texts: Necessary voltage to charge NiMH using Solar Panel

texts:
I'm trying to understand which voltage I need to charge my NiMH batteries so I can purchase the components to do this.
Actually I have 2x AA Ni-MH 1.2 V 1900 mAh and 4x Solar Panel 2 V 220 mA (0.44 W).
I read Solar Cell - Preventing overcharge of an NiMH battery and Voltage input for charging NiMH Batteries but I'm still confused as I'm not an expert in this field.
I gathered this information:

Batteries should not drop under 1 V or they will be damage also not go over 1.78 V;
Constant voltage doesn't work to recharge them (not sure).

I checked out some components to stabilize the current and I found a LM317 in order to stabilize the current to (C/10) 200 mAh and use a MAX471 to check out these values.
But the problem will be the voltage that during the day will drop or go up due to weather so the voltage will never be stable, it is a positive thing?
In the case I need a stable voltage I also found these components (M2578A, TL497A).
I hope to find somebody that can help me. I'm free to other solutions if this one doesn't fit my purpose.


texts: Why harmonic distortion and not at other frequencies?

texts:
Despite searching I can't seem to find the answer to this. In understanding harmonic distortion, one piece of the puzzle that is missing for me is:
- why does the distortion manifest at harmonic frequencies and not other frequencies.

Feel free to simply point me at a textbook / reading that explains it, if that's easier!

I understand that non-linear loads can create distortion. Intuitively, this is because the load can change it's characteristics (resistance, capacitance, etc etc.) in complex (difficult to predict...) fashion.
I understand enough of Fourier analysis to understand harmonics, 1st (fundamental), 2nd, etc etc.
I don't see why the distortion would tend to be at harmonic frequencies.

E.g., if I put a 1KHz sine wave through a non-linear load, why would the distortion show up at harmonics and not something a little less friendly, say, at 1.8KHz, depending on the circuit design?

I come across this in studying audio systems. They rely on THD as a measure of fidelity (for non-clipping signals), but it baffles me why the distortion falls into nicely behaved harmonics...

Thanks!!

Update: thanks to all the great quick answers below, I think I figured it out.

non-linear loads are still predicable: "A nonlinear impedance effects every cycle of the waveform in the same way" (Charles Cowie)
other impacts that do not effect every cycle the same way are transient, or interharmonic. These can be highly unpredictable, due to external forces, etc. They can change the fundamental frequency (e.g., a sharp cutoff)
any periodic (distorted?) waveform "can be represented by their fundamental
component and a Fourier series of harmonics of various magnitudes, frequencies and angles.(this cites another source)" (from relayman357)
there are some great math workthroughs below that illustrate this.

So the piece that I was missing was that the distorted waveform still sits on the fundamental frequency in a periodic fashion, so by definition the distortions are harmonics (different phases/amplitudes,etc.).

Non harmonic distortion (interharmonic) isn't periodic.

Loads like amplifiers don't typically change the fundamental frequency but "give it hair", so it's still periodic.


texts: Is the current through the MCP41010 digital potentiometer independent from its supply voltage?

texts: In the datasheet it says that the maximum wiper current is 1mA. Does this mean that regardless of the supply voltage and the set resistance, I can pass a maximum of 1mA through the resistor? Let's say the supply voltage and logic level is 3.3v, and I set the resistor to 7KOhm. Is it OK to pass a 0.7 mA through the resistor, although the voltage drop is greater than the supply voltage?


texts:
What does "mm/step" exactly mean? Where and how is the distance measured? How can it be converted to °/step?
I have been looking for this, but I haven't found the exact answer.

Here is an example datasheet, where the resolution is in this measure given:
http://www.farnell.com/datasheets/42855.pdf


texts:
I'm using TI's REF200 as a 200uA current source but need something cheaper with similar precision (temperature stability, accuracy, etc). I'm using this in conjunction with an INA337 Inst. Amplifier, giving me great accuracy but too expensive.

This is to read an RTD so the current must be low to prevent self-heating but accurate enough to calculate 0.1 Degree C variations.


texts: MOSFET Miller effect: length of the gate voltage flat area

texts:
As per Miller effect the gate voltage stops to grow at the threshold level until some certain moment:

This can be explained as the drain to gate capacitance drives current through the gate. However - it is clearly can be seen on the picture that the flat area goes far beyond the moment Vds drops to the minimum. I could suppose that Vgs should grow further after 35 nC or so. But it stays still until 85 nC or so.

It is clear that dU/dt (which is the most important part in the equation of the capacitor current) much lower after 35 nC or so.

I checked several datasheets from different manufacturers but the picture is roughly the same.

So the question is:

What holds the gate for extra 50 nC (if we take this TK31V60W5 Toshiba MOSFET as the example)?


texts:
Here is what I read from Ridley Engineering http://www.ridleyengineering.com/images/phocadownload/12_%20flyback_snubber_design.pdf :

I do not get why if we increase the clamp voltage, ie, if we reduce the capacitor and increase the resistance, we reduce the dissipation as the energy to dissipate is always the same and depends only on the leakage inductance of the transformer. Nevertheless i could understand that if we reduce the time during which the inductance release its energy, the transition between the on state and the off state will be faster and then there is less losses. But this has nothing to do with power loss into the snubber. Could someone explain it to me ?
Thank you very much !


texts:
Shaftless hall encoder
I am building a robot, and one of the stumbling-blocks I found was motor positional control.
It seems like the Quadrature encoder is a good choice, but I have no rear axis on the Motors I am using.
Motor:
Micro 6mm motor

I have tried to find a way to use hall effect sensors for encoding, but they seem to all require a magnetic disk on the back

This motor does not have a shaft available for an encoder, and it would probably be too big to use on the robot platform. Is there any way to have the motor mounted parallel to the PCB, with a shaftless Hall encoder?
EDIT:
found magnets that can fit in wheel I am using


texts: Finding the short in my receiver (AMP circuit)

texts:
I will be glad to get your help to solve the mystery in my MARANTZ-SR4500 receiver..
The problem is that after turning on the AMP I got PROTECT MODE and it turned off.

I find out that the source of the short is the Front Right channel, and I find out that 2 transistors, Q658 and Q652 got jammed. I replaced them to a new ones.
after turning on the amp I got PROTECT MODE again,
I find out that I didn't replaced the emitter resistor (R657 - that also got burned), so I replace it and I turned on the power again, in this point I got PROTECT  MODE again and the new R657 got jammed again(got very hot..). I checked the Q658 and Q652 and they was jammed again!
I dont know what else to do, what can cause this short? why does the transistors got jammed again?

Thanks in advance guys


texts: How to know the right amp to power a 12V actuator?

texts:
I have an Arduino Uno. I need to use an electric linear actuator to control the movement of a joint in which I have installed a rotary encoder to know in what angles it's moving.

The actuator is a 12 Volt DC and has only two wires to control it, no libraries or anything. I have a 'double relay' which I think is useful to make the actuator run in both directions, but I'm not sure if I'm going to fry it or not. I also need to connect the arduino and the actuator to batteries or an outlet and I really don't know how NOT to fry them and this is my real problem right now since I don't know what kind of power source to use.

The encoder is to prevent the actuator to move between some angles and to measure the rotation speed, and the movement of the actuator is supposed to be controlled by two buttons, one to go forward while is being pressed, and the other to move backwards.

To picture the design a little better, imagine a leg in which the actuator is in the thigh and it pushes the calf in order to move the leg. The encoder is located inside the knee joint.


texts: Transistor operating region - push pull & current mirror

texts:
While looking at transistor based circuits, I am always trying to understand it with the transistor operating regions.

Question 1:

While looking at a push pull transistor based circuit, I want to understand in what transistor operating region the NPN and PNP transistor will be working. It can't be working in cut-off.
So, is it in saturation state or active/linear state in push pull configuration?

It is always a dilemma between the saturation and active state. I have now figured on how to find out whether a transistor is working in saturation or active state (using the Ic and Ib factors, forced drive or overdrive factors.) But in a simple push pull configuration, there are no resistors. So, I am not able to find the working region of the transistor. Can anyone help with this?

Question 2:

Similarly, in a current mirror circuit, I understand that both the matched transistors need to be in active region for proper working in the current mirror operation. But how do you find out the operating region of the transistor with no Ic or Ib factors?

Please explain


texts: Wiring Stepper Motor / Placement of Stepper Motor Driver

texts:
I'm making a CNC-like machine and I'm in the process of designing PCBs for the head assembly. Currently I have stepper motor driver (with 100uF caps on the power line) on the head assembly and I'm running 24V DC, along with STEP / DIR etc on a 2m individually shielded and overall shielded CAT6 cable to the prototype PCB and the driver drives the stepper as needed.
Now there are other ADC and sensors on the same head assembly that I don't want the stepper to interfere. That was the main reason I placed the stepper driver on the head assembly even though I don't know if it is doing what I intended to do.
Now my question is, If I move the stepper driver to the main board and run the stepper motor cables through 2 of the CAT-6 pairs along with other DC motor etc and run a separate CAT-6 cable parallel to the stepper motor, DC motor etc cable through same conduit would I be running into problems with my ADC and other sensors in terms of EMI? The shielded Cat-6 cable is only going to be grounded at the board side and head assembly PCB has separate ground planes for the DC motors etc so the only way my return currents can go back to main board is through their respective cables and capacities coupling I might get.


texts:
I am making last minutes changes to USB 2.0 differential pair routing on Atmega32u4 based board. I can't re-route the entire board and/or re-arrange the components. So the picture attached is the best I can do.

One thing I don't like about the current routing is that (from the USB + and - pins at 1),  it is using vias (2) and the differential pairs (3) are running below the MCU pins.

I try to keep the USB signals as isolated and simple possible. And running them through vias and under the MCU pins are making me nervous. That said, I have heard USB 2.0 signals are very robust. So I am hoping this is ok.

Please take a look at the screenshot and provide your insight! Will be much appreciated.


texts: Measurement of a signal at microcontroller's output pin

texts:
I have a control board with a microcontroller in BGA package.
I need now to measure a signal on some microcprocessor's
output pin. The problem is that there is no test point around
the microcontroller on the PCB. Does it exist any possibility
how to get to the output pin without a test point? Thanks for
any advice.


texts: Trying to power a 100-watt Cree Xpe array as efficiently as possible with dimming

texts:
I've recently purchased a 100-watt Cree 30-module XPE multichip

http://www.ebay.com/itm/NEW-100W-Red-Blue-Dual-Colors-Cree-XPE-LED-for-100-Watt-Grow-Light-Bulb-Lamp-DIY-/231312859741?ssPageName=ADME:X:RTQ:US:1123

How do I go about efficiently powering this chip?  Having next to no electrical experience, I am overwhelmed by the different types of drivers on the market.  I'd also like to make it dimmable if possible.


texts: how to design a switch which works when an input of 0.10 is applied

texts:
i have an alarm clock , it's output voltage to the alarm buzzer is around 0.15 volt ,
i need to attach an electrical appliance to make it operate on scheduled time ,
for that i had used this circuit (removed the LPT port  part from the circuit):

and attached to the alarm output.
But the 0.15 volt is not driving the opto coupler,
how can i design a circuit switch which will drive the opto coupler or the realy or anything with the 0.15 volt ..


texts: With the Eagle Auto Router, how can I route all signals expect for ground airwires?

texts:
I don't think there is a built in way to do this, but is there a workaround?

If I just auto route, the ground connections are routes as well, but I want to use a ground plane primarily for the ground connections.

If I draw the ground polygon first, and then auto route, none of the signal air wires get routed (is there a say to allow the 'carving up' or the ground plane like this)?


texts: Creating a majority gate using only NOR gates

texts:
I have this digital logic circuit homework and I've been trying to solve it for a day and in the end I got a wrong answer.
Here is the question:

  Create a majority gate using only NOR gates, with 4 inputs a,b,c,d. Which means the output will be 1 if the majority of inputs are 1.

I draw the truth table and Karnaugh map, but they weren't helpful really.

The logical expression will be: a'bcd + ab'cd + abc'd + abcd' + abcd.

If we simplify it we will get: bcd + acd + abd + abc.

I tried to simplify it to a NAND form and I got a very long expression which was not true(I checked it with Proteus).

Can anyone help me please?


texts: Why are the coupling capacitors needed in this DCM converter?

texts:
I have a 48V power supply which needs to be converted to a 12V output. I want to achieve this by using the DCM2322 dc/dc converter.
In the Datasheet the following recommended circuit is given:

My question is why are coupling capacitors needed around the dc/dc converter?


texts: How to know or find if a potentiometer is UL certified

texts:
We have selected a 100kohm potentiometer to dim LED's that are connected to a class 2 power supply. However, according to UL; all selected parts need to be UL recognized for the device to be UL approved. I can not find any information regarding whether certain potentiometers are UL recognized or not. The potentiometer that we have selected is P231-QC20BR100K but it can be any panel mounted 100K pot pretty much

I have a UL lookup where I can find a manufacturer and see if they have UL approved parts but it seems backwards and I have yet to find one that does.

Here is the UL SAM http://www.ul.com/global/documents/offerings/industries/lighting/Downloads/SAM.pdf

I know if I select parts out of the SAM then I am good to go, but I am looking for a more basic solution.


texts:
It's my first time to post my question to this electrical engineering.

Anyway, I'm trying to make a BLE gadget using a BLE112-A BlueGiga.

I could update a firmware of BLE112 but I'm stuck with serial debugging by using a FTDI serial to USB adapter. I need your help.

Goal

・I want to see debug messages which are incremental counter every second.

What already works

・I could update a firmware of BLE112. What I upaded the firmware was this.

https://github.com/slackhappy/ble112/tree/master/serial_debug

What I am missing

・I could't see any debug messages on RealTerm.

What I have devices and firmware

・A BLE device with a CC-Debuger interface. The data sheet is this.

http://runningele.web.fc2.com/ble/REBLE112FR_sch.pdf

・A FTDI USB to Serial adapter.

http://doc.switch-science.com/datasheets/ssci/FTDI%20USB%20Serial.pdf

・Serial/Console/UART Debugging with the BLE112 made by slackhappy.

https://github.com/slackhappy/ble112/tree/master/serial_debug

・The connection between the BLE device and the FTDI Serial Adapter.

BLE device  | FTDI Serial Adapter
P0_2 | DTR
P0_3 | RX
P0_4 | TX
P0_5 | CTS

・RealTerm

As I can see "Status", it seems not be connected correctlly.

Any help will be appriciated.

Thanks,

UPDATE

I confirmed that COM3 is connected to the adapter and the connection is OK.


texts: How is AC load distributed across on-site generation and the utility?

texts:
I’m trying to understand the physics behind AC load distribution when distributed on-site generation is installed and the load is also connected to the grid.

In the diagram below, I have a building that has a PV Array installed and it is also connected the utility.

There a number of hypothetical scenarios that could occur:

1) “Building Load 1” draws 100 kW of power and the PV array is generating 100 kW of power therefore the grid utility is not being used to power the building load.

2) “Building Load 1” draws 150 kW of power and the PV array is generating 100 kW of power therefore the grid is providing the 50 kW

3) “Building Load 1” draws 50 kW of power and the PV array is generating 100 kW of power therefore 50 kW of power is being fed back into the utility.

Are those scenarios correct? If so can someone please explain how this works and also the physics behind this?

Given the “Building Meter” position it will monitor the utilisation of the grid and how much energy the PV array puts back into the grid if the building load is less than the solar generation, but how does this occur? How is the power distributed and how does the net value at “Building Meter” measure this? Lastly, how is this being regulated?

I’d be interested in a high-level explanation as well as a more advanced explanation to help me join the dots.

Thank you in advance.


texts: What does RU (UR) label on DC power relays mean?

texts: I'm trying to figure out what does RU or maybe UR label mean on the body of many many relays. It's labeled almost on all (I've seen so far) DC relays which make me very curious :). Any suggestions?


texts: Can someone give me some ideas concerning the logic of a serial-parallel converter?

texts:
Seriously, I mean the "logic": not AND and OR gates, but the intuition behind it.

This will be an investment of time for whoever answers, so I understand those who don't want to! I'm using this half as a way to get my thoughts in order, but to also get valuable insight from others on this website.

Here is my situation:

I have a CPU that is hardwired to a Kintex-7 FPGA.  From the CPU, I am using "Xilinx System Generator" (an add-on to Simulink) to program the FPGA.  From the FPGA, we have a 6 RX fiber optic cables and 6 TX fiber optic cables.

In our current setup, we are using all 6 of the TX cables in order to send gate signals to a three-phase half-bridge converter.  Obviously, using 6 cables to drive 6 gate signals isn't a very elegant solution.

What I would like to do is remove the need for 5 of the cables.  My plan is to take all of the gate signal information (which should only be 6 bits at a time), and feed it to a "Lattice" FPGA (I think Lattice is one of the major players in the FPGA market, and their products are quite cheap on Digikey).

My idea is as so: on the Lattice, have a counter and an incrementer. On the single fiber optic cable, the first bit would be a clock pulse: this first bit would reset the counter and incrementer on the Lattice FPGA. The following 12 bits would be gates 1-12. By resetting the counter, I think it would be easy to tell which gate signal to go where: the first clock cycle following the reset would trigger the first gate, the second would trigger the second, and so on.

As I was writing this, I realized this isn't going to be trivial: assuring that the Kintex-7 FPGA and the Lattice FPGA are phase- and clock-locked may not be a simple task. I believe this is the area that I need the most help in.  Once I can get the FPGA's clocks to be locked together, I believe this will be an easy task.

Any opinions on how I can accomplish this? Having 6 TX/RX fiber optic cables doing the job of 1 cable makes me cringe; I know I can


texts: ATmega328P current drawn when in Brown out

texts:
I'm experimenting with an ATmega328p on a breadboard using the standard Arduino bootloader. I'm looking at the power consumption as I want to power the device from a solar panel and a large cap. I've got a sketch that get's the device into the lowest power sleep mode. I'm measuring the power supply current and this drops to 23uA with the brownout detector enabled when the supply is above the brown out threshold of 2.7V. If the power supply is adjusted to below the brownout detector threshold then the power supply current jumps up to 881uA. I've tied all floating pins to ground but this doesn't seem to help. Is this expected behaviour or am I doing something wrong ?

/*
 * Sketch for testing sleep mode with wake up on WDT.
 * Donal Morrissey - 2011.
 *
 */
#include <avr/sleep.h>
#include <avr/power.h>
#include <avr/wdt.h>

#define DIVIDER_PIN (13)
#define LOAD_PIN (12)

volatile int f_wdt=1;

/***************************************************
 *  Name:        ISR(WDT_vect)
 *
 *  Returns:     Nothing.
 *
 *  Parameters:  None.
 *
 *  Description: Watchdog Interrupt Service. This
 *               is executed when watchdog timed out.
 *
 ***************************************************/
 ISR(WDT_vect)
 {
   if(f_wdt == 0)
   {
      f_wdt=1;
   }
   else
   {
     // Serial.println("WDT Overrun!!!"); // this shouldn't happen
   }
}

/***************************************************
 *  Name:        enterSleep
 *
 *  Returns:     Nothing.
 *
 *  Parameters:  None.
 *
 *  Description: Enters the arduino into sleep mode.
 *
 ***************************************************/
 void enterSleep(void)
 {
   byte keep_ADCSRA;

   keep_ADCSRA=ADCSRA; // save adc register
   ADCSRA=0; // disable A/D converter

   set_sleep_mode(SLEEP_MODE_PWR_DOWN);   // SLEEP_MODE_PWR_DOWN for lowest power consumption
   sleep_enable();

   /* Now enter sleep mode. */
   sleep_mode();

   /* The program will continue from here after the WDT timeout*/
   sleep_disable(); /* First thing to do is disable sleep. */

   /* Re-enable the peripherals. */
   power_all_enable();

   ADCSRA = keep_ADCSRA;                          //re-enable A/D converter

 }

void setup()
{

  // All pins as outputs set to 0 to save current
  //for (byte i = 1; i <= A5; i++)
  //  {
  //  pinMode (i, OUTPUT);
  //  digitalWrite (i, LOW);
  //  }

  pinMode(LOAD_PIN, OUTPUT);
  digitalWrite(LOAD_PIN, 0);
  pinMode(DIVIDER_PIN, OUTPUT);
  digitalWrite(DIVIDER_PIN, 0);

  pinMode(PD0,INPUT); // rxd input for serial comms
  pinMode(A0,INPUT); // a0 needed as input to read cap voltage

  Serial.begin(9600);

  /*** Setup the WDT ***/

  /* Clear the reset flag. */
  MCUSR &= ~(1<<WDRF);

  /* In order to change WDE or the prescaler, we need to
   * set WDCE (This will allow updates for 4 clock cycles).
   */
  WDTCSR |= (1<<WDCE) | (1<<WDE);

  /* set new watchdog timeout prescaler value */
  WDTCSR = 1<<WDP0 | 1<<WDP3; /* 8.0 seconds */

  /* Enable the WD interrupt (note no reset). */
  WDTCSR |= _BV(WDIE);

 // Serial.println("Initialisation complete.");
 // delay(100); //Allow for serial print to complete.
}

unsigned int val=0;
double voltage;
void loop()
{
  if(f_wdt == 1)
  {
    /* Don't forget to clear the flag. */
    f_wdt = 0;

    /* Re-enter sleep mode. */
    enterSleep();

    // power up the voltage divider and take a reading
    digitalWrite(DIVIDER_PIN, 1);
    delayMicroseconds(250); // settling time
    val = analogRead(A0);
    digitalWrite(DIVIDER_PIN, 0);
    voltage=(val*18.0)/10.24;

    if (voltage>500.0) {
      digitalWrite(LOAD_PIN,1);
      delay(100);         // 0.1 second on
      digitalWrite(LOAD_PIN,0);
    }
  }
}


texts:
Well I need to design three stage amplifier

Im stuck on the output stage, I need that the AC Current on the load will between 20mA to 100mA, but Top current I get is almost 5mA, cant over pass it with use of 12V Vcc. What im Missing?

EDIT:
Redesigned it and now Im gettin 40mA.
Thanks for the HELP GUYS!

My mistake, putting too large load.


texts: optocoupler - Does the current limiting resistor of the led make a difference

texts:
Does the led  current limiting resistor for the led make a difference to the performance/behaviour of the optocoupler?

Is it just like how a normal transistor would work, if you drive the base harder, you will get more current flowing between emitter and collector?

I understand you mustn't drive the led too hard otherwise you let magic smoke out.


texts:
I am trying to connect my HC-05 bluetooth module with PIC16F877A. I know we have to use USART to talk with bluetooth module. So I started with USART of PIC by reading its datasheet.

I am using MPLABX IDE with XC8 compiler and i am not interested in using any libraries.

// CONFIG
#pragma config FOSC = HS       // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = ON       // Power-up Timer Enable bit (PWRT enabled)
#pragma config BOREN = ON       // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = OFF        // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3 is digital I/O, HV on MCLR must be used for programming)
#pragma config CPD = OFF        // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF        // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.

#define _XTAL_FREQ 20000000
#include<xc.h>

void main(void)
{

unsigned int i;
TRISA=0xff;

//UART
TRISC=0X00;
TXSTA=0X20; // TX RS232 settings
RCSTA=0X80; // RX RS232 Settings
SPBRG=31; // Baud rate is set based on Crystal clock

TXSTAbits.TXEN=1; // Enable RS232 transmission
RCSTAbits.SPEN=1; // Enable RS232 reception

while(1)
{

TXREG= 65;
__delay_ms(200);

}
}

I used the above code to send a char 'A' from PIC to USART and was successful in reading it using my serial monitor on PC (with RS232).

Now form what I understood, if I replace the RS232 with my bluetooth module I should get the same char 'A' transmitted to my mobile phone.

I am using Bluetooth Terminal android app to check the reception of data. But the after the app connects to the module it just shows a blank screen. I dont receive anything.

What could be the reason please help me!!!!!!.

Things that I tried :

There is no problem with the baud-rate, both my Rs232 and HC-05 works at 9600. I have ensured the same using my arduino and HC-05.
there is no logic level problem I have used a potential divider to shift 5V to 3.3V.

I am quite new here so forgive me if my question is not that appropriate.


texts:
I have attempted a question (attached below) which is in 3 parts:
First, find new current with new power factor,
Second, find capacitor current.
Third, enter image description here the value of the capacitor.

The first element I have an answer of 27.34A using \$(P=v i \cos(\phi) )\$ however the issue is:
How do I calculate the capacitor current before the value of the capacitor as they are asked in this order?

I know how to find the Value of the capacitor then the current across but not in this order also the method used is quite long.


texts: Can I measure torque accurately by an electrical or electronic method?

texts:
I am a Btech. student from India. We have been given a project in which we have to design a micro-torsion testing device.

We are planning to clamp the specimen and rotate one end by fixed angles using a stepper motor while measuring the torque for given deflection. The shear modulus and the angle/torque at which the specimen fails has to be found out.

The most accurate way to do this seems to be using torque sensors but since our budget is small ( Rs. 10k - arnd 150 dollars) we cant use this. Another way we had in mind was to measure the current drawn by the motor and find out the corresponding torque. But this seems to be prone to errors. Can someone help me out with this ?


texts: +5 to 0v square wave from a 12vdc supply

texts:
I need to build a simple 0 to +5v square wave from a 13vdc (automobile) supply. The frequency of the output needs to be based on a 1vac input signal. I believe it can be done with a handful of resistors, diodes and transistors but I've not done electronics for over 35 years now. Can someone suggest a design please.
Thank you in advance.
Paul.


texts: Startup transient when using a bipolar opamp as a DAC voltage reference

texts:
I have a mixed-signal circuit, with the audio side using a \$\pm15V\$ supply, and the MCU and DACs using a \$3.3V\$ supply. The MCU's internal DAC and two external DACs provide control signals for the audio processing side. I need a rather well controlled ratio of a fixed voltage \$\sim3V\$(which in itself doesn't need to be super accurate) and the DAC reference voltage, so I'm using an external reference for all DACs.

My solution to this is to generate the reference from the \$3.3V\$ supply, with some filtering, and buffer it with an opamp supplied from the audio supplies. Then I can use that voltage to get the other voltage at a precise enough ratio.

After already destroying one prototype due a different mistake regarding the reference, I suddenly became worried about what happens at startup, once the reference is there: to my understanding, an internally compensated op-amp works essentially by charging its internal capacitor with a current proportional to the difference between its inputs, and that the capacitor is usually referenced to its negative rail. Now at startup, if the capacitor is empty, doesn't that mean that the output starts at \$-15V\$ in my case, before settling with the maximal slew-rate of the op-amp to its steady-state level?

My question is: am I right that there will be such a transient voltage, and if there is, will it destroy my MCU or DACs?

The opamp in question is a TL074, and here's the schematic:

simulate this circuit – Schematic created using CircuitLab

There are \$1\mathrm{\mu F}\$ and \$1\mathrm{nF}\$ caps further filtering the reference at the MCU Vref+ -pin, and no further filtering at the external DACs, which are very close to the reference op-amp.


texts:
First, I would like to identify an SMD part in this image, having 02B k printed on it. Where can I find some documentation? I think it should work as some kind of AND gate.

There are three of them on this board, and two of them are probably misbehaving. For both inputs fully open (+12V, +12V), it should output +12V. This way does work only one of them, the second outputs nothing at all, and the third one outputs just a small fraction of the input voltage.

What are these parts?
What may have caused the failures?

Edit:
Whole board:

Well, it seems that the problem is not caused by these transistors after all. On the control circuit (C4-C6) aren't the same inputs, so I suspect the problem will be somewhere else.

Edit2:
This board is a three-color (RGB) LED stripe driver, controlled by an IR remote


texts: Floating input pin with external pull-up

texts:
I would like to improve the performance of my push buttons, which sometimes don't respond when pressed. They have external pull-up resistors and have been initialised as floating input pins. Does not using the internal pull-up reduce performance?
Also, the code is using the internal HSI oscillator instead of external crystal. Could this also be affecting performance of the buttons?

The above image shows the circuit for the push button.
The initialisation is:
GPIO_Init(PORT_SWF, But_Play, GPIO_Mode_In_FL_No_IT);
And here is the code for the button being pressed:
if (GPIO_ReadInputDataBit(PORT_SWF, But_Play) == 0)
{

delay_test(0xff); //decrements from 0xff to 0 for delay

if (Key_Button.Pn == 1)
 { Mode = P1_Run; USART_Send("P1->Play\r\n", 13); }
...
}

The code goes through all the possible buttons that can be pressed (14 in total).
The buttons are being polled every 200ms:
void TIM2_ISR(void)// interrupt every 200ms
{
  Program_Run = Read_Button();
}

Should this period be shorter? Timer 2 clock is at 8MHz
I should say the performance is usually really good, most of the time the response is as expected, but not always, so the problem isn't that the buttons are broken or have stopped working. I would like to make it always responsive, naturally.
Finally, we don't appear to have any problems with buttons coming on inadvertently. They require firm user action.
Thanks in advance for any help!


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

texts:
I have an android phone to which i have plugged an earphones. So at the top of the phone, I get the headphone symbol which indicates that the earphone is connected (In other words, the circuit at the 3.5 mm jack is closed).

Then I cut the two earphones (transducers) from it, and still the headphone symbol shows. When I later cut this cable, below where it branches out, even then it shows circuit completion.

So my question is this:

How does the phone detect circuit completion at the 3.5 mm jack and thus trigger all sound and music to be directed through the 3.5mm jack?


texts: Design a Counter With an Arbitrary Sequence

texts:
I'm trying to design an asynchronous counter with JK flip- flops, with an arbitrary sequence.

The sequence is: 0,1,10,11,0,5,14,15.

I know how to solve this kind of problems, but in this case the sequence repeats one number, 0.

I want to solve this like this guy: https://www.youtube.com/watch?v=Zce6NlHuvfs

But I don't how to manage the problem of the repetition of one number in the sequence.

Any idea?

Thanks in advance.


texts: Best way to connect to UART lines to multiple entities

texts:
I have a sensor that I'm connecting to MCU through UART for data logging and other purposes. However, I also want to program the Sensor independently and I have configured the same UART lines from the sensor with an FTDI chip and USB port (See Figure) .

When this is on breadboard, it is easy to do this as I can disconnect the MCU from the sensor when I'm using the FTDI chip and vice versa. If I'm doing this on a PCB its not possible to disconnect wires. I did think of having jumpers to disconnect the FTDI or MCU when needed so that only one of them is powered on at a time.
Is it a good practice to have jumpers for UART lines? Is there a better alternative?


texts: Is it safe to use a non-isolated buck converter for an LED driver?

texts: I am making a commercial LED lamp. I am using a non-isolated circuit. I am using buck converter. Is it safe? Can I use a buck converter after the bridge rectifier?


texts: Did I connect the FT232 with the Digital isolator Data wired the other way?

texts:
I think I connected the Data wires from the FT232RL to the USB Isolator ADUM3160BRWZ upside down.

I just want to confirm this, Data - of the one should be connected to Data + of the other ?
Datasheet page 7 of the isolator:

NOTE: The FT232RL is not the issue here. The wiring from the MCU to the FT232 works fine, I connected them to my computer and communicates. When I added the isolator between them and connected the computer, It could not detect any device on the usb port. I also tried to connect the usb data cables the other way in case I messed the USB cable, but this did not work either.


texts: Issue controlling MAX7301 GPIO Expander via SPI using Arduino Uno R3

texts:
I'm trying to write a driver to control a MAX7301 GPIO port expander that will be controlled via SPI.

I've used SPI before and it's pretty simple, but I've been working on this for a few days and I can't get a response from the chip when I try to read and write to registers.

I've pored over the datasheet and I can't find anything that strikes me as a solution. I am 100% confident that the signals I am sending are indeed received by the chip, as I've stuck a few oscilloscope probes on the chip's legs.

The one thing I have noticed is that occasionally a 5V blip will appear on the MISO line, often where I would like to see a signal that exists long enough to be clocked. I suspect this may be the root of the problem.

On the MAX7301, Dout is not high-impedance and has to be connected to an external tri-state buffer. I don't think it's in a Z state when I want to read it, but could the buffer be doing something else?

I would be immensely grateful if anybody could provide me with some advice on how to approach the problem.

The MAX7301 datasheet can be found here

My code at present is below:

    /**
 \mainpage Arduino / 2436W10003 SPI Comms.
 \file project5.ino
 \brief Control SPI comms. and display results on PC.
 \details Another time perhaps.
 \author
 \version 0.1
 \date 12/08/2013
 */

/*! SPI.h */
#include <SPI.h>

/*! Baud rate used in serial comms. between Arduino and PC */
#define SERIALSPEED 9600
/*! Pin number of SSSEL_GPIO */
#define SSEL_GPIO 2
/*! Pin number of SSEL_ADC */
#define SSEL_ADC 3

#define NOP 0x00

/**
 *  \brief Brief
 *
 *  \param [in] void
 *
 *  \return void
 *
 *  \details Details
 */
void loop(void)
{
  int result;
  result = readGPIO(0x04);
  Serial.println(result, HEX);
}

/**
 *  \brief Brief
 *
 *  \return Return_Description
 *
 *  \details Details
 */
void setup(void)
{
  // Configure serial comms. with PC
  Serial.begin(SERIALSPEED);
  //Serial.print("Serial communiciations set up at %d baud.", 9600); // sort the %d thing out later

  // Configure GPIO pins
  pinMode(SSEL_GPIO, OUTPUT);
  pinMode(SSEL_ADC, OUTPUT);

  // Slave select pins active LOW, so set inactive HIGH
  digitalWrite(SSEL_GPIO, HIGH);
  digitalWrite(SSEL_ADC, HIGH);

  // Configure SPI
  SPI.setDataMode(SPI_MODE0);
  // SPI_CLOCK_DIV2 --> 128
  // 16 MHz / divider = 16 / 4 = 4MHz
  SPI.setClockDivider(SPI_CLOCK_DIV4);
  // MSBFIRST or LSBFIRST
  SPI.setBitOrder(MSBFIRST);
  SPI.begin();

  writeGPIO(0x04, 0x01);
  writeGPIO(0x04, 0x01);
}

/**
 *  \brief Brief
 *
 *  \return void
 *
 *  \details Details
 */
void writeGPIO(byte address, byte data)
{
  address &= ~0x80; // ensure bit 15 is cleared
  digitalWrite(SSEL_GPIO, LOW);

  SPI.transfer(0x04);
  SPI.transfer(0x01);

  digitalWrite(SSEL_GPIO, HIGH);
}

/**
 *  \brief Brief
 *
 *  \return address
 *
 *  \details Details
 */
byte readGPIO(byte address)
{
  byte result;

  // Ensure that the WRITE bit is set
  address |= 0x80;

  digitalWrite(SSEL_GPIO, LOW);

  // D15 to D8 contain R/W bit and register address
  SPI.transfer(address);
  // D7 to D0 discarded
  SPI.transfer(NOP);

  digitalWrite(SSEL_GPIO, HIGH);
  // Allow a few ns for MAX7301 register to fill up
  digitalWrite(SSEL_GPIO, LOW);

  // No useful data in MSByte
  SPI.transfer(NOP);
  // Results from register should be in LSbyte
  result |= SPI.transfer(NOP);

  digitalWrite(SSEL_GPIO, HIGH);

  return(result);
}


texts:
What is the best way to handle an unused wire inside of a cable.

Let's assume I've got a cable with 4 wires, only 3 of them are used.
I could connect the 4th wire at one end to ground, at both ends or let it float.

In my specific example, the cable connects a Oxford Instruments ILM level meter with a liquid nitrogen level sensor. (Basically two concentric metal cylinders. They act as a capacitor. The nitrogen level modifies it's relative permittivity.) The connections are

Pin Function
1   0V
2   12V
3   Freq.


texts:
I have some trouble with my LM2576-5.0WT. I have an input source of 12 V (8 A max), and I want to convert it to 5 V (3 A maximum.)
Hence I built my circuit as the one on the first page of this datasheet..
On my PCB (with other things) I have trouble with the 5 V. It changes with the load, and it's 10 V with no load (at the beginning I got 5 V, but not anymore).) My PCB is more complex but the schematics of that part is like this:

(The green is a ground plane)
Hence, I made a simple circuit (same as in datasheet, so without the delay (Cd1 and Rd1)) with breadboard. I got 5 V without load. But when I put a motor as a load, to test it, the voltage decreased to 4.1 V. Why is the voltage not stable? How can I have always 5 V? I need to supply a RPi, so I need 5V - 3 A. You can find below my test circuit (same as in the datasheet).

NB: list of component (the codes are from RS, sorry I cannot put more than 8 links)

LM2576-5.0WT: 9101966
Cin 100 µF: 7111731
D1 - 1N5822: 6870877
L1 - 100 µH: 1048443
Cout - 1000  µF: 7111312


texts: designing trace anthtenas for 2 sets of rf rx+ tx

texts:
First of all forgive me for my mistakes, English is not my main language.

I want to design a custom pcb (i'm not an expert just a hobby),
I have a working breadboard circuit of an micro controller and rf reciver and transmitter,
MCU + 433mhz(rx) + 433mhz(tx) +315mhz(rx) + 315mhz (tx)

In order to receive rf remotes 433/315 codes and re-transmit them on demand.

My problem is that every module needs it's on antenna,

That means 4 DIFFERENT antennas.... (!!!!)

I do not want 4 spiral big antennas on m pcb,
So i need to design a trace antenna on the pcb,
Is it possible to combine all antennas together,
Or i need to trace on the pcb 4 different antennas?

A. 4 trace anthennas (433rx+433tx+315rx+315tx)

B. 2 trace anthennas (433rxtx + 315rxtx)

C. 1 antenna (433+315) is it even possible?

As i said, i'm no an expert, what is the right approach to it,
in order for:
1. good design+ good reception,
2. minimum space on the pcb (need to be small).

Will one of you professionals can guide me what length and size and how should the trace antenna supposed to look like.

Thanks allot!,
Your help means the world to me.

The modules are :
H3V4F 3V 433Mhz  (433 RX)
H34B 3v 433mhz (433 TX)
H3V4E 3V 315Mhz  (315 RX)
H34A 3v 315mhz (315 TX)

MODULES:
http://www.ebay.com/itm/3V-5V-315Mhz-433Mhz-MINI-Wireless-Transmitter-Module-Receiver-Module-Transceiver-/331680416810

RX datasheet : http://www.smiery.com/H3V%20Series_EN.pdf

THANKS


texts: How will the output of a 12V transformer wall wart differ from that of a 12V SMPS brick?

texts:
I have been working on a project to drive an electric door strike from an Arduino shield of my own design. Actually, I'm using a Freetronics Eleven and not an official Arduino, which is relevant because the Eleven accepts a wider range of input voltages-- up to 12V.

So, since the data plate on my door strike says it needs 12V and only 450mA, I figured I could drive the strike solenoid using power from the Vin pin of the shield's power header, using a SMPS brick that puts out 12V at up to 2A.

Well, the short version of this story is that the power from the brick only works sometimes. After carefully measuring the power at the terminals of my shield and verifying everything to be exactly in spec, I thought perhaps I simply had a bad door strike, so I procured a replacement.

But the new strike misbehaves in exactly the same way.

After some digging around in the junk bin, I found the 12V transformer wall-wart that originally came with my first door strike (in a kit). I plugged it in, and lo and behold it actuates the strike reliably every time. So of course I measured that beast's terminals and found it puts out ~12.4V-- no great surprise at the slight difference from the data plate, but is that .4V really the difference?

I try using my bench supply to see... Nope, still flakey at 12.5V from the bench supply. In fact, no perceptible improvement all the way up to 14V which is the maximum the strike is rated for.

But, that 12(.4)V transformer works like a champ. SO my question: What is the difference (to a solenoid) between the output of a transformer (rectified to DC of course) and the output of my switch-mode power supplies? Is there perhaps some surge current coming from the transformer that the SMPS doesn't produce?

Oh, and if I fab a cable that lets me plug the transformer into my Eleven (and thence through the shield Vin to the strike), is it going to toast the regulator on the Eleven? (It's only slightly over the 12V spec… but…)

Here is a picture of one of the strikes in question:

You can't quite make it out in the pic, but the strike came with a capacitor soldered across its leads. I presume this is for snubbing voltage spikes when the solenoid is de-energizing?

Edit: Strike plate is manufactured by HAI by Leviton, model 79A00-1 12-Volt DC Electric Door Strike.


texts:
If someone could identify the following it would be much appreciated. I am
assuming it is an oscilloscope of some sort.

The device needs a lot of TLC; grounding the inputs leaves a small Lissajous like figure on the display, so all is not well.

If I could get a manual that would help, I do not have the nous to go in on my own :-(.


texts: Is ACS712 isolation sufficient for SELV?

texts:
Can the Allegro ACS712 current sensor be used to measure mains current with enough isolation so that the isolation between the mains (230V) side and the logic side of the sensor is enough to achieve SELV compliant isolation (see https://en.wikipedia.org/wiki/Extra-low_voltage )?

Datasheet for ACS712:
http://www.allegromicro.com/~/media/Files/Datasheets/ACS712-Datasheet.ashx

As far as I can tell, the device has a too short creepage distance between the low voltage and 230V pins, meaning that it won't be usable to achieve the required isolation for SELV circuits.

I'm thinking one could have a slot in the PCB under the ACS712 and then fill this slot with a glue gun. In this way it might be possible to achieve 7mm creepage distance. Would this be an acceptable solution? Or will the current creep in between the glue and the SO capsule body?


texts:
I am a relatively newbie to electronics but hopefully this question is not very non sensical:

I am following a guide to build a 8 bit computer. The guide requires a RAM which has a 4 address bit and 8 data bits. Unfortunately, the only RAM i have has 8 bit address and 8 bit data. Also, the country I reside in does not have many electronics outlets for these kinds of RAMS. My question is whether I can use the RAM i have instead of the one in the guide by grounding the higher 4 bits to ground? I am thinking by doing so, the higher 4 bits will always be zero and the lower 4 bits can connected to the circuitry of the DIY computer in the same way as demonstrated in the guide?

Thanks.


texts:
I need some help exploring a solution.

I have an ARM Cortex M3 MCU, which has low-power sleep mode implemented. Wake-up sources are any GPIO pin, or an RTC alarm.  A terminal is connected to UART-0 at 115200bps.

When the system wakes, a stream on unintelligible chars is sent to the terminal.  I assume this is noise or jitter.  The board designer did not place any external pull-ups or noise suppressing caps on the UART Pins, so I need to solve this issue in the firmware.

So far I've tried the following, to no avail:

Before entering sleep mode, detach (demux) the UART Tx pin and attach (mux) GPIO input with internal pull-up. On exiting sleep mode do the converse.
As in 1, above, but attach GPIO Output, driving high.
As in 1 & 2 above, but flushing UART FIFOs after detaching, and before attaching.

The following kinda works, but is not very elegant:

After waking, send a stream of backspaces -- for(int a=0;a<64;a++) printf("\b"); But sometimes non-back-spaceable chars (e.g. CR or LF) slip thru and it aint pretty.


texts:
So I'm working with this part the ADAU1761 it's a little dsp codec from Analog.  I'm trying to get I2C communication up between it and my PIC32.  I spent a good part of today trying to get this to work, thinking I would verify it by reading a register.  I was getting ACKs but no data returned.  Finally I tried manually programming the ADAU1761 and then reading registers worked fine.   I'm suspicious that maybe I need to write some clock values to it first, but so far it's not too clear from the datasheet.

I am reading the datasheet and I did read their document on how to program the whole device.  I was trying to take baby steps by verifying my i2c first before trying something more advanced though.

Anyone have an experience with these parts, who might know what I need to do?


texts: Get the max current through relay without activating it

texts:
I have a circuit where the only current I can get to supply my battery is the one that I can get from a relay connected to Vcc.

When it is not pulled to GND I can get current without activating it up to around 12mA.

Is there  some way to get more current without activate the relay?

I've done some tests connecting this to LC filter and a buck converter and I think I'm getting more current, but this circuit seems too sensible to changes (If I want to prevent the relay activation).

Edit:

simulate this circuit – Schematic created using CircuitLab

I need to power this circuit in a place where there is no power outlet or other power supply, so the only place where I can get power is from the relay (But I can't access to the wire connected to VCC, only the wire that goes to GND) .
This is the relay from the intercom of a entry door building (when you press the switch you power this relay so the door opens.
I tried this circuit in several places and there are buildings with AC powering this relay or more voltage so the current I can draw is enough, but other places have to low current capability (only 15mA before relay activates). The max current through the relay is 70mA when SW1 is pressed.

Edit2 (reply to Pipe and more info):
Yes, it is Energy Harvesting situation, but I could not found the best way to solve it to works in any different scenario.
I've tried supercapacitor approach, charger connected directly to the harvest source, and now I get the best results with buck+charger

Edit3:
My circuit draws an average 48mA (connected to Vbat) and the current that I get now from the relay is 10mA at 9V-7V, but the efficiency of the buck and charger is not too high at low currents so I'm charging to 10mA at Vbat (whith 30mA or more the total efficiency is more than 60%), the battery acts like UPS and helps to handle current peaks

Edit4:
I've also checked some MPPT (Maximum Power Point Tracker) way to approach this, but I did not see something valid


texts: How can this high-side IGBT drive work without exceeding maximum Vg-e

texts:
I was reading an article that creates a device that model  the I-V curve using on capacitive loads. In the article they using IGBTs to charge and discharge the capacitor.

This is the circtuit that they are using:

How can this circuit be funcional? Because, for example, in IGBT1, VGE is changing with the charge, and when the charge is complete (Vcapacitor=60V for example): VGE= VG - 50, exceed the typical maximum value for VGE that is +/-20 V.


texts: I'm seeing unexpected data on the A & B outputs of my ALPS incremental rotary encoder. The A & B pins are are attached to a microcontroller with pull-ups enabled and the centre pin is ground The pulses are aligned on their rising or falling edges rather than being 90 deg out of phase as I expected (and documented everywhere). Attached are two capture screenshots, one for clockwise the other anticlockwise rotation. Am I missing something?


texts: Car bluetooth power delay- USB capacitor?

texts:
I just bought a bluetooth adapter for my car. It's input is 5V/0.3A and is powered via a 5V/1A USB power adaptor that is plugged into the 12V/10A/120W max. socket in the center console of my 2004 Honda Accord.

It turns on automatically when I turn my key halfway, but when I start my engine it shuts off, and I have to unplug it and plug it back in to get it to power back on.

I emailed the company, and this is what they said:

  "We are sorry for all the inconvenience it caused to you. As you know, there is no internal battery for the SoundSync. The power is from the car or car charger. For some cars, when we turn the car ON, the SoundSync will power on at the same time. However, when we start the engine, the power shut off for a very short time. It shuts the SoundSync off and the SoundSync will not auto power on again. Therefore, we will change it to button control version in the short future."

I'm trying to figure out a way that I can fix this. Unfortunately, my knowledge of electronics is limited.  If I had a capacitor between the device and my car, would it solve the problem? I.e. the capacitor takes 1-2 seconds to charge, which interrupts the on-off-on of the car starting, and provides continuous power to the bluetooth module?

I have a soldering iron and am pretty tech-savvy, I just don't know where to begin troubleshooting the issue. Any input would be greatly appreciated.

Thanks!

Edit: How would I go about adding a capacitor? Solder together a circuit board, capacitor, and male/female USB pieces? Cut an existing USB cable and use it instead of the USB components?


texts: I have a DC motor that is controlled with an npn transistor with pwm. Everything works fine. I want to brake the motor instantly. I tried to short the terminals with another pairs of transistors but did't work.


texts: How can people say that voltage is like a pressure. They also say that voltage can be seen as on how badly the electrons move. From my knowledge, voltage is the work done per unit charge and so if the work done is high then the voltage / potential difference is high. Also, what do we mean by per unit charge (is it 1 coulomb charge, or what should it be)? Tnx


texts: Graphical Intuition for Band Pass/Stop Active Filter Responses to Square Wave Input?

texts:
In reading my text, it notes that, when a square wave of a certain frequency is applied to band pass/ band stop active op-amp filters:

Band pass filters will output the fundamental frequency of the square wave multiplied by the gain at the center frequency.
Band stop filters will carry all the harmonics of the square wave other than the fundamental.

I have some idea of what this means, but I would really like to see a graphical representation to confirm. I've searched my book, but it doesn't have any accompanying graphs. Not had any luck on the Internet either, though it may be a case of me searching for the wrong thing.

Can anyone help me out? It would be greatly appreciated!


texts: Calculate current of resistor with Norton's Theorem

texts:
I have a problem with the following circuit:

simulate this circuit – Schematic created using CircuitLab

I have to calculate the following data using Norton's theorem:

\$R_n\$
\$A_n\$
\$I_{R_2}\$

For the first I calculate the following circuit:

simulate this circuit

That is:

$$R_n=\frac{R_4\cdot(R_2+R_1+R_3)}{R_4+R_2+R_1+R_3}=\frac{2,5\Omega\cdot(2,5\Omega+5\Omega+2,5\Omega)}{2,5\Omega+2,5\Omega+5\Omega+2,5\Omega}=\frac{25\Omega}{12,5\Omega}=2\Omega$$

To calcultate \$A_n\$ I used superposition: for \$A_4\$ is simple because of current con \$A-B\$ is the same of \$A_4\$, so
$$I_{AB}'=5A$$

Considering \$A_1\$ I calculate the voltage of real current source:

$$V_1=A_1\cdot R_1=15A\cdot 2,5\Omega=37,5V$$

And then the current:

$$I_{AB}''= \frac{V_1}{R_2+R_4+R_3}=\frac{37,5V}{10}=3,75A$$

At the end:
$$I_{AB}=5A+3,75A=8,75A$$

Now my problem come: how can I calculate \$I_{R_2}\$??

I know the result is \$2 A\$ and I tried all I can but without success....


texts: How does RF Coax cable impedance + Microstrip impedance mismatch affect power transfer

texts:
I have a passive GNSS antenna with a 6" 1.13mm shielded coaxial cable that connects to a u.FL connector. From the u.FL connector I have a 2" microstrip transmission line to the RF input of my GPS receiver. Altium's built in impedance calculator shows the trace impedance at 34 ohms not 50 ohms. Other calculations of stripline based on on strip height above ground plane, freq, dielectric material... also show similar impedance.

How does that affect power received at the GNSS receiver? I presume there will not be max power transfer since the impedance are different.


texts: would this be a good design of a stack machine?

texts:
I've got an assignment to design a 8-bit stack machine I was wondering if this would work:

My problem is this i'm not too sure if this design will work, i've hardly found any designs on a zero adress machine and the ones I have found have had a mar and correct me if i'm wrong the mar is an adress register, how can it count as a zero address machine that uses an address register? I may have gotten something wrong somewhere but I can't see it. Will this design work as i'm not using any memory?


texts: Cascaded vs. non-cascaded bridge-tied load circuits using opamps

texts:
A bridge-tied load (BTL) amplifier circuit doubles the output voltage (and potentially quadruples the power, output current limits notwithstanding) by using one "master" opamp for gain followed by (i.e cascading its output into) another "slave" opamp with unity gain but used in inverting config. This is type of cascading BTL circuit is illustrated for example in Fig. 1 in Maxim app note 1122 and in Fig. 73 (on p. 24) in the OPA454 datasheet (OPA454 being TI's highest voltage opamp it is somewhat natural that its datasheet is replete with circuits for increasing output voltage swing even further.) Not all opamps are unity-gain stable (unless externally compensated), but it is possible to adapt the cascading BTL circuit for opamps that aren't unity-gain stable (without adding external compensation) by feeding only a portion of the master opamp's output voltage to the slave opamp through a simple voltage divider. For example, Marston's Audio IC Circuits Manual shows such a circuit using TDA2030 (which is not-unity gain stable) in Fig 4.28 on p. 108. So lack of unity-gain stability of the opamp is not a show stopper for the cascaded BTL approach, although it does increase component count slightly.

On the other hand, a non-cascading BTL circuit can also be built simply by feeding the input signal into one inverting and one non-inverting opamp in "parallel" [sub]circuits and adequately changing the gain (sharing it) between opamps. According to the aforementioned Maxim app note 1122, which shows such a circuit in its Fig 2., that's actually a better approach than the cascaded BTL because "Both [opamps] amplify the same input signal, so neither one reproduces noise, distortion, or clipping introduced by the other". According to the same Maxim app note, a non-cascaded BTL circuit has additional advantages in the case where the availability of a single-rail power supply (such as car audio etc.) dictates that the opamp inputs additionally need to be DC biased (for AC-coupled [that is capacitor-coupled] inputs); chiefly among the advantages claimed in this single-rail supply case, it is said that the non-cascaded BTL circuit "eliminates signal injection into the high-impedance bias source".

After having heard all praises lavished on the the non-cascaded BTL topology in Maxim's app note (that other sources seem have missed), my question is: what are the disadvantages of the non-cascading BTL circuit relative to the more typical (judging by the sources I've surveyed) cascaded BTL? (And, sub-textually, why is the typical BTL opamp-based circuit exemplified using the cascaded approach?)


texts:
Test laboratory of our factory asked me to design an isolated high voltage amplifier. Here are the requirements:

The circuit will be built with transistors and passive components in the lab. (No IC usage - because we don't have any and can't buy)
The circuit will be supplied from lab power supply (Vs < 40VDC).
The input signal will be applied from the function generator (1Vrms sine - frequency may vary between 10kHz and 100kHz).
The output will be isolated and have a peak value of 1.5kV.
Output power will be 100mW max.

Here's my design on paper:

simulate this circuit – Schematic created using CircuitLab

As you can see, the circuit is a simple Class AB amplifier with inductive load. Since the voltage gain is 10V/V, the voltage across the primary will be 10Vrms, so the output will be 1kVrms = 1.5kVpk.

Is there any problem with this circuit? What can you suggest?


texts: When rechargable battery age, what quality decreases?

texts: When a rechargeable (li ion) battery has many cycles and begins to wear down, what quality actually diminishes? I know it can hold less charge, but is this evident in the potential difference it can store (aka will the voltage with each charge diminish)?


texts:
I've been using an Arduino's analog input to read a resistance. The resistance is typically from an LDR or from an adjustable resistor.
It's working fine so far.
I have 10 bits resolution, usually I don't want more than 4 bits, and at the very most, I'll want 8 bits.
I read about op-amp voltage buffers, but given so far everything works smoothly with my 2 devices (sometimes connected over 40m of wires, that is a Cat5 20m cable with the Arduino at one end and the LDR at the other end).
Do I need that op-amp? And if I don't, could you suggest a case where it'd useful?


texts: Why is analog "voltmeter sensitivity" is defined as ohm/Volt?

texts: What is the motivation to define a sensitivity of an analog voltmeter as ohm per voltage?


texts: Parallel RLC Circuit: how to write differential equation?

texts:
Please consider the following circuit:

At t>0 this circuit will be transformed to source-free parallel RLC-circuit, where capacitor voltage is Vc(0+) = 0 V and inductor current is Il(0+) = 4. Now is the time to find the response of the circuit.

Here is the context: I use "Fundamentals of electric circuits" of Charles K. Alexander and Matthew N.O. Sadiku. All the example problems follow the standard procedure: 1) define damping factor and resonant frequency; 2) define the type of response (overdamped, critically damped or underdamped); 3) choose the appropriate response equation; 4)...

I have calculated damping factor and resonant frequency, resolved corresponding characteristic equation and got these natural frequencies: s1 = -1, s2 = -6. This is the case of the overdamped response and I am ready to write the response equation:

v(t) = A1*exp(-t) + A2*exp(-6t); (1)

i(t) = A1*exp(-t) + A2*exp(-6t); (2)

However, I'm perplexed: which variable should I choose: voltage or current? Since the initial conditions (v(0+), i(0+), dv(0+)/dt, di(0+)/dt) are not the same, A1 and A2 will have different values for the equations 1 and 2. For this particular case if the voltage across the capacitor is used as a variable, then A1 = -33.6 and A2 = 33.6 which is incorrect (LTSpice confirm it). If I use a current through the inductor, then A1 = -4.8 and A2 = 0.8 (correct answer).


texts: How to interpret transitions in a QPSK constellation diagram?

texts:
I have one doubt regarding how to analyze a constellation diagram. It is from a QPSK transmitter. The constellation diagram looks typically as books (as a square as you can see in Figure 1), but for shorts periods it changes as you can see in Figure 2. We don't know if it is a problem with the transmitter, a problem with the data that is being modulated, or if it is a bad configuration on the Spectrum Analyzer. What do you think about that? How can we interpret the constellation diagram and the transitions? Thanks in advance.

UPDATE: 27/02/2018
Please see Figure 3 that shows how we set up of the Vector Analyzer.

 (Figure 1)

 (Figure 2)


texts: Is it possible to swap out a 48 MCU for one with 64 pins?

texts:
I wonder if I can upgrade a device that is currently using a 48 pin MCU to a 64 pin MCU?

I can do this by altering the PCB pin layout but I will have floating pins.

The reason why is because it's a more powerful and faster MCU.

I'm a total newbie at this but want to do some crazy stuff.


texts:
As I understand it, in PC-to-MCU communications over USB CDC, specifying a baud rate is only necessary when the MCU sends its received data to a UART. The baud rate is needed by the bridging device to know the signalling rate to be used on the TX/RX lines.

For example, the ATMEGA16U2 used with the ATMEGA328 on Arduino Unos is responsible for receiving USB packets from the PC and translating them to UART signals for the ATMEGA328. So I can see why it is important that the ATMEGAU2 and ATMEGA328 agree on a baud rate.

I've read somewhere that the PC ignores any baud rate setting used with USB CDC. And yet, when a wrong baud rate is set in the PC serial terminal, gibberish is received, even though the data is received over USB without any traces of UART stench on it. The only case where I think baud rate should matter on a PC is when data is being transmitted by the PC to the bridge. I imagine baud rate information is sent along with the data so that the bridge can know at what speed to signal the receiving UART.

What is wrong with my assumptions? When and why is baud rate relevant at the PC's end in USB CDC communications?


texts: What is the purpose of extra parallel resistor R2

texts:
This probably is a very basic question. I looked at a real world device schematic - a "digital pushbutton" and can't figure out why R2 is necessary.

This device is supposed to be connected to arduino. J1.1 is Vcc from arduino, J1.2 is signal out connected to digital input pin, J1.3 is GND.

Resistor R2 is in parallel to R1 so it increases current to ground which in my opinion is negative effect.

So there should be some positive effect which justifies it's existence. Unfortunately I can't find it.

At first I thought that R2 is part of some voltage divider but I don't see it. Firthermore output signal is digital so we would prefer whole Vcc. No voltage divider is necessary.

Then I thought about situation of open switch - then signal might hang in the air. However when switch is open signal is connected to ground through R1+D1.

What is the purpose of R2?


texts:
EDIT: I understand now, but with a microcontroller, why can't I just connect the data pin of the microcontroller to the data pin on the servo and the power form a battery bank to the power on the servo? Won't that just have the same effect?

All I know on this topic is that connecting a microcontroller's power output to most motors will roast the microcontroller because of the high current. People say the solution is a motor driver. How does a motor driver work (let's use a servo motor driver in this case.) Does it, somehow generate it's own power somehow, or is it supplied power from a power source and?

Oh yeah, why can't I just supply any old 5v servo motor with the 5v output pin on the C.H.I.P computer?


texts: How does the maximum current of solar cells combine in series?

texts:
Say I have one 4W PV cell and one 2W PV cell (both producing about .5V). I know enough to say that maximum current of the first cell is 8A (4 / .5) and the maximum current of the second cell is 4A (2 / .5).

In series, what is the maximum current of these cells together in a solar panel?

Is it 12 (the total)? Or is it 4 (the limit of the smaller one)?


texts: Add 5V bias power to use an electret microphone with XLR audio interface

texts:
I recently acquired an audio interface (Behringer UMC22) and, since it's quite a bit better than my motherboard, I'd like to connect my modmic 4 to the XLR mic input. The interface has phantom power available, but it's either off, or 48V, which is way too high. This leaves me with two options: inject 5V of bias power and then connect it to the XLR input with phantom power off, or drop that 48V to a more usable 3-10V.
Which option would lead to a better signal? And which would be easier to implement?
If I was to go with injecting bias power, would a 9V battery provide the best low noise power, or would 5V from the computer also do well?

This looks like a very simple way of adding bias power, I'm just wondering if everything is safe (on the interface) and how to properly connect to the XLR balanced input?

PS: Sorry for all the questions, I found a lot of information, but none that's really complete for this use.


texts: Someone tell me if my concept is clear about voltage?

texts:
I have been learning about voltage and I am still a bit confused.

A battery having 1.5 volt means that it has electrical potential energy difference of 1.5 volt right?

That means this potential to do work or energy is supplied when the battery is connected to the circuit and electrons flow as they recieve the energy?


texts: Is there a lower limit on operating frequency of CMOS SRAM?

texts:
I study computer science, and so I am in the deep end here.
I have set upon designing a machine which requires RAM. I found a listing for Toshiba's 128KB (8 bit per word) SRAM (TC551001BPL).

I intend to run this at a very slow clock, maybe 1-10kHz or so (maybe even single stepping it with a button). Due to this I figure that I never have to worry about any sort of transition, propogation, etc times, as a clock cycle of 100 microseconds is orders of magnitude higher than the timings of any chips today, which is usually in 10's of nanoseconds (bus transcievers, D-Flip Flops, binary counters, RAM, etc). However, this made me wonder, is there a minimum frequency at which I must operate the RAM? I could not find anything like that in the datasheet, but I'm still not sure.

Could the fact that this RAM is asynchronous cause this issue?

This is slightly off topic, but I only need 1024 word, 8 bit word of RAM or so. Any IC recommendations that better suit my application would be extremely helpful.


texts:
As part of a radio transmitter design, a square wave oscillator has to drive a power mosfet. Given the gate capacitance and the frequency, the maximum current should be around 50mA.

The power mosfet is a little bit of an overkill (it works up to 2A), but RF mosfets don't go as high as I need, at least not the one I have. The oscillator can't source that much current, so I need a buffer that can source 50mA at 1MHz. The only buffers I know how to build are BJT followers with a common emitter, but they aren't fast enough. When switching it on and off, it takes time for it to go up to VCC again.


texts: Is it realistic to power a Raspberry Pi & Canoscan 9000f scanner off a solar array/battery bank in an off-grid setup?

texts:
The scanner would be scanning for 15 minutes each hour, and the raspberry pi would be always on or could be turned off between scans. What specs would I be looking for in a solar array?

Canoscan max power consumption: 15W


texts: Put the crystal on the bottom with thru-vias, or on the top with a blind via?

texts:
I'm using an STM32L155 in a very small (0.4 mm pitch) WLCSP package (6x9 array). At this scale there is no room for traces between the balls, so the design requires HDI and/or blind vias to fanout the signals.

I'll only be using about half of the signals. I'm still early in the design process, but I am hoping to use blind vias-in-pad with a six-layer stackup. My intended stackup is Signal, Ground, Signal, Signal, Power, Signal.

I'll be putting components on both sides of the board. I want to avoid using buried vias to save costs.

Here's my problem:

I'm using an external 32 kHz crystal to source an accurate real-time clock. One of the balls isn't accessible on the top layer (see the green signals):

These pin locations are fixed. I'll need to drop a via-in-pad from the inner pin to get access to it.

So, my question:

Since I need to use a via anyway, would it be preferable to:

Use thru-vias on each crystal pin and then place the crystal (and bias caps) on the bottom of the board, or
Drop the inner signal to layer 3 using a blind via; run it to the right, and have it come back to the surface next to the crystal?
Do something much more clever that I haven't thought of yet?

I understand that it may not matter much on a 32 kHz crystal, but I'm looking for best practices. I would have the same problem if I was using the external high-speed crystal (24 MHz); the pinout is similar.


texts: Easiest way to go from analog input to PWM output?

texts:
Project background:  I'm building a plasma speaker.  There are several examples online using a TL494 power supply IC and feeding audio into its feedback pin to get sound out.  A sample schematic:

I'm wondering if there is a better way to do this.  I'm a hobbyist, so I'm not terribly interested in the absolute cheapest method since it's a one-off, and I'll also be tolerant of potentially dangerous or sketchy things since I don't have to get certification for anything.

I have access to a few micros, but little experience with them.  I did get a Launchpad, and my understanding is one of the MSP430s that came with it has a built-in ADC.  While going from analog to PWM seems a little underwhelming for a microcontroller, I do have an additional requirement that I must limit my upper duty cycle to remain below about 95% to prevent saturation of the flyback transformer.  Operating frequency is 120-150khz.

To summarize my question:

Are there more straightforward ways to go from a high-impedance 1V P-P input signal to a 150khz output signal with proportional PWM, capped at a maximum 95% duty cycle?  Unless built natively into the device, I will be building my own output stage to drive the power MOSFET.


texts: Why don't pull-up/pulldown resistors prevent microcontroller I/O pins from changing state?

texts:
Apologies for the vague title, wasn't sure how to summarize the question. I've been struggling with this for two days and feeling a bit desperate.
This is how I understand simple CMOS gates work in principle.

I also understand that microcontroller inputs should not be left floating since due to their high impedance they can self bias if so. So we use pull-up/down resistors. What I struggle to understand is, for example in the below we are providing a constant connection to Vcc. Why doesn't that permanently peg the input high, or at least cause issues since a 10K resistor is a comparatively low value considering the input impedance of the microcontroller?

My understanding is something like this would happen in principle (although of course the pins on the microcontroller would have a somewhat different design than an inverter gate)

Is this correct? If so in principle, unless there are some system specific restrictions, you could choose to design your circuit with either pull-up or pulldown resistors and appropriate switches, as you see fit?
I would really appreciate your input.


texts:
So my place has 2 contactor sizes of 22A and 40A. Now i know that both will be more than enough to power up a 3HP motor. To avoid oversizing in this case, would i need to provide additional fusing to help protect the 3HP motor if it has a 40A contactor as opposed to a 22A?

This is 480V system that is sized for a 3hp motor ( electrical disconnect that is)

There is also a 40A overload to be used with this 40A contactor. It jus means the overload and contactor can handle up to 40A each

Basically it's a electrical disconnect like a fuse breaker (sized for a 3hp motor) u have a ol on the starter I dont think there is an ol on the breaker. Normally with < 5hp motor running at 480 your minimum circuit ampacity is <10A so either 20A contactor or 40A contactor is more then enough.


texts: Setting minimum and mximumu delay from register to asynchronous logic in sdc file

texts:
Is it possible to write design constrain in sdc file to tell synthesyser to limit absolut delay from register to asynchronous multiplexer.
I have 4 phase shifted clocks and signals synchronized with this clock drives output through asynchronous multiplexer.
The delay through the multiplexer is different for each one. Is it possible to stabilize delay in sdc file?
Something like this
  set_max_delay -from clock_0 -to mux_output 5 ns
  set_min_delay -from clock_0 -to mux_output 4 ns

  set_max_delay -from clock_1 -to mux_output 5 ns
  set_min_delay -from clock_1 -to mux_output 4 ns


texts: Cortex M3 reset handler with vector table relocation

texts:
I have a system with an STM32F103, which has a bootloader and a main app. Now, the main app is offset from the beginning of the flash to make room for the bootloader, and on cold boot the firmware is entered through the bootloaders reset handler. Then the bootloader does it's thing and eventually starts the main app by calling an entry point defined in the app image. The main app then relocates the vector table via the vector table offset register SCB_VTOR to set up its own interrupts, and everything proceeds from there.

In this case, the main apps reset handler is never called. Further, according to page 35 of the Cortex M3 programming manual, on any reset (cold or soft) VTOR is reset to 0, i.e. it'll point to the bootloaders vector table.

My question: am I right in thinking that the main apps reset handler vector is never called (unless I call it directly myself), i.e. I can just leave it unimplemented/make it assert etc? Or is there maybe some peculiar reset circumstance where the reset handler in the offset vector table might be called?

The motivation for the question is that if I write some "just-in-case" reset handler, I'd certainly like to test it. However, if

the handler is never called during reset, I can't test it (under real conditions, i.e. whatever state the MCU is in when the reset happens. I could of course call it directly, but that isn't quite the same)
if there are circumstances where the handler may be called during reset, then I need to know what those circumstances are, so I can test my handler.


texts: Crosstalk issues with Photomultiplier Circuit

texts:
I'm working on a circuit involving Silicon Photomultipliers. Two SiPMs are in parallel together, and they go to a feedback amplifier circuit where the current signal gets filtered and converted into a voltage signal as shown below:

simulate this circuit – Schematic created using CircuitLab

Our first design used only one SiPM in the circuit, so we decided to try and see the effects of two SiPMs in parallel together in one amplifier circuit. We decided to go with a design where we have a pair of pads that connect the two SiPMs together, so they can either be connected together in parallel when the pads are shorted, or they can stay on their own individual channel if the pads are not soldered together. For this design, we soldered the pads together so two SiPMs are in parallel together, and we left elements of the unused channel bare, with no parts soldered to it.

One issue that we're seeing is crosstalk. I'm really new in designing boards like this, and I never learned about issues such as this. I never took a design class, so issues such as crosstalk is all brand new to me. The PCB board for the circuit has already been designed, so there's nothing much we can do about the trace length and such. I'll have to keep these design issues in mind for the next board. For now, I was just wondering if there was anything I can do to reduce the crosstalk effects at the output. My first thought was to increase the feedback capacitance from 3 pF to a higher value, say around 6-12 pF. The initial circuit with one SiPM utilized 3 pF capacitance, and there were no issues with it. That was the recommended circuit values provided by SensL. Putting two SiPMs in parallel increases the amount of noise at the input thanks to parasitic capacitance, so I thought that by increasing the capacitance, it would compensate for it, and since it is still in the pF range, the RC time constant is still tiny in the nanosecond range, so the rise time shouldn't be affected very much up to a certain value. Does this sound correct, or are there other ways to reduce the crosstalk?

EDIT: I apologize for being vague in explaining crosstalk. Please let me elaborate a bit more. First off, the PCB board that we are working with contains four SiPMs, each on their own individual channel, and there a set of pads at the cathode of two pairs of SiPMs to put them in parallel if desired. You can see that in the schematic below.  Our current design with two SiPMs in parallel per channel is shown. Our issue is that we used an LED pulser to 'activate' our SiPMs, and we examined output from the two different channels. One channel was being pulsed, while the other channel was being left alone. You can see it in the picture below, with the pulse in purple, the pulsed channel in green, and the non-pulsed channel in blue. The pulsed channel shows a positive peak which is what we expect, but we noticed a negative pulse in the unpulsed channel, which we believe to be is crosstalk. Again, this is all occurring on the same PCB board.

simulate this circuit


texts:
I've been looking into different ways an op-amp can be used for signal filtering and came across the following circuit.

I would like to solve for the transfer function, \$G=\frac{v_{in}}{v_o} \$ for this circuit (we can assume an ideal op-amp for simplicity). My initial guess was to divide up the gain multiplication into two parts: \$G=\frac{v_{1}}{v_{in}}\frac{v_{o}}{v_1} \$, where \$v_1\$ is the amplified output of the op-amp.
Going with this, the first part of the transfer function, \$\frac{v_{1}}{v_{in}}\$, to my understanding would just be a standard lowpass op-amp configuration, hence:
$$\frac{v_{1}}{v_{in}}=-\frac{R_2}{R_1}\frac{1}{1+(sC_1R_2)}$$
The second part of the transfer function, \$\frac{v_{o}}{v_1}\$, is where I found some confusion. To me, it seems like a simple voltage divider between \$v_1\$ and \$v_o\$ should work, but this would not include \$R_3\$ in the equation at all. I also thought that perhaps I need to create a Thevenin equivalent circuit for this part, but I'm not really sure how you could do that for this scenario. But, assuming the voltage division here is valid, I get:
$$\frac{v_{o}}{v_{1}}=\frac{sC_2}{(1+sC_2R_4)}$$
resulting in a final transfer function of the form:
$$G(s)=-\left(\frac{R_2}{R_1}\frac{1}{1+(sC_1R_2)}\right)\left(R_4\frac{sC_2}{(1+sC_2R_4)}\right)$$
So, is this the right way to go about solving this circuit? Is splitting up the circuit essentially into two parts valid here? Is a simple voltage division enough to solve \$\frac{v_{o}}{v_1}\$, without \$R_3\$ being a factor?
Any insight would be much appreciated, please let me know if I've messed things up completely as well.


texts:
I would like to miniaturize an existing antenna I built, which is just a typical ferrite rod antenna.
When makes a ferrite antenna different from an inductor ? Can I just use a same value inductor as a replacement for my antenna ? Provided SRF and DC resistance are good enough for my use cas.
Doesn't the size of the magnetic field depent entierely on the inductance of the coil, regardless of shape or size ?
EDIT : LF antenna, not VLF
An image to illustrate what I mean :


texts: Confusion about the direction of the vectors: motional EMF

texts:
I'm working through an example with motional EMF and I'm having trouble understanding the directions of vectors so that I can apply induction law.

The magnetic circuit seems complex because the circuit is used to analyze other situations but the air gap 3, the coil 3 and the single open loop coil are the ones relevant to this.
We neglect dispersion and the magnetic reluctance of iron.
Section S of the circuit is constant and it's a square of side a.
The air gaps have thickness $\delta$.
All of the coils have the same number of turns.
The open coil has a current $i_0$ that is zero.

Now we have i2=1A and i3=i0=0 which originates a flux $\phi=-1mH$ and $B_3=-0.625 T$.

Now my question is about the next paragraph:

"The motional induction electric field only exists when the coil 0 passes the air gap 3 (I understand that, because only there B is not zero). On that conditions, the elecric field as an orthogonal direction to the figure plan, the same as the current i0 (I think I can also see that...). At the bottom side of the coil we will have $u_0=Bva$ (now that is what I don't understand, what is the direction of B? Is it the same as v? Why? I can't see the direction of the vectors!)."

Basically my question is about the direction of the vectors while applying the induction law.
Can someone help me clarify it? I only need a small draw or some brief explanation.


texts:
In short, what is the difference between buses and nets? Read some questions that seemed somehow related but still it is not clear for me.

Related:

How to use Altium Buses?
http://www.xilinx.com/support/documentation/sw_manuals/xilinx11/sse_c_nets.htm


texts: I am having a 3 pin relay used in bike horns. My need is to turn on and off ground using the positive as trigger. That means the positive terminal of the device is connected to the 12v supply. Usually we are turn on and off positive using ground. I need the opposite. Is it possible? If yes i can connect it to the device. I don't have any test environment. So i have to confirm before going forward.


texts:
I've gotten a question about STM32F10x frequency measurement.
1. what is the maximum frequency which can be measured by this micro and its timers especially the advanced timers.
2. what are the limits of measuring the frequency?


texts: Use of RFID or suitable alternative to remotely communicate change in system state

texts:
I have a physical system which is dispersed over about 20-30 metres cubed and at random points within this space there are electronic nodes which have single binary outputs.

I want to monitor every time any of these outputs goes high from a central location accepting occational losses. The essential criteria in the solution is that each node communicates wirelessly and utilises the minimum amount of power possible.

My question:

1) Is there a way to leverage (hack) RFID technology for this
purpose, perhaps powering an active RFID tag for a transmission and
reading this transmission from the central location?
2) If this is not possible, what would be the most common solution in
such a scenario where power is highly constrained and fault tolerance
(acknowledgement / confirmation) is important but not paramount?
Would Bluetooth LE be my best bet or a different solution?


texts: Determining node voltages and ladder currents in R-2R DAC Ladder with Op-Amp

texts:
I'm really curious about the voltages at the nodes between the R resistors in the R-2R DAC ladder with an Op-Amp. I've tried using KCL and Ohm's law to find them, but I haven't been able to. Simulation shows different results.

The voltage source at the bottom is 3 V, in the ladder configuration, 2R resistors are vertical, and R resistors are horizontal.
R = 3 Ohm, 2R = 6 Ohm. Rf = 5 Ohm. The rightmost resistor is 1 Ohm.
One more thing to note, the switches seem to be on the ground, but when the simulation runs, I give it value of 1, and they are switched to the 2R resistors.
I've used the fact that the Op-amp has a "virtual ground" concept - when one terminal is grounded, so is the other. Therefore, the current through Rf resistor should be 4.98/Rf. The current through the rightmost 2R resistor should be just 3/2R, since one end is basically grounded. Then according to KCL, we have one current entering that node, and two currents leaving that node (one leaving to the 2R, the other leaving to the R). But this approach doesn't seem to be helping much. After a few nodes, the currents inthe ladder (and also the node voltages) stray really far away from my expected values. What am I missing here?


texts: Is there a hobbiest's source for Akros Silicon PoE evaluation boards?

texts:
I am interested in experimenting with PoE for a variety of small embedded controller projects. Is there a hobbiest's source for any of the Akros Silicon PoE evaluation boards? Or is there another bit of kit I should be looking into?

My ideal prototyping board would be something like an Ethernut powered by PoE…


texts:
I've got problem with steering DC motor with L293D and Arduino. I'm using DC motor from old inkjet printer and a quadrature optical encoder from the same printer to track the position. When I'm moving the carriage by hand from left to the right the encoder value in arduino increments properly: constantly from 0 to about 6200 (when i plot encoder value vs time I'm getting straight line). When i plug +5v directly to the motor pin the encoder value also works properly.

The problem is when I'm steering the motor with l293D. When I run the motor with low speed - with 30% PWM signal of 30V which is 9V the encoder value vs. time graph look weird. It seems like the engine oscillates a little bit. When the speed is faster the line is more smooth but it still oscillates and is much more worse than in case when moving carriage by hand or directly supplying the motor where the line is exactly smooth. When it goes right it should not decrease in any moment but it is! Do you have any idea why?

In the first graph you can see the encoder value when i'm moving carriage by hand and the other show the case when it's move by the motor with l293D.


texts:
I am a graduate Aerospace Engineering student. I need to wire a pneumatic actuator's controller and a magnetic position sensor for a small part of my research. I received a connection diagram from the company making the controller, and there is a relevant video showing the procedure on YouTube. Since I, unfortunately, don't remember anything from my electrical course years ago, I don't know what a particular component in the video is called. The connection diagram says PLC, but there does not seem to be any 'PLC' in the form I am vaguely familiar with, nor is there any programming involved in the video.

Video - https://www.youtube.com/watch?v=5lFFg6-doK0 (from 0:05)

What is that device in the center called? It just seems to transfer i/p-o/p

I have also attached the connection diagram I received.
Thanks in advance!!


texts: Calibrating the oscillator of a microcontroller

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I would like to do precise timing of events which trigger hardware interrupts on a microcontroller. I am aware of the stability issues associated with microcontroller oscillators and I think a 30ppm (or smaller) stability in 50 MHz (or greater) oscillator will be good enough for my project. But an oscillator can be very stable and yet be inaccurate as a time keeper because the frequency of oscillator may not be what one thinks it is. So my question is: How does one go about calibrating the external oscillator of a microcontroller board?

Thank you!


texts: Diode sine wave shaper - location of break points

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I'm attempting to generate a sine wave from a triangular wave using the diode breakpoint method where the sine wave is approximated by multiple straight-line segments. Where should the breakpoints be located in order to produce the cleanest (lowest THD) sine wave, all else being equal.

For instance, in the above image where 4 line segments are used, where should x1, x2, and x3 be located in order to produce an optimal sine wave? What if an arbitrary number of line segments are used? I'm planning on using 7 in my circuit.

I've attempted to formulate an error function from the difference between the area under the sine curve and the area under the straight-line segments, then minimize this error function. However, this appears to lead to an optimization problem in many variables, and doing this by hand looks frightening. This looks like something that Excel or Octave could do fairly easily, but I don't have much experience in this area. Anyone have any ideas?


texts: Designing mains power feed for maximum equipment lifetime

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I want to establish how or if mains power feed to mains powered equipment can be designed to optimise equipment lifetimes. In my case I have a specific item of equipment that I am concerned about but my question is a general one about what design rules or lessons  may be applied to even such a simple system to ensure optimum lifetime.

Of interest is how to supply power to or remove power from equipment - whether it is best to leave power supplied and rely on internal switching or to use intermediate switching points, and whether aspects such as mains power surges and spikes or power outages make a significant difference to what is done.

As a specific example - in my case I have a notebook PC (Dell Inspiron 15R) that I use as a desktop PC. I use it in a fixed location and do not have a battery installed (the battery is disconnected and stored away). So this laptop is similar to a desktop PC as regards power supply. This would also presumable apply to batteryless routers, switches, printers etc. There seem to be two options regarding how to supply power.

1) Keep the equipment plugged into a power strip with on/off button and switch on at the power strip when I have to use it and off when use is finished.  In this way, however, the power supply of the equipment gets a voltage spike when I switch on the power strip, and absorbs energy to ground (absorbing the remaining currents) when I switch it off.

2) Always keep the equipment plugged into the power socket at the wall, leaving it connected even when not in use. In this way, instead, the equipment (in my example the power supply and motherboard) is always under voltage and never completely "at rest".

So, from an electronic point of view, in which of the two ways is equipment likely to get less damage and live longer?


texts: Simulated MOSFET circuit - Does not work as expected

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I have designed this circuit to turn off the mosfet as soon as I apply 1.2A of  current for 2ms.
Also I want to know the status through the LED whether the mosfet is turned off or not.When I simulated this circuit,LED starts glowing before the current reaches to zero.Could you please suggest me whether this circuit serves the purpose.

Simulation profile:

I am using FDC5614P from Fairchild semiconductor.Here is my simulation snapshot of drain current Vs Voltage across the load


texts: Offline (unpowered) storage time limit for NAND based drives?

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What's the storage time limit for NAND based drives?  Like Samsung EVO 850 or something similar?

Also, since USB storage drives use NAND flash... what's the storage limit on them as well?

When I ask about the time limit, I'm asking how long can the drive remain unpowered and still contain valid data.  Consider storage of ZIP or other critical bit files, unlike images/pictures/videos etc. that tend to fail when bits flip.

EDIT: I'm trying to understand how long a NAND flash based device can effectively retain information before that information becomes lost due to the known issue of electron leakage from the core storage mechanism.


texts: How can I make cyclic 4 min. delay circuit that works on 5VDC

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I have a automatic liquid drip project, which works based on timing.
Basically there are three manual switches and each switches will select different delays such as 2 min., 3 min. and 4 min.
When first switch is pressed, the 3v motor controlled dropper will ON only after 2 min. delay and also it OFF after 2 sec ON.
Then, the same thing should happen for every 2 min. delay.
The other two switches will select to set the delay into 3 min. and 4 min. respectively for the same above operation.
Now, my question is that, how I can build such circuit using ICs. The only thing is that the circuit should not take more current during its OFF state (no dripping time duration) and also works at about 4.5V. Is there any possibilities ?


texts: Clamping the output ground very close to earth ground

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I've noticed that the output ground of most power supply are not quite the same as earth ground. The DC is nearly negligible, but there is usually an AC component between output ground and earth ground of magnitude 4-6 times the intended DC voltage (probably attributable to floating inductive spikes -- the voltage differential output may slightly float). Only the best power supplies, say a PC PSU, or linear regulated power supply can have output ground nearly equal to earth.

I haven't tested, but the current probably won't be that large. So why not use a Schottky rectifier or something to clamp the output ground to earth ground?


texts: I have a stair made of several steps. I want that when I put a foot on a step, the light of the next step is turned on. Each light is placed just under the edge of the step. If I use LEDs as lights, can I build a system with sensors that can be powered with batteries? Since I have to place a sensor on each step, what kind of sensor should I use? Where can I start to build something like this?


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I have spent quite a bit of time trying to work this out, but I just can't. I want to power my ATMEGA32U4 chip via USB, and at the same time send that USB +5V off to the circuit +5V bus per the picture (as I have other +5 devices to power).

In saying this, I also have a barrel connector in the circuit (not shown in image) that could otherwise power the device without the USB being connected (via the MC33269-5.0).

So I need the circuit to protect itself from having two power sources at the same time and/or the barrel power source overpowering the USB bus, should they be both connected at the same time.

My next challenge, I'm after an SMD diode but not sure what the values should be or footprint? It should never get more than +5V~ as I have a MC33269-5.0 regulating things from the barrel connector. Perhaps I am over engineering it with the diode and fuse?

And finally, I think the C3 cap needs to go to ground - not between the circuit +5V and the VBUS pin on the ATMEGA32U4?

All advice/red lining and or suggestions otherwise welcome!


texts: How to find the frequency of more than one zeroes analytically?

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Hello, I have to draw the Bode plot of \$G(s)=\frac{V_u}{V_{in}}\$ and I want to do it without calculating the full transfer function.

This circuit has Cgd=1pF capacitors at every Mos.
Vt=0.4V, k=2mA/V^2, and Lambda=0.

I have found the poles at 5.5MHz and 86MHz by a simple visive inspection of the circuit.

I know that the transfer function at \$s=\infty\$ has a finite non-zero value (0.1), so there must be 2 zeroes.

I can find the first zero by calculating the frequency at which all the current generated from Vin flows into T1 transistor (93MHz), but I cannot find an easy way to calculate the frequency of the second zero (it should be circa 216MHz).

I know I can calculate it through graphic inspection, but I would like to know if there is an easy analytical method as for poles and the Cgd1 zero.

Thank you.