texts: What to use for logic control circuit without Programming?

texts:
I need to design a digital combinational logic circuit for control a small scale industrial product which normally uses mechanical relays.  There are only few LEDs as indicator and few digital output to trigger actuators. It is very simple task with Arduino or other microcontrollers but company doesn't want any programming. I did it with logic gates but also looking for alternatives for more scalable solution.
working principle is as following:
There are main switch, door switch, temperatur sensors, pressure sensors, motors and indicators.
When door is open, motors should start. This is done with trigger signal to motor controller. Necdessary conditions are: main switch is on, temperature is in range, pressure is in range and door is open.
Another function is to heat up blowing air. This is done with cable. Switches cut or conenct main power. Here alsopre-conditons are same.
Indicator lights shows if motors are working or not. If there is overpressure or not, if temperature is too cold or not.
Sensors are also just a simple on/off switch,
Here is the basic system. This solution is tested and works well but better way could be
On the photo, it is the other system.


texts:
I'm looking for a low cost (less than $100) board with a PCI Express (x1) interface and with some kind of a programmable CPU that can use that interface. I don't need anything fancy, just something that can do PCI Express for some experiments but I can't build the board myself.

Does anybody know where I can get such a board?


texts: Re-programming button found at thrift store

texts:
I found this cheap button at a thrift store and want to change the sound it plays when you press it; currently it plays through a cycle of around 10 audio clips, about 4 seconds each, each time you press it (one four second clip each press). I’m wondering if anyone has ever tackled anything like this?

There’s a very simple circuit where everything of interest looks to be on a chip on board, however it does look like there are two points on the PCB meant to interface with. I have a mid-low level understanding of small electronics, know how to navigate arduino and have a basic arsenal of tools such as voltmeter, soldering iron, etc.

Anyone know how to start here? Maybe removing the resin if noone has seen anything like this?


texts:
I'm trying to find a way to connect PCB boards edge-to-edge so that I can make a "train" of PCB boards in a row.

It seems to me that this should be straight forward to do using a a female to female edge connector, but when I've looked for such a beast I've only found one solution that's both overly large and overly expensive (http://www.digikey.ca/product-detail/en/EAC10FSLN/S9348-ND/2618449?cur=USD).

Any ideas how I can best accomplish this?


texts: Is this resistor necessary for protection?

texts:
I would like to incorporate this circuit in my design so that I could use a low current capacity slide switch to control the 2A current of a Li-poly.

Now, I understand the purpose of having two PMOS for bidirectional current control as discussed here and the purpose of the zener diode D2 for clamping the gate voltage to a voltage below the maximum allowable voltage of the gate as discussed here.

Finally, the BJT Q3 allows for controlling the gates of the two PMOS through a GPIO pin.

But what is the purpose of R3 in this circuit? (Can it be ommited?)

EDIT: Of course, how did I not see that from the start?
To be honest it seemed strange to me that R3 was pulled up to the path between Q1 and Q2 rather that to Vin , but now I understand that it is only between Q1,Q2 that one can be sure there is a path to the supply, since the circuit works biderectionally (i.e if voltage was applied from Vout and R3 was pulled up to Vin, the top end of R3 would be floating).

Thanks for the replies


texts: Proteus Ares Layout - how do I reduce a 4 layer board to 2 layers?

texts:
I am working on a 4 layer board and I want to eliminate the 2 inner layers. Problem is that the autorouter never seems to get the message.

I have set layer pairs as top copper and all the others as bottom

In "Set Layers Usage" I have unticked everything

What have I missed?


texts:
My SIM800C, feeded directly from a 4.0V Li-ion battery (or once, from a Delta bench PSU) through a 1500 µF capacitor, instantly turns off when it wants to join to my 2G+ European network (e.g. in EGSM_MODE) and that's why I want to upgrade its firmware.

I downloded the proper upgrade tool along with the correctly sized firmware and with a CP2102 USB-to-UART converter I wanted to start the process.

CP2102 works both under Linux and Windows, I tried it with a GPS module.

Wiring:

CP2102  SIM800C  Battery
  RX      TX
  TX      RX
          VCC       + (through a 1500 µF capacitor, parallel)
          GND       -
        PWRKEY      - (for 2 seconds)

After I started the upgrade process, powered on the device, and grounded PWRKEY, the STATUS pin went dark but nothing happens. The updater is still in its "Waiting" phase. The situation is the same with the Linux command line firmware updater.

How can I upgrade its firmware or make it to connect to my network some other way?

Further resources I read through:

SIM800C firmware upgrade notes
SIM800C AT commands documentation
SIM800C hardware design

The original, non-firmware upgrading wiring to an Arduino Nano:

Here, VBATT is 4.0V, and R2 and R3 are necessary to keep the RX channel below 2.8V. I use the USB connection to communicate with the module. Without the USB attached to PC, the problem doesn't disappear.

I tried to connect to network with two SIM800C and two SIM800L modules (they have the same breakout pins). SIM800C tends to turn off immediately after 7 blinks while SIM800L restarts in this case. In case of SIM800L I can retrieve the operators successfully with AT+COPS=? before it would restart itself. When either one is set to a wrong frequency on which my operator doesn't transmit or has its phone functionality disabled (AT+CFUN=4) they don't turn off/restart themselves.

The Arduino Serial library I communicate with the SIM module is AltSoftSerial because of its reliability (besides the Chinese CH341-UART Converter found on the Arduino board itself).

I tried the small spring antenna (pictured above, soldered) and a really heavy one, too.

Way to the solution

As SamGibson correctly pointed out, the problem is with power supply. The first measurement with an oscilloscope shows that the power from 4.1V battery (marked with yellow) drastically drops to 3.13V (at ③) right before the module turns off.

The problem is the same with a power supply unit (VCC is noisier due to the fact that power comes from the network). In the next picture colours denote the following lines:

Yellow: VCC, 4.1V
Green: Tx of the SIM module
Blue: PWRKEY
Red: Rx of the SIM module

This full picture shows that at 0s, after an Arduino reset, the Serial library is initialised then PWRKEY goes down for 1.2s turning the module on. From that point a slight power drop occurs and at about 15.5s (after 7 blinks) the module turns off after a power drop to 3.04V (marked with ⑤).


texts: Why does medical ultrasound use pulses instead of chirps?

texts:
My background is in radar where it's quite common to use chirped excitation signals (i.e. pulse compression).
I have noticed that this method seems to not be used in medical ultrasound. Why not?


texts: Use 555 Timer Voltage Doubler to Increase Range of Transmission

texts: I have seen a number of 555 timer voltage doubler circuits. I am building a fm radio transmitter like this one:  I understand that the higher voltage the farther the transmission range. Would this doubler suit my purpose. Also would it drain the battery quicker assumming a four AA supply.  Also, could I replace the 1n4004 diodes with 1n4001 diodes?


texts: Help to identify voltage regulator from markings

texts:
I have a regulator on an Arduino Mini Pro board (Chinese clone) which should be a 3V3, but it seems it's a 5V one (by measured voltage). The markings on the component are BALG. Does anyone know what it is?

Edit: have added a picture of the board. I need a 3V3 one because I have a communication board that requires that voltage.


texts:
I'm testing my first ever PCB design, which is based on an ATMega328, and I've come across some undesirable behavior with the UART:

When I have the UART connected to my computer through a FTDI USB cable, it works perfectly, yet if I detach the cable from the PCB, I can send input on the PCB's Rx line just by touching both Rx and ground with one fingertip at the same time.

I've actually had an issue with fingers causing bad inputs before, and the answer to that was that I had floating voltages.

Of course, the Rx/Tx lines, when they are not connected to anything, would be floating too, which I think is causing the same issue here.

I really need this to be reliable -- in particular, I would like there to be no input on the UART when there isn't really anything sending input.

Two questions, then:

What could be causing this?
What should I do to fix it? Pull-up on the Rx line?

Further information: this is how I was testing.

#include <avr/io.h>

#define USART_BAUDRATE 9600
#define F_CPU 16000000UL
#define UBRR_VALUE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)

#define pin (PC3)

void initUART(void)
{
    // Set baud rate
    UBRR0H = (uint8_t)(UBRR_VALUE >> 8);
    UBRR0L = (uint8_t)UBRR_VALUE;
    // Set frame format to 8 data bits, no parity, 1 stop bit
    UCSR0C |= (1 << UCSZ01) | (1 << UCSZ00);
    //enable transmission and reception
    UCSR0B |= (1 << RXEN0) | (1 << TXEN0);
}
void sendUARTByte(uint8_t data)
{
    // Wait for byte to be transmitted
    while (!(UCSR0A & (1<<UDRE0))) { }
    // Transmit data
    UDR0 = data;
}
uint8_t receiveUARTByte()
{
    // Wait for byte to be received
    while (!(UCSR0A & (1<<RXC0))) { }
    // Receive data
    return UDR0;
}
int main(void)
{
    uint8_t input = '!';

    DDRC = _BV(pin);
    PORTC = 0;

    initUART();
    while(1)
    {
        PORTC |= _BV(pin);
        sendUARTByte(input);
        input = receiveUARTByte();

        PORTC &= ~_BV(pin);
        sendUARTByte(input);
        input = receiveUARTByte();
    }
}

Essentially all it's doing is toggling PC3 (= pin) whenever there's any input on the UART, and just mirroring the input back to the output.

It works just fine when connected to my computer, but then if I detach the Rx line and move the ground line to another pad (so that I can easily touch the Rx and ground pins at the same time), I still get the pin toggling at a high frequency, but I don't get any output back to the computer (even though the Tx and ground lines are still connected).

Here's the relevant part of the schematic as well:

The UART is in the center left.


texts: Adding multiple thermal relief spokes to a large pad in Mentor-PADS

texts:
Regarding Mentor PADS Layout software (v9.5)...

I have a large rectangular pad (the tab on a power FET) which is surrounded by a large copper pour (for current and thermal capacity).

When I pour the copper, by default I am given four thin thermal reliefs at the corners of the pad.  I want to have more thermal relief spokes in order to promote thermal conductivity into the copper pour and reduce electrical resistance.  The FET will be getting warm during use (switching around 4 Amps at various frequencies).

I cannot seem to change the thermal relief settings, how can this be achieved?

I have tried the following...
Select the pad and go to Properties...Pad Stack dialog.  Then select Pad style: Thermal, click the rectangle icon, then setting the values I want.  The preview window shows exactly what I want but selecting OK and exiting the dialog seems to have no effect on the pad's thermals.  Going back to that dialog a second time shows that the settings that I asked for ARE remembered but apparently never applied to the actual design.

I have tried unpouring and repouring the copper but it always remains on the default thermal settings (4 at the corners).

How to I make these changes?


texts:
I have made a simple thermostat for controlling a 12V heater. The temperature range can be from 0 F to around 190 F.  For some reason when the displayed temperature on my LCD goes from 99 to 100 everything is fine but if it goes back down from 100 to 99 the value ends out being 990. I think this is something to do with the rounding in my Thermistor Temp calculation.
Any thoughts?
Code posted below.

 /*
    The circuit:
 * 5V to Arduino 5V pin
 * GND to Arduino GND pin
 * CLK to Analog #5
 * DAT to Analog #4
 * BUTTON to Analog #2
 * Thermistor to Analog #3
 * Heater to digital #7
*/

// include the library code:
#include <Wire.h>
#include <LiquidCrystal.h>
#include "OneButton.h"
#include <EEPROM.h>

LiquidCrystal lcd(0);
int heater = 7;       // heater is connected to pin 2
OneButton button(A2, true);
float settemp;
unsigned long currentTime;
unsigned long loopTime;

void setup()
{
  currentTime = millis();
  loopTime = currentTime;
  EEPROM.read (1); // make the eeprom or atmega328 memory address 1
  Serial.begin(9600);
  // link the doubleclick function to be called on a doubleclick event.
  button.attachDoubleClick(doubleclick);
  button.attachClick(click);
  pinMode(heater, OUTPUT);                       // Set the Heater Valve pin as output
  lcd.begin(16,2);
  delay(1000);
  lcd.setBacklight(HIGH);
  delay(1000);
  lcd.setCursor(0,0);
    lcd.print("  D.W. VEGGIE");
  lcd.setCursor(0,1);
    lcd.print(" BURNER SYSTEMS");
  delay(4000);
  lcd.clear();
  delay(1000);
  lcd.setCursor(0,0);
    lcd.print("  CENTRITHERM");
  lcd.setCursor(0,1);
    lcd.print("     V1.0");
  delay(4000);
  lcd.clear();
  delay(1000);
  lcd.setCursor(0,0);
    lcd.print("SET TEMP     F   ");
  lcd.setCursor(0,1);
    lcd.print("OIL TEMP     F   ");
}

double Thermister2(int RawADC) {
  double Temp2;
  Temp2 = log(((10240000/RawADC) - 10000));
  Temp2 = 1 / (0.001129148 + (0.000234125 * Temp2) + (0.0000000876741 * Temp2 * Temp2 * Temp2));
  Temp2 = Temp2 - 273.15;           // Convert Kelvin to Celcius
  Temp2 = (Temp2 * 1.8) + 32;    // Convert to F
  Temp2 = round(Temp2);
  return Temp2;
}

void loop()
{
  currentTime = millis();
  settemp = EEPROM.read(1); // read the settemp on the eeprom
  button.tick();
  if(currentTime >= (loopTime + 500)){
    double Temp2 = Thermister2(analogRead(1));   // read Thermistor
    if (Temp2 < settemp) digitalWrite(heater, HIGH);      // turn heater on
        else if (Temp2 >= settemp) digitalWrite(heater, LOW);  // turn heater off
    lcd.setCursor(9,1);
    lcd.print(Temp2,0);
    loopTime = currentTime;
  }
  lcd.setCursor(9,0);
    lcd.print(settemp,0);
  EEPROM.write (1,settemp);
  delay(10);
}

// this function will be called when the button was pressed 2 times in a short timeframe.
void doubleclick() {
   settemp --  // remove one to the settemp, the settemp is the ideal temperature for you
   ;
} // doubleclick

// this function will be called when the button was pressed 1 time in a short timeframe.
void click() {
  (settemp ++);  // add one to the settemp, the settemp is the ideal temperature for you
} // click
// End


texts:
In the following circuit

When I simulate with ltspice, why do I get 29.6 mA in Ic with Ib = 100uA ? I'd expect it to be 10 mA, according to the example in the Malvino book, chapter 6.

When R1 = 1K, I get the 10 mA.


texts: Pin should be lock for sample A warning in Pic

texts:
In an ADC i'm trying to configure for a pic PIC 32MX470F512LT its giving me a warning, that like the title says, it's that the pin should be locked for sample A.

I don't know what it's the sample A in the warning.

What is the cause of that?


texts: How to properly send stop condition when using DMA with I2C?

texts:
I'm using DMA transfer to get 1024 bytes from master (STM32F407VG) to slave OLED screen (SSD1306). The library I'm using does this:

extern void DMA1_Stream4_IRQHandler(void)
{
    // I2C3 DMA transmit completed
    if (DMA_GetFlagStatus(DMA1_Stream4, DMA_FLAG_TCIF4) != RESET)
    {
        // Stop DMA, clear interrupt
        DMA_Cmd(DMA1_Stream4, DISABLE);
        DMA_ClearFlag(DMA1_Stream4, DMA_FLAG_TCIF4);
        I2C_DMACmd(I2C3, DISABLE);
        TM_I2C_Stop(I2C3); // send i2c stop
    }
}

But I read that DMA usually finishes before I2C finishes transmitting last byte and if you stop it (TM_I2C_Stop(I2C3)) there the last byte is never transmitted.
So I read on StackOvf that the right way may be to use separate interrupt for I2C and send stop condition there. So I tried:

I2C_ITConfig(I2C3, I2C_IT_BTF, ENABLE);
I2C_ClearFlag(I2C3, I2C_FLAG_BTF);
// Set interupt controller for I2C
NVIC_InitTypeDef NVIC_InitStructure;
NVIC_InitStructure.NVIC_IRQChannel = I2C3_EV_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);

and the handler:

extern void I2C3_EV_IRQHandler(void)
{
    if (I2C_GetFlagStatus(I2C3, I2C_FLAG_BTF) != RESET)
    {
        TM_I2C_Stop(I2C3); // send i2c stop
        I2C_ClearFlag(I2C3, I2C_FLAG_BTF);
    }
}

but the handler never gets called and program gets stuck because it can't send any data through I2C anymore because it says its busy. Now Im starting to think that BTF might not be the right interrupt event, although it says in documentation:

  Master transmitter: In the interrupt routine after the EOT interrupt, disable DMA requests then wait for a BTF event before programming the Stop condition.

But blocking the entire CPU in interrupt routine until I2C finishes seems a little silly, especially when there is BTF interrupt available.
What is the correct way of calling the I2C and interrupts to avoid truncating the last byte?


texts:
I am teaching a course in digital communication and I want to show students how different line coding schemes are implemented in Hardware. For codes like NRZ-L, NRZ-I, manchester, I found circuits based on comparator, logic gate and flip-flops, but for polar RZ, I didn't find anything (may be I didn't search well). So I tried to come up with a circuit myself which is shown below:

The output generates Polar RZ code according to simulation.
My question is: Are there any better and simple circuits to implement Polar RZ code?


texts: How does a capacitor blocks low frequency signal? Please explain it without the impedance formula?

texts:
I know that a capacitor blocks DC because at some point of time it gets charged to the applied voltage. The charge which is accumulated on the plates provide an opposite electric  field to that provided by the DC supply thus... no more current (or charge accumulation) takes place and further DC is blocked.

While in AC the capacitor is subjected to changing polarities and thus it keeps on charging/discharging according to the AC supply frequency.

My question is why is it that capacitor blocks AC at low frequencies, since it also is AC only and is changing polarities at a lower rate so a capacitor can respond by charging/ discharging at low rate? Then why call it a block??


texts: Why does a End-Of-Line Voltage Drop Calc yield a different result than a Point-To-Point Calculation?

texts:
I can't grasp the concept on why these two different voltage drop calculations yield different results. They should both arrive at the same answer.

In our intro EE classes when we were doing any power calculations for any standard circuit we learned that if we sum up all the series/parallel impedances into one equivalent impedance where there is just a voltage source and one equivalent impedance, we would get the same end-result for our calculations than if we were to solve the same circuit in it's original expanded form.

Here's the link to the full original PDF:
http://contechnical.com/wp-content/uploads/Voltage-Drop-Calc.pdf

Thanks for any help, it's been keeping me up at night.


texts: SRAM HM6264 chip write cycle while output enabled (OE low fixed)

texts:
During SRAM write cycle, usually the !OE is disabled, while !WE and !CS are enabled. But for HM6264 SRAM chip (http://esd.cs.ucr.edu/webres/hm6264b.pdf), it allows the !OE to be enabled during write cycle.

it seems it either causes BUS contention or writes its own data? (i.e., write what it reads from itself).

Any thoughts?


texts: How can charging current be understood intuitively?

texts:
The charging current I’m talking about would be the one between un-shorted phases and ground when there is a short to ground in one of the phases in a distribution network or facility. I'm not talking about the charging current in a transmission network where transmission lines at extremely high voltage accumulate charge between them and may possible increase the voltage (specially if the system is not designed properly).

Please see this web page section “Estimating”. The current they are trying to estimate there is the one that I would like to define and understand. Also see this paper

Every article I have seen about estimating charging current takes for granted that the reader knows what charging current is and how it originates, and doesn't properly define it before explaining how to measure or estimate it.

I have been reading and the best definition I have found so far is :

"Each phase of a three-phase system exhibits a certain amount of distributed capacitance to ground, shown here as three capacitors. A capacitive current flows through these (1). If one of the phases shorts to ground causing a ground fault, the charging current for the other two phases will flow through the ground fault (2)."

Apparently the way to directly measure charging current in small ungrounded systems (in which the charging current value is under 10 A) is to short one of the phases to ground and measure the current. As seen:

What is hard for me to understand intuitively is what I have marked as (1) and (2) on the definition:

(1) There is current flowing(leaking) out the circuit to ground from each of the phases even when there are no faults and the value of this current is several Amps! Mind-blowing!!!

(2) If I short a phase to ground. What I will see is the charging current from the other 2 phases coming from ground to my shorted phase through ammeter A2. And what about the current supplied by the utility and that was normally flowing through the phase I have just shorted? What happened to it?

(3) Will ammeter A1 continue to measure 0 after I short one of the phases? Why?


texts:
I am thinking of making my own LED lamp - That is, have an array of LEDs and power them off, maybe, a battery pack? The power source I am lenient, I'll solve that issue when I get to it. My main question is regarding the LEDs

Is it more efficient to individually solder, say, 20 or 50 individual 5mm LEDs like these:

Individual LEDs

By soldering them, I mean taking two pieces of long wire, and soldering the all the positive ends of the LED strip to one wire and all the negative ends to another wire, and power it on from the two ends of the wires.

Or should I simply buy a LED Strip and break it up into little strips and slap them onto a template?

My main concern is energy consumption - the LED strip requires 12v, whereas the individual LEDs require 3.2-3.4v. Since I will be powering them off lithium ion batteries, each battery has a range between 4.2v and 3.2v. I will be regulating the voltage with a buck boost converter. TO power the individual LEDs, I'll need only one battery, whereas for the 12v I will need multiple batteries so that they are not stressed.

As well, are LED strips generally brighter than the individual LEDs, which are 15,000mCD each?

Each individual LED is, say, 3.3v and draws 20mA. for 20, that's 1.3Whrs.


texts: Forward Converter - Voltage through primary winding Question

texts: So my waveform is a step function, where maximum voltage is at Vin = 40V, and minimum voltage is (-N1/N3)*Vin = -200V. The minimum voltage doesn't sound right to me, so I was wondering if anyone can confirm the validity of my results. Thanks for your time.


texts: E/I inductive position transducer sensing device operation

texts: so I have been doing some research on AC servo position flight control surface systems an was trying to find the component used to set the pilot's input command. Found out that a E/I inductive position transducer sensing device are used. I know briefly on how it operates, it consists of 2 magnetic cores with a movable shunting bar and the voltage output depends on the position of said bar. Can anyone explain in detail how pilots use this device to set their commands for flight control surfaces? Any help is appreciated, thanks


texts: How does this SIM card reader circuit work?

texts:
The circuit for a SIM card reader is shown here. The circuit uses a CMOS hex inverter and other simple components; yet, not only does it work but it can also communicate with a PC via serial port!
I am learning electronic circuits as a hobby and I was baffled to see how simple this was. I was thinking of using some kind of micro controller for this. As you can see I am a complete amateur.
Can you please explain how this circuit works?
As a reference, here is the schematic I found on the website and is probably referred to:


texts: Building Led light which work on 230V supply

texts:
I have a couple of 9W LED bulbs(1) at home with blown drivers. I got some replacement boards(3) with driver circuit and LEDs on the board itself. Now that the old LEDs(2) along with the aluminum PCBs are no longer required, I want to make a high power LED lamp which works on 230V AC. The LEDs are connected in series. With a working voltage of 3V each, I may require around ~76 LEDs (please correct me if I am wrong).

Will a simple bridge rectifier and a filter capacitor do the job to light these LEDs?
If yes, which values would you suggest for diodes and capacitor?

Another problem I may face is voltage fluctuation(not frequent) which may range from 200V to 250V. Am I wrong if I assume that this voltage fluctuation is not strong enough to damage the LEDs?

Any advice highly appreciated.


texts: How to multiply fixed point numbers of different format

texts:
Assume I have two 16 bit fixed point numbers in following format being multiplied.

Q3.13 * Q10.6

What is the correct way to multiply them, i.e do I right shift the first number to align it as Q10.6 or left shift the second number to align it as Q3.13? In both cases I will lose data.

May be the correct way is to put them into 32 bits and then shift them and then multiply them. In this case, no data is lost but result will be 64 bits after multiplication.

What Q format the result have after multiplying Q3.13 and Q10.6?


texts:
I'm having inconsistent times on my timer, can be anywhere from 300ms - 4 seconds, what could be causing this?

The code logic looks good to me but the oscope shows different times almost everytime I run it. Here's how I set up the code for the timer. I'm using an arduino as a clock at about 256Hz. The timer should go off at 4 seconds not any sooner like it is.

library ieee;
USE ieee.std_logic_1164.all;
USE ieee.numeric_std.all;
USE ieee.std_logic_arith.all;
USE ieee.std_logic_unsigned.all;

constant C_2SEC_TC : integer := 1023;
signal tmr_cnt  : std_logic_vector(11 downto 0) := (others => '0');
signal tc_2sec  : std_logic;

begin
   -- counter for internal timer
   second_cntr_proc: process(CLK)
   begin
      if (rising_edge(CLK)) then
            tmr_cnt <= tmr_cnt + 1;
            if (tc_2sec='1') then
               tmr_cnt <= (others => '0');
            end if;
      end if;
   end process second_cntr_proc;

   tc_2sec <= '1' when tmr_cnt = C_2SEC_TC else '0';

I initialize a pin high and when tc_2sec goes high I set that pin low. The high time of that pin isn't always the same.


texts: How do I measure internal resistence of voltmeter without ammeter?

texts: I know how to do it with ammeter, but how can I find internal resistence without ammeter?


texts:
I am confused whether voltage across inductor is $$
\ V = - L* di/dt\,
$$
or $$
\ V = L* di/dt\,
$$ Does it have to do with inductor being in AC or DC?

EDIT: okay based on answers I found, confused me that if there is a negative sign in the formula, it is back emf that is been generated by the current flowing through a coil and according to Lenz's law some force have to oppose that change! Now if $$ \ V = - V_{emf}\,$$ than how do I calculate actual back emf generated by an inductor?


texts: Pump power factor OK on mains, but low on generator

texts:
I'm working on a submerged pump application, running on 415V three-phase. I don't know for sure, but I believe the pumps are only a few KW.

The customer is saying that the pumps run fine when the site is on mains power; but when it switches to generator, my motor protection unit trips the pump on Low Power Factor. I’ve asked for the motor protection unit logs but haven’t seen them yet, so that’s all I have to go on. The Low Power Factor threshold should be set to 0.5, but again I can't be sure.

If the generator rotation was incorrect, then the phase fail relay and the motor protection unit should both have tripped, preventing the pumps from running.

If the generator voltage was higher / lower than the mains, then the current would be lower/higher, but the inductance of the motor hasn’t changed so why would the phase shift be different?

I’ve asked a few experienced engineers here, but no-one has any suggestions as to what is going on.

Any suggestions?
Thanks for your help!

.

Edit per request from @Transistor - I'm not sure that the schematics will add anything more than what's described above, it's a simple system. The schematic editor looks Ok for electronics, but not for electrical so I've pulled some wiring diagrams from other sites. These are example schematics from a typical site:

Simple DOL Starters. Ignore the reversing contactors, they're not present at this site (and the Low PF fault is ignored when reversing anyway).


texts: PCIE branching not detecting PCIe device

texts:
I am facing an issue with the PCIe in my circuit. The PCIe detection is not happening.

We are using  an imx6q processor board plugged into our carrier board . The processor board comes with option of

With PCIe bridge
Without PCIe bridge

For supporting processor boards without PCIe bridge, we provided a PCIe bridge on our carrier board. Hence we provided parallel lines to the PCIe lanes so as to support both types of processor boards

In our current setup.. we didn't assembled the pcie bridge option. Hence  the processor is providing all the 3 pcie to our board. But the parallel lines to pcie bridge is still there...

Hence we suspect whether the paralleling options are creating problems Or due any termination problems Also in our pcb routing we used 4 vias for supporting this bridge option.
Kindly go through the block diagram....

board file for reference in this link


texts:
I am working on a problem for a given transfer function given below and am having trouble calculating the magnitude and phase of it. The problem is specifically that I do not know what method to use to seperate the imaginary value out of from the real to allow me to use their seperate values in calculating the magnitude and phase.
$$\frac{Vout}{Vin}=\frac{1}{1-(4*PI^2*0.04)+(j*2*PI*0.2)}$$
Ideally I'd like to end up with something like a+bi to allow me to do the srqt(a^2 + b^2) and the tan equation for the phase but I do not know how to do this.
Could anyone suggest a method to use or some mathematical identity to use?
Thanks!
So implementing what was in the first comment from ocrdu
It simplifies to
$$\frac{Vout}{Vin}=\frac{1}{(-0.579+j*1.25)}$$
Then multiplying top and bottom by inverse of bottom gives:
$$\frac{Vout}{Vin}=\frac{(0.579-j*1.25)}{(-0.579+j*1.25)*(0.579-j*1.25)}$$
But how does this help me?


texts: Should cable shield connect to ground plane on hand-held tethered device?

texts:
I am designing a hand-held device whose power and signals come from a cable. The device circuit will be +5 volt and powered through the cable.  The cable (a re-purposed HDMI cable) has multiple twisted shielded pairs available.  The device will be on a 2-sided pcb.  I plan to create ground plane on the solder side of the pcb and connect that to the cable shield, which in turn will be connected to earth ground at the opposite end. The digital circuit commons WILL NOT be tied to this ground plane. The idea of the ground plane is simply to provide some EMI noise immunity.  Is electrically connecting a ground plane to the shield a good idea or not?
Thanks in advance!


texts: Can you earth ground all different voltages of a system together?

texts: I have various power supplies and circuit breakers of different voltages.can I hook all the PE connections together ? All my neutrals are separate


texts: Is there more to a Microcontroller than a few logic gates?

texts:
I am a software developer (using high level languages like .NET,C,C++ etc) trying to understand how computers work at a lower level.

I asked this question a few days ago: Lower level system development.  I have setup my arduino and I have written a few programs in C and assembly language.

However, please see the following diagram: here.  This diagram suggests that the microcontroller is simply a component with a few AND gates.  Surely I am missing something here? What happens if your program has an OR operation or a NOT operation? I realise this is a big topic with lots of different areas.  However, I have a good GCSE level of electronics and I studied the basics of this at university whilst studying computing.  I just struggle to piece it all together.  What is inside a Microcontroller (physically)?


texts: Detecting metal, detecting a coil - which is easier?

texts:
This is a metal detector question, with one assumption. That is, the detecting is done by eddy currents in the target changing the resonant frequency of the detecting coil.

The question then becomes, would it be easier to detect (say) a piece of Aluminum or a few turns of copper wire (closed circuit coil) of the same mass?


texts: SMD SOT-23-3 device identification - top marking E8LJ0

texts:
I have a small SOT-23 (3 pins, transistor-like) device that burned out (shorted between 2 pins). I need to identify it so I can replace it, but I can't find the code at all. The code is: E8LJ0

Thank you all.


texts: how to compute the average power from AC generator

texts:
I would like to monitor the power produced by an AC generator in a wind turbine. The goal is to monitor how the produced power varies with wind conditions. I connected the power resistor to AC generator to burn out the power. The voltage sensor measures the voltage across the resistor, and the current sensor measures the current flowing into the load resistor.

For computing average power, I rectified the output from the AC generator and use the DC voltage and current to compute the average power using $$1/N\sum_{i=1}^{N}V_{DC}(i)I_{DC}(i)$$
I thought that if I rectified the output, I can compute the average power more reliably. However, I observed that there is lots of variability in the computed average power. In other words, even for the same wind condition, the computed average power changes for different experiments (wind tunnel).

As an alternative, can I use non-rectified AC voltage and the current to compute the average power? Just computing the root mean square of the power time series would results in an sufficiently accurate result? The RPM of the generator is about 500, and the sampling frequency of measuring the voltage and the current is about 1000Hz.


texts:
I'm about to design an 5dB attenuator for RF, using a simple pi resistor network.

The resistor values are 2 x 178ohms, and 30ohms.

The work area is 1GHz to 2.1GHz.

I was looking at different resistor datasheets, but could not see how well they would perform in that frequency area.

I was thinking the resistors probably would start working non-ideally above some frequency?

And how about package size: 0603, 0805, ect.
I guess a small package would add some capacitance?


texts: What kind of capacitor is this? Can anyone describe the 25u 50v

texts:
Is this ceramic or disc capacitor?

And also what do the values "25u 50v" on that component mean?

Why can't I see those values when I search for 104m capacitor?


texts: Why Op amp amplifier's voltage difference zero?

texts:
In studying the OpAmp amplifier, the derivations always take the voltage difference between the inverting- and non-inverting input to be approximately zero. But I can't find any explanation "why". This consideration is always taken for both the inverting- and non-inverting amplifier.

Why is this voltage difference always approximately zero? Any explanation?

I found a lecture of my senior professor, where he said that "as the ideal op-amp's input impedance is infinite, its positive- and negative terminal are virtually short. I mean very little voltage drop which can be neglected."

I can't understand why a very high (practical case) input impedance may cause a very little voltage drop.


texts:
I understand that for an RC circuit acting as a load of a driver will afftect the delay of the output after the RC load.

So as long as RC for different values of R,C are equal, delays are equal, is this right?
For example R = 8 Ohm, C = 0.25p, RC = 2
and R = 5 Ohm, C =0.4p, RC=2

I simulate with these above 2 configurations of RC values but i get different delay values after the RC load, and also different rise/fall time.

I think that delays in these 2 cases should be equal and so do rise/fall times.

Are they any constraints on the R, C for to compare delays based on different RC time constant.


texts: Arduino Nano v3 atmega 328p avrdude: stk500_getsync(): not in sync: resp=0x00

texts:
i get this error:

avrdude: stk500_getsync(): not in sync: resp=0x00

when trying to upload a example sketch.

pin (0,1) are not occupied;
it is the right serial port with latest drivers
i choosed the right board

The RX led blinks 2 or 3 times when i try to upload.

Full log:

avrdude: Version 5.11, compiled on Sep  2 2011 at 19:38:36
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2009 Joerg Wunsch

         System wide configuration file is "D:\Utz\Downloads\arduino-1.0.4\hardware/tools/avr/etc/avrdude.conf"

         Using Port                    : \\.\COM3
         Using Programmer              : arduino
         Overriding Baud Rate          : 57600
avrdude: Send: 0 [30]   [20]
avrdude: Send: 0 [30]   [20]
avrdude: Send: 0 [30]   [20]
avrdude: Recv:
avrdude: stk500_getsync(): not in sync: resp=0x00

avrdude done.  Thank you.


texts: How does a cellular network deal with a duplicate SIM?

texts:
I was pointed here from WorldBuilding.

Say I had a cellphone, let's call it cellphone A, and made a perfect copy of it - SIM card and all - and let's call this one cellphone B.

If I were to call someone on cellphone A, what exactly would happen to both cellphone A and B?

This stems from a short film I'm planning where a character goes back in time with his smartphone, and his younger self - that is now in the same time as him - makes a phone call. I want to be as accurate as possible, and I don't know enough about cellular networking.

Extra Information: This takes place in modern-day Australia, specifically Victoria. Also, the call from cellphone A is to emergency services.


texts: I wanted to know how to calculate the power dissipation of a micro-controller. If I have the information on which pin is sourcing how much current, how can i calculate the power dissipation of the MCU? Also i would like to know how this power dissipation varies with frequency and calculations for the same.


texts: How come 18650 Li-ion cells aren't meant to be sold loose?

texts:
I've heard that 18650 Li-ion cells aren't meant to be sold loose. They're meant to be built into packs and the "good" manufacturers won't actually sell them for any other purpose. FWIW, there's the Panasonic NCR18650 - which I believe are sold loose.

So, my question is: why aren't 18650 cells (perhaps LiPo cells in general, for that matter) meant to be sold loose?


texts: Need help understanding the mosfet trailing edge Dimming

texts:
I am working on a circuit to control AC loads up-to 1.5KW by using Mosfets(FCHD125N65S3R0-F155) Circuit is

I have few concerns

The current is flowing through the body diode of Q2 for positive half cycles and current is flowing through the Q1 body diode for negative half cycle.There is so much of power wastage is happening i.e 1.2*6.25=7.5W is there any better way to solve this issue.
Is there any advantage of using IGBT and what will be the changes?
What are R3,L3 and C3 values for over current and over voltage protections (VDS=600V).


texts: What is these factor multiplying the current of the copper wires_?

texts:
I was reading some solved problems about transformers but I don’t understand how was calculated the losses in the copper.

- Enunciate:
A one phase, 10kVA, 2400/240, 60Hz distribution transformer has the following characteristics:
 - Core loss at full voltage=100W
 - Copper loss at half load=60W
Determine the efficiency of the transformer when it  delivers full load at 0.8
power factor lagging.

Solution:
P=10*0.8=8kW

Pcore=100W

PCU,FL (Full load)=60(\$**2^2**)=240W\$

The Efficiency is then
(8000/(8000+100+240))*100=95.92%

Not a big deal, but why the copper loss at half load was multyplied by \$2^2\$? What is this?


texts:
I am wanting make an embedded device that can communicate with a web-server in a secure fashion. My preference would be for it to use standard SSL so the web-server views my device similar to a web browser.

Are there any prebuit libraries for
the embedded side to do this?
What about an IC that can handle the
handshaking and decryption for me?
If not how would I go about doing
this myself?


texts: multiprocessor programming and memory management

texts: I'm working for a project (an embedded storage system) that requires to increase a memory access speed using a multiprocessors programming, so that we can execute a memory access program (storing data) in parallel with computing program. I'm a newbie in these topics (multiprocessor programming, memory access tools). I got lost in the net and I could found just some books that talk superficially about this or just introduce it. I believe there are some resources that can offer a practical deep understanding. I need your help to find some practical resources about these topics, some code sources or... As a newbie in these topics, any suggestion would be helpful.


texts: Home Built Hybrid EV Battery Charge current limiting

texts:
I have a hybrid EV that I'm working on which uses 2 48V DC motors with a maximum load of 300 Amps each, for a total maximum load of 600A. I have 2 alternators running off a gas engine generating 125 amps each wired in parallel for a total static current of 250A. I want to use a battery system to pull the remaining 350A in short bursts of power. I've sourced a 100Ah 48V Li-ion pack in order to supply the necessary current.

My issue that I run into is that I want the alternators to charge the batteries when they're not being fully drawn, but the charge current for the batteries shouldn't exceed .5C, or 50A, so it's not an easy alternator -> battery -> motor-controller setup.

So, what do I need in order to connect all these components together in order to have the system I'm looking for?


texts: Mutual Inductance Between Two Same Axial Inductors

texts:
I was searching for few hours on this topic but I was unable to find any formula/research so I'm asking here. Please if this question is a duplicate let me know.

Right now I do not have the equipment to prove or deny the following formula I came up with.

I have two (same) tht axial inductors. Those in a 1/4w resistor-like shape (with PVC coating). I do not know the core material or the number of windings. But I'm trying to estimate the Mutual inductance M.

Knowing that inductance L of each inductor is given by:

L = u0 * ur * N^2 * A / l

(Better here: http://www.electronics-tutorials.ws/inductor/inductance.html)

And having the M impedance formula (found here: http://www.electronics-tutorials.ws/inductor/mutual-inductance.html)

M = u0 * ur * N1 * N2 * A / d

(Distance referred as 'l' in the article replaced with 'd' for clearance)

Assuming the following:

ur - all cores are of same material
N1 = N2
A - all cores areas are same

I came up that M of two same axial inductors with inductance L, length 'l' at distance 'd' is:

M = L * l / d

...sounds too simple, to be real... But is this correct? It mean that my 47uH inductors with l=2.9mm at a distance d=6mm has  a mutual inductance M=22uH sounds huge?


texts:
I tried this circuit with a power LED, without gate resistor and with \$R_s=4.7\Omega\$:

I discovered that when the Vin+ is at GND, there is still some leakage current which keeps the LED ON very dimly.

Edit: the implemented final circuit is this one

I discovered that when should be OFF, the gate voltage is slightly below the \$V_{\text{GS}}\$, which is around 3 or 4V. I'm supposing that this behaviour is the amplification of the offset of the LM324 which is able to open slightly the MOS. But it is not generating a sufficient voltage drop on the sense resistor, and it is comparable to the offset and as a consequence the correction from the op amp stops when the drop on the sense resistor is comparable to the offset at its inputs. Keeping everything in this equilibrium with the LED almost OFF.

How should I proceed to guarantee a better OFF status? I thought of using a MOSFET with a lower threshold, and/or better op amp with a lower offset. But I don't think that this guarantees a priori a complete OFF status.


texts: How can a foxhole radio tune in on a frequency without a capacitor?

texts: A primitive foxhole radio only consists of an antenna, coil, diode and headphones. There doesn't seem to be an LC-resonator, so how does this radio tune in on a carrier frequency?


texts: how to convert a PWM AC dimmer circuit from normally-closed to a normally-open one?

texts:
Hi,
As you see in schematic, the circuit is a normally-closed AC dimmer. Therefore when the connection between microcontroller - which produce pwm - and mosfet get halted, the lamp will be always on without any dimming.
I want to make this circuit in a way which eliminating microcontroller would turn the lamp off. Is it possible?


texts: STM32 BLE profiles - multiple sensors active ST BLE Sensor App

texts:
I have done the MOOC for the stm32wb55 BLE profiles and now I am trying to introduce more BLE characteristics.
I managed to make the sensors work and to transmit them to the ST BLE Sensor app. However I can only have one screen active at a time. So for instance I can either have the temperature or humidity transmitted at a time, but not both at the same time.
I have created a custom template for both of them, and as I said separately they work fine, however I can't figure out how to have both of them at the same time on my ST BLE Sensor app.
Each template has its own UUID(in template_stm.c), specific to temperature and humidity, however I don't really understand this portion of the code from app_ble.c:

    /**
 * Advertising Data
 */
#if (P2P_SERVER1 != 0)
static const char local_name[] = { AD_TYPE_COMPLETE_LOCAL_NAME ,'T','R','Y','P','I'};
uint8_t manuf_data[14] = {
    sizeof(manuf_data)-1, AD_TYPE_MANUFACTURER_SPECIFIC_DATA,
    0x01/*SKD version */,
    CFG_DEV_ID_P2P_SERVER1 /* STM32WB - P2P Server 1*/,
    0x00 /* GROUP A Feature  */,
    0x04 /* GROUP A Feature */, //0x00040000
    0x00 /* GROUP B Feature */,
    0x00 /* GROUP B Feature */,
    0x00, /* BLE MAC start -MSB */
    0x00,
    0x00,
    0x00,
    0x00,
    0x00, /* BLE MAC stop */
};
#endif

My transmission works only when I change the mask to 0x00040000 for temperature (the temperature screen in the app and the transmission work fine) or when I change it to 0x00080000 for humidity. How would I manage to have both of them at the same time?
I read the documents associated in their entirety and also I checked the example apps, but I can't seem to figure it out.

Also as a separate issue, when I try to send the data to the pressure UUID, although the code is exactly the same to the other 2 examples, on the app it shows me "Not available".

Does anyone know how to solve these 2 issues?

Thank you!


texts: MOSFET voltage follower for non-inverting op-amp biasing

texts:
Question is based on this document.

Quoting from there:

  Voltage Follower Biasing: This method is exactly the same as the voltage divider
  biasing, except it uses an op-amp (or transistor) to buffer the bias voltage, so choosing
  small resistor values is no longer necessary.

The schematics for op-amp voltage follower for biasing is provided:

Then we feed the bias voltage instead of ground in negative feedback loop of non-inverting amplifier:

But there is no schematic in the document for voltage follower using transistor.

I've tried to find circuit on internet, but it seems most of the time it is different type of voltage follower, e.g. like this one:

From my understanding this is not going to work for biasing non-inverting op-amp, since we take voltage from resistor i.e. we introduce it to negative feedback loop, so we can not use large value resistors, basically making this circuit senseless - we can't save power on it, it will be almost the same as just using voltage divider(split resistor biasing).

The I tried to design my own circuit to mimic op-amp voltage follower, I came up with something like this:

simulate this circuit – Schematic created using CircuitLab

The Vbias as with op-amp circuit goes to negative loop instead ground.
But this does not work, the behavior is somewhat random, signal jumps around, etc.
The logic I was using is that we need to have capacitor on the output to prevent gain from changing(because we don't introduce resistors to the loop). I tried different caps and resistors values, but nothing changes, so basically my circuit is wrong fundamentally.

So the question is - how to build a Voltage Follower for biasing the negative feedback loop of op-amp? Or better said - how to do what the first circuit in this post does, but with MOSFET?
Mimicking means:
1) Possibility to use large value resistors to decrease power consumption
2) Do not change the gain of non-inverting amplifier


texts: Activating and deactivating a solid state relay with 3v and 2v, respectively

texts:
I have a normally closed solid state relay (link to datasheet below), that I would like to activate with 3V and deactivate with 2V. The load is a 24V 100mA LED. How should I go about this?
Datasheet for SSR: https://docs.rs-online.com/4030/0900766b81471bd5.pdf
Please let me know if I should provide more information.


texts:
Hello All,
I'm new to this board and looking for some opinions. I've searched the board a bit and found similar questions but not quite what I'm looking for. I'm looking for some help deciding on an SoC to use for embedded system applications.

I've taken a intro embedded systems course at my University, however the normal professor left the semester before so a CE grad student was forced to teach the class. As a result I feel like I didn't get the best education from it. In the course we used a smartfusion SoC, I feel like I know that board pretty well however I don't want to go out and spend over 100$ just for the board. Also I'd rather not have to interface the MPU to an FPGA.

Before the end of the semester and doing a lot of research I hastily bought a Rpi 2. Doing a bit more research and playing around with it, I've come to the conclusion it isn't the best board for baremetal C. A lot of the code is already given to you when what I want to do is write the code and drivers myself.

In the end I want to get into robotics with whatever platform I'm using. My question is this... should I stick with the Rpi and just learn to rewrite some of the libraries or should I get a different board such as the beaglebone? Another issue I have with the Rpi is if I want to do baremetal C, then flashing the MPU is a pain, so preferably I would like an IDE to debug and flash my code.

For now the embedded system design is just a hobbyist thing, but in the future I'd like to be able to actually work as an embedded designer. I want to get close to the metal as opposed to high level abstracted away design. Ahead of time, thank you for your responses.


texts: In a ~3 amp circuit, is it required for all ground trace widths to be the same?

texts:
I am designing a PCB for controlling servos.

My voltage regulator can provide 3 amps to the servos. My Arduino Uno also draws power from the same line. Using an online calculator, I was able to determine that I need 53 mil traces for power and ground lines coming directly from the regulator, and from devices powered by the regulator, respectively. Since the Arduino can draw at most about 500mA, I know that I don't need any special width for traces into and out of the Arduino's inputs and outputs.

The Arduino has its own voltage regulator, and a few ICs are powered by its 5V and 3.3V supplies.

Do I need 53 mil ground lines everywhere from these chips? Since the Arduino can't pump 3A, I can't imagine any one of these chips needing such a huge trace for ground lines.


texts: Are external data connections considered "unintentional radiation" by the FCC?

texts:
Does a device with an external communication port of some kind fall under "intentional radiation" or "unintentional radiation" according to the FCC for testing and certification requirements?
For the purpose of this question, the external connection would be outside of the device's enclosure and must be connected via wire to communicate; it does not use the air as a communications medium.  For example:
Lower frequency ports:

CAN Bus (which is the reason I'm writing)
RS232
I2C
SPI

Higher frequency ports (Are there others of note for the purpose of this discussion?):

USB
Ethernet
MoCA (multimedia over coax)

Are there some above that would be considered intentional and others that are unintentional radiation?


texts: When wiring an electret microphone is using the wire shielding as ground ideal?

texts:
Currently with a "single-conductor" shielded wire I have connected the (+) pole of the mic capsule to the wire, and the (-) pole to the shielding strands.  I am wondering why the ground wire doesn't also need shielding -- can performance be improved by using a "two-conductor" shielded wire for the (+) and (-) coming from the electret?

My understanding is that shielding acts like a faraday cage and prevents the wires from acting like antennas and passing electromagnetically induced currents (i.e. unwanted interference) .


texts: Current and voltage distribution on a beverage and on a rhombic antenna?

texts:
Afternoon.

I've been learning about antennas a lot lately, and right now i'm reading about both of these, been trying to find a read about their voltage and current distribution but so far i haven't found anything.

Care to tell me how it's on both of them with a little short explanation? I'm kinda new to this topic.

Thanks


texts: I have a circuit on a PCB where I am using PIC microcontroller to connect with DS1307 via I2C. I am having trouble while programming it so I am planning to purchase a logic analyzer so that I can see what is the actual data sent or received in I2C lines. But the problem is as I am newbie to logic analyzer, I really don't have any idea about how to use them. I know i'll have to connect the wires to the line but as I have a PCB so I don't know where should I connect those wires. Can anyone here please help me out.Thanks


texts: What causes amplitude clipping of single stage CE BJT amplifier with a bypass capacitor?

texts: Where is a single stage CE BJT amplifier with a bypass capacitor supposed to clip with a normal 4-resistor biasing circuit? Like I seem to be able to get the upper peak of the output voltage all the way to VCC before it clips without a bypass. With a bypass, the gain is actually a lot larger, but clips a lot sooner, as in before the upper output voltage peak reaches VCC. I get the clipping without a Bypass is caused by it reaching the voltage of the supply, but what about with a bypass, what causes it to clip before reaching the supply. I see something similar with CC and CB amplifiers. Though maybe it's all for similar reasons.


texts: Understanding pull down resistor current flow

texts:
I'm working on an introduction to Arduino and circuits course and I've run into a stumbling block.
Everything works the way the course says that it should - I just don't understand WHY it works.
Here's the schematic:

The program is easy to understand. When digital input 2 receives input it lights the LED. The whole path with the LED makes sense to me, no need to discuss it. It's the path with the red wire and green wire going into the DIP switch.
My understanding is that the DIP switch is connected to both the digital input and the resistor and the resistor provides a path to ground for any stray voltage that gets induced on the wire by the environment.
What's confusing me is - isn't the digital input also a path to ground? If not, how does the circuit ever get closed? If there is stray voltage the resistor is providing a path to ground, but if the switch is closed then suddenly the digital input is the best path to ground?
When the switch is closed, the 5 volts can either go to the digital input or through the resistor and the resistor path has more impedance and so the 5V goes into the digital input. When the switch is open, why would any stray voltage not take the same path that the 5V takes?


texts: Is the purpose of an internal resistor in a practical voltage source to set the maximum possible current that can be drawn?

texts: Going off the example circuit I attached below, is the purpose of an internal resistor to limit the maximum current that the voltage source can output? Since adding any passive component in series with the internal resistor would just reduce the current.


texts: How is the output impedance of a closed loop opamp derived?

texts:
The output impedance of a close loop OpAmp(voltage amplifier) is:
$$ Z_{out(CL)} =\frac{Z_{out} } {1+A_{VOL} B} $$
How is this equation derived?
The Z_out(CL) decreasing by a factor of (1+AB) is like implying that the current increases by the same factor.
I don't get why current will increase since in my eyes, the current is just a simple:
$$i_{out} = \frac{V_{diff}*A_{VOL}} {Z_{out}} =\frac{V_{out} } {Z_{out}} $$
Thus Zout(CL) is just equal to Zout.
What am I missing?


texts: How to find the polarization (phase) of the virtual source if image theory is used

texts:
Consider a radiating element (actual source) is placed above a ground plane, and if we apply image theory to determine the E-filed, the virtual source will be placed below the ground plane and ground plane is removed.

I understand how and why image theory is applied, but what I don't understand is that, how to choose the polarization (phase) of the virtual source. I would be grateful if someone can help me with this problem.

I studied this part in an antenna book but i don't understand the explanation, which is as follow:

and the figure is:


texts: Speaker Amplifier for First Alert Keypad

texts: I have gone back to the drawing board and rebuilt this for simplicity. The problem I have now is the if I use the Keypad Buss 12VDC power I get oscillation. It will not oscillate if I use a separate power source, but the only option I have for power is the keypad buss.


texts: Can you help me to understand this thevenin circuit's mesh?

texts: Why didn't we involve the 4 Ohm resistor while doing the mesh i2 ?


texts:
I'm trying to short two pins on a chip when an audio signal is received and float them otherwise (same effect as a tactile switch). I thought the best way would be to use a voltage peak holder and a NPN transistor (but is it?). Here's my simulation and I don't think I'm doing it right:

It looks like I can control the voltage across R4, but is this the circuit for shorting and floating two pins? That is, can I connect the two pins across R4 to achieve the effect? My take is that when the transistor is off, there's a voltage at the collector (V(out_r4n)). If I were to connect the two pins across R4, then the downside pin would be getting a voltage when it's not supposed to. Am I missing something?

Any advice appreciated.


texts: Charging capacitor bank with current limiting circuit

texts:
I would like to charge a capacitor bank with a 4.8 volt supply that I have. With the help received in response to this question, I now have a a useful current limiting circuit (shown below), that allows me to select a maximum current through a load. I have reimplemented the solution in CircuitLab . . .

The circuit is set to give a 480 mA max current. As the load resistance increases, the SER of the limiting circuit drops away. The following plot shows current through the load versus load resistance . . .

However, what happens if I want to charge a capacitor bank using this circuit. Where would I put it? Current needs to flow through R_sense to cause a voltage drop in order for the circuit to function. If I just add a capacitor after the sense resistor . . .

. . . and then measure the voltage across the capacitor, some crazy stuff happens . . .

What am I doing wrong ( -120V .. really )?

EDIT:

Following Oli's advice by adding a leakage resistor and paying attention to initial conditions . . .

.. I now get a logical looking output, although the voltage is not up to Vcc

If I place the capacitor where R_Load is,

Then the voltage of the cap jumps up to 4.8 volts immediately (which I'm guessing would draw a massive current, fry my supply, and negate the point of the current limiting circuit)

This looks pretty logical to me. If a cap is connected to an ideal voltage source, it will get an infinite current and be at 4.8 V instantaneously. What do I need to do in order to reproduce the effect shown in Oli's lowest plot?


texts: If i need a 1500 ohm resistor, could I replace with 2 resistors in series, 1000 ohm + 500 ohm without affecting the freq cutoff?


texts: I am using a Dallas DS18B20 thermometer that communicates with Maxim's one wire protocol. I'm having issues at the initialization sequence. I have pulled the line high for 500 uSeconds, pulled the line low for 510 uSeconds (the reset), pulled high for 45 uSeconds, waited for 120 uSeconds for the thermometer to pull the line low as a response (the presence pulse), and then sampled the signal to make sure it was low. If it is not low, something went wrong. When I look at the signal in my 'scope, I see it get pulled down for 510 uSeconds and the pulled up for 680 uSeconds. This means the thermometer did not respond at all (45 + 120 + 500 = 675 uSeconds). What am I doing wrong?


texts: Arduino breakout schematic for FDS100 Photodiode

texts:
This is the first time I'm drawing a schematic, thus why this question seeks to get clarification from you experienced engineers :-)

A little background information:

I'm trying to draw a circuit for an oximeter "breakout board" for my Arduino. The circuit contains respectively two 860nm LEDs and two 940nm LEDs. (I'm not sure which LEDs to buy yet, hence why the resistors are not given any values)

To measure irregularities in the emitted light from the diodes, I bought the FDS100 photodiode from Thorlabs - Which also is the component that confuse me upon drawing the schematic.

I'm planning to supply the board with 5V from my Arduino, and from the datasheet, it seems as if the FDS100 can handle much more - hence why I haven't added any resistors.
The FDS100 has 3 legs, where one of them is a case(??) - I've read in another post, that it is good practice to ground the case, but not necessary. (I have done it anyway)

Furthermore, I understand that the FDS100 is "reverse biased", meaning that current flows in the opposite direction, hence why the analog port in my Arduino should be wired to the cathode of the FDS100, in order to be able to measure how much light that the FDS100 picks up.

Below you can see my preliminary Eagle schematic:

Have I done this correctly, or am I missing some important details, i.e. resistors and other components concerning the FDS100?


texts: Seeking 4x3 keypad for Atmel UC3 microprocessor

texts:
I was doing a combined project with a friend, with me on s/w and him on h/w. After a year of coding on my part & not much activity on his, he announced that he is "too busy" to continue.

That leaves me, a pure s/w guy with little or no h/w knowledge to continue. I need a 4x3 keypad which will work with an Atmel UC3 series 32-bit microprocessor - can you advise?

Preferably something with sample code.

As I have no o/s, should I go interrupt driven or polled? (told you I am not a h/w guy ;-)

Thanks in advance for any help.


texts: How to determine the inverse Z-transform using partial fraction?

texts:
Task: Determine the inverse z-transform of a discrete-time system
represented by the rational expression below using the partial fraction
expansion method. The impulse response of the system is absolutely
summable.
This is what I did:

Was I able to get the values for the partial fraction correctly? What do I do after this?
I'm stuck :( Thank you for your help!


texts: How well does telephone delay correlate to geographic distance?

texts:
I have a friend who lives on the other side of the world, and every time we speak over the phone, there's roughly a second of delay between one of us saying something and the other hearing it. I've tested this by having her put her phone on speaker so my own voice is detected and returned back to me over her phone as feedback, and the delay over that particular distance is quite consistent.

While surely there are a number of other factors contributing to phone delay beyond propagation time, many of these factors are constant regardless of distance. So if the distance between us were halved, would the delay be as well?


texts: How to check the flow of assembler instructions execution?

texts: I'm creating a project that uses I2C serial communication in assembler and I'm having some issues transmitting data and receiving back so I thought I should somehow debug the whole program, besides oscilloscope and maybe proteus I thought if I knew the flow of the program execution I might know where the problem is, if ack is set or noack, first thing that came to mind is a delay and a led after each instruction is done, is this a good approach or do you suggest something different, if it is a good approach  give e some ideas and how much of the delay are you proposing? Thank you.


texts: Explain what is a transistor in plain English!

texts:
Can someone care to explain - in plain English - what a transistor is and how it works. I know computers are full of these but don't know much about them.

P.S. I know about this site from another one in the family of StackExchange (I have no engineering background) and hoped someone might help me with this. Please don't link to the wiki explanation. I've read that and I'm more confused.

I'm looking for a 7 year old explanation.

Thank you!


texts: What destroys a LED in the reverse direction?

texts:
When a LED is included in a circuit that applies a reverse voltage that exceeds the reverse breakdown, a reverse current can flow and the LED might be destroyed.  But what is it that actually destroys the LED:  is it the reverse voltage itself, or is it the reverse current that is made to flow, or is it simply the overall power dissipation caused by the reverse current and voltage exceeding the device rating?  Or something else?

So, for instance, if I connect a 12 volt source in reverse to a LED that breaks down at 5 volts, via a resistor, the passage of reverse current will cause a voltage drop across the resistor which in turn can limit the voltage on the device to its reverse breakdown value (and thereby define the current that would flow) - rather similar to what happens in the forward direction.  Would this in itself destroy the LED as long as the total power was within the LED rating?

Normally of course, one would place a regular diode in parallel with the LED in the reverse direction to limit the LED reverse voltage to 0.7 volts or so, but there may be situations where this might not be possible or economic to do.  I am just trying to understand how much circuit design flexibility I might have to meet different requirements.

And if it is possible to expose a LED to a reverse voltage, what precautions should be taken to avoid damage, and which spec parameters are relevant?


texts:
I'm trying to control a DC motor by H-bridge in my board.
The motor works well by PWM signal but, in breaking mode, only the lower switches are on, motor is not locked completely.
When I turn the motor shaft by hand, the shaft moves easily, but not as easy as freewheeling, all switches are off.

I have MAXON motor controller, EPOS2.
I have tested the motor by EPOS2, but in lock mode, it is hard to turn the motor shaft.

How is the EPOS2 able to lock tightly?
I checked the motor's power line by oscilloscope, a very short duration PWM signal is on the power line, but the shaft is not turning.

When turning low speed, I can stop the motor by my hand, but on EPOS2, I can not do that.
I have to move the external load by motor in lower speed, but I think motor can not do that because lower torque for my board.
In my board, I can stop the motor shaft easily in low speed, also.

This is my schematic.
LTC4449 is N-channel MOSFET driver.
When L_PWM and R_PWM are low, Bottom Gate(BG) of LTC4449 are high, so Q3 and Q4 are on state.

Please advise me.


texts:
As a forewarning, this is my first PCB. I am experiencing issues with the I2C bus. There are two I2C slaves on this bus (SSD1306 display and BQ27441 Fuel gauge, currently the program only sends commands to the display at 0x3C, so I'm not worry about the other device causing problems right now.)

My first concern was noise issues because I did not realize it was poor practice to route the I2C signals next to each other, so I cut the traces and re-routed using magnet wire. This resulted in the same exact issue. The issue is: the screen only displays for about a second, not even, and then cuts out. I changed out the pull-up resistors to pretty low values (1.1k, originally 4.7k but the rise time on the oscilloscope looked pretty bad). Important note: the screen did not work at all before this change. However, the screen is still very intermittent, which leads me to believe this was not the direct cause.

The SDA trace is 71.5mm and the SCL trace is 80.8mm, I didn't think length matching would be important at 400kHz, but thought I would include the information. Also, would cross-coupling be an issue here potentially? The clearance is about 5mil I believe. It probably wasn't the best idea to route under the ESP32 either...I've definitely been learning the hard way on this project.

It is a 2-layer board, most of the bottom layer is a ground plane, there are a couple very small sections of the I2C traces that go down to this layer. Top Layer and Bottom Layers are 0.03556mm thick separated by an FR-4 dielectric of 1.6mm.

Please note that this code was verified on the ESP32 DevKitC V4 and was working perfectly. I also tested different frequencies on the I2C bus as well (100kHz, 400kHz, and 700kHz).

From the oscilloscope capture, my first guess would be too high of a bus capacitance, but I would like some other opinions before I am forced to do another board revision.

I also captured the communication with a logic analyzer as seen below. It repeatedly is doing a setup write to 0xF8 which does not appear in the code at all (based on oscilloscope capture I would not expect anything meaningful from a logic analyzer anyways, but for completeness), again pointing to a hardware issue.

It does not appear to be power issues either because both 3v3 and 5v rails seem stable.

Edit:
I've cut the traces going to the fuel gauge to eliminate any possible bus contention, still nothing. I also added schematic, along with oscilloscope set-up and another oscilloscope capture with repeated "data". It is interesting that the signals appear to be pretty much exact opposites.

Red: SCL (CH1), White: SDA (CH2), Orange: GND

I managed to capture this ^^ as soon as I plugged my board into micro-USB....interesting. This shouldn't be a power issue, the DC-DC converters are rated for over an amp each at their voltages of 3v3 and 5v, not drawing anywhere near that.

EDIT: I was stubborn regarding answers about the oscilloscope ground, but for the wrong reason! The J2 header is having ground issues apparently, I was able to capture this on the scope using one of the mounting holes as a ground reference for the scope, I will have to check the solder connection for the header, or maybe even replace the header as there was a tiny bit of flux that surrounded the header and may have got stuck in there? I did verify the GND pin on J2 goes directly to the ground plane on the bottom layer.


texts: Accuracy issues with capacitive touch screen

texts:
Previous question I asked here.  Posting a new question because my previous approach included many incorrect assumptions.

I'm working on a product with a motor, a fan, and a LCD with capacitive touchscreen.

The most basic description of the problem is that the reported touches are inaccurate sometimes.

The touchscreen has an integrated FT5426 controller. This is the LCD in question: NHD-4.3-480272MB-ASXV-CTP (note the thumbnail is inaccurate).

The touchscreen is powered from a 3.3v linear regulator with a 100uF cap near the regulator output, and a 0.1uF decoupling cap near the ribbon connector. The 3.3v regulator input comes from a 5v switching regulator, which in turn comes from an external 24v power brick.

Below is what I've learned so far.

When they are incorrect, touch coordinates are always left of the actual touch location.
The Y coordinate never seems to have issues.
The issue does not occur at all with some power supplies, and it occurs frequently with others.
None of the power supplies have negative connected to earth.
The issue does not occur if you touch the metal LCD bracket (which is connected to system gnd at several points).
The severity of the issue increases dramatically if the motor or fan is running. Both have snubber caps and flyback diodes.
The touchscreen controller talkes to a PIC32 via I2c. There is a 0.1uF decoupling cap close to the ribbon connector, as well as TVS diodes on the data and power lines.
The 24v input from the power supply appears to be quite clean on an oscilloscope. Although there are sawtooth dips in the voltage when the motor is running.
Connecting negative to earth gnd fixes the problem (but there's not an easy way to do this in the final product).
Connecting the oscilloscope to the point where 24v power enters the board drastically reduces the problem, even with the scope earth is disconnected.
The scope connection even helps somewhat when the scope is powered with lipo batteries and an AC inverter.
I tried connecting an additional 0.1uF cap where the scope was connected  (even though there is already extensive decoupling nearer to the voltage regulators). This didn't have any effect.
I tried disconnecting the earth from the AC input into a good supply, in case there was some kind of capacitive coupling to earth, but that had no effect.
The motor and fan running exacerbate the issue somewhat even when they are disconnected (PWM still going to mosfets).
The board has a solid ground plane, and generally follows good decoupling and routing practices. It also passed CE testing. That is to say, I don't think the design is excessively noisy.
I tried adding a choke to the input power wires (although the power brick already has one, and that had no effect).

My questions are. Has anyone seen this issue before? And what are some possible causes, or things I can try to fix the problem?

What could the power bricks be doing that eliminates the problem? Neither shows excessive noise, and there is no gnd connection.

My goal is to make the touchscreen reliable with the good and "bad" power bricks.

Edit: Bingo, Sunny appears to be correct. I'm measuring huge common mode noise at 60hz (if I'm measuring correctly). The scope is connected to earth, and I have the probes connected to positive and negative where they enter the board. The ground clips are NOT connected.

Here's what I'm seeing:

And here's a good supply:

So finally I can see a difference between the two!

I'm going to try adding a huge common mode choke. But does anyone have an idea for how to fix this without changing the power supply?

Edit: The common mode choke had little effect. I wrapped a pair of magnet wires around a torroidal ferrite, approximately 24 turns. When the probes are placed before and after the ferrite on the negative line, the signals are identical. ..The signal on the negative line is also identical if I turn off the machine (which disconnects the positive line from the power supply).


texts:
In several projects so far, I have been using old "fashioned" transformer based power supplies. However, this time around I want to use a switching mode power supply. The supply will be used to power some 5V micro controller and supporting electronics. The power requirements are equivelent to that of a old usb phone charger (which for several reasons is not going to be used.)

After some research on the internet I found a very neat tool by NXP, which helps with most of the complicated mathematics involved:
http://nxp.transim.com/fb/design.aspx
So far i have been using the default specifications (universal mains, 5V, 5W, integrated FET, TEA1721)

Unfortunately i get stuck at the part where i have to choose the transformer (the bottom 3 choices from the "design" tab).

For instance, i want to use the following transformer:
http://nl.farnell.com/bi-technologies-tt-electronics/hm42-10001lftr/transformer-gate-drive-300uh/dp/2192063
The tool proceeds to ask questions such as: Winding ratio, primary inductance and last asks the specific transformer you use.

The datasheet of the transformer(sorry, cant post more than 2 links) i was planning to use (and also several other transformers out there) do not answer there questions. Because of this I get the feeling that when designing a SMPS also a specific transformer is designed.

So the above boils down to: where can I find the data required to completely fill out the design tool?

Any help is much appreciated, thanks in advance!

Kind Regards,
Victor


texts: How to keep users from breaking push button switches

texts:
I'm designing an enclosure for a device with a push button switch. The external button on the enclosure is physically large so I am concerned people will apply too much force and break the switch or break the switch off the board (if it's a right angle push button switch).

Most push button switches either have to be bottomed out or have a small widow where they are active so it doesn't seem like I can design the enclosure to ensure the user can always activate the switch but not allow the user to bottom out or over travel the switch.

I realize this is in someways a mechanical question but in other ways it's a question about the robustness of switches and I'm not finding much information on this.

How do I design for a push button momentary switch or what switch do I use to ensure that the user won't break it?


texts: Can I connect Analog and Digital Voltage Source together?

texts:
Is it bad if I connect the A_VDD and D_VDD Pins together if I want to use the same voltage? Or maybe I should ask: Why can I hook up different voltages other than galvanic decoupling? This is the IC I am talking about:
AD7792
I am trying to measure Thermocouples.


texts: Remove ground loop hum by 180º phase shift?

texts:
I have a homebuilt subwoofer for my surround sound audio system.  400W constant, 900W peak.  However, there appears to be an AC hum on the input line, and it becomes especially noticeable when I connect a preamp inline at the subwoofer end of the line.  As in, house shaking 60Hz hum.  That hum's gotta go.

Is it possible to remove the effect of a ground loop by feeding an equal amplitude, ~180º out of phase copy of the loop frequency?  I've been thinking about this and it seems like there would be some feedback or something.

Would it work to use this schematic?  If not, please correct it.

simulate this circuit – Schematic created using CircuitLab

And I'd love to have a simpler solution for active ground loop/AC hum elimination if there exists one.


texts:
I have to design a PCB board for a project where I need to add Ethernet connectivity (100Mbps) which only will be used during the setup process (it won't be connected all the time).

The problem is that where the PCB will be placed there's not space for a Ethernet RJ45 connector so the requirement is to place it off the board (the Phy driver would be on the main PCB).

So I'm planning to design a small PCB only with the differential lines and the Ethernet RJ45 connector, this PCB will be connected to the main board through standard 2.54 mm pitch pin connector strip, like this (with more pins):

Should it work fine like that, as long as I keep the track matching length on the Ethernet lines? or should I have to use another special dedicated board-to-board connector?

Thanks in advance.


texts:
I am going to start with ARM development (after 2 years of AVRs) and have picked up the STM DISCOVERY board with the stm32f4 microprocessor on it.

I have decided to go with eclipse + ARM gcc since I don't like the code limit on Keil and I don't have the money to get a paid version.

Following the tutorials I have installed eclipse along with gcc ARM tools + openocd + make utils etc.

My question is about the 'packages' plugin. Like every beginner, I am confused as to whether to use new STM HAL or the older SPL.

My understanding is that HAL has implemented abstraction to a level where it can be referred to as Arduino equivalent for arm. SPL on the other hand provides just enough abstraction to make coding faster but you still need to deal on chip level.

With this understanding I would like to stick with SPL to understand things better rather than using HAL.

What I would like to know is, does using packages for STM implicitly force me to use HAL? If so, can someone point me on how to use SPL with my setup?


texts: barrel connectors which guarantee outer contact before inner contact?

texts:
Is there any feature I can look for on a barrel connector to ensure that the outer conductor (the negative terminal in my case) makes contact first before the inner conductor?

I can't seem to find this information, and for the pair we have, it looks like the inner conductor usually makes contact first.


texts:
For 3 unknown resistors (\$P\$) connected as a triangle, one can measure
the 3 point-to-point resistances (\$R\$) to deduce the unknowns:
$$
P_{ij} = \frac{4B - A^2} {2 (A - 2R_{ij})}
$$
This formula uses the sums: \$A=R_{12}+R_{13}+R_{23}\,\$, \$\,B = R_{12}R_{13}+R_{12}R_{23}+R_{13}R_{23}\$
Is there a generalization of this to bigger meshes?  For example, how
should I calculate the resistors if I have 4 points (knowing that one
resistor has been placed between any pair of points) and am given all 6
point-to-point measurements?  Is there a buzzword here to find
generalizations of this formula with Google?


texts: Considering the power dissipation of a transistor

texts:
These two waveforms are the power dissipation vs time graphs on two bjts (npn and pnp). I got these using LTspice ( alt + right click on the bjts ).

The thing is, while considering will my transistors be able to dissipate those powers without burning themselves, which value of the powers should I use? For example they peak around 3 W, however their average is (ctrl + letf click on the label) shown as around 1W. So, can I consider this 3 W peak as too short to damage the transistors?

transistors are : 2n2222 and 2n2907


texts: Low frequency present on sampled waveform

texts:
I am trying to sample a 50kHz sinewave @ 200 ksps using a 16-bit ADS8517 ADC. I am having a problem in that there is a lower frequency signal present on my input signal as shown:

I have scoped the input and it is a perfect 50kHz 500mV signal. The ADC is setup for +/-10V and all circuits follow the datasheet. If I sample a 1kHz signal I get:


texts:
I am trying to create a UPS circuit purely to provide battery power when main input power is lost. I think I've figured out part of the circuit that stops the battery input when the main power is still on:

simulate this circuit – Schematic created using CircuitLab

But, as you can see, when main input is lost, the battery will end up providing voltage to Q2, ultimately grounding Q1 ... Creating some sort of paradox there Lol ... I'm thinking that there is another high side switch, or PNP that I need to add to this circuit for it to work. This is all theoretical, and Main Input = Battery Input.

UPDATE

From the comments and answers, I think I've found that diodes could solve this circuit ... Here's my new schematic ... It seems to work in my head Lol:

simulate this circuit


texts:
Just a general question. If using a X2 rated safety box capacitor on a 240V AC line, will 275V voltage rating value be appropriate?

I know that peak of the sine wave can reach 310V but can these capacitors handle them or should I choose a higher rating?

This is the type of capacitor I'm referring to. It's rated 275V


texts: Charger Delta Electronics ESR-48/40A E Voltage and Current Adjustments

texts:
Does anybody know how to change (i.e. program) the output voltage and limit the output current in the Delta Electronics ESR-48/40AE charger? The following web pages: this one and the next one have pinouts for two other Delta chargers that seem to match my charger. I'm linking these images directly here:

Delta ESR-48V/56AC 54V(54V~59V)  50A

Delta ESR-48/30G C 54V(43V~58V)  32.22A

I have attached pictures of my charger and technical specifications from a two page fact sheet PDF.


texts: Best way to power 2 motors with 1 power supply?

texts:
I have 2 identical DC motors rated at 12 volts each. I also have a 12-volt power supply. If I put these in parallel, would the motors draw their required current, or is it limited to the current drawn from one motor? I.e. if both motors draw 0.1 amps each, will there be a total of 0.2 amps drawn from the power supply if the motors are in parallel, or will the total current be limited to 0.1 amps because 'amps are shared in a parallel circuit'? Or, perhaps, would it be best to power the 2 motors in series with a 24-volt power supply?

The power supply will easily be able to handle the currents that the motors draw - it is only a small scale application.

I don't feel like much context is needed for this question, but please ask if necessary.

Many thanks in advance!


texts: Help identifying a switched potentiometer please

texts: This is a switched potentiometer from a LED uplight; it has two lights: (1) a switched only lower light controlled by a rotary switch, and (2) a switched and dimmed one for the upper light controlled by a switched potentiometer.  This has failed (knob turns continually, no switching action) so the upper light won’t switch on. It’s a 20v circuit. I’ve taken out the (really cheap) switched potentiometer as shown and have included pics of the circuit board. I’ve got a multimeter but am not sure what to measure as the rotary action of the pot is mashed up internally. The only marking on it is "B1K" as shown.  If anyone has any idea how to identify this I would be really grateful!  If it comes to it, I could replace it with another rotary switch and lose the dimming function.


texts:
This scheme will be designed for weight scales. Why is there a transistor installed.
And I want to understand why need capacitors and resistors in this circuit. (their purpose)
The documentation does not describe the connection diagram, there is only an example of connecting to a load cell.

HX711


texts:
The system I designed uses switching power supply Microchip MCP16311 for operation.
The problem is that during Run test, which i let the board communicate with other system via Modbus, the communication seems to fail for some time while I am gone.
While there can be many possible reasons, especially including the software, I suspect that the switching power supply may be malfunction intermittently.

Above is the switching supply circuit.
Can LC filter at the input of the switching regulator cause problem?
CD2~5 are 10uF capacitors.


texts: Encapsulating an inductor with epoxy and ferrite powder

texts:
Say I have some SMD inductors and I'm trying to limit their EMF from the rest of the board, can I simply potty it with epoxy mixed with ferrite powder (or perhaps iron filings), if I make sure the powder does not create shorts?

A similar idea is done with shielded inductors.

What about potting several of inductors in a section of a board with a single epoxy and ferrite blob? Say, those grouped inductors that are in the section of the board that is responsible for power switching and conditioning? Shouldn't be that much different from placing shielded inductors with their ferrite housing touching each other.


texts: Connecting an external control to a DPDT switch

texts:
Anyone familiar with the SMD1 Stepper Motor Driver Kit ?
I am trying to figure out how to connect external control to the lugs on the switch assembly (DPDT push switches).

The lugs already have the leads soldered so leads for the following

run/hold
Counter and Clockwise
Power

Really new to the electronic stuff though (Two months in). It could be that I am not understanding how to control the leads so that they behave in a similar fashion to the switches. The kit has already been pre-built the only missing piece is the external controls.

Interestingly (at least for me... still grasping), a lead is soldered to the right end of Resistor 3. The manual says the only requirement is that the control's state is equal to 5 vdc when energized. So ... in simple (new to electronics) layman terms how does one connect it say to a breadboard with a 5V supply.


texts:
I'm using the sparkfun inventor's kit. I'm using the code listed at the end fo this post, to controll a servo with a potientiometer using the arduino.

Unfortunately, the servo behaves very jumpy. Even if the value written to the servo does not change, it keeps jumping forward and backwads very fast by ~5-10°.

I also tried the same thing but using a soft potentiometer instead of the bend mesure and the 10kO resistor. The servo was jumping in the same way.

Any ideas how to fix that?

Circuit overlay:

#include <Servo.h>

Servo myservo;  // create servo object to control a servo

int potpin = 0;  // analog pin used to connect the potentiometer
int val;    // variable to read the value from the analog pin

void setup()
{
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
}

void loop()
{
  val = analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023)
  val = map(val, 0, 1023, 0, 179);     // scale it to use it with the servo (value between 0 and 180)
  myservo.write(val);                  // sets the servo position according to the scaled value
  delay(15);                           // waits for the servo to get there
}


texts:
I have a very theoretical doubt. I'm trying to fully understand the load flow analysis and its application. So I have a network with about 300 nodes (AC transmission network). Inside every node I have load and generation. Also the nodes are connected each other by different voltage lines (110kV, 220kV and 380kV). So, my task is to create the admittance matrix of the system. Therefore, I have to assume certain conditions. The nodes are regions of a certain country, so inside them they are cities and substation and whatever necessary. Im only considering the lines that come in and out from the nodes. So, my doubts are:

1.- How do I deal with nodes connected by more than one line? specially when these lines have different lengths and max I capacities.

2.- How do I establish generation and load nodes (base on the load flow analysis theory http://en.wikipedia.org/wiki/Power_flow_study) Should I divide the nodes? (Considering that the equations for these kind of nodes vary in relation to the known variables).

3.- The transformers are inside the nodes (as I said my idea is to consider only the lines coming out and in from the nodes) Is this correct? can I neglect the transformers and consider only the lines?

4.- The only way for having the whole network entirely connected is considering all the voltages lines as one. Explanation: a region is connected with other by a 380kV line and then this one connects with other by a 110kV line and so on. Is this correct?

It is hard to understand on the fly the load flow analysis as I have to jump into a complex problem with a short notice.


texts: PCB layout - Create common ground connection for 5V signal and 12V power

texts:
For my board, which drives dc motor, I want to create a common ground that connects 5v gnd and 12V gnd, as shown in figure 1. The problem I am encountering, as shown in figure 2 is that eagle cad combines the two nets from each ground. After searching for answers, one possible solution is to use a zero ohm resistor between the two nets, as shown in figure 3. Is this the ideal way, to create a common ground?

!!
!!


texts:
The pins that the arrows are pointing to are for the power button on my camera. If I take a small piece of wire and touch the two leads (they seem microscopic), then the camera turns on and off. I need a way to short these leads out so I can control power to the camera.

Two questions:

Can I solder straight onto the button, or do I have to scrape back a little bit of the orange plastic?
Is a Raspberry Pi capable of performing this function? That way I can setup a cron job to turn this camera on and off.

This photo is magnified with a helping hand magnifying glass, it is a very small button.


texts: I guess the way that the power consumption in our homes is calculated, is by calculating the amount of power that each appliance in the home is using. Since power is current times voltage, does it mean that the current that is drawn by each appliance is multipled by the voltage and this is how the power consumption is calculated? is this how we get billed for the electricity each month?


texts: MOSFETs in push-pull configuration: possible short circuit during transition?

texts:
I have created a test schema since I received a late response that I might be short circuiting my own push-pull setup in this post Offsetting Op-Amp output offset in combination with charge pump. It puzzled me whether that could be the reason for some longer transition times in that circuit, but moreover: I just could not answer the question whether there is a short circuit or not. So this question is more a 'back to basics'.
In my test I have a 0 to 6V square wave, driving a transistor to +6V and one to -6V in what I believe to be a textbook example that  an answerer to my previous post learned me to understand. But in all honesty: I have just ordered a textbook to validate this.

https://www.circuitlab.com/circuit/wmvfe5969ymu/mosfet-pushpull-test/
When I simulate this I indeed get something that I fear is a shortcut by both M6 and M2 switched on at the same time during every transition. Is this the case indeed? If so, why is it not the same with both transitions given that the circuit is quite symmetrical? Also, is this really 1A in reality if the power supplies can source this (it was 4A even in the simulation of my original circuit)? Am I just doing it plain wrong? Thanks!
Below the simulation result:


texts: Galvanic isolation in multiple battery design

texts:
I'm trying to design a board to control a couple of DC motors (or stepper motors) for a small robot. The device will integrate a control logic based on a uC and the necessary H bridges for the motors. DC motors speed will be modulated with ~1 kHz PWM signals.
No great powers involved: logic is powered at 3.3 V while motors work at 12 V maximum (haven't decided yet, may be 5 V too) with a current draw limited to 3 A.
The goal is to integrate batteries and their charge circuitry as well. Li-Ion cells will be used, along with DCDC converters to generate the required voltages.
I've used the plural because I'm planning on use two different batteries: one dedicated on the control logic section and the other for the motors and the H bridges (power section). I had some past experiences with disturbances and voltage drops when using a single battery to power both sections, so I'd like to separate the two power supplies in order to avoid any future issues. However, I recognize that these experiences may be caused by a poor circuit design.
And here comes the questions: does it really makes sense to use two different batteries or it is sufficient to design an effective ground path and to use bypass capacitors, taking into account the low currents and voltages involved?
Moreover, if using two batteries is a good idea, is it worthed to galvanically isolate the two sections to completely avoid ground loops and disturbances propagations? Or, again, a good ground path design on the PCB is enough?
If more details are required, I can add them.
Sorry if I made some grammar errors, English is not my mother tongue.


texts: Saving one measurement one display and recalling it using Arduino

texts:
I am using an Arduino with 49E Hall sensors and a 16x2 LCD display and buttons. If I push the button, I want to display the current measurement of the hall sensor (one number). And if I push the button again, I want to display the new current measurement of the hall sensor.
The only thing I could find on the internet is to send the measurement to a drive and recall that. However, I could not find how to save one measurement and I think it could be done much easier. Does someone have an idea?


texts: Can someone help me establishing the polarity of this dc jack on my laptop motherboard?

texts:
So my laptop charger port is fried and I wanted to establish the polarity of the points on the board so I can solder a off the shelf jack instead of the original one which is not available anymore. I will use the original charger and replace the tip on its end to match the new jack so there shouldn't be any voltage/amperage issues. Here are the pictures of the same.

<img src="https://i.stack.imgur.com/HzuIu.jpg" alt="The photo of my charger and the the kind of plug I wanted to replace current jack with
" />


texts:
Datasheet for 1N5406 diode states "3.0 ampere operation at Ta = 75°C with no thermal runaway".

What does this mean exactly? Can I place these in parallel to increase current capability?