texts: What type of 8-pin ribbon cable connector is this?

texts:
What type of ribbon cable connector is this in the picture below? I would like to order a compatible male end for a converter plug I am designing.

Edit: The pin spacing (as measured with a digital caliper, by averaging the inside and outside measurements of two pins) is approximately 0.1", so I think the Molex KK is correct.

For the curious, this is from an OWI robotic arm kit.


texts: Can I use a 555 to ignore short DC pulses in simple switch circuit? Not same as usual debouncing

texts:
I have a reversing camera in my car that I wish to:

switch on whenever the reverse lights come on
turn off when reverse lights go off.

Problem is, my car's computer will periodically send these short (let's say 100 ms) 12V pulses to the reverse lights to test whether they are present (simple resistance test).  These pulses are too short to light up the bulbs, but they are short enough to switch on an electronic circuit.

Q. Can I use a 555 timer to ignore those short pulses?  I know I can probably do it with a RC setup, and I realise that I'll end up have resistors and capacitors around the 555 circuit. A delay in switching on the reverse camera is OK.

Cheers!


texts:
I recently bought a Chines massaging chair hoping i can intercept the serial communication between its wired remote and the chair itself, I've cut the wire and connect the Rxd and Txd of the chair to my arduino pin 3 and 4 and ofcourse the ground pin, i used a software-serial code as below but couldn't quit get any readable value. at some point even when the chair is not connected the program shows some value 255, 128, 128...on the serial monitor, could this be a baud rate issue? when i plug the remote all its pads light up at first and only a few with the power button led continuously blinking in about a second, but when i give 5V power to the remote all the pad light light up and freeze so by this i know that the chair sends some signal through its Rxd for the remote (same thing happen when i connect all wires except the Rxd of the remote, which is the Txd of the chair. am I doing something silly here or totally wrong ? am new to this SO Please help.

The wired remote has four lines connected to the board with markings Vcc, Gnd, Txd amd Rxd which clearly shows the communication to be some sort of serial protocol

Code used.

#include <SoftwareSerial.h>
#define rxPin 3
#define txPin 4
SoftwareSerial softSerial =  SoftwareSerial(rxPin, txPin);
void setup()  {

 pinMode(rxPin, INPUT);
 pinMode(txPin, OUTPUT);
 softSerial.begin(9600);
 Serial.begin(9600);
}
void loop() {

 int data = softSerial.read();
 Serial.println(data);

 delay (1000);


texts: low noise, low distortion analog multiplexing

texts:
I'm trying to design a low noise, low distortion, low cost op-amp circuit for multiplexing analog (audio) signals. Experience, research and some experimenting already led me to the following components in combination with a proper low-noise power supply:

NE/SA5532A dual low-noise op-amp (datasheet)
HEF4053B analog CMOS switch (datasheet)

This question is in essence about integrating the switch. I do know that relays are an alternative to CMOS switches, but at approximately 5 to 10 times the cost they are not really an option in this design.

There have been fine questions with sensible answers about op-amp circuits with (switchable) variable gain, e.g. here. This question is not about this issue, as the title suggests. But bear with me and let me elaborate on it as an introduction.

Consider this circuit with variable gain:

The position of the switches in this circuit is perfect. They are at ground level, so no offset influences the switch resistance. As a result, in this position the switches do not generate modulation distortion.

In the signal path, the switches are also away from the sensitive op-amp input pins. Rin, Rf, Rg1 and Rg2 can all be located very close to the input pins. If the switch would be at op-amp input side, this would not be possible.

Now to the real core of my question. Here are 4 different possible configurations of input multiplexing and none of them come close to the ideal configuration above of the variable gain solution.

The circuit around U3 is there for completeness, but it's the least sensible.

In the circuits around U2 and U4, the switches see a variable voltage level and that will lead to modulation distortion.

The circuit around U1 has the switches at virtual ground, but the position of them is also at the inverting input pin. I have implemented this in the past and from experience, this layout leads to high noise sensitivity. I'm not talking about inherent noise of the circuit, but noise from the surrounding electronics.

My question is if anyone has experience with the best trade-off that can be made, or can suggest any tricks that can circumvent the disadvantages summed up here, or can suggest a clever, different schematic that achieves the same goal.

edit

In the answers and comments, several aspects of the main issue were touched. In essence, I was asking about the best topology and it has drifted towards switch properties (on-resistance, on-linearity, off-capacitance) and side effects of the mixing configuration (node charging resulting in plops when switching), crosstalk,...

I'm well aware of all these issues and I might have oversimplified the question in favour of clarity and focus.

Andy aka has raised valuable considerations that I will pursue further, but the solution suggested is exactly as I've done in the past, with less success than I hoped for.

τεκ raised a simple but interesting alternative that I'll also look into.

My intermediate conclusion is that I'll try to get hold of the Douglas Self audio book. I'll be digging into switch and FET properties and try to simulate their effect in the different topologies. That might lead to new insights and I'll report back. I'll definitively be prototyping different solutions in the end. So it might take some time, but I'll come back with new  insights and report back.


texts: Best Altium component practice for resistors, capacitors

texts:
In the past when drawing resistors in Altium schematics, I have only  used "Res3" from the supplied Alitum default library "Miscellaneous Devices.IntLib". For each Res3 I place, I only changed the value and footprint as required. Although the project worked and all the information about values and footprints are shown in a BOM, the disadvantage using this method is tracking previously used components when you need to decide which resistor to use.

In a new project, I have moved to a model where I copy the Altium "Res3" to a new schematic library and modify the value, footprint and power dissipation etc, as I would when adding a new IC. It is also easier to update changes later to the same part in all schematics, add in suppliers etc.

Depending on the situation, I can see there are many different ways to manage Altium components. What is your preferred way / best practice when using resistors and capacitors in schematic sheets where the values differ but other specs are the same - reuse the same component or create a new component in a schematic library?


texts: Is it possible for a Wireless device charging pad to fry RFID / Contactless cards?

texts:
Lets say for example that a person has a wireless charger in their car centre console (an option on some new cars)

This person puts their wallet and phone there and the charger kicks in. (wallet between charger and phone)

Given that RFID / NFC / Contactless etc cards have an induction coil to power the chip, is it possible for the chip to be destroyed by the effect of the charging field?


texts:
I've gone through school and done all the work but looking back at it i still don't quite get it.

The rule is current in a capacitor leads and in an inductor lags. The inductor makes perfect sense but the capacitor doesn't.

We live in a causal world. Nothing from the future can affect the present. That said the inductor lags but then why does the capacitor not lag even more?

Is this only a mathematical construct?


texts: What's the difference between PWM and VPW?

texts: What's the difference between pulse-width modulation (PWM) and variable pulse width (VPW)?


texts: How to check the signal integrity of CAN lines?

texts: Its a general question.I would like to know what to look for when testing CAN circuit on CANH and CANL lines.What are the issues that are common?


texts: How to properly develop a PCB everytime without taking too much photoresist off

texts:
Its been a while since I made a good PCB and I can't remember what I did to make it perfect, but after reading various resources, I have determined the following as to why most of my design was removed in the photo development process:

Maybe my lighting unit is incorrect. I bought a black light from a party store that has a long black tube and internal circuitry. I remember once trying a black light in a halogen bulb with kind-of better results.

I then printed two identical copies of my circuit (I chose mirror mode in software) on transparencies in a 600DPI laser printer and tried the process with the toner side towards the light (maybe I should flip that around?)

I then made myself a lightbox for my circuit board by inserting my blacklight inside a "shadow box" from a decor store called Homesense. I'm not sure if this will be a problem. In the past I used regular glass with good results, but someone online mentioned plexi-glass is better for circuit boards but I'm not sure how much better if any.

I then placed my board about one inch away from the light to make sure the light shines on the board. Is this too close?

And finally, what kills me the most is exposure time and development time. I then proceeded to expose my board for about 45 minutes because people say longer times are better.

Since I had no measuring tools, I filled a bottom of a 5in by 9in plastic container with water about 2cm high, then I slowly poured developer for about a second. I placed my board in. For the first 5 seconds, nothing happened. then I slightly shaked the container to mix the contents and to my dismay, most of my design disappeared All I saw were my large ground tracks. Since it was a waste, I might as well continue. So I did and about 10 seconds later those tracks were removed.

So here's my question. For the developer stage, what's the minimum amount of positive developer and water I need for a board 15cm long and 7cm wide? Is there an equation I can use? I can't seem to find one on the internet except all the bottle instructs me to do is use 10 parts of water to one part of developer.

Also, what should I look for when the board is in the mixture to indicate progress or error? (I want to take it out the moment it is likely to be overdeveloped)?


texts: How do I calculate the required value for a pull-up resistor?

texts:
There are many tutorials that use a pull-up or pull-down resistor in conjunction with a switch to avoid a floating ground, e.g.

  http://www.arduino.cc/en/Tutorial/button

Many of these projects use a 10K resistor, merely remarking that it is a good value.

Given a a particular circuit, how do I determine the appropriate value for a pull-down resistor?  Can it be calculated, or is it best determined by experimentation?


texts: How do I keep my constant current source constant?

texts:
So I am trying to created a current source that will be used to drain a battery at specific time intervals for a specified duration.

simulate this circuit – Schematic created using CircuitLab

Here is the circuit that I am attempting to use, pulses from the square wave source will trigger the transistor allowing the current to flow and thus draining the battery.

This needs to be implemented three times for my design but the first two (which are 10uA and 10mA sources) work fine and do not vary much with changes in the battery voltage, however I am struggling a bit with my final current source which needs to draw 100mA+ from the battery.
The issue is not with getting the correct current, but in fact getting the current to remain constant with changes in the battery voltage, that is the voltage at the collector of the transistor.

I was advised that I could possibly need a current buffer before the base pin of the transistor and I implemented this but it still does not yield a steady and constant current source!
This is the circuit for the 'current buffer', not really sure what it is but that is what I was told to do:

simulate this circuit

As you can see all it is a pnp ahead of the previously show circuit. Again my issue is not with this, I just need a method of keeping the current very constant, ie. No significant change until the battery voltage has dropped < 1V or something like that!

Any help would be greatly appreciated!


texts:
I was supposed to find state space representation and its matrices of this system:

and I have no idea, how to do this. We were told not to transfer the system to time domain, but I can only do state space representation from time domain schemas.

When I tried to solve this, I got matrices
$$A =  \left( \begin{array}{ccc@{\ }r}
    -a & k  \\
    -b & -p \\
    \end{array} \right)$$

$$B =  \left( \begin{array}{ccc@{\ }r}
    0  \\
    b \\
    \end{array} \right)$$

$$C =  \left( \begin{array}{ccc@{\ }r}
    1 & 0  \\
    \end{array} \right)$$

$$D =  \left( \begin{array}{ccc@{\ }r}
    0
    \end{array} \right)$$

I went like:
$$X_2(s) = (U(s)-X_1(s)) \cdot \frac {b}{s+p} $$
$$X_1(s) = X_2(s) \cdot \frac {k}{s+a}$$

That could mean:
$$sX_2(s) + pX_2(s) = bU(s) - bX_1(s) \to \dot x_2(t) = bu(t) - bx_1(t) - px_2(t)$$
$$sX_1(s) + aX_1(s) = kX_2(s) \to \dot x_1(t) = -ax_1(t) + kx_2(t)$$

and output sould be:
$$y(t) = x_1(t)$$

that would lead to matrices I wrote. But I don't know, if I can do that this way, or if that is what was the task, cause we were told not to transfer to time domain, but I can't imagine how to do it without transfer I did.


texts: Can I cross the output inductor trace with input power line?

texts:
I'm attempting to learn a little more about SMPS design while referring to existing designs and posts such as this one: SMPS PCB Design Critic

I'm implementing an AL8805 based constant current buck for an LED and I'm looking at the evaluation board data sheet that diodes inc have done (link)

This is the circuit diagram with my attempt at showing the loops:

And this is their top layer implementation:

U1 is a little hard to see because I scribbled on it but that's the 5 pin AL8805 with (anticlockwise from top left pin): SW, GND, CTRL, SET and VIN.

I don't have an image of what the bottom of the PCB looks like but I have to assume that Vin, routed on the bottom, crosses that top trace from the inductor to the LED. It ends up to the right of C1 at that pad with the 6 vias. And that looks like crossing a split ground plane with the input power trace. I thought you weren't supposed to do that for EMI purposes? Is it ok here? Could they route it some other way like under L1 !? (As L1 is shielded).

If I redesign, I can flip the inductor 180 degrees but then I have possibly a worse problem trying to route the CTRL trace out - is it generally a bad idea to route control lines that this anywhere near power switching lines? I'm wondering how much space you are supposed to give.

Edit: Addition of other reference layouts for this same buck regulator:

This is the layout (Eagle) for the Picobuck (from Sparkfun) which is a triple AL8805 LED driver.

The position of the LED decoupling capacitor is interesting. I would be concerned about the CTRL line running right underneath it to P1 but I'm not sure...

This is the layout for the Femtobuck (also from Sparkfun).

It's odd the way the control has its own ground (pin 3 and 4 on the right hand connector) which snakes under the AL8805 and is viaed under the inductor. The control line seems to go out of its way to flow underneath the resistor which I'd imagine would be a source of noise.

Interesting how the return from the LED into pin 2 of the inductor is also made to flow under the output to the LED from the resistor...


texts: Gear motor with encoder: minimum drivable step

texts:
I am fancying this motor http://www.pololu.com/catalog/product/2271/specs to motorize an X-Y stage. (Alternative High rpm motors with high reduction ratio and high encoder counts/rev are welcome ;)

If possible I want to not use stepper motors, as they are harder to control, and also it might be difficult to achieve speeds about 1k rpm?

What bothers me is the minimum angle/ amount of steps that motor can reliably be driven from rest.

Can anyone provide a good estimate what minimum number of steps I can expect?

Edit:
I have a laser to measure a surface's depth, now I need to translate the surface in a zig-zag pattern. This requires one motor to do one very small step at the end of each line. In this case: <= 1/50 * 360° = 7°, which translates to <70° of the motor shaft, due to the gearbox.

Edit2: angle corrected.


texts: Transfer Function of two Common Emitters

texts:
I'm sorry about the pictures and  used circuitlab.

I am dealing with a circuit that has two common emitter transistors.
Until now I was only dealing with a circuit that that is common emitter.

This is an example

So when the following question comes :
Draw the AC- circuit and find the transfer function of the function

I would draw the ac-circuit and then find the transfer function which is this

I am faced with the following circuit so I am a bit lost on what would the final transfer function be


texts: Circuit for auto repeat switch off/on USB Data-

texts:
I recently aquired an APC UPS and connected it to my (Mac) server through USB. However, the load percentage is only updated (via pmset -g ps) when unplugging/plugging the USB cable. I found out it's only the DATA- line that has to be diabled for a second or so.

I wondered if using an NE555 in astable mode connected to an SPST analog switch (TS5A3157 or MAX4644 f.i.) will serve my purpose (switch off the data- line for a second or so every 30 seconds). Any info on (USB) side effects would be very helpful.

(And yes, I've searched the interwebs, contacted APC, installed latest software/firmware et al. ;-)

Thanx in advance for any info.

Adam.


texts: Difference between thin film and thick film precision surface mount resistors

texts:
I'm using some 0.1% precision 10k and 150k resistors. They are thin film 0603 surface mount. For a lot more, there are also thick film types. Fundamentally and practically, what is the difference between these two?

Thin film example

Thick film example


texts:
Given a certain instruction set, and that any high-level code is just converted to machine code anyway, then except simulating human intelligence, is it sufficient enough to do anything you want a computer to do?

For example, can the instruction set of the Arduino be used to generate high definition graphics on a modern computer monitor and play games? Why or why not?

*Note: I mean the Arduino instruction set only, not the board itself.


texts: What are some methods to achieve constant LED brightness over large temperature ranges?

texts:
I would like to regulate the light flux output of an LED or laser diode over its entire operating temperature range by varying the current.

What are some different methods to achieve this?

Edit: This is for a sensor application. I'm attempting to measure position by blocking the light over a photodiode. If the LED flux changes however, it will seem like position is changing, when in fact it is not.


texts:
I'm currently working on a project which uses the STM32f103c8 blue pill to read analog signals from a 3 current sense amplifiers.
I noticed that the values were correct most of the time but would randomly jump to zero or close-to-zero values even when the analog signal was verifiably constant.
At first I figured it was because of noise or something related to my PCB design so I removed the blue pill and placed it in a bread board and ran its own 3.3v supply straight to the 3 analog inputs B1 B0 and A7.
I saw through my kiel debugger that I was getting the values 4095 but they would still randomly jump to 0 or some very low number like 4 and 16 for example.
I also replaced the blue pill to ensure that the only other variable is my code. There has to be something I'm doing wrong when initializing.
The code below is a snitbit of what I've got for the ADC initialization.
void ADCInit () {
  RCC->CFGR |= RCC_CFGR_ADCPRE_DIV6; //sets ADC clock freguency to 12mhz accoring to datasheet
  RCC->APB2ENR |= RCC_APB2ENR_ADC1EN | RCC_APB2ENR_AFIOEN;  //enable ADC and alt fuction pins
  RCC->AHBENR |= RCC_AHBENR_DMA1EN; //enable DMA

  ADC1->SMPR2 |= ADC_SMPR2_SMP7_0 | ADC_SMPR2_SMP7_1 | ADC_SMPR2_SMP7_2; // setting sample rates to max
  ADC1->SMPR2 |= ADC_SMPR2_SMP8_0 | ADC_SMPR2_SMP8_1 | ADC_SMPR2_SMP8_2; // setting sample rates to max
  ADC1->SMPR2 |= ADC_SMPR2_SMP9_0 | ADC_SMPR2_SMP9_1 | ADC_SMPR2_SMP9_2; // setting sample rates to max
  ADC1->SQR1 |= 3 << 20; //turning sequence mode on
  ADC1->SQR3 |= 9 << 0; // setting channel 9 as the first in sequence
  ADC1->SQR3 |= 8 << 5; // setting channel 8 as the second in sequence
  ADC1->SQR3 |= 7 << 10; // setting channel 7 as the third in sequence
  ADC1->CR1 |= ADC_CR1_SCAN; // setting ADC to scan mode
  ADC1->CR2 |= ADC_CR2_DMA;  // turning on DMA for ADC

  DMA1_Channel1 ->CPAR = (uint32_t)(&(ADC1->DR)); // passing data register of ADC to DMA
  DMA1_Channel1 ->CMAR = (uint32_t)currentSen; // passing array to DMA
  DMA1_Channel1 ->CNDTR = 3; // set DMA to count 3 times
  DMA1_Channel1 ->CCR |= DMA_CCR1_CIRC | DMA_CCR1_MINC | DMA_CCR1_MSIZE_0 | DMA_CCR1_PSIZE_0; // DMA settings
  DMA1_Channel1 ->CCR |= DMA_CCR1_EN; // enable DMA

  ADC1->CR2 |= ADC_CR2_CONT; // turn on ADC continuous mode
  ADC1->CR2 |= ADC_CR2_ADON; // turn on ADC
  ADC1->CR2 |= ADC_CR2_CAL; //Enable calibration

  while ((ADC1->CR2 >> 2) & 0x1UL); //Wait until calibration completed

  ADC1->CR2 |= ADC_CR2_ADON; //Set CR2_ADON again to turn on ADC and start converting

  for (int y = 0; y < 1000000; y++){}
}

This is the function that is called to initialize the ADC; below is the code that sets the GPIOs:
void GPIOInit() {
  RCC->APB2ENR |= RCC_APB2ENR_IOPBEN;
  RCC->APB2ENR |= RCC_APB2ENR_IOPAEN;
  // enable port a clock
  GPIOA->CRL = 0xc8bbbbbb; //sets all portA to alt push pull except A6 for MISO and set A7 to input pull down pull up for ADC
  GPIOB->CRL = 0x444844CC; //set B1 and B0 to input pull down pull up
}

I'm hoping that is easy enough to read and hopefully someone can help me figure out what exactly is causing this weird behavior.


texts:
I am trying to simulate the operation of an optocoupler with a triac to trigger the triac using the AC current. I have come across a few circuits that are all similar:

My question is regarding the connection of pin 4 of the optical isolator to the load as well as the gate of the triac. Shouldn't it be connected to the gate only? Doesn't connecting it to the load by pass the triac and defeat the purpose of using a triac?

The configuration above works in the Multisim simulation but only because the current seems to be flowing through the 1k resistor; the triac doesn't switch on when I place an oscilloscope across it.


texts:
I want to design a brand new PCB board for Altera Cyclone III FPGA with 144 IO pins, such as ep3c25e144. However, I am clueless of how the process can be done in Eagle Cadsoft.

Even when they provide one package for EQFP144,I still don't know how to map the pin. Also, as far as I know, we also need to map 8 IO Banks of the FPGA.

Can someone please provide some guidance?


texts: What a weird operating range, 2.97V to 3.63V

texts:
I've seen several microcontrollers rated to operate from 2.97V to 3.63V. Others I've seen rated from 3V to 3.6V.

What's with the extra 30mV on either end of the scale? It doesn't seem like it would make any difference, but maybe I'm missing something.


texts:
I have a circuit which works with a battery normally. The nominal voltage of battery is 3.7 V and I am using boost converter to make it 5 V. And I have a charging circuit of this battery too. So, my aim is when the USB cable plugged, I want to boost circuit stop working. So, it is like a switch controlled by a 5 V. Like normally closed relay.
How can I do this? I tried MOSFET and BJT transistors at the input port of the boost circuit but these are caused voltage drop.
As a result, how can I disconnect 3.7 V from boost circuit when 5 V is plugged?
Boost circuit:

Charging Circuit:

USB input:


texts: Connect(solder) a Arduino to some buttons

texts:
I don't have much experience with electrical engineering and teachers have given us(mostly me, I'm the Software Engineer the rest are Media Designers) a pretty challenging task. We have been given a coffee machine and we need to connect that to an Arduino. They gave the tip to solder wires to connector to the buttons on the front panel. Now we spend a day dissembling the thing and have the buttons exposed. At this point we're clueless how to proceed.

The button itself is simple...

...but where do we need to solder the wires to? All four pins or just two of them? I have no documentation about what it's using(voltage wise ect.) and measuring them would be difficult since the thing is apart and we cannot power it. Could someone point me to the right direction and/or give me some on-topic reading?


texts: Error when creating a task in separate file in verilog

texts:
module tb();

    reg [7:0] a = 1;
    reg [7:0] b;

    initial begin
      AddTask(a, b);
      $display("%d", b);
    end

    task AddTask;

        input [7:0] a;
        output reg[7:0] b;

        begin
          b = a + 1;
        end

    endtask

endmodule

The above code is compiled and simulated correctly; But I want to cut the task "AddTask" from the module "tb.v" and place it in a separate module "AddModule.v"(that is in a separate file) for clear coding. When I do this, modelsim can compile it but can't simulate it and give the error:
" Unresolved reference to 'AddTask' ". Although I include AddModule.v, it can't recognize AddTask. Can you help me please, what's the wrong ?

module tb;

    reg [7:0] a = 1;
    reg [7:0] b;

    `include "AddModule.v"

    initial begin
      AddTask(a, b);
      $display("%d", b);
    end
 endmodule

AddTask in a separate file:

module AddModule;

    task AddTask;

        input [7:0] a;
        output reg[7:0] b;

        begin
          b = a + 1;
        end

    endtask

endmodule


texts:
I've bought a cheap 12V 3-pin DC brushless fan a while ago. I didn't know much about why it had 3 pins instead of 2 when I bought it but now I know the third (yellow) wire is for measuring the fan speed. However, the fan does not spin when given the 12 volts between the black and red wires (ground and positive). It wobbles around a bit and then stops.
My first thought was that it's an AC 3 phase fan, but that makes no sense, first of all it clearly states "DC" on the fan, which could be a lie. Secondly, if it was an AC fan it would not wobble around at all when given 12 V, so what's going on here? Maybe I just bought a bad fan that doesn't work, maybe some of you guys know what's going on?


texts: How do I avoid a reset when using the watchdog in interrupt mode and changing the timeout?

texts:
I'm writing a program for an ATtiny85. I want to use the watchdog to wake up from power down in certain intervals. It all works fine as long as the intervals for a watch dog event don't change within the program (i.e. I don't change bits WDP0-3 after they're set once).

As soon as I change the timeout of the watchdog, it does an unwanted reset. I don't have the WDTON fusebit enabled, so the whactdog is not always on but rather has to be enabled by software. (In fact the fuse bits are: Low=0xe2, High=0xdf and Extended= 0xff make the controller run at 8 Mhz from the internal oscillator).

Here is a snipplet of my code:

#include <avr/wdt.h>
#include <avr/power.h>
#include <avr/sleep.h>
#include <avr/interrupt.h>

void Config_wdt(uint8_t timeout) {
    cli();
    wdt_reset();                  // reset watchdog timer
    MCUSR &= ~(1<<WDRF);          // clear reset flag
    WDTCR = (1<<WDE) | (1<<WDCE); // enable watchdog
    WDTCR = (1<<WDIE) | timeout;  // watchdog interrupt instead of reset
    //+reset, timeout can be 15,30,60,120,250,500ms or 1,2,4,8s
    sei();
}

EMPTY_INTERRUPT(WDT_vect)

void Sleep_now(uint8_t i, uint8_t timeout) {
  Config_wdt(timeout);
  for(i=i; i>0; --i) {
    set_sleep_mode(SLEEP_MODE_PWR_DOWN);  // set type of sleepmode
    power_all_disable();                  // disable unneeded loads
    wdt_reset();                          // timer should start at zero
    sleep_enable();                       // approach sleep mode
    sleep_mode();                         // enter sleep mode (confirm)
    sleep_disable();                      // entrance point when woken up
    // Another Config_wdt(timeout); here or re-enabling WDIE doesn't help either
    power_all_enable();                   // re-enable the loads
  }
}

int main() {
  Config_wdt(WDTO_500MS);

  Do_some_stuff();
  Sleep_now(5, WDTO_500MS); // WORKS AS EXPECTED, SLEEPS 5 TIMES 500ms = 2.5s

  while(1) {
      Make_other_things();
      Sleep_now(3, WDTO_30MS); // DOES AN UNWANTED RESET, ...
      \\+I.E. STARTS FROM THE BEGINNING BEFORE "Do_some_sfuff()"...
      \\+IF I REPLACE "WDTO_30MS" HERE by "WDTO_500MS" FROM ABOVE...
      \\+THE CODE WORKS FINE.
  }
}

The datasheet has this to say:

  If WDE is set, WDIE is automatically cleared by hardware when a time-out occurs. This is useful for keeping the
  Watchdog Reset security while using the interrupt. After the WDIE bit is cleared, the next time-out will generate a
  reset. To avoid the Watchdog Reset, WDIE must be set after each interrupt.

But even if I set the WDIE bit immediately after waking up from sleep mode, it still does the unwanted reset.

So how do I change the watchdog timeout in my code, without the unwanted reset?


texts:
Consider the two circuits below, the first is the original:

When HIBERNATE goes high, it switches the MOSFETs Q1 and Q2. However, because of the 10 kΩ bias resistors built into BJT Q3, it pulls considerable amount of current from HIBERNATE. Since this device is operated with a coin battery, it is a problem.
I have replaced Q3, with an N-channel MOSFET, like in the image below:

I have measured it all, and both circuits work. But I need some comments on it. Perhaps a different MOSFET? Also I am not sure what will happen if the circuit is fed with reverse current. The first design is protected against reverse voltage, but maybe it will not work as designed with the BJT replaced with a MOSFET. I need comments please.


texts:
I am looking at having my dumb (3 and 4 gang) switches upgraded to smart switches. The biggest issue I foresee is that one of the switches is a 2-way switch.
My understanding is a 2-way switch is 2 switches that control the one light.
Do I need a special smart switch to be compatible with my current 3-way switch set up? Specifically, I'm asking from a wiring perspective.
The other issue could be that turning on both switches "smartly" will have no effect because of the way a 2-way switch is wired. Does anyone have experience/advice with this?


texts:
I am trying to do reflow soldering with a stencil for the first time. I have done some reflow soldering before, but every time I manually applied the paste using a small syringe + needle. These attempts went well and I was able to solder some QFN and 0603 components. In my newest PCB I am using 0402 passives, a 0.5mm LQFP64 IC, an LGA IC, a BGA IC, and overall significantly more components. As a result, I'm trying out using a stencil for the first time.

I had double-sided, 4-layer boards made by OSH Park and 5 mil Kapton stencils made by OSH Stencils. I am using Chip Quik lead-free solder paste , which is the same as I used in my previous run, but a fresh batch . I am using the lead-free version because the BGA is lead-free and am trying to reflow it at the same time as the other components.

The problem I have run into is that during solder paste application, the solder paste doesn't seem to want to stick to the pads. I am doing the following steps:

Clean board and stencil with IPA, let both dry
Align stencil and pull flat (Kapton stencil has curvature, I'm guessing they cut it from a roll)
Apply solder paste (small amount was dispensed cold and left for ~3hrs to warm up) to stencil using a needle, making sure to cover each aperture.
Press plastic card at ~45deg angle, scraping the excess paste off the stencil with 1 swipe
Gently lift stencil starting from one side, trying to keep it from moving in areas that haven't been lifted.

The problem becomes apparent at step #5. When I lift up the stencil, some of the paste is applied (mostly on the larger pads), but a significant amount of the paste is kept in the stencil apertures, most notably on the fine pitch components. Right after scraping off the solder paste, I have checked to make sure that all the apertures are filled with gray paste. The paste is definitely inside the apertures before I lift up the stencil (before starting step #5) and it stays aligned on the pads. I designed the paste layer to be ~80% of the area of the pad with a rectangular aperture shape.

Does anyone notice any glaring errors with my procedure or have any hints on what I can do to make the paste stick to the pads better during stencil removal?


texts: What is more accurate definition of Ohm's law?

texts:
What is more accurate definition of Ohm's law and resistance?
is it

$$R=\frac {V}{I}$$

or

$$R=\frac{dV}{dI}$$

This is doubt that developed in my mind during a class where professor derived power equation where he used second one for resistance in the derivation. I checked Wikipedia. They showed the first relation as accurate. Of course if the first relation is correct and resistance \$R\$ is constant, then we can use second  relation. But what if resistance is not constant?

For a practical problem, suppose my voltage source is current dependent and is given by

$$V=I^2+2I$$

Then how will you find resistance of given circuit at a given value of current \$I\$?


texts: Is electric field of capacitive sensing circuit harmful and is it radiation?

texts:
I have constructed a circuit for capacitive sensing. The code charges and discharges a conductive plate. This uses an Arduino which is connected to a computer via USB.

I have decided to measure the electromagnetic radiation of the metal plate. I have used a "Trifield Meter Model 100XE". The measurements are close to the plate. Magnetic field is low as well as RF/MW. However the Electric field is showing values of around 200-400 V/m.

I have seen most standards of radiation refer to milligauss not V/m.
Is this radiation and is this harmful?
The meter is supposed to measure AC electric field. My device is 5VDC. Where is AC coming from? Is the AC a result of the capacitive sensing algorithm?
How can I know what frequency this field/radiation is?

I have found data about allowed values of EMF for humans, but I am not sure how to interpret them.

Is there a formula for the Electric field I am measuring?

Per the design of this sensing method, I am using it while it is connected to a computer over USB so it is "grounded". The fields exist also if I am connected to a laptop using a battery.
If I connect the Arduino to a DC battery then sensitivity drops and so does the field (to about 40 V/m).
If I connect the Arduino to a AC-DC power adapter (without a computer) then the field becomes higher than 1kV/m.


texts: why have the same V before and after resistor?

texts:
I'm starting in electronics, and some measurements are surprising to me...
Why i have the same V before and after a resistor? I've taken two photos to illustrate it, any advice will be very appreciated!

Thanks in advance!

simulate this circuit – Schematic created using CircuitLab


texts: Does the antenna type matter for receiving?

texts:
There is a similar question to mine already asked, but it does not address completely what I want to know, so I am going to create a new question.

I am using long-range RF69 900MHz radios in an Arduino project of mine. I'm trying to keep this as low cost as possible. I have noticed that high-gain SMA antennas are quite expensive (about $5) as compared to just regular wire. It makes sense that I would want something specialized to transmit data. My question is if I need such an expensive antenna for receiving, or if a few centimeters of regular wire will be roughly equivalent.

The data sheet for my RFM69HCW radio specifies that with line-of-sight communications and fancy SMA antennas a theoretical range of 3 or more miles is possible. If I only utilized a 900MHz SMA antenna for the transmitter, kept the transmission strength up at around 20db, and used just a wire antenna for the receiver could I still get this range? Or is the SMA antenna just fundamentally better at receiving these radio waves as well. Thanks!


texts: How is the current measured in this setup?

texts:
I came across this article where they measure the current called leakage current, but they are not using an ammeter or DMM.

I couldn't understand what(which device) they use to measure the current. What is the way of measuring current and what device is used in this case?


texts: Remove over-current protection of battery protection circuit

texts:
I have a hardware that is powered by a standard polymer battery (http://www.ebay.com/itm/3-7V-Polymer-Rechargeable-Battery-2000mAh-PCM-103450-for-GPS-ipod-Tablet-PC-MP3-/262605237924).

The hardware draws a lot of current, more than 3A, perhaps up to 5A. This triggers the overcurrent protection of this battery. The protection circuitry includes two SOT23-6L (http://www.phaselink.com/QA/SOT23-6L.pdf) ICs:

DW01-P (https://cdn.sparkfun.com/assets/learn_tutorials/2/5/1/DW01-P_DataSheet_V10.pdf)
8205 (http://www.ait-ic.com/uploads/2011-01/05/_1294200000_5amsl7.pdf), corresponding to M1 and M2 of typical circuit below.

As replied on this question (Over current protection for a 1-cell battery), the overcurrent protection is probably set up for 3A (25mohm ron of mosfets).

I would like to "decrease" the overcurrent protection up to 5A without losing the overdischarge protection. My options are:

either replacing the dual mosfets. But I can't find any SOT23-6L with Ron=10mohm. 25mohm seems to be the minimum.
or shorten M1 to disable the overcurrent protection. But I think it will disable the overdischarge detection voltage.

How can I fix my problem?


texts: Does anyone know of a decent (repeatable) way of making planar transformers/planar inductors in Altium? And if so, how was the experience? Drawing out the tracks and checking trace/space clearance manually is a pain (not to mention unreliable). I should also mention that I would prefer some kind of plugin or script or tool or something, making a custom library part is not what I had in mind, I am looking for something a bit more flexible that would permit quick design changes


texts: Help in understanding transformer ratings

texts:
So I am learning about power supplies buy buying and building this kit.

http://shop.tuxgraphics.org/electronic/detail_microcontroller_powersupply.html

I need to build my own power source and it recommends these...

http://tuxgraphics.org/electronics/201005/bench-power-supply-v3.shtml#3lfindex9

Finding the diodes and caps is easy but I am struggling g to find a "24v 3A transformer"

Most things I find are AC to DC supplies which I don't want (do I?) I assume I want just a plain AC to AC transformer, but they seem to be hard to find and are not rated for a current as it seems to imply.


texts: Are drift current and diffusion current *momentary* in unbiased diode? Why drift current = diffusion current in unbiased diode?

texts: When free electrons from P side drift towards N side,it constitutes drift current.But more free electrons are generated in P side due to thermal energy from temperature,so again it drifts towards N side.So i think continuous drift current flows in unbiased diode.But i don't know about diffusion current.


texts: How do I make the Ardumoto shield work properly?

texts:
I'm having issues with the Ardumoto shield. I want to use a motor at 5V with a 12V 2A power supply connected to the Arduino board.

From my understanding, the ardumoto shield gets its power directly from the Vin pin. How am I supposed to reduce the voltage for the motor? Also, should I worry about the big amperage coming in from the power supply?

Thank you for your help.


texts:
I have a Problem with an Audio circuit. I have a Signal Line that carries two way Audio (duplex). This Audio line is connected to the Audio-In of a Mainboard and to the Audio-Out of a Mainboard. The Problem is, that if I send Audio out of the MB it will also be received again by the MB.

How can I prevent this?

My Idea was, to use a transistor to get the original Signal and the inverted Signal and add those together to get (almost) no feedback.

The other idea is to use an Inverting Opamp to Shift the Signal by 180° in phase and add the Signals together...

Would this work?

If not, why not?


texts: It is written in our course book that the magnetic field outside a solenoid is negligible and almost zero. Why is it negligible? Is it negligible compared to the field inside solenoid or is it nearly equal to zero?


texts: Why do networks need a common ground cable?

texts:
I was reading about Serial communication in computers and embedded systems and found the following statement -

  Computers connected by wires must have a common ground reference,
  typically provided by a ground wire in the cable. (Source)

What is the reason for this? I thought that the ground wire was only for protection against electrical leakage. What would be the need for a common ground wire in communication networks?


texts: Preference of MOS resistor as load in MOS inverter

texts: Whys is a MOS resistor preferred over diffused resistor as load in design of a MOS inverter?


texts: logic gates with 2n222 transistors and leds not working

texts:
I am a complete newbie to electronics,
But here i go.. I am trying to make some super simple logic gates for now an AND gate. In this logic gate i want to show which out en inputs are high by using a led. I have tried the following schematics:

AND GATE:

simulate this circuit – Schematic created using CircuitLab
In this case i want leds D1 and D2 to light up when there respective switches are pushed down / make connection. And when both switches are down / make connection i want the output to be 5v and the output led to light up aswel.

But at the moment the inputs leds barely light up and the output led never goes on. What am i doing wrong here? All help and suggestions are welcome.


texts: If I want a breakout with two sensors on it, one operating at my MCU's voltage (3.3V) and the other requires a drop to 1.8V, do I need two sets of pullup resistors for both voltage lines? Can I do with pullups just on the 3.3V line? The blue circles in the schematic indicates my area of question. Thanks


texts: Finding node voltage of a "Y" resistor network

texts:
I am trying to find the voltage at NODE1. My initial approach was to find the current starting from the \$15\$V source then going through \$R_1\$ and \$R_3\$ to ground. Then calculating the current from \$14\$V source through \$R_2\$ and \$R_3\$ to ground. Then adding the two currents and using Ohm's law with total current and \$R_3\$ to find voltage from NODE1 to ground. This seems plausible to me only because of KCL (total current entering a node must equal current exiting node). However my answer is incorrect as I have proved both in SPICE and on breadboard.

What am I missing? I would appreciate any suggestions that don't totally give me the answer.

simulate this circuit – Schematic created using CircuitLab


texts:
Im trying to find a part online, but I cant seem to find what I am looking for.  Maybe it has a specific name?  I am looking for a D-shaft potentiometer that has two selections.  One on top and one on bottom.  As you can see from the pictures below, the small dial sits on top of the larger bottom dial. The top dial connects to the D-shaft, while the bottom connects to a bronze sleeve that goes around the d-shaft, but isnt connected to it.

This is a 60 year old potentiometer, its possible this was a custom piece and there is no modern equivalent.


texts:
I have a simple arduino driven charger for solar energy to pass into 12V lead-acid battery. However, to use the stored energy I need an analog circuit to cut off discharge at 11.5V. I think a voltage divider ( or 10V zener ) to a N-MOSFET (IRF630), or via a small signal N-MOSFET (2N7000) to a P-MOSFET (IRF9630), plus some extra bits, may be sufficient to switch a relay. I would prefer ditching the relay but then I'd need to heavily heatsink the MOSFET.

My main concern with the relay method is that the relay itself pulls about 0.33W when normal-closed (to clarify, this is also when I discharge the battery), which is a waste. Is there a best practice for cutting off 12V batteries? I have found many on google, of course, but most are 'instructable' type methods, others are rather bulky.


texts: Why can't I apply nodal at the ground terminal of this Op amp?

texts:
This question is asked to find the value of \$V_o\$ in terms of \$V_s\$ that i already got so don't want solution for this.

I have one doubt,while applying nodal I applied nodal at the ground terminal (that red line pointing) too that gives me incorrect answer.
that i did't understand why can't I apply nodal at that point?

what i understand is if I give that three branch separate ground then that will not be a node anymore.


texts:
In my earlier post, I was using LM317 for SIM900 but due to some voltage drop problem, I decided to go with LM2576. I am trying to step down the voltage from 12v to 4.5v using LM2576. I have studied the voltage calculation formula described on page 21. For the time being, I am just testing it on breadboard so have not connected the capacitors and diode at the output. Following is the schematic

According to the voltage calculation formula:

O/P Volts = Vref(1 + R2/R1)
O/P Volts = 1.23(1 + 4700/2000)
O/P Volts = 1.23(1 + 2.35)
O/P Volts = 4.12v

So the calculation shows output voltage of 4.12v but in practical it is showing 5.64v.

Is my calculation wrong or I am doing something wrong in the circuit. Please help.?


texts:
I am presented with the circuit shown in the figure below.

The hand calculations are as follows:

When I build the circuit in Multisim as shown in the image below:

My calculations are not matching up with the simulation results. Im pretty confident in my hand calculations. It is the simulation I am not sure about, but I could be wrong. Can anyone see what I did wrong?


texts:
I have this homemade LED-USB thingy to illuminate my desk:

simulate this circuit – Schematic created using CircuitLab

I guess it's not a very technical schematics, sorry, I'm not even near the EE area. The LED is 3V, and according "to the internet" (there was no manufactorer info on it) a blue LED usually supports up to 0.03A.

Thing is, it's not bright enough, so I want to attach more LEDs to it.

Since I have spare current from the USB I thought I should build a parallel circuit. Now, the last class on circuits I had was on high school, so I don't know if my calculations and schematics are correct:

i_total = U_wanted ( 1/r + 1/r' + 1/r'' ), r=r'=r''
i_total = U_wanted ( 3/r )
0.5A = 3V ( 3/r )
0.5A = 9V / r
r = 18 Ohms

simulate this circuit

Is this correct? If so, what material should I use as wire? A copper wire? Also, is it safe to touch it while it's on? I've been avoiding it, but I guess it's a low current and voltage...


texts: Where am I wrong in this symmetric circuit analysis?

texts:
Regarding the following circuit, SPICE calculates the current I3 through R3 as 3.333A.

I try to solve that myself and can only reach that result if I first set V1 as zero(short) and solve for the current and then set V2 as zero(short) and solve for the current. Then the total sum through R3 becomes 3.333A.

But there are some parts which are not yet clear to me.

How can we set V1 or V2 as short? How can the current produced by V1 can pass through V2 at all? As far as I know they can do that in AC small signal analysis but here we have DC currents. How come a theoretical voltage source or a power supply in real pass DC?

If I was asked this question I would first remove V1 and solve for the current through R3 and then  remove V2 and solve for the current through R3 and add these currents. But that would give 5A which is not the case.

So my thinking is somehow not matching the results, because I cannot imagine how current produced by V2 can pass trough V1 or vice versa. I would think the power supply would block such current. And even if not the case, here V1 = V2 how come current flows through the voltage sources?


texts: Circuit protection with different voltage inputs via switch

texts:
This may be a beginner question but I am kinda lost here.
My Vin is either 24VDC or 12VDC - controlled by a rocker switch.
If 24V is selected it gets regulated by a buck to 12V ~7A max.
If 12V is selected it skips the regulater and I just connect it to the 12V port.
Now I was wondering for a protection in 2 Way:

User has switch set as 12V but connects 24V - Could I put in a fuse to make it "break" on purpose?
User sets switch to 12V and connects 12V - What happens to the output side of the 24V regulator, it get's 12V and loads up the inductor ? Do I need to stop the 12V from going there and if how?

Example schematic (no realistic values):

simulate this circuit – Schematic created using CircuitLab
Thanks for your help !


texts:
Im trying to fix an egg incubator, currently has a mercury switch (when the temperature reaches two points on the glass, the mercury completes the circuit, it has small holes and some metallic strips and a wires), making this an NO Switch.

Im trying to keep the resistor and the fan ON... until the temperature switch closes.

How I make a circuit that keeps the relay LOW until the switch closes?
I was thinking in a two relay solution, but will be better if they were two transistors?


texts: I am learning some basic idea on using op-amp and other simple electronics by myself. I am trying to build up my first circuit for using opamp (TL084) by following some online examples. In the datasheet I found for the chosen opamp, it is said that it need the input voltage -12V to +12V and with operating current not more than 120mA. I don't have the right voltage supply for that opamp but I got a very old variable voltage and current power supply, it said it supports 0 to 20V DC, 0 to 1A current. So if I turn the current to 0A and increase the voltage slightly up to 10V, do you think this will work also. I only have 1 TL084 and I don't want to break it. The shipment is not cheap so I would like to confirm that with someone before I try it on.


texts: How to modulate a LED to send data and recieve with a photodiode

texts:
What is the concept of modulating a light source (white led, IR led, etc) to send data and then demodulating it with a photodiode back into data?

I am wanting to experiment with trying to use IR/White diodes to send data at various frequencies above 1mhz over open air. I know some pre-existing parts exist such as 36khz IR receivers, but I am wanting to understand the background theory of how the TX and RX sides fit together with the various steps/parts so that I can reproduce it and then see if I can modify it to work at higher frequencies or further ranges.

I have a basic understanding of the process works (for instance how remotes work), but an in depth explanation for the TX/RX sides would be helpful from a micro controller toggling the TX LED all the way to a micro controller RXing the data with the necessary parts that may be required on both ends (if applicable). Explanations about the actual protocol specifics of the data transfer can be left out.

Thanks for the help.


texts: 2051 Microcontroller Octave effect project

texts: Is it possible to create a Guitar Effect on such microcontroller? I'm still new to these stuff and would like to know if it is. Basically what it will do would be reducing or halving the frequency input to create an octave down effect. But I'm not sure if the 2051 would be able to handle it.


texts: Switching between ac-to-ac transformer taps in regulated linear voltage power supply

texts:
I am new to electronics and working on building regulated linear bench power supply 0v to 30v, 3A as my first project.
For better performance, wanted to switch between multiple tapas of ac-to-ac transformer depends on required output DC voltage. So my switching device(relay/ some other) output will feed into full bridge rectifier and then voltage and current control circuit.
What is the best method to switch between transformer taps other than relays? Any example semantics and part numbers?
The transformer taps 12v/24v 100va.
Thanks for the help.


texts: Do I need a flyback diode for a 24 volt DC 5.4 watt coil inductive load on my PLC relay?


texts:
I am trying to build a simple AND gate using 2 2N2222 transistors and the +5V source from an Arduino board. At first I tried the circuit without the R1 and R2 resistors but the output was 1 when B was 1 (second input) and 0 otherwise, regardless of A. After adding R1 and R2, if only B is 1 and A is 0 then the LED is dimly lit and if both inputs are 1 then the LED is brightly lit. Can I make it such that only when both inputs are true the LED is lit and off otherwise?

I also measured the current between R2 and Q2 and I'm not quite sure how to interpret the readings or what they mean. With the ampmeter on the scale 2m, with A = 1 the display reads .406 (which I presume means 0.4 mA?) and with the scale 20m, with A = 0, the display reads 2.23 (2.23 mA?) and with A = 1 the display reads 0.43 (which means 0.43 mA?). Am I reading the values correctly off the ampmeter and why does the current through B change if A is connected orn ot?


texts:
In the context of direct digital synthesis, I need a low pass filter to reconstruct the analog signal at the output of a DAC. I'm generating only sine wave signals and the maximum carrier frequency is 220 kHz.

Are there any rules of the thumb for setting the filter's cutoff frequency, so that a 220 kHz sine wave passes through almost unfiltered, and everything higher than that gets attenuated?

Obviously, the cutoff frequency should be set "just above" 220 kHz. But how much is "just above"?


texts: TTL Logic for displaying large 7-segment values

texts:
For fun, I was trying to imagine how I might implement large values in 74 series logic (or any commonly available discrete logic from the 1970s).  An example might be displaying prime numbers up to 100-bits, or displaying partial sums of a divergent series up to similar values, or working with computations in cosmological scale, etc.  Really \$2^{100}\$ isn't very large, but computing using TTL and displaying the results in decimal on a bunch of 7-segment displays seems like an interesting challenge.  It actually seems like it might be effectively impossible without a very large amount of work.  I am curious if anyone has seen something like this done.

Clearly you can't simply program all the 7-seg values into memory and address the chip with the binary values since there are no memory chips with 100 bit address.  Multiplexing is out of the question for so large a set is displays (at least across all 31 decimal digits). The logic for binary to BCD is not cheap, the chips that did that in the 74 series (74185) are rare and expensive, and to implement the same in gates would be herculean without first having some sort of program to generate the circuit for you (no human is going to sketch out that logic in simple gates for 100-bits in a single lifetime).

Maybe that is the way to handle it? Just brute force an algorithm to give you the circuit using a few hundred (? thousand?) gates?  Or maybe build your arithmetic logic to use BCD to begin with somehow? (I don't think I've ever seen that...)


texts: Adding a constant load to the input of an Opamp

texts:
I was looking at this circuit, and there was a resistor connected to ground after the output of a signal generator(50 ohm on the top left) . The explanation was that adding it allows the signal generator to see a constant load. Note: On the right is an op-amp.

Can someone explain what that means or why its added ?


texts: Is maximum BJT VEBO rating exceeded in this miller effect compensation circuit?

texts:
I have an switching circuit containing a transistor to switch the inductive load. There is a miller effect compensation capacitor (C1) in parallel with a base resistor. (The values of the two components have been deliberately increased to better show the effect.)

What happens is, that the base voltage gets negative if the signal source voltage is 0V. It could get below -5V. The datasheet of this particular transistor states that VEBO maximum rating is 5V.

Is this already exceeding it's maximum ratings for VEBO?

simulate this circuit – Schematic created using CircuitLab

Simulation in LTspice shows a bit different (worser) results.

There you can see additional ringing 6 times the frequency of the signal generator in this particulary case. And also presumably because of back emf there are (desired) spikes in collector voltage that gets capped by the 3 zener diodes at 36V.


texts: Can I limit the amps drawn by a charging battery

texts: I want to connect two 12V car batteries. A part of the connection is limited to 15A (cigarette lighter). Is it possible to limit the amps on the wire so I can safely connect the batteries via the 15A fuse & 1mm^2 wire?


texts:
I'm having trouble making sense out of this requirement, in terms of how to test for it.

I have a specification stating that for an RF power level measured in dBmi (let's call that power level S dBmi), a specific result should be obtained in a test.

As part of that test, I have a receive antenna that I must use and it is not isotropic. Not only that, it includes gain and loss internally, so its performance is just not a matter of the beam shape. A measurement at its output would include its pattern gain and its internal gains and losses.

There is a passive transmit antenna of known gain at a known distance away and a controllable signal source suitable for producing the required signal. (Let's assume it's a CW signal, to keep it simple.)

How would I set up for that test? How and where would I verify that the RF signal level is correct?

I assume the requirement means that if I had an ideal isotropic antenna, with no internal gain or loss, then the RF power measured at its output should be the specified level S in dBm (where the "i" for isotropic is now implicit in the setup). If that's the case, I could just measure the RF signal at the antenna output and radiate from a source at the power level that meets that requirement.

But where do I go from there? I can calibrate using passive antennas, like horns, but ultimately, I need to know how to set this up with the required antenna.


texts: Wifi throughput and relationship with wifi range

texts:
I've a question about how are related Wifi throughput and it's range. For example, if we assume a simply antenna like PCB antenna or ceramic antenna and a wifi frequency of 2.4Ghz, what is a partical rate of Wifi based on your experience?
Something like, you can have 50Mbps at 5m and 10Mbps at 10m with 1% packet loss. Or if there is a particular relationship between range and rate.

I premise that I'm looking to have an idea of wifi ranges without a particular antenna gain.


texts: How do I wire a 12V DC fan to 120V AC source?

texts:
I am trying to install this miniature computer fan in a heated incubator that operates at 50 Celsuis 24/7 in order to encourage air flow throughout the box.

Small fans like this run on 12 DCV power, but because it will be running constantly, a battery wont do -- I need constant power, forever.

I understand that I could use a step-down transformer to convert 120 ACV to 12 DCV, but I'm not sure about how to match the specifications of the transformer with the specs of the fan. This fan says it's "rated current" is 0.06A.

Given this info, I'm not really sure how to shop for a transformer that will work and is safe. Do I have to perfectly match power supply to the fan, or just make sure that it's powerful enough? So if I bought a 144 Wt transformer, does that mean there will be 12 Amps (or more like 1 Amp?), and is it OK to wire this to a fan with rated current = 0.06 Amps?

Can I power two or more fans with this same transformer? I would like to wire these in parallel, so that I can unplug one or the other. Would that work, or do I have to wire them in series?


texts: Suitable electronic components and digital logic gates for simple application

texts:
I'm designing some educational toys to teach children about electronic and logic circuits. They are quite literally individual electronic components (switch, resistor, transistor, capacitor, ...) and digital logic gates (and, or, not, ...) in 3D-printed encasings that can be easily and safely clicked together.

I'm familiar enough with the theory, but I have near zero experience reading data-sheets and choosing the right physical components. I would appreciate some names / serial numbers, or anything else to point me in the right direction. Ideally they'd be just large enough for me to solder them by hand and they'd work on a AAA battery or similar.

If needed, I could assemble the logic gates myself, but I'd prefer not to. I only need a single gate per physical component (1 or 2 input pins, 1 output pin, 1 pull-up/pull-down pin), though I can imagine they may always combine several in one. And if they're cheap enough, that's fine.


texts: Why is this IDT6116 SRAM chip overheating?

texts:
I am building a memory module for an 8-bit computer, and am running into an issue.  (Following this schematic, but using an IDT6116 instead of the AS6C6264 shown)

The chip is receiving 5V, which is within the tolerances listed on the datasheet.  I have connected the outputs to 8 LEDs and tied all address inputs low.  The CE and OE pins have been tied low (as shown in the schematic), and the WE pin is tied high.  At first everything works as expected.  I can view each byte of junk data the SRAM has been initialized with.  After a while in this state the chip will begin to heat up and then all of the outputs switch to low, regardless of their previous state and without any intervention on my part.  The datasheet I am referring to for the IDT6116 SRAM chip can be found here.  The SRAM chip does not appear to be damaged by this, as when power is cycled off and back on again it returns to working normally.  I have observed this behavior with all 3 IDT6116 chips I ordered.


texts: What's the best way to reduce the wattage on an audio amp output?

texts:
I am building a simple audio circuit that will only be used for headphones. It is starting with a very low signal going into a passive volume and tone control board. The output of the volume/tone board goes into a small amp that has a 3.5 watt output. When the vol/tone board is turned to max it is too loud for headphones. I want to limit that 3.5 watts to maybe 3/4-1 watt so when the volume is turned to max it doesn't blow the headphones or my ears. What is the best and most reliable way to reduce the output of this small amp?

Thank you


texts: Setting baud rate for Atmega328p with setbaud.h

texts:
I'm working with an Atmega328p, running off the internal 8MHz oscillator, divided by 8 to produce a 1MHz clock. I set the fuses according to the calculator here. Confirming this with avrdude:

avrdude -p m328p -c usbasp

avrdude: warning: cannot set sck period. please check for usbasp firmware update.
avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.00s

avrdude: Device signature = 0x1e950f (probably m328p)

avrdude: safemode: Fuses OK (E:FF, H:D9, L:62)

The timing seems to be correct - blinking an led on and off every 1000 ms takes ca. 1 second, as expected.

I am confused when it comes to setting up serial communication to my computer. No matter what I try, the connection is set to 1200. The program I'm using is:

#include <avr/io.h>
#include <util/delay.h>
#include <USART.h>

int main(void) {
    DDRB |= 0b0000001;

    initUSART();

    while (1) {

        printString("\n\r==== Looping ====\n\r");

        PORTB = 0b00000001;
        _delay_ms(750);

        PORTB = 0b00000000;
        _delay_ms(250);
    }
  return (0);
}

Where USART is from Elliott Willams' book. It includes the following:

#include <avr/io.h>
#include "USART.h"
#include <util/setbaud.h>

void initUSART(void) {                                /* requires BAUD */
  UBRR0H = UBRRH_VALUE;                        /* defined in setbaud.h */
  UBRR0L = UBRRL_VALUE;
#if USE_2X
  UCSR0A |= (1 << U2X0);
#else
  UCSR0A &= ~(1 << U2X0);
#endif
                                  /* Enable USART transmitter/receiver */
  UCSR0B = (1 << TXEN0) | (1 << RXEN0);
  UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);   /* 8 data bits, 1 stop bit */
}

// more code follows, not included here

My Makefile generates the following commands:

avr-gcc -Os -g -std=gnu99 -Wall -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums  -ffunction-sections -fdata-sections  -DF_CPU=1000000UL   -DBAUD=9600UL -I. -I../../AVR-Programming-Library -mmcu=atmega328p -c -o blinkLED.o blinkLED.c
avr-gcc -Wl,-Map,blinkLED.map  -Wl,--gc-sections  -mmcu=atmega328p blinkLED.o ../../AVR-Programming-Library/USART.o  -o blinkLED.elf
avr-objcopy -j .text -j .data -O ihex blinkLED.elf blinkLED.hex
avrdude -c usbasp -p atmega328p -P /dev/ttyACM0 -U flash:w:blinkLED.hex

Baud is set in the Makefile, in this case to 9600UL. If I set it to 19200UL, everything works the same. In either case, everything behaves as it should, but when I connect to the serial line from my computer (via screen /dev/ttyUSB0), the output is garbled unless I specify BAUD = 1200. (i.e., screen /dev/ttyUSB0 1200).

I've been struggling through a bunch of webpages, the Williams book, and the atmega datasheet, but I'm still not getting this. Is the baud rate fixed for this chip? If not, how do I set it to a rate higher than 1200?

At this point I actually need to set it any higher, but I'd like to understand how this is supposed to work, and what I'm getting wrong.

Update

Note that I have explicitly set BAUD and F_CPU with the avr-gcc flags: -DF_CPU=1000000UL -DBAUD=9600UL. Even if I set these macros in the code (as #define BAUD 9600UL and #define F_CPU 1000000UL as the first lines in the file, I'm still stuck with BAUD of 1200.

Update 2

I have isolated the problem to the setbaud.h file. If I set the baud rate 'by hand', that is, using the following code in place of the call to initUSART(); above, it works as expected - the BAUD is correctly set to 9600. This sets the prescaler to 12 (0b00001100) and enables USE_2X. So my problem must be that I'm using setbaud.h improperly, but I can't see how.

UBRR0H = 0;
UBRR0L = 0b00001100;

UCSR0A |= (1 << U2X0);

/* Enable USART transmitter/receiver */
UCSR0B = (1 << TXEN0) | (1 << RXEN0);
UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);   /* 8 data bits, 1 stop bit */


texts: Measuring Li-ion battery manage to get a number in mAh

texts:
How can a circuit functioning to measure Li-ion or else type battery manage to get its mAh capacity, how is this circuit's method ?
EDIT

Known it from a reviewer fed into an e-commerce site I forget (likely China's)


texts:
I'd like to find the s-domain transfer function of a full bridge diode rectifier with capacitive output filter.  Surprisingly, there doesn't seem to be much literature on this.

Analytically, I am unsure how one would approach this problem, but I imagine the simplest method would be to use simulation to get the frequency response.

So, I tried to do this using PSIM software, but did not get very good results.  I'm not actually sure what to expect from the magnitude plot, but I do think there will be a 90 degree phase shift from the capacitor.

Is anybody here aware of some analysis regarding this?  Or if someone has a working simulation?  Here is my schematic, but I'm not quite sure where I have gone wrong.

thanks


texts: How to calculate snubber for switched inductor?

texts: I'm driving inductive load with PWM and my MOSFET can not handle hard switching without reduce dv/dt ramp between drain-source. So I need to add RDC (resistor-diode-capacitor) snubber, but I don't know how to calculate propper values for it. Could you explain the calculation methodology to me, for snubber parallel to coil L1 and snubber parallel to MOSFET Q1? My load is about 12V and 1A of countinous DC (peak current is probably much higher :D ).


texts: 12v nichrome wire water heater. Is it safe?

texts:
I want to heat the contents (water) of a two liter thermos flask using a low power (50-100 watt) 12 volt DC heater.

Rather than buying a tiny little immersion heater, I've got some nichrome wire knocking about my workshop, would it be electrically safe to use a length of bare nichrome wire directly in the water to heat it?

My natural reaction is not mix electricity with water, but when I think about it I can't really envisage any real problems.

My intention is to use two length of wire, one about 100watts to heat the water in the first place, and a 2nd, about 3 watts to keep it warm once it's boiled.

Update for the curious... The flask is a traditional glass thermos, my intention is to to use this in a caravan with solar cells charging a 12v battery. The hope is that I can provide myself with a low power solution that will give me a permanent supply of hot water for occasional tea/coffee. Experimentation has indicated that I can keep a 2 liter thermos at about 95 degrees with only a couple of watts, and it only takes a few minutes of 100watts to heat the water again after drawing off a cup.

I think the electrical safety questions have been answered, but I'll try to do a bit more research about how healthy nichrome wire in drinking water may be.

Thanks


texts:
Kid car use a 12 volt batterie, that need to be charge.
We need to Open the front car motor cover and unplug the connector for the batterie and plug the charger direct to battery for charging
I would like to to like a real car charging station
External or the car
With a light red when need charging and green when the charge is done install on the car
And a male female plug in for charging
What would be the circuit
I did one with a relay, my issue is when I plug charger, relay go ON light go ON but when I unplug the charger the 12 volt battery keep the relay ON
Thanks


texts: What is the exact order of execution to access SRAM using a multplexers?

texts:
Hello Electrical Engineering community,

I am new to this community and indeed new to electronics
So please be gentle, Thank You, In Advance...

I have 2 x Alliance Memory ASC4008 SRAM IC Chips,
I think they are 512Kb size each.

I also have 3 x Texas Instruments SN74HC595 multiplexers
(I think that is what they are called)

And I wish to write code that runs on the MCU that will allow me to read and write to the SRAM memory.

I wish to use the SRAM as a video buffer for a 1280 x 720 display

I am not sure if I will be able to write to the SRAM while the MCU is reading the SRAM video buffer and displaying it onto the screen (in a continuous cycle)

I wanted to write to one SRAM IC while the other was being read.

I am unsure of the exact steps to take to complete this action.
I have no idea whether to:

shift the address into the multiplexer and then chip enable the SRAM and try to read the data out?

or

chip enable the SRAM then shift the address into the SRAM via the multiplexer and then try to read the data out?

I imagine the sequence would be:

Set SRCLR Low on 74HC595 chips (clear shift registers)
Set OE Low on SRAM
Set WE High on SRAM
Set CE1 or CE2 Low (which ever SRAM IC I want to access)
set SRCLR High on 74HC595 chips
Send Address 1 bit at a time to 74HC595 chips
When all 19 bits of the address have been sent to 74HC595 chips then set OE HIGH on the 74HC595 chips

At this point I no longer know what to do next, or even if my list of steps above is correct.

Please can someone educate me on the correct method of manipulating the pins in order to complete the read access properly.

I understand that if I get the sequence wrong then data will be lost or mixed up and in effect turn up as gobble-dee-gook.

I have tied the 74HC595 shift-register-clock pin and the storage-register-clock pin together to free up one pin, but if need be I can dispose of the programming interface and that will free up two pins so that I can use one for clock registers and then separate the shift register and storage register clock pins.

Finally, I did read the data sheets, but as I come from a programming background, its very difficult to understand.

ASC4008 Datasheet

SN74HC595 Datasheet


texts: Diode ring mixer (difference between strong and weak LO)

texts:
I've built a simple diode ring mixer according to this video. The mixer works, checked it on several frequencies. The application of the mixer is to isolate the IF from a 27 MHz FSK signal.  As my LO I have a 27 MHz colpitts with 120 mVpp, and as RF I connected another 27Mhz colpitts with different capacitor values to produce a small frequency difference (although I suspect the difference would've been there even without extra measures). Here's the output on the scope:

I have a couple of questions in regards to the setup.

1) The LO voltage is quite low, around 120 mVpp. As far as I understand the mixing still happens even if the voltages are below the diode forward voltage, however would the IF frequency be more pronounced if I increased the LO voltage? In other words, does increasing the LO voltage increase the "quality" of mixing? I tried feeding the signal into a low pass filter however the low frequency signal was almost entirely lost, so I thought maybe increasing the LO voltage would make filtering and demodulation easier.

2) Any environmental change (what items are around the circuit, if I am touching the power cable or not) tends to change the frequency, which is quite problematic if we are talking about FSK demodulation. Is this something to be expected? I don't understand how me touching the power cable should change the oscillation frequency of either LO or the RF I am feeding into the mixer. Can I somehow reduce this effect (besides building proper enclosure)?


texts: Getting opposite expected voltage with electret microphone

texts:
I am trying to build an electret microphone amplifier circuit run from a 9V battery.  The mic doesn't have a part number on it, so I have been making assumptions based on similar datasheets.  Most have impedance measured at 2.2k, but I have measured mine as 1.2k.  I'm assuming it will draw the same max current, 0.5 mA, and chose a resistor value of 15k.  With 0.5 mA running through it, theoretically there should be a 7.5V drop across the resistor, giving a Vmic of 1.5V and powering it.

simulate this circuit – Schematic created using CircuitLab

However, when I built this up, I was getting 7.5V across the Microphone, and 1.5V across the resistor, which I cannot figure out.  I'm guessing it's not a voltage divider, and the mic is acting more like a cap.  Is it not an electret microphone, or am I missing something?


texts: Im currently making a project. In my project I have to drive 36 pull type 12vdc solenoids using pic18f4550.. In order to control the solenoids I used a darlington  transistor TIP122.. I tested one solenoid and it works fine. My problem is if I  control all the solenoids, what battery will I use? And it should last long enough to drive all the solenoids?  Should I consider a pwm scheme to conserve current ?


texts: Serial programming of several AVR microcontrollers simultaneously via ISP interface

texts:
I'd like to put several PCBs in a panel with only one ISP connector routed to each MCU in parallel.

I hope that it will be no problem that many MCU's outputs will be connected together as it is intended that the output data will be always the same.

However I can not be sure that the programming device (STK500 in my case) will be electrically able to handle many devices (and how many in this case?) I think it is hopeless to try to find any specification as the programmers intended to be connected only to one MCU in a single time.

I did find a similar topic here, but Brian asked about parallel programming but I need to do it serially. And the question was related to relatively small amount of MCUs (3 in the picture) when I'd like to do this trick with a 20 or 30 devices!

So is there anything slept out of my sight? I could make an experiment with 2 or maybe 3 devices but I don't have enough boards to provide a full scale test, so probably someone did this? I'd like to have more PoVs before I will place a panel in the production.

Any thoughts?


texts: Why are silicon wafers used in semiconductor production round?

texts:
Wafers used for making semiconductors are round -- but this wastes quite a few chips around the periphery of the wafer in the fabrication process. Wouldn't it make sense to make the wafer as a square or rectangle instead?

Is there some aspect of the lithography process that requires that the surface be round?


texts: Minimum electrical resistivity of contact material for human protection from lightning

texts:
The context of the question is camping and sleeping outdoors in the unprotected elements. If you’re sleeping in a tent close to the ground, and lightning directly strikes your tent or the vicinity within up to 100m of it, what minimum safe electrical resistance (in Ω.m) would the material(s) between the bare earth and you (such as tent base, sleeping mat, sleeping bag etc - however many pieces, the resistance in total), be?

Knowing this minimum Ω.m resistivity (of worst case scenario where one side of your whole naked body, including proximity to vital organs, is in contact with such material connecting you to the ground and the lightning is direct), can help determine what materials may be suitable to safely choose from when considering lightning protection.

I will point to this wikipedia collation as a reference for the apparent electrical resistivity os materials (at 20° C).


texts: Solar Powered Trash Compactor (Chicago Big Belly)

texts:
I live in Chicago and I walk past these trash cans every day that have a large solar cell on the top of them. These trash cans are supposed to collect energy which runs a trash compactor inside. This theoretically results in more room for more trash which means the city can spend less money picking up garbage.

My instinct tells me that this plan doesn't work. I just want to ask the community what your thoughts are about this.

The trash cans are in downtown Chicago, surrounded by skyscrapers. Do solar cells need direct sunlight in order to be able to generate a usable level of energy? I can't see the cells getting more than 3 hours a day of usable sunlight.

Also, the solar cells are covered with a plastic shell to protect the cells from dirt, grime, etc. However, the shells are thereby dirty which further inhibits solar energy from reaching the cells.

Is this idea technically feasible in the "hostile" environment that these trash compactors are in?

A little tid-bit on the side - I had a college professor once tell me that he worked for an oil company building a solar array to power radios that would go on oil rigs. A problem they had was bird feces. Apparently bird waste is high in uric acid which would stain the plastic covering of the cells, thereby reducing the amount of energy that could get to the cells. There's lots of pigeons in Chicago, although I've never seen one perched on a trash can :).

edit: spec sheet for the BigBelly compactor


texts: Determining Voltage Overshoot, Voltage Droop & Current Step

texts:
I have a buck converter design in excel where i am trying to determine the output capacitor using the formulas in page19 of the ADP1850. It says select the largest result of the previous three equations. I am not sure how to determine the variables \$V_{Overshoot}\$, \$V_{Droop}\$, \$I_{Step}\$.
My specifications are as follows:

Frequency: 220kHz
\$V_{in}\$: 12V
\$V_{out}\$: 8.1V
Delta \$I_L\$: 10
\$I_{out}\$: 25A
Resr: 30m\$\Omega\$

Are they determined after prototyping ?


texts: Multiple characteristic frequencies determined by one capacitor

texts:
I'm trying to figure out how to construct a filter with the following constraints. If it isn't possible, this would also be acceptable, albeit disappointing (and I would hope for some kind of proof). The important feature is that filter would only have one capacitor, but multiple characteristic frequencies, which both depend on the capacitor.

For instance, a normal bandpass filter has two frequencies \$f_L\$ and \$f_H\$ which can be easily identified, but they each depend on a different capacitor. Similarly, there is a filter to remove just one frequency (and narrow surroundings) from a signal, by attaching a resonant load across the circuit, but this has only one characteristic frequency -- the resonant frequency.

I would like to build something like that has two frequencies that it resonates at, or where the lower and upper boundaries of the bandpass filter are both derived from one common capacitor, but I can't find any simple way of doing this. I suspect that any answer will require a fairly nontrivial topology (eg. a lattice filter where all components are different). The circuit must also consist only of passive components.

Thank you for any help!


texts: Can I limit 12v 25A current to 18A without dropping that 12v?


texts:
I'm using an NPN to pull a 12v (5mA) signal low from an MCU (logic level). My problem is that when I pull the 12v line low, 7.4v are still present at the 12v side of the line using the circuit below:

When I remove R2 and connect the signal directly to the collector pin on the NPN, about 110mV are still left on the line. See below:

Why isn't the NPN fully pulling the line low, and what can I do to fix it?


texts:
simulate this circuit – Schematic created using CircuitLab

I made this simple NE555 Flyback driver. I used a 9V Battery to power the NE555 and a 24V 6A power supply to power the flyback. The problem is that the MOSFET gets very hot in a few seconds. I tried using a fast diode with a reverse recovery time of 100nS in between the source and drain of the MOSFET, but that didn't do anything. My MOSFET died after a minute of usage. What can I do to prevent it from heating/dying? Also, If I use another power supply instead of the 9V which is something like 12V @ 500mA - 1A, The chip gets hot and explodes. Why is that? If I use the 9V battery, the chip works just fine. Also, the MOSFETS are kind of expensive. I only have 2 left. Help would be really appreciated.

[Edit: Spectator added the following redrawn schematic]


texts: Identifying a component symbol in a schematic

texts:
Problem: So I have ran across the following part and I simply don't know what it is. I tried searching for if you will a description of it. (I.E. two diodes on top of each other pointing opposite directions) This of course did not help.

Help: So what is this?

Advice: So when you run across something you don't know how do you solve this? I mean besides using context clues from the circuit. If its just a symbol and you can not identify the part. Advice?

Notes: It is from the block diagram of the datasheet of the MC14468.


texts: With this MOSFET driver IC, is the output voltage range 0 to Vin or 0 to Vcc?

texts:
I am using this driver IC, ZXGD3005E6TA. I am using a Pi as my controller, which has an output of 3.3V. The Vcc of my system is 12V.

I cannot determine if the IC will output the 12V when I supply 3.3V at the Vin pin or if it will only match the Vin and output 3.3V on the source pin - while still providing higher current.

How will this IC actually behave?


texts: How Can A Coded Firmware Control Hardware

texts:
I really want to know how could a virtual coded program really affect and imitate and animate a piece of hardware.

I Have Always Seen The Diagram Of Processors In the Book Showing ALU and CPU as The Main part of the Microcontroller and Microprocessor.
I Also Know that each Command in the Assemble Has A Specific Opcode.

After The Program Is burned into the Microcontroller as HEX files,What Does This Hex File Contain, I Mean,

1->Does  the opcode represent the physical state of the buses where only the buses required to perform the following task are HIGH while Others are LOW?
I wonder How things work nowdays in X86 and 64 Bit Processors.
I have Tried Using Ollydbg

2-> How is the control unit able to control various components of a processors?
For Example:When The HEX Code is Burned In The ROM everything is Static Then What Does The Control Unit While Sequentially Reading the ROM.

3->What is the relation between Processor Bit (Data Bus)  and No of Available Opcodes?
For Example 8085 is a 8 bit Processor has a Data bus of 8 bit.

4->What Does the Opcode No/HEX Signifies And How Does it effects The DataBus? (in hardware terms)
For Example:Each Opcode in Microprocessor 8085 has a HEX code Like
For HLT(Halt)-->72H


texts: Implementing F using a demultiplexer and an extra AND gate

texts:
Use a   1-to-8  Demultiplexer   and an  extra   AND gate    to  create  the function:

F(x,y,z)    =   ∑m(1,3,5)

If I were using an OR gate I think this would be trivial, simply put the 1 3 and 5 from the demultiplexer in to an OR gate and have the output go to F. But using an AND gate for this, I have no idea how?


texts:
I am working on a remote gate opener setup. It will be powered via a 12v battery (12-13.5v) and charged via pwm solar charger at up to 14.5v. I would like to use the HT7333 LDO datasheet here
It has a max input voltage of 12v and I would like to avoid the magic smoke :)
I am looking for a way of reducing the voltage to a safe range so the LDO will work while not draining the 7 Ah battery much when on standby.
Background:
The small micro controler will sleep for 1000ms then wake, turn on radio and listen for a signal for a few ms then back to sleep so the bulk of the time the current will be < 20 uA however when awake and opening gates its CPU:10 mA + 2xrelays 70~150 mA.
My thoughts so far:
LDO vs Switching Regulator - LDO as its sleep current is only 4 uA most SR are in the mA range and will empty my battery in winter. Also I have long range radio and the switching of the regulator will cause issues or make my PCB design more complex.
Use another LDO with voltage range i need - There are many designed for greater voltages but nothing in that class comes close to 4 uA current while CPU sleeps in fact most are 2-3 mA.
Use diodes to reduce voltage before the LDO - This seems the most promising as they will only consume power as it is drawn and not much if anything when not. However from the datasheets I have looked at it appears voltage drops on diodes are not static and change significantly based on the current load, so keeping it in a safe range could be tricky and I don't want so many that I have to extend the PCB (could fit in 4)
So I thought I would ask smarter people than I :) thanks in advance for your help.


texts:
I trying simulate my dc to dc boost converter in ST microelectronics Edesign suite.
there are some input parameters need to be enter.
Vin- 12V
Vout- 36V, 100mA
What is Rd I am not getting.
any help..?
Edesign suite link-
https://eds.st.com/console/#/app/led/ic_led_catalogs/filter/%5B%5D/selected/led5000:floating%20boost


texts: Electrostatic precaution for sensitive chip

texts:
I just figure out today that I always manipulate chips with the "Electrostatic sensitive devices" sign by hand. I never use a grounding bracelet or even a clamp. Even if I doesn't take such precaution, chips behave as expected. Is that normal?

What come in mind is that maybe a particular part of a chip can get damage instead of another. (particularly on µC) Is that true?

What can I do to reduce these effects? I have no grounding bracelet but I can use a clamp (a small one usually use for hairs).


texts: Common mode Choke for AC voltage measurement

texts:
I'm trying to measure Mains AC voltage of 230V RMS/50Hz with the ADC of a MCU.
Therefore I need some isolation and voltage division (+/-325Vp down to +/- 1V).

The voltage division is easy to solve, but for the isolation I was thinking about using a Common mode Choke.

The idea is to use the Common mode choke as a small transformer, by connecting it to the Mains power (230V RMS), in series with a resistor.

On the secondary side I would place a resistor, and hopefully the voltage across this resistor would be dependent on the 230V RMS.

But can I use a Common mode choke in this way (at 50Hz)?
These chokes are normally for RF.


texts: How do battery powered thermostats with LCD screens run for so long?

texts: My thermostat runs on batteries but it has an LCD, similar to (http://smile.amazon.com/Honeywell-RTH2300B1012-5-2-Programmable-Thermostat/dp/B007BHLUWM/ref=sr_1_1?ie=UTF8&qid=1425045609&sr=8-1&keywords=thermostat) but I thought any type of display (LCD) would suck up the battery. Am I missing something, is this a special type of display?


texts: Effect of Surge, EFT events on Current Transformers

texts: I have an on board, Current transformer with ratio 1000:1.  The inputs are likely to face surge and EFT events ( 4kV level). Would like to know the behavior of CT. Will it just let through the surge, EFT voltages or will it attenuate in the secondary side?


texts: monitor tp4056 charge current on a scope

texts:
I assembled a li-on charger with the TP4056 module as I've repaired a few solar lights for friends and a lot of the times the batteries are just low.

Recently I purchased an Oscilloscope to use with other projects. I would like to monitor the charge current on my scope but am having difficulty finding the correct pin.

I recently found an, "older," youtube video:https://www.youtube.com/watch?v=wfrm6lbt8Pc&t=626s" on this but he uses an older module which I believe doesn't have the protection circuits that mine has.

Am including the video link as it may assist other along with a link showing my tp4056, "https://1drv.ms/u/s!AjZLOy6GbYksgdJBMVos5ID12jcBsQ." The input solder joint was fixed after I saw the image enlarged. TIA, Steven


texts: Posting to php server using SIM900 GPRS with AT commands

texts:
I am using a SIMCOM SIM900 GSM/GPRS module in an embedded hardware application. Rather than sending device data to a server by SMS (what I've been doing so far) I want to switch and start using GPRS to post data to a server with a PHP script I've written.

The SIM900 literature (pdf) is abysmal. Section 13 gives an example sequence for connecting GPRS, which I've pieced together with a few other bits, but I can't get it working:

*COMMAND*           *RESPONSE*  *COMMENT*
ATD*99#             CONNECT     Establish connection
AT+CGATT?           +CGATT:1    Check connection
AT+CGDCONT=1,"IP"   OK          Set context
AT+HTTPINIT         OK          Enable HTTP mode
AT+HTTPPARA="URL","www.google.com"
                    OK          Set the address
AT+HTTPDATA="data"  OK          Send some data

I am getting the expected responses, but nothing happens after the last step.


texts:
Apologize if the question seems silly, searched for the answers on google but couldn't get an answer, so please manage to help.
I am studying detailed charging process of a smartphone battery,(software and hardware also). need to know in detail how the usb charging and TA charging works. would be grateful if anyone can explain.
In Li-ion "TA/USB Battery charging", what does "TA" signifies?
Is there any difference between charging using wall adapter and USB charging except the amount of charging current?if yes, what is that?

Also i asked question related to battery charging on Physics and stackoverflow, they recommended StackExchange.


texts: DIY electromagnetic shielding (CNC mill)

texts:
I'm building a DIY CNC router. I'm running at a low RPM and only planning on cutting soft materials (wood and under, maybe a PCB).
I'm currently having problems with magnetic interference. When starting the spindle, hard end stops would trigger, and sometimes my controller (arduino) would become unresponsive. For now I've turned off hard end stops, while building the rest of the machine. I'd like to re-enable hard end stops though.
I'm planning on moving my controller further away, and potentially placing it in a metal box. For the end stops however, I'm not sure how to solve it in an as DIY way as possible.
I've got a couple of questions:

How can I measure interference, and below what levels should I stay?
Will it help to simply wrap aluminum foil around my wires and hook that up to ground?
Does it work to hook up shielding to DC ground/zero, or should I hook it up to my AC ground in front of the AC/DC converter?
Where can I find a "beginners guide to magnetic interference"?


texts:
So I have built a custom PCB with a NRF24L01+ 2.4Ghz transmitter breakout board on it. I have heard the modules are incredibly sensitive to input voltage, so I have it connected to its own dedicated 3.3V regulator and a 100uF tantalum capacitor. When I turn this board on, I still have a significant amount of drops per minute. When I take the tantalum capacitor off the SMD pads and solder a 100uF Aluminium Electrolytic capacitor on the pins of the breakout board, the problem seems to go away.

I have the schematic and board shown below.

After doing a significant amount of testing, I have found the following results and plotted them on the following graphs. I let each test run for 10 minutes and then averaged the drops per minute. I kept one of the NRF modules on another PCB connected to a Aluminium Electrolytic capacitor on its pins, and changed the others capacitor configuration.

Can anyone tell me why this is? I can't figure out why just moving the capacitor from the SMD pads to the pins of the NRF increases stability. I also don't understand why an Aluminium Electrolytic capacitor would be better than a tantalum capacitor, but that seems to be what the data is showing.

Another issue that I found is that when no capacitor is connected to NRF module at all, this line of code stalls and stops. Anyone have a clue why that might be?

  if (!radio.write( &myData, sizeof(myData) )) {    // Send data, checking for error ("!" means NOT)
Serial.print("Transmit failed ");                   //When Capcitor Not Conencted, Code Freezes in this if Statement;
count=count+1;
RF_Flag=false; }

If anyone can help me with any of these issue that would be greatly appreciated! I cannot seem to figure out why this is.


texts: How can I ensure low-resistance ground contacts to an aluminum enclosure?

texts:
I am building an electronics project with an aluminum enclosure. I need to ground it—and very well—for human safety. (The system handles 300 A of current, and I want to be sure that if there is an internal failure in the unit causing a panel of the enclosure to become energized, a fuse will blow rather than the panel becoming lethal to touch.)

Of course aluminum forms a 4 nm layer of aluminum oxide within 100 picoseconds of contact with air, and aluminum oxide is an electrical insulator with a resistivity of 1x10^14 Ω·cm.

Putting those together means that there is a 31.5 megaohm resistance between a piece of aluminum and a 0.5" conductive disc (such as a metal washer) in perfect contact with it if the aluminum oxide layer is intact.

I know that (for example) mechanically tightening things, particularly using a locking washer with teeth, can easily penetrate the aluminum oxide layer, but I am looking for industry specifications or best practices on choosing washers and torquing the connectors to ensure this happens. These ground connectors might also need be removed and replaced when servicing the equipment, and I want to provide specifications for reinstalling them to make sure this is done properly to ensure the aluminum oxide layer is pierced and conductivity is maintained.

As an example, I'd like to be able to write in the repair manual—with calculations based on sources I can cite—something such as "replace the lock washer with a new one, part number XXXXX, then tighten the bolt to YYYY Newton meters of torque, which will ensure an electrical resistance to the enclosure of less than 2.5 mΩ. Verify this by taking a four-point resistance measurement between test points 17 and 29, which should be 5.0 mΩ or less."

I'd also be interested in things such conductive greases, which I could put on self-tapping studs, that might work particularly well on aluminum to prevent the formation of the oxide layer, and could then be left in place.

Can anyone offer some pointers to resources I could use to learn best practices in working with aluminum as a conductor, and which I could use to develop a set of guidelines for repair and rework of electrical conductors in contact with aluminum?


texts: Voltage drops are greater than source voltage. How is it possible?

texts:
This circuit was given in my textbook. The source voltage is only 10 Volts, but the individual voltage drop across resistor and inductor are 6 Volts and 8 Volts respectively, which is greater than the source voltage. How is it possible?

Is it possible in real practical circuits?