traverse objects in RF transmissions?

texts:
Or perhaps, what are the best bands/modulations to choose from if I need to efficiently transmit data in a path with heavy metal obstacles?

I need to build a number of devices to periodically transmit short bursts of data in a large storage facility full of metal containers (which are either empty or full of unknown contents). I've been performing tests with ZigBee transceivers (e.g. Atmel's ZigBit line) with various degrees of success. I've had very poor results in the 2.4 GHz bands and very acceptable results in the 900 MHz bands. However, I've been told by some people I've met that they've had the exact opposite experience (in their case, they were using 2.4GHz/900MHz XBee modules). I'm aware that 433 MHz is also a common band, and there's of course 5.8 GHz too.

So, the main part of the question is if there's some kind of chart or common knowledge about what frequencies are particularly good or bad for this kind of transmission. I'm interested in the bands I can use in small devices (e.g. phone sized) with battery power. A range of 50~100 meters/yards with obstacles would be very nice. Also, there should be some kind of chipset or module commercially available to deal with the RF part of the device (i.e., modulation, RF front end, clear-channel detection, preamble detection, etc.); I can deal with the higher level protocols myself.

Ideally, it would be a band for which I can use some kind of antenna that would not detune too easily if placed very close to a large metal object (1 inch/2.5 cm. from it). I've been testing mostly with whip and helical antennas. My devices must be placed very close to the metal surfaces it needs to overcome!

I cannot, however, count on: antenna directionality, device location/orientation, fixed transceiver locations, etc. All devices will be placed very randomly and scarcely. I just need to make the best I can. Only one thing I can count on is that the devices will stand always in vertical position.


texts: Correctly debugging switching (DC-DC) boost converter with Oscilloscope

texts:
I have an LED driver (LM3410) that adjusts it's voltage based upon how many LEDs you place in series to it and I'm curious to see what voltage it is actually outputting. To test it I connected my oscilloscope probe on the v+ output and ground and after getting a little smoke I'm a little worried about trying again. I'm pretty sure I put the thing into over-drive as it tried to "power" my oscilloscope. My over-voltage protection seems to have saved it since it still seems to work (miraculously).

So my question is: what is the proper way to measure voltage output from a DC-DC boost converter that changes it's voltage based on load?


texts: Approaching to Integral from Limit of Sum ->Finding voltage drop due to uniformly distributed load current on a distributor

texts:
As shown in the picture above, I want to calculate the voltage drop due to a distributed load.

l is the length of the distributor;

n is simply no of segments, n=l/Δx;

I have written down the sum to determine the voltage drop. But what actually I want to do is to find the "LIMIT OF SUM" of this integral is Δx → 0.

How can I carry out the solution ?


texts: How to calculate gain of two cascaded stages low pass filter (passive)?

texts:
I built the following circuit and I would like to calculate the gain. I would like to predict the output voltage by knowing the input voltage. Also, I would like to predict the phase shift.

I got the transfer function from this question:Deriving 2nd order passive low pass filter cutoff frequency

I use this website to do math quickly instead of using my own calculator. The website provide the same transfer function of the previous question: http://sim.okawa-denshi.jp/en/CRCRtool.php

Here is how I use the website: I set the range of frequency from 999 to 1001 to get the gain and phase shift precisely at the frequency of 1000 Hz.

My practical measurement of gain does not match the transfer function:

The transfer function says: The gain at 10 Hz would be -0.00125 dB that means the ratio between the output voltage and input voltage is 0.999 but mine is 0.5959 !!

Vout and Vin are in volts.

Gain = Vout / Vin

dT is the phase shift in seconds.

Phase shift is in degrees.


texts: Driving a LED with an open drain digital output

texts:
I need to drive an LED from an STM32F217ZG.

So I was thinking about a classic circuit with a BJT.
But then I saw that GPIO outputs of the microcontroller are configurable as open drain.
Would this circuit work?

The LED has a 20mA forward current and a 2V forward voltage. Considering \$R=(3.3-2)/0.02\$ it should be on, if GPIO is Hi-Z and off, if it is GND, right?

I don't see why this circuit would not work but I've never seen it before, so I just want to be sure before designing it.

Edit:
Then you mean it is better to do this:

Edit 2:
Finally here is the schematic I'll be using (the output GPIO LED6FAIL is 3.3V and it's a push-pull):


texts:
I'm confused with the terminology that is seen in the LM2576XX Datasheet:
"Specified 3-A Output Current". Does this mean that it will always drive 3A output current or does this mean that it is capable of driving a 3A load where I don't necessarily use 3A (my application only requires about 100mA max)?


texts:
I am building a class D amplifier and need to design passive low-pass filters for H-bridge with cut off frequencies at about 400 Hz. However, I am unsure about few things, this is the simplified equivalent circuit:

simulate this circuit – Schematic created using CircuitLab

Speaker values were measured using an RLC meter set to 100 Hz.

Lets say that the signal is coming into the L1 coil. Should I calculate the cut-off frequency only for L1, C1 pair? If L2 is grounded, do L2 and C2 have a noticeable effect on L1, C1 filter? How can I calculate it then?

I often see a capacitor in parallel with speaker what exactly is its purpose? I am thinking it is to lower reactive power of the speaker, right? To what \$cos\phi\$ should I lower it, and should I use middle range values for voltage and current?


texts: How do I control the speed of a universal AC motor and measure the voltage and current flowing through it?

texts:
It is desired to be able to control the speed of my rotary drill as well as measure the average torque (or is RMS torque a thing?) of the universal AC motor.
I am using this torque equation: τ = (I * V * E *60) / (rpm * 2π).
My best guess is to measure when the AC 120V signal crosses zero, and fire a Triac to let current flow to the drill. In fact, here is a module that would do it all for me: https://www.amazon.com/RobotDyn-controller-control-Arduino-Raspberry/dp/B072K9P7KH/. The issue with this is it will most likely be fried if I run the drill anywhere near max power. Not to mention the Arduino library is sub-par.
Another idea I have is to use a solid state relay, and just have it on 50% of the time- maybe turning on and off ~100 times per second, if that is even possible. However, the voltage depends on time and if the relay is turned on when the AC signal is at 0, it will be a different RMS voltage than if the relay is turned on when the AC signal is at its maximum. So maybe I still need a zero cross detector, and then fire the relay accordingly. Then I could use some math and find RMS voltage from there, using these equations: https://www.physicsforums.com/threads/how-to-calculate-rms-voltage-from-triac-phase-angle.572668/.
I have a current sensor in series with the drill, so current can be measured easily.
Is this the best way to go about it? I am no electrical engineer so this is all very new to me. Any help is greatly appreciated. Thanks!


texts: Isn't the voltage reading in this image wrong?

texts:
The conductor is moved from top to bottom through the B-field. Shouldn't the reading be negative on the volt-meter?
Right-hand-rule gives that the positive charges experience a force towards us. Then the positive charges must accumulate at the terminal closest to the letter "V" in the image and the other terminal would then have negative charge. Then, if voltage is measured with the negative probe on the positive terminal of the motor the reading should be negative, right?

Source.


texts:
I read that FinFET transistors were introduced to avoid the problems due to downscaling of MOSFET size, ie reduce the Short Channel Effects (SCEs) like DIBL, Hot Electron effects etc.

But how does the FinFET overcome these problems?

Or am I wrong? Is FinFET released to overcome any other problems in present planar MOSFETs?


texts: How can I create an SCR using a PNP and NPN?

texts:
Several times I have seen an SCR described as similar to a PNP and NPN transistor linked together. But any attempt to replicate the idea seems to fail. In the circuit below, for example, the LED is always on.

simulate this circuit – Schematic created using CircuitLab

What am I doing wrong?


texts:
I have a GPS module with an accuracy of 1.5m + 1 ppm.

Query: What is meant by 1 ppm accuracy, what does it symbolize?


texts: Help designing a Bluetooth controlled square wave generator

texts:
I am an EE student, and I am working on my first quasi-freelance project.
I am designing a PCB, and part of the design requirements is a square wave generator whose frequency is controlled by a Bluetooth receiver. I need a range of 20-1000 Hz. I know electronic circuit theory, but I have never worked with Bluetooth protocol before, and I don't know where to start.


texts: use MOSFET as a switch in saturation region

texts:
According to this data sheet at 6v GATE voltage , the saturation drain current is about 1.25A. now I want to switch a device (say a tiny motor) which demands 1.25 A at 2volts , Indicating the resistance 1.6 ohms. now I am supplying the drain source voltage 4 volts.(as usual the motor and the MOSFET is in series) which means the mosfet is saturated , and capable of supplying 1.25A , now the question is , usually we are advised  to use ohmic region to switch, but how about this? won't this switch work?
the schematic is here :


texts: Choosing a via for automated PCB assembly order

texts:
Apologies if this has been asked before - I'm new to the field, and to Stackexchange EE - so route me to relevant posts if some exist.

I'm aiming to order PCB assembly from a manufacturer (i.e. both PCB making and component placement). The board I'm using is two-sided, with components on both sides. So far, I've been making PCBs by hand, and connected the two sides simply by soldering a wire through a hole onto pads in both sides. However, I don't recon they will do this in an automated process, so I need to choose a proper via. Unfortunately, I have zero experience with vias, so I don't which to choose/where to look for a suitable one. So how to choose vias for automated PCB component placement process?

The board is 15 x 31mm in size, with the pads currently being 1.4mm in diameter, and holes being 0.4mm (or bigger) in diameter (see images attached). Although they can be flexible. The board is .4mm thick. Any suggestions, and if so why?


texts:
I have a book with some projects examples that use Arduino, one of the projects use piezo to detect vibrations. The book says the following:

  When plugged into 5V, the sensor (piezo) can detect vibrations that can be read by the Arduino's analog inputs. You'll need to plug in high value resistor (like 1-megaohm) as reference to ground for this to work well.

The book also says in other page:

  Lower resistor values will make the piezo less sensitive to vibrations.

What does this mean? What does "resistor as a reference" means? And why would the piezo be less sensitive with less value resistors?

I don't have any experience in electronics, I started learning one week ago, and resistors are one of the most confusing things for me.

Project's circuit scheme:


texts: VHDL: Infinite loop for constant, but no problem with literal

texts:
I wrote a Testbench for a simple architecture. When I use the literal "1 ms" instead of the constant ct: time := 1 ms everything works. But otherwise GHDL stucks in an infinite loop.

Can you see an error in the code or is this a bug of GHDL?

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity s is
port
(
    a: in std_logic;
    b: out std_logic
);
end s;

architecture v1 of s is
begin
b <= not a;
end v1;

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity testbench IS
END testbench;

architecture v1 of testbench is
component s
    port
    (
        a: in std_logic;
        b: out std_logic;
    );
end component;

signal a: std_logic := '0';
signal b: std_logic := '0';
constant ct: time := 1 ms;
begin

    a <= not a after ct; --constants not working?
    -- but no problem with a <= not a after 1 ms;

dut: s
    port map
    (
        a => a,
        b => b,
    );
end architecture;


texts: How to find the transfer function of a frequency counter?

texts:
I am designing a mathematical model for my control systems project and in that there is this block which measures the frequency of the wave.
For the practical application I fed this wave into a micro controller and then wrote an algorithm which takes in samples of the wave at a fixed rate and finds out the minimas and maximas and using them finds out the frequency.
But I dont understand how to proceed doing it mathematically so that I create a block of this counter whose input will be the wave and output will be the frequency.
Any idea on how to proceed with this?


texts: Attaching electronics to a spinning surface without a battery

texts:
I am working with a friend to develop a spinning disk with LED lights on it.

The issue we are having is wrapping our minds around the idea of electronics on a surface that is spinning.

How do we interface with the LED lights without cords getting tangled around the spinning rod?

Is there a way to provide power to electronics on a spinning disk without having the battery directly on the disk?

Does this make sense?

Thanks.


texts: Why do we need to know power factor in electrical loads? How does it affect the loads?

texts: From my level of understanding, power factor is \$\cos(\phi)\$, \$\phi\$ means angle between voltages and currents. I thought from this any mismatch of angle between voltages and currents, loads will not properly work to our desired.


texts: Is it enough to place surge arrester on the terminals of the transformer in a substation, or every power line entering the substation should have its own?


texts: Can 4-20mA transmitters send through a 1kOhm resistor?

texts:
I have a 4-20mA sensor at work and I wonder if it's possible if a 4-20mA transmitters send through a 1kOhm resistor?
I guy I talked to said that 4-20mA normaly can't send through 1kOhm because it's to high resistance.
So what is true? Is it common that most of the industrial sensors (12/24V) cannot send 4-20mA through a 1kOhm resistor or more?


texts: How to choose a Bipolar Junction Transistor (BJT) for a switching frequency of 400KHz.


texts: RF load (terminator) at the end of RF attenuator

texts: Do I need to install RF terminator at the end of RF attenuator? Let's say that max power output for RM port is 50W and I'm using 100W 50dB attenuator. What if I was using 50W 40dB attenuator? Is there a possibility that without proper RF load some power may reflect from the end of attenuator?


texts:
Could someone please point me in the right direction for finding derivations showing how normalised filter table values come about?  What should I be searching for to find the derivations?

I've included an example of the type of table that I'm talking about.


texts: Fourier serie coefficients of real function

texts:
Let's take a periodic wave function defined by f(t) = (1 - t) with a period of 1.

The Fourier coefficients can be calculated:
$$
\omega_0 = 2\pi/T=2\pi \\
F(n) = \int_{0}^{1}(1 - t)e^{-jn 2\pi t}dt=-\frac{j}{2\pi n} \\
F(0) = 1/2
$$

There is a property of Fourier series which states:

  If f(t) is real and can be developed into a Fourier series: F(n) is purely imaginary and odd if and only if f(t) is odd.

My question is, why is the F(n) expression I get is purely imaginary if my f(t) function isn't odd (nor even in fact).

I might just be blind, I might not see something, in either case I would appreciate you point it to me, but I get that:

f(t) is not odd, nor even (\$f(-0.3) = 0.3, f(0.3) = 0.7\$)
F(n) is purely imaginary as \$ F(n) = -j/2\pi n \$ (no real part)

So does this example contradicts the stated property of Fourier transforms, or is it due to something I don't see? I expected to get a complex F(n), with both a real and an imaginary part. Might turn out to be a dumb question, oh well...

Thanks


texts: How can you find Quality Factor of an arbitrary RLC Circuit?

texts: I'm having a trouble with this circuit. Apparently I know how to deal with a simple RLC circuit but this one is tricky


texts: I want to charge a 2-cell Li-ion battery with CN3722 charging IC. According to my circuit design, the float voltage at the battery terminal should be 8.4V. But, the float voltage is measured as 13.44V when input is of 15V. Also, when I connect the battery,it draws 220mA current for 1 second and after that it goes to 0A. Any idea, why this charging circuit is behaving like this?


texts: Using a AC capacitance voltage divider through diodes to charge a DC capacitor?

texts:
What I need help designing is a circuit that will be capacitor voltage divider that will be fed by a high Ac input voltage, but be able to discharge each capacitors through diodes at a set lower voltage for dc output.  My main goal, which I suspect this voltage divider/charge pump set will do, is to charge the capacitors in series at a higher voltage, and discharge each capacitor through diodes in parallel.  Assuming this functions as I suspect it might, I will want to be able to sum up all the parallel capacitor discharges(after each capacitors respective diode).  Will this function as I think it might?  Thank you for the advice and I apologize for the shadows in the crude wiring diagram.
I added a 2nd diagram, after thinking about this design, does this diagram make more sense?


texts: What can I add to a DC circuit, to limit the voltage to 24V and current to 16 amps?

texts:
I have a battery pack that can put out around 25V and 20 amps, but it needs to be limited to 24V and 16 amps.

Update:

This is a follow-up to my question from yesterday: Protected 18650 batteries shut down after I introduce a capacitor to the circuit, why?

I have a battery pack made of 18650 batteries that each have a protection circuit. When I add some large capacitors to the circuit, I assume that they drain too much power from batteries, making those batteries to shut down immediatelly after I flip the switch. So that's my issue


texts: Can alkaline batteries withstand reverse current transients?

texts:
I am designing a device that can be powered either through two AAA alkaline batteries, or through its USB port, with priority with the USB port. I thought of a discrete circuit that fulfills my needs (simple, almost no power consumption and very low dropout when on batteries, ...).

So everything seems fine, except that, when the USB power is removed, there is a quite high reverse current transient that goes back to the batteries, because the main capacitors that were charged to 3.3V then have to go down to the batteries level. It can be as high as 200mA during about 10µS, then quickly decreasing but still being at about 1mA during as long as 15 seconds. (There is a 10µ ceramic cap and a 0.035 supercap in parallel).

Is this acceptable ? Or will it make the alkaline batteries release gas / leak / loose all their capacity / burn in fire / and if I repetitively plug-replug the USB cable, kill me in my sleep ?

And if some other people decide to use rechargeable batteries (any kind) in this device, will it cause the same / other problems ?

Edit

Ok, here is the schematics of said circuit, for reference. It tries to combine several constraints, which are not fully explained here, but anyway. Just keep in mind that the question is not about this schematic or how to switch between USB and batteries.


texts: How to set initial state of 4 bit "exclusive output" Latch?


texts: "Waking" a 18650 Cell with Higher Voltage

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I bought a 2 brand new pcb protected 18650 cells (UR18650RX) about 4 months ago that I had planned to use in a build. Before I got going I measured their voltages and both we're on 3.58v, not ideal (below 3.6 empty voltage) but I'd thought I'd charge them up; left them about 4 hours on charge and when I got back I noticed they had not charged at all (they stil measured 3.58v). The charger I used is the HX-2S-01 BMS configured in the following manner:

I measured the voltage on the P+ and P- tabs and they are getting the required 8.4v.

I checked out a few articles and videos and most mentioned to take a good, charged 18650 cell, connect it in parralel to the "sleeping" cell and keep it there until the dead cell measures ideally 3.6+ then put in on nomral charge. I do not have a good 18650 cell with me, and so I came about an bloke that mentioed I can use a quick 3-5 seconds jolt from a 9V battery to "wake" the cell. Is this safe?

I have a varibale 3-12V 1A DC adapter, maybe I can try and wake it with that instead?


texts: Op-amp comparator and differential signals

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On a board I'm working with, there's a 120 ohm termination resistor. I need to measure the voltage across it and compare it against a reference voltage.
I'm wondering how to make the connections.
The op-amp has 2 inputs. The inverting input will be connected to the fixed reference voltage.
The non-inverting input should be hooked to the point where I can measure the voltage across the resistor.  Voltage is usually measured between a point and the ground reference, but the voltage I need to acquire is between the two leads of the resistor.
How would I be able to connect it to the non-inverting input? Should I use a differential to single ended buffer or something of this nature?
Edit: ignore the switch.


texts:
I have opened up my friend's laptop and cleaned up the fan and changed the thermal paste. Then, I closed it up and the screen did not work. Also, connecting a monitor via VGA doesn't help, the monitor does not show anything.

On the motherboard, near the screen connector, there is an IC with designator U1, and I am guessing it is an LDO. It is marked 1Y=61J.

Two pins, 4 and 5, are shorted together and I measure 3.4 V on them. On the other pins, I measure nothing, and they are not shorted to ground except for one pin, pin 2, which is obviously the ground pin. Pin 3 goes to a capacitor and to the screen connector. I've checked the fuse and it is shorted.

Here are some close up photos, click on them for high-resolution:

Edit:

The problem was with the male connector. I have accidentally damaged some pins while connecting it. Problem is solved now. Also, it seems like this is not an LDO, instead it has some kind of transistors that pull some pins to GND.


texts: Why the mismatch between frontend and backend width?

texts:
Looking at Qualcomm's Krait core microarchitecture, I noticed there is a mismatch between the width of the frontend and the backend:

  11 stage integer pipeline with 3-way decode and 4-way out-of-order speculative issue superscalar execution

Why is that and how does it affect the performance of the processor (for better or for worse)?

Source: http://en.wikipedia.org/wiki/Krait_(CPU)