texts:
I am using an Arduino Uno and would like to simulate a capacitive tap with zero human contact on my iPhone 5 screen.

What seems to work right now is putting a coin on the screen and connecting the coin to a power source (such as Digital I/O Pin) and when voltage is sent to the coin it triggers a "tap" on the screen.  Is this safe?  Is there a better way to do this?  I just read somewhere else that any grounded conductive object should work.  Is it better to ground the coin or to connect it to a power source?  Also, how can I stop sending current to/grounding the coin so the simulated touch is stopped.  Right now, I can't get the arduino to stop "touching" the screen.


texts:
I have made a voltage regulator:

simulate this circuit – Schematic created using CircuitLab

And here is the zener circuit:

simulate this circuit

I have already tried to charge a device with this circuit,but it actually acts as an external battery.The device starts charging,but the battery's percentage doesn't go up,it remains the same.This must be happening because of low voltage or current supplied.What should I modify in order make the voltage regulator output more current and voltage(if necessary)?.The mentioned device charges at 5 V and 2000mA(charger's specifications).


texts: How solder inductance affects RF circuits?

texts:
I'm assembling a VHF oscillator (90 MHz) and plan to reach UHF and SHF some day.

Should I worry about solder inductance affecting an oscillator performance?

If no, then when should I take it into account?


texts: Mosfet suggession for large drain current Sample Hold application

texts:
I'm using a MOSFET for a sample and hold circuit controlled by a microcontroller. I want to control the charging and discharging of a capacitor by a solar cell. For this I'd be using two MOSFETs. The solar cell can have a large area and can source upto 3.2 A of current. This flows through the drain of the MOSFET. I want this flow to be switched ON and OFF by applying a gate voltage from an MCU. I can boost the MCU output to required gate voltage levels, but what would be a suitable MOSFEET for my application? I'd need approximately 250 ms ON time and 750 ms off time during switching. The IC (or transistor) package may be any one of the packages that may be connected to a breadboard easily that is NOT surface mount.

EDIT: Strictly speaking, the purpose isn't sample and hold but its very similar. I'd like to characterize the solar cell IV by sampling the voltage across the cap and the current flowing to it while charging.

Schematic here.


texts: Amplitude modulation transmission distortion

texts:
I need to clarify a question.
Let's say that in a wire I carry a current modulated in time so that it is an amplitude modulation of a sinusoidal carrier with a modulating sinusoidal wave. In frequency domain it corresponds to the superposition of three deltas, the one for the carrier and the ones for the modulating frequency, as usual.
Then this current generates a magnetic field that is picked up by another wire, and from Faraday law of induction the voltage difference induced at the ends of the wire will depends on the derivative about time of the magnetic field.
So the three deltas will be derived (in other words multiplied by jω) then in the end they will have an amplitude that will depend on their frequency.
So the received signal will be no more an amplitude modulation like the transmitted one, the right lobe will be emphasized with respect to the left (i.e. low frequency) lobe.
Therefore, with a perfect envelope detector, the reconstructed signal will be modified with respect to the one sent by this inductive link (think of it as a transformer), am I right?
Thank you


texts: Interference between signals having OFDM and DSSS modulations

texts: If there are two signals, one having OFDM modulation and other one having DSSS modulation occupying the same bandwidth and over the same part of spectrum, will i be able to demodulate both signals correctly? Asking this question because it is said that DSSS is immune to narrow-band interference and OFDM basically consists of many narrow band sub-carriers.


texts: How to calculate the impedance of a rectifier?

texts:
I am working on RF energy harvesting. Now I am trying to calculate the impedance of the rectifier, in order to do the impedance matching. An antenna (50 ohm) receives RF signal (915 MHz) and finally become DC by the rectifier and stored into the capacitor.

simulate this circuit – Schematic created using CircuitLab

In the figure, the value of L1, C1, sensor node needed to be found.

How to calculate the impedance of the rectifier?
Should I consider the impedance of the wireless sensor node? If needed, how to measure the impedance of the sensor node?
Is a DC-DC converter necessary between the C3 and sensor node?
As the antenna receive 915MHz rf signal, the frequency of the AC current in the rectifier is also 915MHz?

I had built a rectifier without impedance matching and had done an experiment. I had measured the voltage change of C2,C3 but the result is strange. The voltage of the C3 will remain 2V for about 250ms. However, theoretically, the voltage should be double of the V(c2) which is 100mv.
Another is why the period of the charge time of C2 is 10ms? I thought it should be 1/4 of the period of the AC source (1/915MHz).
Or am I misunderstand it?
These questions seem to be stupid.. forgive me.. LOL.


texts: Thermal cutoff for a high current mains application

texts:
I'm designing an inrush current limiter for a large rack which will under normal conditions draw ~25 A at 230 VAC. I'd like to be able to trip the current carrying live wire if the temperature in my thermistor gets too high (temperature not yet defined, likely far above 100°C). Ideally the fuse would be resettable only by manual intervention, e.g. pressing a button or by replacing the fuse with a new one.

My plan would be to mount a thermal fuse physically close to the thermistor. The thermistor would be in series with the thermal fuse.

My problem is that I can only find thermal fuses rated for carrying 25 A or above rated for carrying DC voltages up to around 60 V, not 230 VAC. These seem to be for laptop batteries and mobile phones. Do such devices exist for mains voltage and this sort of current? Or do I have to go for something more complex, like a temperature sensor linked to a relay on the live wire instead?


texts:
I would like to design a RF power amplifier for an output power of 10 Watts. Since I would like to have a good efficiency, my amplifier should operate in the class F mode (or class E, whatever is easier do design). I have some experience with low-power amplifiers (class A and stuff), but I have never done a class F one. I found a PDF about class F amps:

http://www.highfrequencyelectronics.com/May11/HFE0511_Grebennikov.pdf

On page 5, it gives a design equation for the class F load network (equation 6). As far as I understand, the Z_net impedance depends on the supply voltage and the required output power. Assuming I use class F and the amplifier produces a perfect square wave, the fundamental amplitude is

$$ \hat{V} = \frac{4\,V_{DD}}{\pi} $$

and from this follows

$$ P = \frac{ 8\,V_{DD}^2}{\pi^2\,Z_{net}} $$

which can be solved for Z_net:

$$ Z_{net} = \frac{8\,V_{DD}^2}{\pi^2\,P} $$

Is my assumption correct? As soon as Z_net is known, one can design the transmission-line load network for the transistor. I would like to use the CGH40010 as well, which is used in the linked PDF. I made a PCB (on FR4) with the designed load network, but that amplifier didn't work because it oscillated.

a) am I doing things wrong with my load network, or
b) is my calculation correct and probably just my PCB is crappy?

How should I proceed with the amplifier design? I purchased a book "RF Power amplifiers for wireless communication" from Cripps, as well as "Advanced techniques in RF power amplifier design" but both books were not of great use for my design, unfortunately.

The intended frequency is 2.2 GHz.


texts: Marking for Operating Tempature Range on Diode's data sheet?

texts:
My diode is:

  VISHAY GENERAL SEMICONDUCTOR 1N4004-E3

  Diode

  Diode Type:Standard Recovery;
  Repetitive Reverse Voltage Max,
  Vrrm:400V; Forward Current, If(AV):1A;
  Forward Voltage Max, VF:1.1V; Forward
  Surge Current Max, Ifsm:30A; Operating
  Temperature Ran 78K2120;

Source, please, search for 78K2120.

Questions

What does "78K2120" mean?
According to the new reply, it is an identifier but what does it mean? Why is it chosen? Does it contain some information except being a random identifier?
Is there some standard, seen too many manufacturers just throwing similar lines but with different meaning?


texts: Is a 0.01s time base really useful in a frequency counter?

texts:
I am currently designing a frequency counter based on the PIC16F628A. It is working as expected but I would like to add some useful features.

According to the images found by googling, I noticed that many commercial frequency counters have the 0.01s time base feature. I know 10 seconds is for 0.1Hz resolution. 1s for 1Hz. 0.1s is 10Hz resolution but it is very useful when adjusting an oscillator frequency and see the changes immediately on the display. 0.01s is 100Hz resolution but what is it really useful for?


texts: Why doesn't the depletion zone cover the entire diode?

texts: When you form a PN junction you're basically closing a circuit so why don't the free electrons in the N and the holes in the P diffuse completely as they would in any other circuit?


texts: Is Millman's Theorem approach here correct?

texts:
The question is as follows:

My answer is as follows:

However, per the source the answer is:


texts: I have a laptop AC Adapter thats rated for 19.5v/3.34A DC output for a total of 65W. The input is rated at 100-240V/1.5A AC. My question is what is limiting the output to 65W? It seems like the input can support up to 100*1.5=150W minimum. I"m assuming you lose some in the AC to DC conversion, but 65W would be more than 50% loss. So, is the adapter able to support more than 65W or is there something here I'm missing?


texts:
I've read that at high AC frequencies, current concentrates near the surface of a conductor, which is known as the skin effect. Does this also mean that current concentrates near the edge of thin metals? Specifically, I'm simulating (with OpenEMS) a gaussian pulse (\$0-18\,\text{GHz}\$) propagating down a microstrip transmission line. When I view the current density as a function of time, I see this

As you can see, the current density is greater near the edges of the microstrip than at the center. Is my simulation a qualitatively accurate representation of reality? Why would currents concentrate near the edge?


texts: How to measure AC current using ACS712 and interface with ESP32?

texts:
Actually, I want to measure the AC current using ACS712 connect with ESP32 module.
I know this module only works under 3.3v. So, I used voltage divider circuit and step down 5v to 3.3v which is being come from the acs712 20A (You may consider any of your 5A/20A/30A chip). I also tested the "ACS712.h" Arduino library. Still, I do not get proper current which I compared with 2 multimeters. Maybe I need to change in hardware side means place op. amp in between circuit. So, Help me to resolve my issue.
Thank's in advance.


texts:
In an attempt to interface a motor controller, battery management system and maximum power point tracking device on a CAN bus, I used the MCP2515 and TJA1050 CAN breakout board. All these devices send out CAN messages at the same bit rates.
When interfacing with the motor controller, the messages were properly interpreted by Arduino. However, with both the other devices, there is an issue with the SPI read function.
I am using the Seeed library, the documentation for which can be found here: https://github.com/Seeed-Studio/CAN_BUS_Shield/blob/master/mcp_can.cpp

The following function returns the code that suggests that there is no message. The readStatus condition fails.

byte MCP_CAN::checkReceive(void)
{
    byte res;
    res = mcp2515_readStatus()              // RXnIF in Bit 1 and 0
    return ((res & MCP_STAT_RXIF_MASK)?CAN_MSGAVAIL:CAN_NOMSG);
}

The readStatus function is as follows:

byte MCP_CAN::mcp2515_readStatus(void)
{
    byte i;
#ifdef SPI_HAS_TRANSACTION
    SPI_BEGIN();
#endif
    MCP2515_SELECT();
    spi_readwrite(MCP_READ_STATUS);
    i = spi_read();
    MCP2515_UNSELECT();
#ifdef SPI_HAS_TRANSACTION
    SPI_END();
#endif

    return i;
}

The i value returns a 0.
Each of the devices has a termination resistor, so a 100 ohm resistor was added at the CAN module end. The voltages were measured with respect to CAN ground, around 2.7 and 2.1 on CANH and CANL lines respectively.


texts: how can i increase the output current in a transformerless power supply?

texts: I am designing a 12VDC, 200mA transformerless power supply using 1N4007(diode) for rectification, a ceramic capacitor 475k and 10R resistor for limiting, a zener diode (1N4742A) for a regulated output. After the connections am not still getting the output current, the current is needed to drive a relay of 12VDC 160mA.


texts: Why does switch change parallel current after junction?

texts:
This is an image demonstrating the use of a pull up resistor.

I've just started studying electronics and have been learning about ohm's law. Ohm's law says that current within a circuit is equal to the potential drop across that circuit (or section of circuit) divided by the resistance of that circuit.

I understand that the pull up resistor prevents a short and limits current flow; however I am confused about how pressing the switch actually changes the current being delivered to the control chip. The circuit of the control chip (coming down from the top and exiting at the right) still has the same voltage drop and still has the same resistance regardless of whether the switch at the bottom is open or close. According to Ohm's Law this means that the current should be unaffected.

I'm sure there is an error in my logic, however I'm having difficulty figuring out where. I appreciate the help!


texts: I am designing a basic 2 layer pcb board with altium and I have a huge doubt. Basically I used polygon pour to put my ground plane on both layers but, I wanted to clean some areas around ICs and some capacitors, like shown in the figure, I did this using polygon pour cutout, however after this, the dashed lines stay in the design, is that a problem?, It seems they could cause a short circuit


texts: What would be the best/economical solution to detect an AC device activation?

texts:
I want to know when a device is turned on/off and generate some statistics.

Microcontroller: ESP8266
AC voltage: 220V

The first thing that came to my mind was using a power consumption sensor which will translate to OFF when consumption = 0 and ON when consumption > 0.

But probably there's a more efficient or economical way to get HIGH/LOW states (3.3v)

TIA


texts: Why power factor correction for Capacitive load is more difficult?

texts:
When we want to correction power factor of a motor(inductive load) its simply can done by adding an capacitor in parallel with the motor but its not possible to correction power factor of an capacitive load such as LED lamp by adding an coil in series and have to use a special circuit to do that, why?

simulate this circuit – Schematic created using CircuitLab


texts: Find Power Spectral Density of given signal

texts:
I am given a question with very brief notes to study from. The question is this:

Now I was wondering, are the following part of the notes relevant at all:

Is this the appropriate method to solve the question? Would I need to consider converting frequency to phase?


texts:
How is redundancy of power supply from converters done in satellites? can anyone explain with complete details.Is it possible to get the actual design from power system of any mini-satellites ? Is the redundancy of converters actually done?

i want to know how redundancy is maintained for the converter in a satellite.it's the most crucial part as the failure of a converter is highly possible and how is this problem tackled?
by saying converter i mean dc/dc converter


texts: How to measure the longest width of a square wave?

texts:
I'm blanking on how I did this in the past.  I'm trying to measure the longest a block of code on a microcontroller will take to execute by toggling a GPIO around that code block.  The firmware works, now I'm just not able to bend the oscilloscope to my will.  The signal is not periodic.  Is this a trigger mode?  I vaguely remember a tracing or history fading option.  I know this may be oscilloscope-dependent, but what that feature is called can help my search in the manual.

The specific scope I'm working with right now is: infiniivision mso-x 4154a


texts: Proposal for building Low-Current 220VAC Current Detector

texts:
I have been reading many such articles and have found no way to simply detect flow through a mains wire at low current.

At .27A for one LightBulb, I was calculating .05mA out of commercial 1:2000 inductance sensors, and no IC Hall Effect sensors are rated for less than 1A.

I only want On/Off Resolution to feed into a transistor and trigger a relay, so I consider my options to be:

Use a drill to wind a ~4000turn coil with very thin resin coated copper, wrap it around the wire and pray for o.1mA that I can amplify (Darlingtons? Is this possible? Is it stable?)
A Hall Transistor, also with lots and lots of gain?
With Capacitance Coupling "make the probe itself as a small coil and amplify the voltage dropped (not induced)" These will share a common Ground.
(Is there some freaky way to make a magic resonant coil around the wire... yes i'm looking at you Tesla.) This seems like I am LOSING power to the mains, but at least I can sense it.

Anyway, if I get this working I will share share share cos there are a lot of frustrated forum posts around but no damn answers.

Please comment / recommend / crush my delusions of grandeur so I don't have to waste all my time failing around.


texts:
There's Mux4Way functional table:

I have already know right way for implementation of this chip by using another 3 Multiplexor chips when mux functions as following:

/**
 * Multiplexor:
 * out = a if sel == 0
 *       b otherwise
 */

Let's say we have already build Muxtiplexor chips, to build working 4 way mux we would have something like that in HDL:

// First selection bit
Mux(a=D0, b=D1, sel=sel[0], out=mux0);
Mux(a=D2, b=D3, sel=sel[0], out=mux1);

// Second selection bit
Mux(a=mux0, b=mux1, sel=sel[1], out=out);

And it's working! But I've no idea why! So, in such particular way it behaves as expected but all my tries to build truth table was with no success.

It would be great to have any idea how to prove why this particular way is correct and even why it is working.


texts: Is the Nyquist plot a plot of Re(G(s)) v.s. Im(G(s) or Re(G(jω)) v.s. Im(G(jω))

texts:
It seems that people in control theory are divided over whether the Nyquist Plot/Diagram (that is the plot, not the contour!) is a plot of $$\text{Re}(G(s)) \text { v.s. } \text{Im}(G(s))$$ or $$\text{Re}(G(j\omega)) \text{ v.s. } \text{Im}(G(j\omega))$$

After a quick internet search, I have found that

The popular web resources that uses the former convention includes:

http://lpsa.swarthmore.edu/Nyquist/NyquistStability.html
http://www.facstaff.bucknell.edu/mastascu/econtrolhtml/freq/freq6.html
http://sandeepsingh.net/Control%20Systems.htm

People who uses the latter convention includes:

http://www.cds.caltech.edu/~murray/books/AM05/pdf/am08-complete_22Feb09.pdf pg 273
http://www-control.eng.cam.ac.uk/gv/p6/Handout6.pdf
http://www.roymech.co.uk/Related/Control/Nyquist.html

The rest does not seem to care about this distinction and does not label their plots properly.

In any case, from a purely academic perspective, which is correct? I need as many electrical engineers to weigh in  as possible.

Side note: if this is any worth I think the former is correct since we are not only mapping the Nyquist contour on the imaginary axis but also over whichever semicircle happen to be on the contour, and those are not on the imaginary axis!


texts:
I have an instrumentation amplifier, INA 126. I am using it to amplify the physiological signals from the eye movement. The circuit I have constructed has 2 stages: 1st stage has INA 126 with a gain of 1000 and the 2nd stage has another INA 126 also with a gain of 1000.

My question is that the 1st stage only has one output so where do I connect this output?I have tried connecting it to Vin+ and grounded the Vin- of the 2nd INA 126, is this the right thing to do? I have read the datasheet and it does not mention of having one input only.

P.S
I am using dual supply.. +12V and -12V and I have connected the Ref pin of the INA126 to ground as mentioned in the datasheet.


texts: I’m trying to adapt a new speed controller onto my motor. It uses 0-5v for the throttle input. The throttle I have now uses a hall sensor that can only do 1-5v so the motor will continue to roll even when the throttle is not being pressed. What is a way that I could get the voltage down to 0v but still have the voltage be 5v at max.


texts: How do I deal with acoustic noise from a transformer under PWM load?

texts:
I am working on a hobby project involving controlling LED strips (working at 12 volt and drawing up to 5A). The light intensity of the strip is controlled using a single MOSFET transistor (specifically FDA8440) connected to the MCU. I am controlling the light intensity with the microcontroller using PWM.
The project is powered by a Mean Well LRS-100-12 power supply.  The problem is that I hear an audible and bothersome noise when the LEDs are not fully off or fully on, which comes from the transformer inside the power supply unit.
Other that the LEDs, the PSU is also powering the PSU (an ESP32) trough a buck converter (a circuit based on the XL4015 chip ). At the moment the wiring is done over a breadboard.

The amount of audible noise depends on both the frequency and duty cycle of the PWM signal (the frequency of the sound seems to be very roughly that of the PWM somehow scaled down by the duty cycle). If I set the frequency at around 100 Hz I hear a more or less constant amount of noise. Decreasing the frequency from there reduces the noise but then LEDs start to perceptibly flicker, which is not ideal. Increasing the frequency above 100 Hz makes the problem worse and the amount of noise I hear acquires a dependency on the duty cycle: It seems to pick two or three resonant frequencies between 0% and 100%. If I try to escape the audible range by setting the frequency at something like 50 kHz, I still hear loud noises when the duty cycle is about 30%. This also makes lower duty cycles (10% or so)  not work well as I observe LEDs flickering substantially.
I note that if I add some constant and high enough load (a resistance), then the PSU is quiet. How could I make it quieter? Maybe some kind of capacitor bank would help making the transformer vibrate less?


texts: What is the purpose of the pin and hole on some pairs of tweezers?

texts: I use a set of tweezers as part of my toolkit, and they have a hole in one arm and a corresponding spike in the other. Why?


texts: Does the JQX-115F-Q power relay step down voltage?

texts:
Could someone help clarify how the JQX-115F-Q power relay works?
I appreciate  this is a about a specific component so I've included a picture to show the markings. It's the markings that has got me confused, hopefully someone who understands this type of relay will be able to help.

The markings show 250VAC then above 9VDC and what I'd like to clarify is how should I interpret these markings?

I'm guessing it means one of the following but which?

The relay works with either inputs of 250VAC and 9VDC or,
Input of 250VAC will step down to 9VDC.

Side note: I'm trying to troubleshoot why my oven has stopped working. I've tested the input to be just under 240VAC (red and orange wires show in the picture) but I'm getting zero volts from the output (red wire). I think the relay is faulty so I want to bypass it but before I do I want to be clear that the expected output is same as the input and the replay is simply acting as a switch.

Here's a picture of the relay.


texts: sending data over bluetooth to my hardware through a matlab serial GUI

texts:
I have a hardware with RN-41 bluetooth module and the lpc 214 arm microprocessor.Currently my device only sends data to the PC and I am trying to configure it to be able to receive some commands over bluetooth and perform certain actions e.g. blink LED,Shutdown etc.

I have a serial GUI in matlab which has buttons on it (LED ON,LED OFF,SHUTDOWN etc)where each button on being pressed sends a value associated with it to the hardware over a virtual serial port to perform a certain action.

Till now I have not been able to get my device to perform any action correctly.I definitely see the hardware responding to a button press in strange ways but never performs the desired action.I feel I may have configured the UART incorrectly. I am pasting some code associated with this issue here.

Any help would be greatly appreciated.

Thanks!

void setup_uart0(int newbaud, char want_ints)

{
baud = newbaud;
U0LCR = 0x83;   // 8 bits, no parity, 1 stop bit, DLAB = 1
U0DLM = 0x00;   // set for baud high byte
U0DLL = 0x06;   // set for baud low byte
U0FDR = 0xC1;
U0LCR = 0x03;
VICVectCntl1 = 0x00000026;
VICVectAddr1 = (unsigned int) UART0ISR;
VICIntEnable = (1<<6);
//PINSEL0 = 0x0F001555;
}

void UART0ISR(void)
{
    unsigned int i;
unsigned char ch;
U0IER = 0x01;

while(!(U0LSR&0x01));
uart0_rx_buffer[uart0_rx_extract_idx++]=U0RBR;
uart0_rx_extract_idx %=UART0_RX_BUFFER_SIZE;
ch = uart0_rx_buffer;

for (i=0;i<8;i++)
uart0_rx_buffer[i]= 0;

return U0RBR;

if(ch ==0x0A){
   VICIntEnable &= (~0x00020000);
   eventMarker=1;
   ch=0;
}

else if (ch ==0x0B){
    shutdown();
  ch=0;
  }
else if (ch ==0x0C){
blink(1,ON);
 ch=0;
 }

else if (ch ==0x0D){
blink(1,OFF);
    ch=0;
}

VICIntEnable |= 0x00024000;
VICVectAddr= 0;
U0IER = 0x00;

}


texts:
I'm testing my BluePill and I'm trying to turn on the built-in LED.
Everything seems fine but one thing. When writing to BSRR I would expect the LED to turn on.
When I write 1 to BS13 bit GPIOC->BSRR = (0x2000) and turn off when I write GPIOC->BSRR = (0x2000) << 16u (writing 1 to BSR13 bit). To my surprise, it works backwards - LED turns on when GPIOC->BSRR = (0x2000) << 16u and turns off when  GPIOC->BSRR = (0x2000). Am I missing something?


texts: Understanding connection of inputs and outputs of digital circuits - voltage and currents requirements

texts:
I looked for resources to find solutions to these kinds of problems online, but I couldn't find them. Please, feel free to recommend resources to study from. This is a homework question. I can't find the answers to this. I read the chapters of the book.

We need to connect outputs of circuit A to inputs of circuit B.

Circuit A has the following parameters:
Powered by 5V source.
V output high minimum is 2.7V.
V output low maximum is 0.5V.
I output high is 400uA.
I output low is 16mA.

Circuit B has the following parameters:
Powered by 3.3V source.
V input high minimum is 2.3V.
V input low maximum is 1V.
I input is 1uA.

For the proposed way of connecting the circuits, A and B are compatible for low logical value, both voltage and current vise. The question is, are they compatible for high logical value? If they are not, how to make them compatible?

Here is a photo to simplify things:

How would it affect compatibility for high logical level if we changed one parameter of circuit A - V output high minimum is 3.5V?


texts: Help identifying right angle (or 180°) USB connector part number

texts:
I am searching for the right angle (or is it 180°?) usb connector used in the product on the following webpage - https://thepihut.com/products/solderless-zero-dongle-for-raspberry-pi-zero?variant=31945282289726&currency=GBP&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&gclid=CjwKCAjwnK36BRBVEiwAsMT8WNUBdSzfdw_7kKOf7eKUF22Hht75-InsgJOA9PI0k-gfSMt71pO49RoC338QAvD_BwE
Assuming the relatively low price of the product I would assume it's relatively low priced and not some ultra specialised product. I have searched Farnell, Digi and Mouser with no success.


texts: How to calculate total harmonic distortion in PSpice?

texts:
How can I calculate the total harmonic distortion of a sinusoidal Oscillator in Pspice?

I am using eldo and ezwave for the simulations and waveforms.


texts: Length of Transmission Line & Characteristic Impedance

texts:
Just a simple Question for clarification: Does the physical length of transmission line affect its impedance?

We all understand that the height of dielectric (space between line and ground) affects the capacitance of transmission line and width of the line affects its inductance. But then why is it so important to keep the length of transmission lines (Microstriplines for example) a multiple of Lambda/4 or some other specific number when designing feed lines for antennas?


texts: Would like to get an insight on how to build an environment with FreeRTOS +LWIP on eclipse for building a specific application on STM32. What do you recommend?


texts:
Okay let me try again as nobody seemed to understand my query the first time.

The cutoff frequency f of this Sallen-Key 2nd-Order Low-Pass Filter is f = 1 / 2(pi)RC

For equivalent values of RC, do different combinations of R & C give different signal integrity in practice.

For example R = 1000, C = 5x10-6 has an equivalent cutoff of as R = 100000, C = 5x10-8. But will one be better than the other in practice.

My question is, are there best practices for reducing signal error with regard to the ranges of resistance and capacitance aside from tolerances.

Edit: I am assuming R1=R2 and C1=C2 for a smooth dropoff


texts: Simplifying CMOS schematic to reduce number of transistors

texts:
I know the basics in creating a schematic in CMOS, wherein in a(n inverted) boolean expression, if there is a:

NOR - NMOS should be in parallel, PMOS in series;
NAND - NMOS in series, PMOS in parallel.

Recently, we were tasked to do the CMOS equivalent schematic of an XOR gate. With the knowledge I have above, I came up with the schematic below having 12 transistors (including inverters, which are not shown in the figure):

I then googled if what I did was right. It was, but I saw better ones with lesser number of transistors.

This has nine:

I tried simulating the schem above and it worked.

EDIT: The third schematic doesn't work as XOR. Thank you, Curd!

This has four (I'm not sure though if it works, I haven't tried simulating it).

Question is, how do you simplify a CMOS circuit?


texts: switching sensor output between two arduinos

texts:
I'm relative new to electrical engineering, so this might be a obvious question. I'm trying to allow two arduinos to communicate with one i2c sensor. One of the arduinos is deeply integrated within the system and on the same i2c bus as the sensor, while the other one is just a standalone arduino only used occasionally for debugging and data collection and is not on the same i2c bus.

I guess I'm looking for a IC that can switch between the two devices so that it can isolate the sensor and form a i2c bus with the second arduino when needed, and switch back to the other i2c bus otherwise.

Thanks!


texts:
I would like to know the precise formula for the Free Space Path Loss in case of a Magnetic Field in the Near Field region.

We all know the popular FSPL formula, but this is only for the far field, where we have planewaves.

Source: https://en.wikipedia.org/wiki/Free-space_path_loss

I am looking for a near-field magnetic field path loss formula. How much strength does a magnetic field lose per distance from the source?

Is there any way to model this system. I could not find a formula on the entire internet, I was hoping somebody here would know.


texts: How to think while working with VHDL or Verilog

texts:
All of my experience belong to general purpose programming languages e.g; c/c++ etc where each instructions are executed one after the other but it seems in VHDL/Verilog, all the instructions are executed at once (parallel processes)

Just wondering if there is any resource out there for programmer of general languages to understand how VHDL work?

Reference: http://en.wikibooks.org/wiki/Programmable_Logic/Parallel_Execution


texts: Boost converter, why the voltage derates when frequency rises?

texts:
I am simulating a boost converter in ltspice.

vin=3V, vout_bst=12V, ideal inductor, capacitor, diode and voltage source.
When I use an ideal switch, raising the frequency doesn't affect the output voltage but when I use MOSFET transistor BSZ036NE2LS the voltage drops when I raise the frequency.

*The highest is @100kHz, the lowest @1MHz (100kHz steps)
I understand the transistor causes it but I didn't find a frequency restriction in it's datasheet and I don't know how to explain this derating.
edit: Rload=17.142 (I wanted for the simulation Iload=0.7A)


texts:
I've developed a circuit for my model aircraft, which requires 3.3V @ 100mA. My aircraft uses a 3S LiPoly, which ranges from 9V - 12.6V. When the motor is off, the 3.3V supply is good; very low ripple. However, when it spins up, the battery voltage ripples, and the supply voltage to my MCU occasionally dips below ~2.5V, and this occasionally resets it, and at the very least it causes problems with the rest of the analog circuitry.

I've attached a diagram of my system.

What can I do to reduce this problem?


texts: How many bins can I code using a resistor on an ADC

texts:
I have a device that can have different things plugged into it. I'm trying to use a resistor on these things to uniquely identify the thing. That is, if I plug in Thing A, I can read the resistance as 100Ohms and know that it's a Thing A. If I plug in Thing B, I can read the resistance as 200Ohms and know that it's a Thing B. I know resistance varies with temperature, and tolerance, so I want to have some wiggle room on each unique code.

I'm using a voltage divider and an ADC to measure the resistance. Assuming I have a constant 3V input, a 12 bit ADC reference of 2.5V, I will use resistors with a 1% tolerance, and I want as many unique codes as possible, with a small gap in between each, how do I calculate how many unique codes I can get?

I was first thinking that I could use a 2k resistor, and then the second resistor could be anything from 0 to 10k. With 4095 steps in 12 bits that means .6mV per step. At 1% tolerance, that  means the top bin could be anything from 9900 to 10100, so 200 ohms wide. That's only 80 bins, though. However, a 100 ohm resistor would only vary from 99-101, or 2 ohms wide, so a linear formula is clearly not appropriate.

How can I figure out the correct number of unique bins that I can reliably detect?


texts:
I have Chpkit Uno32 with PIC32MX320F128H, I am trying to enable interrupt  and I have written the following code:

// PIC32MX320F128H Configuration Bit Settings

// 'C' source line config statements

// DEVCFG3
// USERID = No Setting

 // DEVCFG2
   #pragma config FPLLIDIV = DIV_2         // PLL Input Divider (2x Divider)
   #pragma config FPLLMUL = MUL_20         // PLL Multiplier (20x Multiplier)
   #pragma config FPLLODIV = DIV_1         // System PLL Output Clock Divider    (PLL Divide by 1)

   // DEVCFG1
   #pragma config FNOSC = PRIPLL           // Oscillator Selection Bits (Primary    Osc w/PLL (XT+,HS+,EC+PLL))
   #pragma config FSOSCEN = OFF            // Secondary Oscillator Enable (Disabled)
   #pragma config IESO = OFF               // Internal/External Switch Over (Disabled)
   #pragma config POSCMOD = XT             // Primary Oscillator Configuration (XT osc mode)
   #pragma config OSCIOFNC = OFF           // CLKO Output Signal Active on the OSCO Pin (Disabled)
#   pragma config FPBDIV = DIV_1           // Peripheral Clock Divisor (Pb_Clk is Sys_Clk/1)
#pragma config FCKSM = CSDCMD           // Clock Switching and Monitor Selection (Clock Switch Disable, FSCM Disabled)
#pragma config WDTPS = PS1048576        // Watchdog Timer Postscaler (1:1048576)
#pragma config FWDTEN = OFF             // Watchdog Timer Enable (WDT Disabled (SWDTEN Bit Controls))

// DEVCFG0
#pragma config DEBUG = OFF              // Background Debugger Enable (Debugger is disabled)
#pragma config ICESEL = ICS_PGx2        // ICE/ICD Comm Channel Select (ICE EMUC2/EMUD2 pins shared with PGC2/PGD2)
#pragma config PWP = OFF                // Program Flash Write Protect (Disable)
#pragma config BWP = OFF                // Boot Flash Write Protect bit (Protection Disabled)
#pragma config CP = OFF
#include <p32xxxx.h>
#include <sys/attribs.h>

void __ISR(_TIMER_1_VECTOR, ipl4) Handler(void) {
    LATFbits.LATF0 = ~LATFbits.LATF0;

    IFS0bits.T1IF = 0; // Clear interrupt flag
}

int main() {

    T1CONbits.TCKPS = 3;

    PR1 = 0xFFFF;
    IEC0bits.T1IE = 1; // Enable Interrupt for Timer 1
    IFS0bits.T1IF = 0; // Clear interrupt flag for Timer 1
    T1CONbits.ON = 1;

    __asm__("EI");

    TRISFbits.TRISF0 = 0;
    LATFbits.LATF0 = 1;

    while (1);
    return 0;
}

PS : I know this question is so repeated but I read most of the datasheet and reference manual and have been stuck with it for a while.


texts:
I am trying to build a voltage generator 0-10V to  feed the input of a PLC ADC card (for simulation purposes). The PLC card has an input impedance of 133k.
I am thinking to use the circuit from the picture below:

Since the signal will be applied with a pair of probes I want to implement short circuit protection. The protection is a classic one with a sense resistor (R8) and transistor (Q2).

When a short will happen (or the current will exceed the limit of 15mA) Q2 will open, limiting the base voltage of Q1 which in turn will limit the output voltage protecting the circuit.

Now... The voltage of feedback network (R6,R7) will go low. Because the op amp wants to have both inputs at same voltage will try to increase it's output voltage until the output will be close to it's positive power supply (LM358 it's not rail to rail).

My question is: an op amp with it's inputs at different voltages and an output close to positive power supply risks to be damaged?

Thank you in advance for your answers.


texts: How do I connect to a cheap wifi (wemos) relay board?

texts:
I got a cheap wifi relay board off wish.com and I want to connect it to my network. When I apply power (no less than 12v) I can see AI-THINKER_xxxxxx when I attempt to connect to it, I'm asked for a password. There was no documentation supplied with the device - how am I supposed to guess the default password to connect to the device. I want to use a smart phone app like Smart life (or anything that will work) to connect the device to my amazon echo. I got cheap RGB LEDs from the same place, but at least it came with a password - this relay board came with nothing and I cant seem to find anything out there on setup.

Please help. Thanks!


texts:
Background: I'm building a quadrocopter. In such RC models, usually brushless engines are being used and these require ESCs (Electronic Speed Controllers) to work properly. Most ESCs are equipped with a BEC (Battery Eliminator Circuit), which converts (for instance) +14.8V from battery to +5V and allows powering up whatever is using the engine (Radio receiver or, in case of quadrocopter, the flight controller board).

I'll be using KK 2.1.5 FC board, which looks like the following:

The board is powered from the BECs - there are no separate pins for power input.

My ESCs have linear BEC with output +5V, 3A.

Question: Is it safe to connect all ESCs to the FC? Or should I remove the +5V cable from all but one ESC?

FC's and Rx's power requirements oscilate around 0.1A.


texts:
How would I go about electronically limiting the flow of a liquid (such as water) through a garden hose (or similar)?  I'm building an automated system for refilling a pond since I'm sick of doing so myself.  ;)

The only requirement I have is that it fails closed, i.e., it closes the valve when power is lost.

The only flow control valves I've been able to find are for large liquid volumes such as HVAC and such.

Any ideas?

Edit: It's also worth mentioning that I only need to have an "ON" and "OFF" state, I don't need variable control over the amount of liquid flowing.


texts: Hi.  I'm curious if it would be proper to do something like in the attached pic.  You'll notice that I have a AC wall wart basically in parallel with a battery (say six AA penlights), both nominally supplying 9V to V_Supply (minus a diode drop).  If the wart is unplugged, then D1 should be back biased and no current should flow through D1 and the battery should provide 9V minus a diode drop to V_Supply.   If both wart and battery are present and the battery is fully charged, then no current should flow, since D1 sees 9V on either side.  If the battery has lost some charge and is less than 9V, then some current less (than 10mA) should flow into the battery from the wart, and the battery should provide V_Supply with some voltage minus a diode drop.  So, the idea is to trickle charge the battery, which might or might not be a rechargeable type.  I wouldn't think that a current less than 10mA even to a non-rechargeable battery would cause the battery to heat up, explode or leak and I've heard conflicting stories as to whether it's safe to charge a non-rechargeable.  But assuming it's rechargeable(s), would that be a reasonable way to trickle charge the battery and a non-problematic circuit?  Thanks.


texts: Combine C and C++ in STM32 application development

texts: Generally, developing embedded systems applications is based on abstraction. We expose some functions from lower layers that can be used in the application layer. My question is: Can I develop the application layer in C++, using the POO approach (classes, inheritance, etc ...)? Is it possible to combine both C and C++ in the same project ?


texts: ESP8266 current spikes influence analog sensor

texts:
I'm using Wemos D1 mini with enabled and connected Wi-Fi and photocell connected to A0 with a 10K voltage divider.

Because of ESP8266 behavior with huge current spikes up to 400mA, photocell acts like a random signal generator.

I wonder if it's possible to eliminate those silly voltage drops/current spikes.

I've tried adding 5 parallel connected 470uF electrolytic caps as close to ESP as possible, but it didn't help so much.

Thank you for sharing your ideas


texts: Open Source or free electric field mapping software

texts: Looking for recommendations for 2D (or 3D) electric field mapping software.  I want to be able to populate a series of electrodes in a plane and understand the equipotentials present when these electrodes are driven to different voltages.  Would like to model virtually first before realizing the design in a PCB/PWB to reduce cycle time.  Must be low cost or FOSS software.  Will be modelling fields in free-space and with patterns of electrodes, so no fancy lossy di-electrics or esoteric material need be supported.


texts:
I searched through the internet but couldn't find an answer to my question. Maybe I just don't know what to search for.
I want to convert an audio signal coming from a stage box from analog to digital. I found some integrated circuits which seem to be suited just for that (like this one).
But here is the problem. The audio signal coming from the stage box is referenced to the wall plug ground. Which means that the audio signal oscillates between negative and positive voltages. But the analog-digital converter I linked works only for positive input voltages. I found that there are also some ADCs (like this one) which seem to be able to handle also negative voltages. But is it the best solution? Is there some way to "lift" the audio signal potential so that it oscillates only in positive voltage range?
Thank you in advance for all your suggestions.


texts: Diagnosing voltage reading on battery pack. Possible Insulation leakage?

texts:
With reference to this question I asked the other day: How can I measure a voltage between two conductive surfaces that are completely isolated?
There was a good answer there so I didn't want to continue in the comments but It didn't solve the main issue I had which is the 120V potential between the isolated case and the battery terminal. To quickly re-iterate, the battery pack is 350V and there are multiple layers of insulation between the pack and the case.
The multimeter used to measure the voltage was a Fluke 87V. This meter has a 10Meg input resistance. I've drawn the below diagram to illustrate this. I don't believe it's accurate because this is not a pure voltage source, more a measured voltage likely due to insulation leakage. Here, Rx is the unknown impedance between the terminal and the case. R1 is the meter input impedance. In this scenario, I measure 120V.

simulate this circuit – Schematic created using CircuitLab
Now, if I connect a 10k resistor across these points to see if there's any power behind this voltage, I now get the following two circuits when I measure voltage & current.

simulate this circuit
The voltage read is now 0.5V and when putting the meter in series with the 10k resistance, I read 50µA. My guess to what's happening is, the high input impedance of the multimeter is comparable to the insulation impedance between the case and the terminal, in that case, the meter's impedance has a large effect on the circuit, causing this voltage reading. When I connect the 10k Resistance, the voltage collapses by reducing the equivalent parallel resistance.
So my question is, what is actually happening here and is the 120V voltage I'm reading dangerous?


texts:
I'm designing a circuit with RFICs using differential signaling. I'd like to keep noise to an absolute minimum. Let's use the mixer (LT5560) as an example. All of the reference schematics match to 50 ohms and use a balun to convert the differential inputs and outputs to single ended. I would like to use differential signaling to and from the mixer as my IC's on either side are differential. Converting to single ended and then back to differential seems wasteful. Why would none of the reference schematics take advantage of differential signaling when the datasheet strongly recommends it?

My main question is this: I know how to match the impedance of single ended signals, but how do I match the impedance of differential lines? My source impedance is not 50 Ohms.

LT5560 Datasheet

edit: to clarify, I am not trying to match 50 Ohms, I need to match 2 different complex differential impedances. So, in this image, how do I calculate the correct component values to ensure maximum power transfer?


texts: 7405 TTL Chip outputting nothing when given low input

texts: I’m struggling learning how to use some of these components for a lab. One thing I noticed is that when giving the 7405 hex inverter a low input, the output when checked by my logic probe shows there’s no voltage coming to the output. I’ve ensured my chip is powered and grounded. Any ideas?


texts:
I am using a Zener diode along with a flyback diode with a relay in order to speed it up a bit. This works very well but I am currently using a rather over-sized zener from the inventory.

For proper design, I'm trying to determine what the power (or current rating) of the zener diode in the above schematic should be. The coil current of the relay is 80mA. Let's assume the zener has a breakdown voltage of 24V.

If the coil current is 80mA and zener voltage 24V, then power dissipated is approx. 2W - but this is a continuous rating, isn't it? How do I choose a zener with enough current and power rating that it will withstand the kickback effect of the relay?


texts: What is the ground impedance used for in an inverting amplifier circuit?

texts:
Why people use \$Z_g\$ in the following circuit:

simulate this circuit – Schematic created using CircuitLab

As \$Z_g\$ doesn't appear in \$V_{out}\$ equation: \$-Z_f/Z_i \times V_{in}\$


texts: What are possible reasons for this not to work

texts:
I connected a 5V relay to an Arduino. It then opened and closed the relay, which had on a terminal (doesn't matter which one?) a wire that went to an iPhone' screen (with tin foil at the tip). On the other terminal I had nothing. The middle terminal had a wire that went to my hand.

The relay switched from floating to ground (from my hand), but the touch was sometimes not registered, sometimes it jumped around, and when it worked at best, the touch was registered, but the "touch end" didn't work even after the relay went to floating position.

Any ideas as for why this didn't work? I feel that either the relay is too big and disturbes the signal or the software behind the screen works in a way that doesn't allow this method to work.

Thanks!

Schematic: (70 ohms on the relay's coil)

Circuit


texts:
Boylested says that during the positive voltage half cycle diode D2 is cut off.
But why can't there exist a current flowing through the outer loop via C1, the secondary of transformer coil, C2, and D2 in the positive cycle when the input voltage begins to decrease and the capacitor voltage is greater than the transformer voltage?


texts: Regarding symbols used for current amplification factor

texts: We just studied basic semiconductors on the high school level and we ended on transistors and we got three notations alpha beta gamma which corresponds to three different transistor arrangement with common base emitter and collector, now surely there must be some reason why common emitter arrangements current amplification factor is called beta while common base is alpha and commin collector is gamma can someone tell me the historical reason for these assigned symbols or any physical interpretation?


texts: "low current", "high efficiency", "high intensity" LED's

texts:
"low current"
"high efficiency"
"high intensity"
... ?

I read these terms in various places and every single time the LED's are just used as a signaling LED in a small circuit, requiring only a few milliamps to light up.

What is the difference? Or is it just marketing speech from different manufacturers?


texts: How does a Capacitive ID / Signatures / Sensing system work? e.g. Google Bloks

texts:
In the 'Google Bloks'  project. A tangible programming experience is created by allowing children to place physical instruction blocks next to each other.

The computer is able to read the sequence of instructions and turn it into a program to e.g. control a robot.

It uses a capacitive sensing / capacitive ID system to detect whether an instruction card is a "GO FORWARD" or a "TURN LEFT" card (for example).

Each instruction card contains no electronics.
Each instruction card is somehow assigned a 'capacitive signature'
Instruction cards are decoded via some capacitive sensor matrix

Since there is no technical whitepaper. My question is how would this work in practice?

How to design the sensing system for this?
How would you create a capacitive signature for an instruction card?


texts: I2C pull-up resistors calculation & where to place them

texts:
I'm connecting a PIC18F46K22 (master) to a PIC18F4620 (slave) using I2C. The wire between the devices is ~30cm. I'm using 400kHz without slew rate control. Later on, I'll add another 18F4620 on ~5cm from the master (~35cm from the other slave).

How do I calculate the pull-up resistance needed on both the SCL as the SDA line?

Does it matter where I place the pull-up (near the master, near the slave, both, in the middle, ...)?


texts: Which libs to use with a STM32F103C6 microcontroller?

texts:
I'm very new with ARM microcontrollers and I've been doing a lite lecture of about 4 books to know how to configure this devices to start programming them. First I did a reading an how to use mbed but I think that I need to do some porting or a bootloader to make it work in my microcontroller.
Then I've decided to look for examples on how access GPIO ports and I know that first I need to configure clock to the port that I will use. I've found the example of Keil with the library stm32_Init, this library uses the file stm32f10x_lib.h and has an excellent config wizard made for it but I think is deprecated or something like that, in addition, the header stm32f10x_lib.h is not found by Keil v5.30 nor the installation folder and obviously not in the project folder.
After that I've read about CMSIS and that it was created to portability and uniformity of code between developers so I taught I can use this but the form of using it is confusing to me...or I don't understand anything about CMSIS, I don't know yet.
My code is right now:
#include <stdint.h>
#include <ARMCM3.h>
//#include "STM32_Init.h"
//#include <stm32f10x_lib.h>// STM32F10x Library Definitions
SystemInit();
int main()
{

}

CMSIS uses a function called SystemInit() whose meaning as I saw is basically configure the system clock but even when I've included CMSIS support in my project when I use that function  and It gives me the following errors and warnings when I pass the cursor over the exclamation symbol in the same line:
Error: Conflicting types for 'SystemInit'
warning: type specifier is missing, default to 'int'
warning: this function declaration is not a prototype.Code

and when I compile the file it gives me the following error:
C:/Users/valery/AppData/Local/Arm/Packs/ARM/CMSIS/5.7.0/Device/ARM/ARMCM3/Include/system_ARMCM3.h(48)
: note: previous declaration is here
extern void SystemInit (void);

I see this like the project isn't seeing the CMSIS library or something like that.
Like you see I'm a little bit confused here so I need help on how and what to do here.
How can I start here?
NOTE: The file that has the config wizard is STM32_Init.h


texts: If a battery case falls apart is it safe to just glue it back together?

texts:
I've got a battery with two Li-Ion cells inside that has a two-parts rectangular case and those parts were somehow tightly connected (I guess glued together) but then fell apart and now the cells and the service electronics are in one half and the other half is just on its own. There's nothing like ventilation holes in that case.

If I just glue the case parts together carefully - will that pose any risk?


texts: Unsolvable 5-Band contrary color band sequence!

texts:
I am beyond puzzled with identifying the values of a wire wound, axial, through hole resistor that I'm replacing on a MRC Super Brain 989 relic that I burnt up after 50+ hours of charge/discharge cycles of (20) 6-cell NiMH battery sticks that make up the IMA battery in my Honda Civic Hybrid; in efforts to rebalance the pack.

The failed resistor, or actually a series of (4) identical resistors are responsible for the 10A discharge rate the 989 is capable of. I was pushing the discharge circuit beyond limits with dozens of discharges on these sticks at a 10A discharge rate at a 0.9mV/cell peak cut-off, resulting in a  6180mAh discharge capacity per stick.

The charger pauses the discharge cycle when the internal temp reaches 185ºF and resumes discharge when temp drops to 175ºF. This pause/resume would happen several times during a discharge.

All that being said....The resistors in need of replacing measure 17mm in can length and 6mm in diameter, and all 4 resistors read out on a MM with a resistance value of 0.5-0.7 Ohms.

*****THE 5-BAND COLOR SEQUENCE******

{  |BROWN|  |BLACK|     |SILVER|           |RED| |BLACK| }

The best I can come up with is: (0.1 Ohm with 2% Tolerance) by ignoring the ending black band and treating this as a 4-Band Resistor.

The goal is to replace the resistors with a better grade, add more fans, and extend heat sink to get the charger in a workable condition to finish the project at hand.

Thanks!!

g8.jpg


texts: Proper use of the ENC28J60 Ethernet controller

texts:
I am using the Microchip ENC28J60 Ethernet Controller in a microcontroller design.
The datasheet contains the following reference circuit:

I am designing a custom PCB, getting inspiration from a sample Chinese board I am doing my development with, which contains the chip, magjack and a few more components. I have traced it to be an almost 1:1 implementation of the above reference design, but there is a difference, being that pin 5 of the Ethernet jack is connected to the midpoint of the 50R resistors on the receive side (TPIN+/-), where the 0.01uF cap is also connected.
Pin 5 comes from the center tap of the receive transformer, as follows:

So first question: Is this an error on my board or something I should put in my design?
Second question: what ferrite bead am I supposed to use in the transmit circuit? I couldn't find any reference to the required 100MHz impedance in the datasheet.
Another question is about the magjack (HANRUN HR911105A), whose datasheet has the following note: Connect CHS GND to PCB ground. This would be pin 8, but it is left unconnected on my board. Should I connect it?
Also, I guess "CHS ground" is "chassis ground". Does this mean it's connected to the outside metal shield of the magjack? I'm asking, because the shield gets into two holes on the PCB, which are connected to ground on my board but they are not actually soldered, and the metal tab just hangs in the hole without touching its sides. Should i ground it?
Thanks a lot!


texts: Best elements for downhole and high temperature circuits

texts:
I want to design a data-logger with PIC MCUs. This data-logger is going to work in chamber in the oil wells in the depth o 500 meters. and it is going to record temperature and pressure for 20 hours.

The pressure in that depth is about 9000 PSI and the temperature is about 130 degreeC. I want to know what kind of elements is the best elements for this project. I mean if I need a 1uF capacitor, which kind of capacitors is my best choice?  Electrolytes? Polyester? Ceramics? Multi-layer? Which one is less temperature sensitive? What about the resistors? and also all the other elements.

Please shed any light you can on this issue. Any point will really highly appreciate. Does any body have similar experience?


texts: What is the difference between a PT3 and a PT4 power lead?

texts:
I want to know the difference between a PT4 and a PT3 power lead.
 Can I use them interchangeably?

http://www.cctvcamerapros.com/CCTV-Accessory-PT4-p/pt-4.htm

http://www.cctvcamerapros.com/Power-Cable-Lead-p/pt-3.htm


texts: Determining the input voltage range of an adaptor

texts:
The label of a power adaptor is damaged so no information if the input voltage is 110V only or 100-240V range.  The output is 500mA at 5.5V.

I would like to use the adaptor in a 220V country.  How can I test/measure the input range of the adaptor and check whether it can be used with 220V?


texts: How to calculate power from this diagram? (Another one)

texts:
I asked a similar question before, but now with another diagram.
I have a solution but I am not sure if it is right.

First half:
$$i_1(t)=\frac{t}{T}A$$
$$u_1(t)=1V$$

Second half:
$$i_2(t)=\frac{t}{T}A$$
$$u_2(t)=-1V$$

Power:
$$P =
{\int_0^{T/2}( {t \over T}   \,) \mathrm{d} t + \int_{T/2}^T ({-t \over T} ) \, \mathrm{d} t \over T} =
- \frac{1}{4}W$$


texts:
I am trying to solve this problem but I have failed.
These are 2 BJTs:
1.Assume V1=2V, what is the value of VE?
2.Assume V1=-4.5V, what is the value of VE?

Actually I do not understand how to deal with 2 transistors in the same circuit, so any explanation would be very useful.
Thanks.


texts:
Honestly, I have a good deal of questions so this may not be for the faint of heart.

I will do my best to ask them in a logical order with specific language.  I really appreciate the helpful answerers out there.  My questions are related to many aspects of the whole device, so it might help a lot if you actually read the datasheet before and/or after reading my questions.  I will assume you have read it when asking my questions, it will save a lot of space (save the trees, man) and time for reading this. Without further adieu...

Here is a link to the datasheet for the NCS36000 device.

What would the possible purposes be of changing the oscillator frequency?
Would using a voltage regulator to up the outputting VREF voltage (since my PIR sensor might need a higher in voltage) change the values of \$V_{h}\$ or \$V_{l}\$ such that it will ruin the mechanism used to 'detect' a signal from the PIR?  Any other problems with this?
What is a push/pull output as referenced at top of pg. 3?  I am confused as to how this is the output for the device when \$V_{oh}\$ and \$V_{ol}\$ are not mentioned anywhere else.
So am I correct when I say \$V_{ref}\$ powers the PIR, and the OUTPUT of the PIR (when it senses) goes to the OP1_P pin?  How do the pins \$V_{ref}\$ and the OP pins relate?  I am having trouble conceptualizing it from the datasheet alone.
On page 4 it says the LDO Regulator has a nominal voltage reference for the sensor of 2.7V +/-5%. What is my sensor needs 4 or 5Vdc to even power it?
For the window comparator, why would COMP_N ever trigger?  Why would the PIR sense something and spit out a low voltage instead of high?  I know I can just use single pulse mode and either way would give identical signalings, but I'd like to understand as much as possible.
Is the xLED_EN pin active low? Looking at figure 6 the timing diagram at the LED pin sequence it says if LED_EN = 0 (so it allows the LED pin to toggle when motion is detected) the LED goes from hi -> low.
Again, how do clock cycles come into play?  I figure it is within this realm (last two questions-ish, but why might I change such a thing).
Note 10 on page 7 says R4 can be replaced by a potentiometer to adjust system sensitivity, yet this is the only mention of sensitivity.  What am I missing in regard to understanding the role R4 plays?


texts: How to drive a linear actuator in both directions

texts:
I would like to drive in both directions my linear actuator (12VDC, 13A max).
My electronic board outputs two signals (obviously, I also have GND signal):

Forward: +12VDC (2A max)

Backward: +12VDC (2A max)

When I press the forward button, the forward output is +12V, on the contrary, when I press the backward button, I have +12V on the backward output line.

The battery for this system is an AGM battery, 12VDC, 200Ah.

I know that the correct way would be to use a driver, but it is expensive and I do not need lots of functions, I only need to open and close the actuator.

I was thinking to trigger two relays by using the forward and backward signals, but I can't figure out how to connect them in a correct way.

Can you give me some suggestions, please?


texts: Is this MOSFET a good choice? PWM -> FET -> DC Fan

texts:
I am planning on using a PIC microcontroller's IO pin (3.3V Logic) to drive this MOSFET that will drive a 12V DC fan:

MOSFET N-CH 60V 2.7A SOT-23-3

According to the datasheet, there is a diode in the equivalent circuit, is this diode used as a flyback diode, and is it suitable for a 12V DC fan (without an external flyback diode)? Also, how over/underkill am I going with this thing? I haven't used motor control in an embedded system before, so any tips are welcome.

The kind of fan I plan on powering is a simple micro fan.

Thanks,

Mike


texts:
after having googled I would like to Post this question here because I couldn't find reasonable answer.

I have noticed at my University that hardware developers are mostly tending to use SOT Packages. like SOT23, SOT23-5, SOT23-6, Thin SOT Packages in LDOs, Clock Oscillators, etc. I wonder because there are also packages with same number of Pins like SC70 in comparison to SOTs. I would like to know if there is a specific reason my supervisor is favouring SOT Packages or I would be interested to know what advantages / disadvantages do these packages have in comparison to their competetors.

I strict to only SMD packages in context of question.

Thank you for sharing your experiences.


texts:
Here's the circuit I'm working on, it's a robotic stringed musical instrument thing, that uses 6 DC motors and an Arduino Duemilanove -

The resistors are 0.25w 1KΩ
The transistors are TIP122 Darlington PNP
The diodes are N5401

The motors require 3v and 1.17A each, but the Arduino likes to work on about 6v-9v and only a few mA. I'd like to know the easiest way to use a single DC power supply unit (Of any appropriate spec), to power the whole circuit.

Cheers.


texts: In a radio tuning capacitor that consists of semicircular plates , are the plates connected in series or in parallel ?


texts:
Sorry for the amateurish question. I am planning to tap into my car battery's reverse fuse to signal when it's time to receive a wireless signal from a rear-view camera. The camera-feed receiver in my circuit needs a 5V power source, which I want to activate when the reverse lights are on. Normally, the 5V is powering the phone, which receives data from the receiver. Anyway, I was wondering if I designed the circuit correctly.

I have my doubts about the connection to the base of the transistor and whether it will receive any current at all when the reverse lights are on. I know that in parallel circuits current flows through all possible routes from high potential (positive) to low potential (negative), but I am not sure where the negative terminal is for the circuit that includes the transistor. It seems to awkwardly end at the base of the transistor. Would appreciate any thoughts on why this may or may not work.

simulate this circuit – Schematic created using CircuitLab


texts: Simple AM radio - how to modify it so it can work without ferrite rod antenna?

texts:
I am a beginner in electronics and I'm currently the most interested in RF-related topics. I did build simple AM receiver usind good old TA7642 and, after adding small 9V amp, the radio broadcast can be heard across entire house. It works well.

But now I want to modify the circuit so it can use different antennas and coils, so I can change receiver frequency range, RF signal strength etc.

This is the antenna input cirucit part. That's basically default TA7642 setting:

Now tests with different coils and antennas:

Ferrite rod with 2 coils separated magnetically - WORKS.
Ferrite rod with 1 coil, but with additional output in the 1/3 coils length - WORKS. It's interestig that RF signal is taken directly from the coil, without separating it magnetically.
Just a coil (not ferrite), capacitor and external antenna - NOT WORKING. Even though that's the most basic design actually.
3rd case is definetly wrong, I don't receive anything desired but very distorted... FM stations. Capacitor rotating doesn't change anything, adding or removing external antenna doesn't help, too.

Why doesn't it work? How to fix this?

I have a few air coils without ferrite or three outputs. I also have external antennas: one for SW on the balcony, another one (long-wire) for LW. But I cannot use them as the only 1 & 2 designs do work.

Can you help me, please? Thanks!

BTW: If I attach external SW or long-wire antenna to circuits 1 or 2, I can receive tons of shortwave radio stations, but rotating capacitor doesn't allow me to tune in to any station. I understad it as follows: the external antenna gives so strong signal that it overrides what ferrite rod gets. Because of high capacitance of variable capacitor (20 - 500 pF) and/or high inductance of ferrite coil (probably 400 - 500 uH) such radio is totally not selective, so I cannot tune in to anything.
Is this explanation true?


texts: How to store a const string at a memory location in Microcontroller?

texts:
I have two questions

  #define PORTBASE 0x40000000
  unsigned int volatile * const port = (unsigned int *) PORTBASE;
  *port = value; //write to port
  value = *port; // read from port

Can I use the above method to store a value at desired memory
location and access it?
How can I store, for example, a software version information
string(V1.2AG4ML) in the same way at a location?

SPC5 32-bit controller is used.

Regards,
Joe


texts:
I took this motor out of a drier and want to run it.

It has 3 wires:

  Yellow: connected to the capacitor
  Brown: connected to the capacitor other end
  Black: not connected to anything.

Capacitor is 8 uF

I measured:

  Yellow to black measures 40 ohms
  Brown to black measures 40 ohms
  Yellow to brown measures 80 ohms

more photos here:

https://photos.app.goo.gl/m1w3zwpYSZrEr93KA

I tried connecting black to ground and yellow/brown to main and it short circuited my house


texts: A conceptual question about voltage multipliers

texts:
Imagine a micro-controller's pulse output is coupled to a voltage multiplier with many stages such as in the case of a Dickson voltage multiplier. We then can increase the DC "voltage" level of the pulse this way..

But since we still use the micro-controller as supply, unlike in amplifier case we are limited with the micro-controller's pin's max current output right??

So we have a situation where we can increase the voltage but we are still limited with the max current can be driven by the load.

If I understood it right in my above paragraph, what can this be used for? Any useful applications?


texts: Circuit Testing failed (Reverse polarity and Buck-Converter)

texts:
Hello guys,

today I tested my circuit. Its a simple Reverse Polarity Protection Circuit with a Buck-Converter. As I supplied voltagae to my circuit, everything was well (3.5V output). Going higher with the voltage was okay, too. Until I got to ~30V. Then my power supply gone into current limitation.

I think my TVS Diode (which I choosed too small..) gone to Breakdown Volatge and caused a short circuit (is that possible?). I Supplied voltage only to the pins of the Buck but its still not working, so I think something destroyed the buck but exactly what?

EDIT: With "the buck dont work" I mean, when I supply voltage to my circuit, my power supply goes into current limitation because the circuit wants to drain a lot of current. So if I dont supply from J1 and J5 and supply the IC pins of the buck directlyy its the same failure.

Datasheets:
Buck

PMOS

Bipolar TVS

Schottky

Zener


texts: Formula to calculate the isotropic range of a signal

texts: I am wondering, is there a formula to calculate the range of a signal with a given frequency and output power? For example, how do i find the range of a 580khz AM signal on entirely flat terrain with a power of 10 watts, using a perfect isotropic antenna?


texts: Collective Term for (FPGA, GPU, CPU, DSP, NPU)

texts:
I am looking for a collective term for these compute blocks (FPGA, GPU, CPU, DSP,NPU). I found it in some journal but I cant recall. I want to use it in an article I am writing.

P.S I made up to term "compute blocks" to refer to them but there is indeed a generic term for them


texts: What is this Ribbon Cable Connector called?

texts:
Even after extensive scrolling through Google Image Search, I could not find this connector or one similar to it:

I am especially interested in finding the mating connector.


texts: Can continuity test cause component damage?

texts:
In order to test some tracks on a mounted PCB, I would like to use a multimeter for continuity test.

However, then I measured the open-circuit voltage of two multimeters at hand, and the results were:

Fluke 87 V: 7.3 V
Keysight 34465A: 9.4 V

Both have a current limit of 1 mA, but when doing a measurement without connection, it applies the rather high open-circuit voltage.

I was pretty surprised to discover that these widely used high-end multimeters apply an open-circuit voltage for continuity test that is above the absolute maximum ratings of common chips like CMOS 7400-series 3.3-V logic with high impedance inputs, which is for example 6.5 V for TI SN74LVC00A.

Am I being overly concerned here, or is there actually a risk of damaging the components when doing continuity test on mounted PCBs with these multimeters?

Is there any suggestion of how to do continuity test with lower open-circuit voltage?


texts: VHDL: Metastability check for hold time fails

texts:
I'm trying to model an SN74HC573 D-type latch in VHDL to get back into it. Here's what I got so far:

-- simple model of a SN74AHC573 D-type Transparent Latch
library ieee;
use ieee.std_logic_1164.all;

-- entity declaration
entity sn74ahc573 is
    port ( oe_n, le : in std_logic;     -- control signals
           d : in std_logic;            -- data input
           q : out std_logic );         -- data output

    -- TODO: add detailed timing constants
    constant t_pd   : delay_length := 9 ns;     -- Propagation delay
    constant t_w    : delay_length := 5 ns;     -- Pulse duration, LE high
    constant t_su   : delay_length := 3.5 ns;   -- Setup time, data before LE falling edge
    constant t_h    : delay_length := 1.5 ns;   -- Hold time, data after LE falling edge
end entity sn74ahc573;

-- rtl architecture to check metastability
architecture rtl of sn74ahc573 is
    signal intern : std_logic := 'X';
begin

    -- concurrent replacement of behavioral process
    -- TODO: replace with state machine for more precise propagation delays
    intern <= 'Z' when oe_n = '1' else              -- high-impedance state
               d  when oe_n = '0' and le = '1' else -- latch input
               unaffected;                          -- else, nothing happens

    -- check metastability of latch enable signal
    checkMetaStability : process is
    begin
        -- wait for LE falling edge
        wait until falling_edge(le);

        --check pulse width
        assert le'delayed'stable(t_w)
            report "LE pulse width too short!"
            severity failure;

        -- check setup time
        assert intern'delayed'stable(t_su)
            report "Input changed during setup time!"
            severity failure;

        -- check hold time
        wait for t_h;
        assert intern'delayed'stable(t_h + t_su)
            report "Input signal changed during hold time!"
            severity failure;

    end process checkMetaStability;

    -- update output
    q <= intern;

end architecture rtl;

I'm having trouble with the process checking metastability. Checking for pulse width and setup time works, but checking hold time will fail:

-- Test Bench for SN74AHC573 model
library ieee;
use ieee.std_logic_1164.all;

-- entity declaration
entity sn74ahc573_tb is
end entity sn74ahc573_tb;

-- test bench architecture
architecture test_bench of sn74ahc573_tb is
    signal oe_n, le, d, q : std_logic := '0';
begin

    dut : entity work.sn74ahc573(rtl)
        port map ( oe_n, le, d, q );

    stimulus : process is
    begin
        -- start in high-Z mode
        oe_n <= '1'; wait for 10 ns;

        -- WARNING: These signal changes violate metastability
        oe_n <= '0'; le <= '1'; d <= '1'; wait for 4 ns;
            -- violate minimal pulse width
        -- le <= '0'; wait for 1 ns;
            -- violate setup time
        -- d <= '0';  wait for 1 ns;
        -- le <= '0'; wait for 1 ns;
            -- violate hold time
         wait for 1 ns; le <= '0';
         wait for 1 ns; d <= '0';

        -- wait forever
        wait;

    end process stimulus;

end architecture test_bench;

This test bench will "fail" for pulse width and setup time, but not when checking hold time. What am I missing?

I'm using GHDL 0.36-dev on Arch Linux.


texts:
The stm32f4 discovery datasheet DS8626 specifies vil and vih as below

So I have some questions based on the documentation

How do I know that what value VDD is operating at if I use the usb to power the board?
Why are there two Min or Max values for Vil and Vih? Does that have to do with CMOS vs TTL idea? Which one do I choose?
.

Background

I am trying to make a simple circuit where I have a push button and led on a bread board make the led blink with the push button using the pins on the stm32f4. Basically rather than using the push button/led that is available on the board I want to try making the same circuit but just on a breadboard and use the stm32f4 board to process inputs from the push button to get some practice.

So I am confused about how much voltage I need to supply push button vs what the board needs to determine logic levels.


texts: What current should be used to calculated the drop across the diode? RMS current or average current?

texts:
I was designing a power supply, following is the output bridge diode current waveform from LTSpice simulation .

My intention is to calculate the power drop across the diode. What value of current (RMS value or average value of the current) should be taken to find the voltage drop from Forward voltage drop versus current curve of diode.

My basic understanding is to go with the average current, But not sure about the theoretical aspect.


texts: Controlling the power through a heating element?

texts:
I need a 25mm x 30mm 120V 200 watt band heater.

Unfortunately, the only 25mm x 30mm 120V band heaters I have found are 300 watt.

What sort of circuit could I construct or purchase that could regulate the current flowing through a large heating element like that?

Ideally looking for something off the shelf.

I'm used to limiting current (say, through an LED) with a small resistor. I have no clue how to design for something high current like this.

Doesn't have to be adjustable, literally all I want to do is ensure the heating element dissipates 200 watts, not 300. I'm guessing the element is resistive.

My power supply is 250 watts, so I'm not trying to dissipate any power in the control circuit.


texts: Digital gain control with a digital pot?

texts:
I want to make an audio amplifier with digital volume control. I figure that by adjusting the feed back path that I won't change the input impedance and won't affect the frequency response. (other than the gain bandwidth product)

Does the following setup look reasonable?

Would a digital pot be good for this application?

Are there any drawbacks of digital pots that i'm not aware of that would make them undesirable for this application?

simulate this circuit – Schematic created using CircuitLab


texts: Multiplexer with enable at a karnaugh map

texts:
We have multiplexer 2->1 with reverse enable:

(sorry for the child-like graphics)

the function table is the following

e  c  Y

1   X   0

0   0   x0

0   1   x1

I tried to make a karnaugh map, but I don't know if I have to put the enable at it. So it went as something like this:

with the result being y = e'c'x0 + e'cx1

Did I do the map wrong?
Should I exclude the e from it?


texts: Why does Bluetooth Low Energy use 3 advertising channels?

texts: Why are there three advertising channels (rather than two or four, etc)?


texts: Can an XBee in API mode receive data through serial?

texts:
Following the python-Xbee library and an example, I am trying to communicate between 2 XBees

Using XBee S2C
Setup:
Coordinator API=2, running the code in python @ Mac
Router AT mode, running python code @ Mac

Below data sending code runs in API mode at coordinator

#!/usr/bin/python

#this code runs on the xbee coordinator that is set to API mode 2

import serial
from xbee import ZigBee
from xbee.helpers.dispatch import Dispatch
import time

PORT = '/dev/tty.usbserial-A104IC2U'
BAUD_RATE = 9600

UNKNOWN = '\xff\xfe'
WHERE = '\x00\x13\xA2\x00\x40\xF7\x0A\x50'
dataString='Hello\n'

# Open serial port
ser = serial.Serial(PORT, BAUD_RATE)

zb = ZigBee(ser)

#sends data to xbee address
def sendData(address, datatosend):
    zb.send('tx', dest_addr_long = address, dest_addr = UNKNOWN, data = datatosend)

#test data sending method
while True:
    try:
        sendData(WHERE, dataString)
    except KeyboardInterrupt:
        break

zb.halt()
ser.close()

And in the router (AT mode) I run below code

#!/usr/bin/python

import serial

#router port
PORT = '/dev/tty.usbserial-A104IAUX'
BAUD_RATE = 9600
ser = serial.Serial(PORT, BAUD_RATE)

#myaddress - its the router
ack='0013A20040F70A50'

while True:
    incoming = ser.readline().strip()
    if incoming != '0013A20040F70A50':
        print '%s' % incoming
        ser.write('%s' % ack)

ser.close()

This works fine and I see the output 'Hello' on the router side python terminal at Mac. Now I also need to receive data in the coordinator side. So I do this in the coordinator code - after sending, it also reads the serial and prints data

while True:
    try:
        sendData(WHERE, dataString)
        incoming = ser.readline().strip() #added to receive serial data at coordinator
        print '%s' % incoming
    except KeyboardInterrupt:
        break

But as soon as I add those two lines, the communication stops. Is this because coordinator is in API mode and can't receive in serial? And I have to write the receive code for API mode? Any suggestion?


texts: Balancing Rise and fall times at input and output in CMOS Design

texts: How do I make sure that my rise and fall times are balanced between input and output in a CMOS design?


texts: How do I run a 12V 450mA DC motor using a 12V 1A DC adapter? It is for a small water pump for one of those decoration waterfalls. Should I simply add a (R=V/I) resistor? If so, what is the approximate R value I should go for? Also, where should I put the resistor in the circuit?


texts:
I have a piece of code that performs self-test on various components of the board, like MCU, BLE, IMU, OLED, flash memory,  and etc.

What I'm trying to make is a document that would represent what these tests cover, or when you run the IMU test and it says "PASS", what does that actually mean. Or going from another direction, if I want to test BLE/OLED/MCU, what set of tests I need to run to have confidence that it's all working as expected.

Now, I know how to represent this data in a text format or in some table but even when I try my best this information gets too convoluted, confusing and looks like someone just threw up a bunch of data and you need to make sense of it.

What I'm looking for is something like industry standard way of representing this information, or best practice that would allow someone to take a look at a document and say: "Yes, this BLE test ensures that my chip is soldered properly, crystal is present and oscillating, firmware is running fine but it doesn't test the actual BLE antenna and tuning/matching component". Or from bottom up, someone says "I wan't to test that IMU is working properly, so I need to run these set of tests and they will ensure that chip is soldered properly, GPIOs are working, and device is registering 1G along X/Y/Z axis"

Any suggestions, examples or pointers on what to look for would be very appreciated.


texts:
It would work that way:

An IR sensor is used as input, if it receives some IR signal, the input is 0.
If it detects that input, it should output some voltage.
If it detects that input again, iy should make the output 0.

(Basically, if it detects something on input, it should reverse the current output.)
It's pretty easy to make it using Arduino, but I think it's a waste of hardware. Is there a way to make it using only electrical components?


texts: Impedance matching in RF Circuit - Determine the required Q

texts:
I am working on an RF project and I notice that many sources I have used, recommend using a pi network (CLC), such as the image below, to impedance match the RF trace to the antenna.

I have a really short distance between my RF output and antenna and the impedance is controlled the entire way.

If the antenna impedance is well matched to my characteristic impedance, can I then simply ignore my pi network, open up the caps, and short the inductor ?

If the antenna impedance is does not match, and requires tuning, I've been shown this website (https://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html)

When I enter I know, as seen below, there is one parameter I do not know how to determine - Desired Q. The default is set to 3. In this example, I set the source and load to be 50 ohms.

How do I select an appropriate Q ?
What is the general workflow when working with RF that requires impedance matching or tuning ?


texts: P-Channel Mosfet Gate Drive Topology with 20V Vgss Protection?

texts:
NOTE: This question concerns topology - circuit values are omitted intentionally.

I'm strongly considering the use a P-Channel mosfet to serve as a high-side switch within a circuit.

All P-Channel mosfet options with low Rds(on) (10mOhm or less) have a Vgss limit of 20V or less. This circuit will operate to Vdss of -30V. Driving the gate between Vin and Ground will exceed Vgss. I have not found a gate driver IC that will accommodate this factor.

I've included a schematic below for a topology that I'm considering. The topology uses a smaller TTL N-Channel mosfet paired with an bipolar totem-pole driver to levelshift the signal and drive the P-Channel Switch. The Emitter Follower is biased to the regulated output of the buck converter (14V above ground) which puts Vgss between Vin and 14V - this will be within Vgss spec for most P-Channel mosfet options.

My question: Is there a better option or topology for this circuit? A solution that uses a Gate Driver IC will be well received. A better topology which uses discrete components will be appreciated as well.

Some circuit details below.

The circuit must operate when attached to either a 12v system or a 24V system. Fully charged 24V systems can achieve voltages as high as 30V - this is the upper Vin limit.
When the circuit is connected to a 24V system, the mosfet will be switched at 250KHz as part of a buck converter to regulate voltage to 14V.
When the circuit is connected to a 12V system the mosfet will be fully on. This is why the P-Channel mosfet is desirable for this application.

BONUS QUESTION: How would you add reverse polarity protection to the circuit topology below?


texts: Program memory question (working dispite insufficient memory)

texts:
I am writing this program to a Microchip PIC.

 char * we_are_display = "hello";
 char ahimouz[2];
 sprintf(ahimouz,"%s %s",we_are_display,"5");
 WriteStringToLCD(ahimouz);

This program works despite the memory allocated to array ahimouz is only 2 bytes. Why is that so?


texts: Why there is a grounding on device with two prong cord?

texts: I am curious why there is the grounding on a device with two prong cord? As far as I know there should be 3 prong cord to make the grounding working.


texts: parallel connecting 24v 1500mah NIMH battery packs and how to charge

texts:
After several of searches on the internet for information about charging NIMH batteriers, i feel the need for some clarification. I've gotten my hands on a bunch of battery packs. Each battery pack is 24V 1500mah, they are built on 20 x 1.2V 1500mah GP AA batteries.

My goal is to parallel connect 10 packs achieving 24v 15A. Until recently i thought this was easy and safe.

questions:

Is it safe to connect and discharge 10 packs in parallel?
How is it possible to charge all 10 packs at the same time? (wall plug)
Is it possible to use a 24V PMM solar panel
Do i need a cutoff when voltage is getting low?

Thanks in advance :)


texts: Can I store lawnmower Li-Ion batteries in cold storage during the winter?

texts:
I purchased a Li-Ion battery powered lawnmower. I'm not entirely sure what the actual exact battery chemistry is, but I believe it is not lithium iron phosphate due to its voltage typical of non-LiFePO4 batteries.

I was advised by a relative that I shouldn't store the batteries of the lawnmower in cold storage during the winter. The temperatures can easily get below -20 degrees Celsius here during the winter.

However, when thinking about this again, electric cars use lithium ion batteries too, and they can be used in very cold temperatures. Not only stored, but also actually used (for example, you can charge your electric car at any temperature). However, electric cars sometimes use a slightly different battery chemistry, like lithium nickel cobalt aluminium (NCA) oxide for Tesla.

Is it in general possible to store a lithium ion battery with unknown exact chemistry in very cold temperatures, if the charging and use happens at near room temperatures? For practicality, I was planning to store them fully charged (minus whatever minor self-discharge they may have), and at most less than a year at a time, as the next summer I again require the lawnmower.


texts: Designing a simple CW transmitter/receiver

texts:
I'm interested in building my own radios for use on the air. I'm still rather new to electronics so I'm looking for simpler projects that I can build to learn on the way, and I'm thinking that a CW transmitter and/or receiver would be appropriate (unless someone wants to tell me otherwise?). I've been reading the ARRL Handbook and "Experimental Methods in RF Design" trying to find the information needed to build one of my own but to no avail. While there are circuit diagrams available in those texts, even the simplest ones are too much for me to understand (I did read the accompanying text) and I feel like if I were to just build it and have it work, it wouldn't progress my understanding of it at all and I'm not confident in my ability to build something large without error if I don't have the possibility of testing the smaller subcircuits individually.

Looking at the block diagram below, I decided to look into the workings of an oscillator, since it doesn't need any other parts of the radio to function, so it'll be easier to test on its own. I understand how a simple RLC circuit behaves (mathematically), but when it's combined with other components to make a complete oscillator, that's when I get lost.

"Experimental Methods in RF Design" mentions the NE602 IC which has an oscillator and a mixer, making it easier to make a complete radio. Another way I could go is using this for the radio and work on the amplifier and antenna, then replacing the IC with discrete components, but I couldn't find any circuits using this IC that are simple enough that I can confidently build it error-free.

Any advice on the path I should take (be it one I've mentioned above or not) and useful resources to get me started or get past the barriers I'm facing?

Thanks.


texts:
I've been researching on backup power system for embedded devices that must run uninterrupted on mains or backup.

I was trying to study an energy meter board i have with me and came upon a circuit i was unable to analyse completely.

The system is an energy meter running on TI's MSP430F4793. The circuit runs on 3.2VDC, and seams to use the MSP's SVS module (Supply Voltage Supervisor) to monitor battery voltage, because the a voltage divider from the battery goes to the input of the SVS module (SVSIN). pin1 of Q1 is fed with 4V from the main power supply before it is regulated to 3.2volts, while pin2 of Q2 is fed from the backup battery rated at 3.6Volts.I want to have an understanding of how the circuit works, but i cannot see the name of componets Q1 and Q2.

When on mains power, the

I got the following readins for Q1:
pin1 reads 4Volts,
     pin 2 reads 3.6Volts, and
      Pin3 reads 3.2Volts

FOR Q2:
pin1 reads 3.6Volts, pin2 reads 3.6V and pin3 reads 3.2V

On battery power, i get the following readins:
Q1:
pin1 reads 2.6Volts,
     pin 2 reads 3.0Volts, and
      Pin3 reads 3.0Volts

Q2:
pin1 reads 3.0Volts,
     pin 2 reads 3.6Volts, and
      Pin3 reads 3.0Volts

From the figure bellow, and the voltage readings above, can anyone determine what the Q1 and Q2 might be and how this circuit switches power?

Q1 is pulled up to 4V by the resistor marked 205

edit
I believe the circuit is designed to switch between mains voltage and battery backup. the 4VDC which comes from a regulator is dropped to about 3.2V via a diode which then connects to VCC. components like indicator LEDS, optical communication and relays on the circuit are fed from the same 4VDC via a separate diode so they are not powered by the battery when mains is not there.


texts: Cermet potentiometer temperature coefficients

texts:
I'm engineering a system that is temperature-sensitive, between ~-10-30C. I've moved to using cermet potentiometers because of their sub-200PPM/C temperature coefficients.

If I wire such a pot with the extremities at gnd and Vcc assumed to be temperature-invariant, and take the wiper as a Vref, then can I assume that the "lower" and "upper" parts of the pot on either side of the wiper have equal temperature variance and so Vref's temperature variance will be nearly zero?


texts: STM32 SPI: strange behavior on empty TXFIFO (previous bytes history?)

texts:
The following code configures and enables SPI2 as slave on my STM32F303RE board, writes 0xAA, 0xBB, 0xCC, 0xDD bytes to DR register and loops in a while(1):

/* Enable clocks for GPIOB (SPI2 pins) and SPI2 peripheral. */
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOB, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_SPI2, ENABLE);

/* SPI pin mappings. */
GPIO_PinAFConfig(GPIOB, GPIO_PinSource12, GPIO_AF_5); /* SPI2_NSS */
GPIO_PinAFConfig(GPIOB, GPIO_PinSource13, GPIO_AF_5); /* SPI2_SCK */
GPIO_PinAFConfig(GPIOB, GPIO_PinSource14, GPIO_AF_5); /* SPI2_MISO */
GPIO_PinAFConfig(GPIOB, GPIO_PinSource15, GPIO_AF_5); /* SPI2_MOSI */

GPIO_InitTypeDef gpio_init_struct =
{
    .GPIO_Mode = GPIO_Mode_AF,
    .GPIO_OType = GPIO_OType_PP,
    .GPIO_PuPd = GPIO_PuPd_DOWN,
    .GPIO_Speed = GPIO_Speed_50MHz
};

/* SPI NSS pin configuration. */
gpio_init_struct.GPIO_Pin = GPIO_Pin_12;
GPIO_Init(GPIOB, &gpio_init_struct);
/* SPI SCK pin configuration. */
gpio_init_struct.GPIO_Pin = GPIO_Pin_13;
GPIO_Init(GPIOB, &gpio_init_struct);
/* SPI MISO pin configuration. */
gpio_init_struct.GPIO_Pin = GPIO_Pin_14;
GPIO_Init(GPIOB, &gpio_init_struct);
/* SPI  MOSI pin configuration. */
gpio_init_struct.GPIO_Pin = GPIO_Pin_15;
GPIO_Init(GPIOB, &gpio_init_struct);

SPI_InitTypeDef spi_init_struct =
{
    .SPI_Direction          = SPI_Direction_2Lines_FullDuplex,
    .SPI_Mode               = SPI_Mode_Slave,
    .SPI_DataSize           = SPI_DataSize_8b,
    .SPI_CPOL               = SPI_CPOL_Low,
    .SPI_CPHA               = SPI_CPHA_1Edge,
    .SPI_NSS                = SPI_NSS_Hard,
    .SPI_BaudRatePrescaler  = SPI_BaudRatePrescaler_2,
    .SPI_FirstBit           = SPI_FirstBit_MSB,
    .SPI_CRCPolynomial      = 7
};

SPI_I2S_DeInit(SPI2);
SPI_Init(SPI2, &spi_init_struct);
SPI_CalculateCRC(SPI2, DISABLE);
SPI_TIModeCmd(SPI2, DISABLE);
SPI_NSSPulseModeCmd(SPI2, DISABLE);

SPI_Cmd(SPI2, ENABLE);
SPI_SendData8(SPI2, (uint8_t) 0xAA);
SPI_SendData8(SPI2, (uint8_t) 0xBB);
SPI_SendData8(SPI2, (uint8_t) 0xCC);
SPI_SendData8(SPI2, (uint8_t) 0xDD);

while(1) { }

With a master that requests 2 bytes per chip-select, the master receives:

0xAA 0xBB
0xCC 0xDD
0xAA 0xAA -----> TXFIFO should be empty here, why not "0x00 0x00"?
0xAA 0xAA
0xAA 0xAA
0xAA 0xAA
0xAA 0xAA
0xAA 0xAA
0xAA 0xAA
......... (0xAA 0xAA infinite times)

I would have expected that the master receives "0x00 0x00" after TXFIFO becomes empty. Why do I get "0xAA 0xAA" continuously instead? I couldn't find something that would point to such behavior in the manual.

UPDATE 1

Waiting for the transactions to finish just before the while(1) and writing zeros on the SPI afterwards, like this:

while(SPI_GetTransmissionFIFOStatus(SPI2) != SPI_TransmissionFIFOStatus_Empty) { }
while(SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_BSY) != RESET) { }

#define ZEROS_CNT   (1)
for(int i = 0; i < ZEROS_CNT; i++)
    SPI_SendData8(SPI2, 0);

while(1) { }

renders the following master behavior for different values of ZEROS_CNT:

ZEROS_CNT = 0 => master receives after TXFIFO is empty: 0xAA infinitely
ZEROS_CNT = 1 => master receives after TXFIFO is empty: 0x00 1 times, followed by 0xBB infinitely
ZEROS_CNT = 2 => master receives after TXFIFO is empty: 0x00 2 times, followed by 0xCC infinitely
ZEROS_CNT = 3 => master receives after TXFIFO is empty: 0x00 3 times, followed by 0xDD infinitely
ZEROS_CNT >= 4 => master receives after TXFIFO is empty: 0x00 infinitely

It looks as if the SPI peripheral has some kind of history of what was written in the TXFIFO and when it becomes empty, it sends bytes from that history.

UPDATE 2

It behaves the same irrespective of how many bytes the master requests in a single chip-select. I have tried requesting 1, 2, 4 and 5 @ a time.


texts: What is this radio signal coming from my phone?

texts:
I've built myself a crude EMI probe:

I then pointed it at the top part of my phone when the phone was powered on, and I saw the following waveforms on my scope.

First off, there are spikes every 525ms:

These spikes consist of exactly 6ms of some kind of waveform:

Zooming in on the gap shows the following short-long-short-long-long-long ...thing. Also interesting to note is that the gaps are exactly 3us.

And then if I zoom further in on the rectangular part of the wave, I see the following 13.55MHz sine wave:

What's going on here?


texts:
I just got my first SSD and on the back of it there are the common RoHS and No Trash logos but there is also an FCC logo.

Why would the FCC logo be on my SSD if it doesn't have any wireless radios in it?


texts: Question about transient behaviour in op-amp circuit

texts:
Consider the following circuit. The switch closes at \$t=0\$. The voltage source is \$V_0e^{-t/t_0}\$. We assume to op is ideal, so there's no voltage difference between the input terminals and no current through the input.

Approach 1

For \$t > 0\$ we have immediately that \$V=\frac{R}{R+R}V_0e^{-t/t_0}=\frac{1}{2}V_0e^{-t/t_0}\$.

Let \$i_L\$ be the current through the inductor from \$V_{out}\$ to \$V\$. We see that \$i_L = V/R = \frac{V_0}{2R}e^{-t/t_0}\$. We have \$V_{out}-V=L\frac{di_L}{dt}=-\frac{V_0L}{2Rt_0}e^{-t/t_0}\$, and we find \$V_{out}=V-\frac{V_0L}{2Rt_0}e^{-t/t_0}=\frac{V_0}{2}\left(1-\frac{L}{t_0R}\right)e^{-t/t_0}.\$

Approach 2

Let's analyse the circuit in the Laplace domain. We thus let the voltage source be \$V_0e^{-t/t_0}H(t)\$ in the time domain, where \$H(t)\$ is the step function. The Laplace transform of this is \$V_0\frac{1}{s+1/t_0}\$.

In the same way as before, we find \$V(s)=\frac{V_0}{2}\frac{1}{s+1/t_0}\$. We also have \$V_{out}-V=\frac{sL}{sL+R}V_{out}\$, whence \$V_{out}=\frac{sL+R}{R}V=\frac{V_0L}{2R}\frac{s+R/L}{s+1/t_0}=\frac{V_0L}{2R}\left(1+\frac{R/L-1/t_0}{s+1/t_0} \right).\$
Taking the inverse gives \$V_{out} = \frac{V_0L}{2R}\delta(t)+\frac{V_0}{2}\left(1-\frac{L}{t_0R}\right)e^{-t/t_0}.\$

Questions

Apparently, we pick up a delta-distribution with the second approach. Obviously, this cannot occur in a real circuit, so I assume the problem somehow lies in our assumptions about ideality of the OP?

Is it then in general true that we cannot analyse transient behaviour of ideal OP circuits in the Laplace domain? (Or rather, if we do so, we have to neglect all non-physical terms?).

simulate this circuit – Schematic created using CircuitLab