texts:
I've been working on my electrical switch with 10 million cycles lifetime, and changed the design from using mechanical contact to hall effect sensors as per the advice of stackexchange. However I can't stop thinking about the problem of making a mechanical switch with that sort of lifetime and find it to be an interesting experiment. Is it a solvable problem?

Here is a quick drawing to show my basic idea:

Plates A, B and C are 1 milimeter thick and made of conducting metal. Plate A is perhaps half a milimeter below B and C and thus never touches them directly. When the button is pushed in current goes from B to A and then to C thus forming a closed circut.

If the current is of low voltage (3 to 5 volts, Arduino digital port voltage) then electrical arcs should not form and thus no damage to the plates, am I correct?

The switch is sealed with airtight rubber to prevent moisture from getting in and thus the plates should not oxidize, correct?

What kind of metal do the plates need to be made of to survive 10 million cycles? Preferably something not to expensive.

Perhaps material would fall off from the casing due to wear and tear and fuse with the plates? If so could this problem be solved by placing the airtight seal right in front of plates B and C so that nothing inside the sealed area touches anything and thus no wear and tear there?

Am I missing something or would this work?


texts: Acquiring an accurate clock input for my computer

texts:
Building a timegrapher is quite straightforward, it is nothing more than a piezo transducer connected through to an amplifier. However, in order to actually utilize the results, one need an accurate clock to benchmark the results against.

How should I go about acquiring this signal? The end result should, I suppose, be a input signal that I can feed into the program I use to analyze the sounds from my watch.

I understand that there are USB-powered GPS units that generate a very precise 1 pulse per second (PPS) output. But how do I feed this into my software?

What other (preferably low-cost) options are there?

Something built using an NTP-server? But will there be problems with lag?
Building a radio receiver that uses a time signal. I have understood that this can be a bit messy (interference, etc).


texts: Where does Differential noise come from in a switching power supply

texts:
I would like to know where does differential noise come from in an SMPS. I understand where the common mode noise comes from. It mainly comes from the fact that there is capacitance between switching voltage node and ground earth. I understand that it is noise as this input current for charging/discharging the capacitances is useless for the purpose of the SMPS. In other words, if there were no capacitances it will still work. I m not considering here the input noise that could come from external environnement. I consider that the SMPS is working in a perfect environnement without noise.

In the other hand, I have some troubles to understand where the differential noise comes from. I have a book "Switching Power Supply A to Z" from Sanjaya Maniktala (nice book !) which tells that the DM noise generator is the voltage ripple caused by the ESR of the smoothing capacitor. Here is the model :

Here is the extract about ESR :

It is true that the ESR of the capacitor modify slightly the voltage across the smoothing capacitor. And if it modified it seems logical that the current drawn by the transformer (for example) will not be the same as if there were no ESR. So at this point, I though the noise where coming from here.

I did a simulation (simulation with no ESR and a simulation with ESR and parasitic parallel capacitance across the diode rectifier as when the frequency increase some current drawn by the SMPS can be seen at the input). My simulation may be bad...

Perfect model (ie without source of noise):

Model with source of noise:

Here are the settings :

Here are the results :

And finally I did an FFT of the two different currents : (Warning with the colors !!!)

An other view :

As a conclusion, I see that the ESR is introducing noise at frequencies higher than 100 KHz (switching frequency) but it tends to lower the "noise" at lower frequency. What does it mean ? Is it normal ? Is the 2 spectrums have the same energy ? In other words, does the higher frequency current replace the lower frequency current ? In this case, how could we consider it as noise ? In my mind, noise is something which is useless (at least in this application).

What do you think about the fact that the ESR is introducing noise ? and what about the parasitic parallel capacitors of the diodes ? When I tried to see the influence of the parasitic parallel capacitor (10nF @ a switching frequency of 100 KHz) with a model with a 1 Ohm ESR. By comparing a model with and without a parallel parasitic capacitor,  I clearly see nothing significant.

Thank you very much and have a nice day :)


texts: Finding pulse period for output compare on ATmega128 (10-bit fast PWM)

texts:
Ok, so I have ATmega128 board. I have clock of 16MHz with a prescaler of 8 (2MHz). I am using fast 10-bit PWM to generate a waveform with a top value of 1023.

Given a number, the value put in OCR1A = pulse_period *(number/100).
The wave will be high for pulse_period * (number/100) and low until it reaches TOP, where the timer will reset.

However, given the information I have (which I gave in first few lines), how do you find the pulse_period when top is 1023?

Thanks for any help :)


texts: How come SMPS regulators doesn't show current limiting circuit?

texts:
for example the LM2678-ADJ is a famous buck converter, there are also many others. I have googled and looked through other regulators, there are many schematics in the datasheets of how you make the output voltage adjustable.

But there does not seem to be any info about current limiting for buck converters. Why is that? Is it harder to make current limiting work on a smps rather than a linear regulator?

LM2678 datasheet: http://www.ti.com/lit/ds/symlink/lm2678.pdf
Thanks!


texts:
I am using STM32F100xx and want to set the SysTick timer to 1 ms. How could I do it?

I am reading this part from the reference manual, but I can't understand fully.

  SysTick calibration value register

  The SysTick calibration value is set to 9000, which gives a reference
  time base of 3 ms with the SysTick clock set to 3 MHz (max HCLK/8).


texts: How to effectively downscale input voltage of a device?

texts:
Oscilloscopes let us measure input voltage in a variety of input signal ranges (either AC/DC, +/- 500V or Gigahertz's of frequency).

I am wondering: how they make it happen?

Say, an oscilloscope has a microprocessor/microcontroller/ADC unit at its heart, which usually works with 0..5 V DC voltage. The input signal could be not DC, but AC also and may have huge peak values, in comparison to the 0..5 V range.

There should be an input cascade, which downscales this voltage to a reasonable range (for example, +/- 2.5 V) and offsets it to be in the working range of ADC/MPU/MCU (0..5 V). It is also possible to have a slightly narrower range to allow for error/peak values, say 1.25 .. 3.75 V.

There are three ways I know, which allow for a downscale and offset of an input signal:

potential transformer (probably won't work for DC)
resistor-based voltage divider
operational amplifier configured to have fractional gain (in range (0..1))

A potential transformer won't work for DC.

Resistor ladder / voltage divider will work, but will be very sensitive to the overall device resistance:

simulate this circuit – Schematic created using CircuitLab

From what I know, the rest of a device may have variable resistance, and thus the calculation of resistor values won't be reliable (provided that Rdevice may vary).

The opamp input cascade might do the trick, but the IC should have very specific characteristics, since the input voltage offset, temperature drift, slew rate and bandwidth might significantly distort the signal.

And I am not quite sure whether providing high voltages or AC voltage will work fine with opamp.

My question is: is there an effective way of downscaling the input signal of either AC/DC, high frequency (up to GHz range) or high peak values (up to 400 V)? Or how it is implemented in oscilloscopes?


texts: Confusion regarding the I-V characteristics of a solar cell

texts:
We know that I-V characteristics of a solar cell are described through the following equation :

This equation can be translated graphically to the following (ideal) circuit :

Now according to the following equation and circuit, the solar cell current consists of two-component currents, one is for the diode current Id and the other due to the light generated current IL. Now I have the following questions :

I think that I am confused about the understanding of the operation of the solar cells. According to my understanding, the solar cell depends on the light generated current that is generated due to photons energy. This current is simply due to the minority carriers generated in each semiconductor region ( p and n) and this current is supported by the built-in voltage and exists between the p and n regions. Also, the solar cell depends on the diode current ID that simply represents the portion of the IL lost by recombination in the bulk region before reaching the depletion region. This discussion was according to the formula above I=ID+IL and also my discussion agrees with the fact that the solar cell is a source not a passive. So do I understand right?
V in the above equation represents the built-in voltage which is around 0.6 v for silicon as we know. Now this means that we need to apply an 0.6v across the solar cell to make it work? If we do so then the sollar cell will not become a source because now we have inserted some sort of electrical energy to it although it should solely depend on light energy?
In the above equation there are two quantities Io and IL, the reverse saturation current and the light-generated current. The reverse situation current is the current that flows in the opposite direction due to the minority carriers but this is the same as IL as I have discussed above, then what are the differences between them?


texts: Are capacitor voltage ratings for max charge or exposed source?

texts:
If I have a 100V rated capacitor, can I expose it to a 200V source as long as I cut off the source before the the capacitor is fully charged?  For example remove the 200V source when the capacitor itself reaches 80V of charge.

Does it perhaps make a difference on chemistry/material as well?  I was thinking of doing this with the electrolytic can type.


texts: How can I measure the brightness of a LED?

texts:
I'm interested in converting voice of the customer (VOC) to LED brightness specification.

In order to do this, I would like to be able to measure LED brightness using a cost effective instrument.

What are the available instruments to measure LED brightness and respective cost effective techniques?


texts: Sending data using 4 pin 3.5mm jack into smartphone

texts:
I have been looking around for some time and haven't found helpful information on how this is done. I am working on a project that intends to send data through the headphone jack to be processed by a smartphone. More specifically, I want to measure the temperature of water using an IR sensor. The voltage of the sensor will be sent to a smartphone where it can be analyzed to tell me what the temperature is. Is this a feasible idea?

I don't know too much about how 3.5mm connectors work on smartphones so links would be helpful as well. I know this is a vague description of the project and I'm just looking for some sources to steer me in the right direction. The project requires the usage of the headphone jack on smartphones so I can't use USB.

Side note: I am a novice undergrad engineer that might be in over his head.


texts: Can I sell and install homemade smart light switches legally?

texts:
I have designed and made prototypes for a smart light switch. It involves inserting a PCB into the work box behind the switch and is powered by the household AC.
The goal was to sell these locally and optionally install them for people, and continue to improve and upgrade.
I assumed there’d be safety requirements, but I don’t know where to get a list of these, so I put that on hold until now when I’m almost ready to market.
I’ve also heard that in the US only a licensed electrician or the homeowner via DIY can work on the electrical system.
So, am I SOL for the installation part? If so, can I still sell them if I rework it as a black box?


texts: How to convert 12 V DC to 12 V AC 50/60 Hz PSW?

texts:
This started with me trying to power 12 V AC LED swimming pool lights - which are always spec’d as AC for historical (and consequently safety certification) reasons - from a hefty 12 V DC leisure battery. While they work fine using 12 V AC, they don't work off the battery.
Most normal “AC” LED lights have a bridge rectifier on the input, so can run from DC. For whatever reason my pool lights can't. I tried up to 17 V DC just in case the lights relied on some peak threshhold detection, without success. There's clearly some AC coupling involved.
These pool lights are too $$$ expensive – and sealed – for me to tear down. There's no marking on the lights identifying them, and my local supplier isn't helping with this.
I could convert 12 V DC to 120/230 V AC using a cheap commercial inverter then transform down again to 12 V AC (or possibly replace the inverter’s output transformer). And this may be the easiest and most cost-effective solution - but it's not ideal.
I have an electronics background and designed stuff many years ago. Intellectual curiosity took hold, and wondered if I could make a simple low voltage 12 V DC to 12 V AC 50/60 Hz PSW converter based on a modern PSW inverter control chip – plus I wouldn’t need such high-voltage components for the power stage and keeping everything LV makes it inherently safer.
As everything is off-grid and solar/battery powered, I'm looking for high-efficiency solutions. And I'd prefer the output to be pure sine wave - at a low (50 to 60 Hz) frequency, as I know the lights will work then. A MSW/square wave output may damage components over time, and as I said, these lights are expensive...
While this started in response to a lighting challenge, it's now a more generic enquiry. I only need a 20 W output, but haven't found any low voltage low power inverters. I was wondering if there are simpler approaches, especially modular ones.
I’ve been looking at single board drivers like Sunyima’s EGS002 module using their EG8010 controller chip. Can anyone share their experience of trying to do something similar?
I've got some good comments below on solutions to power my lights - but still interested in hearing if anyone has used low-cost PSW driver boards...


texts: Can reverse voltage gain for a BJT be negative?

texts:
While observing the input characteristics of a Bipolar Junction Transistor(BC547), I observed from the graph that the reverse voltage gain came out to be negative. Is this possible and if so, what is it's physical significance? If not, is this observation simply due to the non-ideality of conditions of the experiment or just some error?

simulate this circuit – Schematic created using CircuitLab

Note that both sources shown in schematic are not actually just 30V, they can be varied from 0 upto 30 V.

Updated the schematic. Note that I am plotting graph of VBE vs IB with VCE constant for input characteristics and graph of VCE vs IC with IB constant for output characteristics.


texts: Using Circuit of Plasma Globe to Power a Tesla Coil

texts:
I had this old plasma globe laying around so I opened it up and found what I think is a ZVS circuit(I have ZERO knowledge of high voltage electronics and I may be wrong). I also have a wound tesla coil with about 650 turns of 21.5 cm diameter pipe for secondary and 30 turns of the primary. The wire thickness for the secondary is REALLY thin(about the thickness of our hair) and the primary is thicker(about 2.2mm diameter with insulation).

Can I just plug in the output of my ZVS into one end of the primary and the ground of the ZVS circuit and hope it works?
Will that work or do I need something else? Any help is really appreciated.


texts: Metal anti-static wrist band better than fabric wrist strap?

texts:
Anti-static wrist straps come in 2 flavours: fabric strap or metal band. A metal band is more expensive, but is it better? Or is it just for cleanrooms?

The fabric strap is attached to a little metal piece which makes contact to your skin to conduct static electricity away. The fabric strap itself often has a surface resistance of +/-1E5 ohm on the inside and +/-1E12 ohm on the outside.
The metal band makes contact around your whole wrist, because it's made of stainless steel all the way around. It's very conductive on the inside, but the outside is often painted.

Is there any change of static build up on the insulating outside of a stainless steel anti-static wrist band?


texts: Unknown short-circuit between GND and ANTENNA pins of GSM module

texts:
I have a Quectel M72FA GSM module, brand new one. I have just soldered it onto my PCB and found that: there is a short-circuit between the GND and RF_ANT pins.

This is the pinout:

I have checked the soldering with a magnifying glass, it looks OK the pins are not connected by the solder. It can be seen in the following picture:

Here is the functional diagram of the module:

The functional diagram of the module shows, there is an ESD protection diode between the RF line and the GND.

Can this short-circuit be caused by the malfunction of this ESD
protection part, (malfunction of the module)?
I am measuring 1.1 Ω resistance between the RF and GND pins, it can not be normal, can it be?
All in all, I have checked the soldering and the PCB trace of the RF_ANT pin, both seems to be good. What else should I check before suspecting that my brand new module is a
factory defective piece?

Antenna reference design from datasheet (it is all about the antenna design, beside this and the functional diagram there is no other information about the RF design of the module in the datasheet):

  M72 provides an RF antenna pad for antenna connection. The RF trace
  in host PCB connected to the module RF antenna pad should be coplanar
  waveguide line or micro-strip line, whose characteristic resistance
  should be close to 50 Ω. M72 comes with two grounding pads which are
  next to the antenna pad in order to give a better grounding.

I use the default setup, so there are no additional capacitors to the GND. I have an antenna like this. I have not connected it yet, as the SMA connector is not soldered (see picture above) because it would make more difficult to solder the module.

Meanwhile, I have contacted the manufacturer about the issue and they have confirmed that; it is a normal behaviour.

  Regarding you question of RF_IN short with GND, it’s normal.  You can ignore this point.


texts: How to turn on LED using RF as a catalyst?

texts:
I am trying to build a circuit that turns on a LED diode when it detects AM radio waves, in order to create a "radio wave detector".

Before I explain further, please note that I am not trying to power the LED solely using RF power from the air. In fact, this wouldn't be possible because I read that radio waves that we pick up are typically around 50-100 μV. Thus, it wouldn't be possible to power the LED using just this power.

Instead, what I want to do is amplify the relatively faint AM radio signal using extremely basic components like a transistors (i.e. BC547) and 9V battery, so that the LED turns on when the circuit picks up AM radio waves.

I'm pretty new to electronics, and so for the sake of simplicity, we can keep this circuit permanently tuned to 1000 KHz (as an example) so that we don't need variable inductors or capacitors for the LC circuit. Furthermore, I don't need any fancy features - just a most basic AM radio wave detector using some simple parts (no IC's please!).

I spent a lot of time on the internet trying to learn how to do this, but I haven't been able to find any examples of this. Something useful that I did find, however, is a "single-transistor radio" (ex: this link). I followed instructions for these types of radios (but I replaced the speaker with an LED), my LED just remains lit the whole time, regardless of whether or not the antenna picks up radio waves. I just want it to light up when it picks up radio waves (which can be tested by connecting and disconnecting the antenna?).

How do I build a switch that can be activated with RF?


texts: How to monitor device's AC current profile?

texts:
I have a specific question at the bottom of this post, but a little background is needed.

I recently got a new medical device (a CPAP machine).  Its power supply looks very similar to a typical laptop supply:

AC Input:  100-240V 50/60Hz 1.0-1.5A or 115V 400Hz 1.5A
DC Output: 24V 3.75A

When I plug in the adapter to the mains it causes all the LED lights on that house circuit to flicker erratically at about 1 to 2-second intervals.  The flicker is just a slight momentary, barely perceptible dimming.  The flicker is similar to (but more subtle than) that caused by a laser printer "waking up" out of sleep mode, but this power brick shouldn't draw anywhere near enough amps to cause the same effect.

This happens even with nothing plugged into the "load" side of the adapter.  The previous CPAP device caused no such flickering.

Here's a picture of the label (click for larger view):

Question: Before I call ResMed tech support I want to determine if the power adapter is really causing momentary high current surges.  Is there an off-the-shelf device I might be able to rent or borrow that would produce a moment-by-moment record of the current draw?  It would probably have to have pretty high resolution, at least 60Hz.

Side question: Would someone design a power supply so that it takes short pulses of high current from the mains instead of continuous low current?


texts: Calculating Equivalent Resistance between arbitrary pair of nodes in finite grid

texts:
I am having trouble understanding the concept of equivalent resistances. In the finite grid network pasted here, i know that if i want the equivalent resistance between the nodes at which the current source is attached (node 3 and 9), i do node analysis, calculating the node voltages. then at point node 9, where the current should leave the circuit, i am able to find the equivalent resistance by dividing the voltage difference between node 3 and 9, by the current injected by the current source.

However, suppose in this same network, i wanted the equivalent resistance between 3 and any other node say node 5? now the net current sum at node 5 will be 0 as a node gathers no current, so i am unsure of the denominator.
As a hack, i could disconnect the current sources output port from node 9 and place it node 5 (image 2) and perform the procedure. However, then i am not sure about this commentor here saying that the equivalent resistance is independent of where we attach the current source. in that sense we should have been able to calculate the resistance with the current source attached at 3 and 9 as earlier as well.

tl;dr:

I guess what i am asking is, that how to calculate equivalent reistance between A and C when I have applied the voltage/current source between A and B. or does this question not make sense, and to measure equivalent resistance btw A and C you need to apply the source btw A and C.
If it can be done, how would you calculate the current at C when the source is between AB. ( the current at the node C sums to 0)


texts: Increase the drive strength of the circuit

texts:
Hi I am trying to send a pulse over one circuit and recieve it at another.
For reference I have replaced the circuit that revices the signal with a resistance connected to ground to act as the load. On changing the load values I find that my circuit is not able to drive the pulses and I wanted to know what can be done to help it increase the drive current.

I can't increase the impendence that is make the load lighter so I am stuck with trying to improve the drive strength of the circuit.

I have attached a waveform with a 1k load and no load as reference


texts: How to access GPIO pins on Atmega with memory mapping?

texts:
I'm programming the Atmega328P in embedded C. I'm going to use 16 pins for turning on LEDs, and I have to use PORTB, PORTD and PORTC for this. I would like to just iterate a pointer so I can turn them on/off instead having to deal with what port each pin relates to. So an example would be how I need three if statements to iterate through the 16 pins like shown below:

// Enable outputs
DDRB = 0b00111111; // 6 outputs
DDRC = 0b00110000; // 2 outputs
DDRD = 0xFF;       // 8 outputs

// LED pins
uint8_t ledpin[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
uint8_t idx = 0;

// Set LEDs
if (idx < 8)
    for(int i = 0; i < 8; i++)
        PORTD |= (1 << ledpin[i]);

if( idx > 8 && idx < 14)
    for(int i = 8; i < 14 ; i++)
        PORTB |= (1 << ledpin[i]);

if (idx >= 14)
    for(int i = 14; i < 16; i++)
        PORTC |= (1 << ledpin[i]);

I would rather use a memory map where I could just say "pin0 address + offset" like this:

// Base address of ports
uint8_t base 0x00
uint8_t offset = 0x04;

// LED pins
uint8_t ledpin[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};

// Set LEDs
for(int i = 0; i < 16; i++){
    (base + offset) |= (1 << ledpin[i]); // Pseudo code
     offset += 0x04;
}

The code above is obviously not optimized, nor totally functioning code but I think it gets my point accross as to what I want to achieve. Ultimately I will use this in a code to control a LED cube which will work quite differently, but it's essential that I don't need to decode what port each pin belong to all the time. Is there a good way to solve this with virtually no overhead?

EDIT

After investigating and trying out a lot of stuff with good help from the answers I have found that it's not possible to address individual bits in the AVR ports. Each PORTB/C/D have their own address, but it's not possible to manipulate the bits with memory mapping, like incrementing a pointer address.  Atmega328P datasheet page 280 shows the memory map of the IO ports (image below).


texts: Generate pulse when any of inputs changes

texts:
I have a microcontroller with only one pin left which supports external interrupts. It is supporting 3 encoders which outputs can generate either rising or falling edge.
I would like to find the way to generate a pulse whenever any of the encoder pin generate rising or falling edge in order to trigger interrupt routine and read the values.
I was trying to find solution but I'm stuck. Maybe someone could give me a hint what can be used for such purpose ?


texts:
I am attempting to get my stepper motor to rotate 90 degrees, stop for a second, and repeat these steps.

Please note I am a beginner, but I have taken physics courses so I do understand most basic electronics concepts such as voltage, amperage, series, parallel, resistance, etc...

So the way I am setting this up is with a raspberry pi connected connected to an a4988 Pololu stepper motor driver which outputs 2 amps at optimal cooling and 12v, with a bipolar stepper motor that is rated at 2/amps per phase and is receiving 12v. The motors are being powered by a 30 amp, 12v power supply.

Everything is wired according to the attached diagram, and has been tested many times. Many different scripts have been used, and currently we are using a Python script from the RPI that runs 50 steps (90 degrees), then waits one second. This code works and is correct, because sometimes it works. When running, the motor does heat up, but not hot to the touch. Additionally, when powered but not running code, it buzzes and clicks sometimes, not moving. Online sources said this was okay.

It seems to be very random when it works and when it does not work, for example when testing the current going through one of the coil wires using a multimeter wired in series, the motor works perfectly, but when the multimeter is not there, the motor freaks out, buzzes, and changes direction erratically, one theory of mine as to why this is is due to the added resistance, in which case putting a resistor in series may fix the problem, but doesn't seem to address the root of the issue.

Other actions taken: -Using an arduino uno instead of Pi, same issues -Running the code using different ways, different libraries etc. -switched to different motor, and driver. -re-wired everything multiple times -adjusting the voltage control screw on the driver. -provided adequate cooling to the PSU and driver (2 120mil computer fans)

-- wiring layout

https://i.imgur.com/undefined.jpeg -- picture of setup

-- code used

any help or suggestions would be greatly appreciated, too many hours have gone into this. LMK if any additional info is needed.


texts: I need package delay values for the package XC7Z020CLG484. I downloaded IBIS models from the xilinx website. The file under name "zynq.ibs" has the following values for the package XC7Z020CLG484. Are these the values I need use with formula Delay= SQRT(C*L) to generate package length values for each pin?


texts: How precise resistor value needed in feedback?

texts:
I'm trying to design an isolated feedback loop for a Flyback converter using TLV431 and an optocoupler. One of the TLV431 pins is the reference voltage, where the output's resistor divider (R1 and R2) should be connected so the reference voltage there is 1,24V.

However I saw some Flyback converter designs and the resistor values aren't the most precise (I mean they don't give 1,24V reference in case of Vout=5.0V), calculating the output needed for 1,24V reference they give about 4,8V instead of the 5.0V nominal output. Does that mean that those designs aren't giving 5.0V output, only 4.8V? If not then how is that regulated to 5.0V and how precise the resistor divider has to be?


texts: Arduino Motor Shield overcurrent detection & protection

texts:
I have motor on my Arduino Motor Shield that draws <500mA when running and maximum 1A when stalled. I want to add some form of stall protection so that when the motor stalls the power is removed and the host system is alerted.

I have a three-level host system: a Raspberry Pi sending high-level instructions to a Arduino Mega 2560, that traces states of the motors that is hooked to several Unos and controls them using basic digital commands. The interrupt should be raised to both Pi and Mega 2560.

What is the best way to implement that? Is a comparator and pot a good idea?


texts: Help explain the math behind this high-side current limiting circuit

texts: I was playing around with my first attempt at building a high side current limiting circuit.  I was expecting a lot of trial and error to get anything functional, but low and behold my first try worked pretty well.  The circuit below limits the current to about 16 mA.  Can anyone explain how it works mathematically?  What if I wanted to have it limit to 30 mA?  I'm sure I could swap out some resistors and get it working for 30 mA, but I was hoping I could get a deeper understanding.


texts: Is there equalizer on the monitor's HD-SDI interface

texts:
Is there usually an equalizer on the monitor's HD-SDI input interface? In fact is it an requirement for HD-SDI monitors? Maybe HD-SDI signal is attenuated too much at the input of monitor, but equalizer inside the monitor will be equalized the cable loss? I don't mention a specific monitor, just wonder that equalizer is such a built-in property for monitors or not.

Thank you.


texts: Have I bricked my ATMEGA3328p by setting

texts:
I was playing around with setting the "system clock prescalar" (CLKPR).

I'm now in a situation where I can see that the clock is 244.9KHz, using my logic analyser and the "Clock output on PORTB0" fuse.  (I am also using the /8 fuse.)

My code is still running on the ATMEGA, even after powering off/on.

AVRdude will no longer let me write to it, either to the flash or the to the fuses.

$ avrdude -p atmega328p -c avrispmkII -P usb -U flash:w:main.hex -F

avrdude: stk500v2_command(): command failed
avrdude: stk500v2_program_enable(): bad AVRISPmkII connection status: Unknown status 0x00
avrdude: initialization failed, rc=-1
avrdude: AVR device initialized and ready to accept instructions
avrdude: Device signature = 0x88ab81
avrdude: Expected signature for ATmega328P is 1E 95 0F
avrdude: NOTE: "flash" memory has been specified, an erase cycle will be performed
         To disable this feature, specify the -D option.

avrdude done.  Thank you.

Is there a failure mode where setting the AVR's clock too slow can make it unprogrammable?

The device's signature seems to have changed, it now randomly takes values which include:

0x888b02
0x88ab81
0x886bf8
0x888b02

I have already tried powering-off the ATMEGA and the AVR ISP MK-II.

Is there any way to fix this chip?


texts: time axis confusion in signals and systems

texts:
I am learning signals and systems and we are given a impulse response swhich is discrete and from -5 to +5 on X axis.
I do not really understand that it has a negative part as everything starts from 0 or some positive number(assuming you delayed your experiment).
Some signals also have negative parts which a bit troubles me. I do not understand how to make sense of time axis in this course.


texts: Is it possible to implement basic DSP (such as an FIR Filter) on a Cortex M0 or is the architecture too limited?


texts:
I am trying to use an TI UA741 opamp and supply it with +12 VDC and -12 VDC. To obtain -12 VDC, i configure the power supply like i have shown below on the picture. Can i get -12 VDC (V2 on Figure 1 that i connected the circuit without any regulator)using this configuration in real life? I am also using a negative voltage regulator L7912CV. I have shown how i intented to design with regulator in Figure 2 that i have roughly shown without peripheral resistors or capacitors. If you share your comments i will be happy. You can advise any other methods to achieve negative voltage. I am just trying to clutch the logic. Thank you.

Figure 1:

Figure 2:


texts: i can't find the resonant frequency in a rlc circuit

texts:
I have an exercise where I have to find the resonant frequency but the equation can't be solve.

What happen in those cases? It is possible to say that te RCL circuit does not have a resonant frequency?


texts:
I want to create a PWM on any PIN and therefore using ISRs to achieve this. The setup I chose, working with my ATMEGA328p and Timer0 is:

static inline void initTimer0(void) {
    // Timer Counter Control Register B
    // Must b4 /64 or more for ISR timing
    TCCR0B |= (1 << CS00) | (1 << CS01);

    // Timer Counter Interrupt Mask Register
    // both output compare interrupts
    TIMSK0 |= ((1 << OCIE0A) | (1 << OCIE1B));

    // Timer Counter Overflow Interrupt Enable
    TIMSK0 |= (1 << TOIE0);

    sei();
}

/* Timer/Counter0 Overflow */
// called whenever TCNT0 overflows
ISR(TIMER0_OVF_vect) {
    PORTB |= (1 << 0);
    OCR0A = brightnessA;
}

// ISR fired when a match occurs
ISR(TIMER0_COMPA_vect) {
    PORTB ^= (1 << 0);
}

int main(void)
{
    setup();
    int d = 10;

    while (1)
    {
        for (int i = 0; i < 255; i++) {
            _delay_ms(d);
            brightnessA = i;
        }

    }
}

I would have expected that the LED on PORTB would dim up but nothing happens. I think I have a gap in understanding here. I would have assumed that TIMER0_COMPA_vect ISR would fire everytime I reach the new OCR0A compare value and turn the LED of, therefore control the duty cycle.

Can you help me?

Thanks


texts: How can I measure the charge of a pulse imposed on a signal?

texts:
simulate this circuit – Schematic created using CircuitLab

Hello All,
So my question is regarding how I can determine the charge of the square voltage source. For example, I need to build a detector that would detect when the pulse of the square wave is at 50 pico Coulombs, how would that be calculated. How can I determine the charge of the square wave from its voltage.
The square wave is imposed on the 60Hz voltage.

Thanks in advance.


texts: About use of complex number in AC steady state analysis

texts:
My question is essentially about the polar representation of complex numbers used in steady state analysis of AC circuits.

As far as I know a complex number \$a+jb\$ is represented as \$M \angle \theta\$, where M is the magnitude of the complex number and \$\theta\$ is the angle that it makes with the positive x-axis.

But in circuit analysis we replace \$A\cos(\omega t+\theta)\$ by \$A\angle\theta\$, which does not agree with how complex numbers are represented. According to me, \$A\cos(\omega t+\theta)\$ should rather be written as \$Re(A\angle\theta)\$, because it is the real part of the complex number \$A e^{j(\omega t+\theta)}\$ (I know that we drop the \$\omega t\$ part as it remains the same for all the currents and voltages in a circuit consisting of linear components).


texts:
I'm going to use 26650 Li-Ion batterys with a suitable battery charger IC in my hardware. I'm looking for an adequete battery holder for two 26650 batterys like this for AA batterys. But I find only 3D printed or modded battery holders for 26650 with no connection to the battery poles in it. They are relatively expensive, and I have to solder to the pols of  the batterys. The direct soldering of these batterys is not recommended, that is why I'm looking for a holder like the AA batterys have.

Could someone suggest a holder for 26650 batterys like the AA batterys have?


texts: Is there any downside to using a larger than needed smoothing capacitor?

texts:
I work with low-power DC voltage regulators.  I am already aware of the formula to calculate the size of smoothing capacitor(s).  This can be an iterative process of testing one size with a scope and then using a larger size or adding more until the scope shows acceptable (very low) levels of ripple and noise.

Besides the cost of the capacitors, is there any tradeoff to rounding up (a lot) and just using a very large capacitor(s) rather than trying to calibrate the sizing to "just enough" but not more than that?


texts:
I'm trying to implement a current sense amplifier in my application, but I have a question about setting it up with regards to current flow.

Basically, in this case, you put a very small shunt resistor between the source and the load, and the current sense amplifier measures the voltage across it, and outputs a voltage in accordance with the current flow. This is shown below using the INA293.

However, this assumes a positive voltage at the load supply with respect to GND, being 0 volts, and most likely, \$R_{Sense}\$ is small enough such that the voltage drop is negligible. For my application, I'm considering using it with the LM2673 circuit that outputs a negative voltage shown below. In this case, GND would be the more positive node w.r.t. \$V_{OUT}\$, so current will flow from GND to \$V_{OUT}\$. So, to rework the current sense circuit, the Load Supply would be GND, GND would be \$V_{OUT}\$, and the opamp's GND node would be connected to \$V_{OUT}\$.  If I were to place the sense resistor between the Load and \$V_{OUT}\$, would the current sense amplifier work properly, or is there something that would not cause it to work?

EDIT: Proposed Application Circuit:

simulate this circuit – Schematic created using CircuitLab

Rough Schematic idea with Comparator OpAmp:

simulate this circuit


texts: Color Changing LED Circuit upon power on

texts: The circuit I plan to make will have 3 RGB LEDs in it and what I would Like is for it to change colour each time it turns on to a random colour. I'm a beginner level so any help will be greatly appreciated.


texts: I have a receiver with sensitivity -50 dBm and an input signal from an antenna of -90 dBm, is it prudent to amplify the signal with a cascade of low-noise amplifiers? The LNA I found for my frequency band, 902-928 MHz, has a gain of 23 dB and NF 1.2dB, but it seems that I would need to amplify my signal by 50 dB to get an appropriate implementation margin for the receiver, requiring the use of multiple LNA's (or just amplifiers)


texts:
Am a bit confused about battery terminology,to be specific about discharge capacity,hence a quick question.
What is meant by depth of discharge?How does one know if a 12V,7.5Ah battery is discharged to a depth of 50%? Does it mean that it has been supplying 7.5A for 30mins ?


texts: ESD tests: when device is powered and not

texts:
I have some questions on ESD tests performed when device connected with power and not and searching for help here. I am asking this question because I think ESD can go into the power through TVS diodes, if the device is powered.

It seems that most ESD tests are performed when device is
powered(connected with power). Am I correct?
For same ESD, will the harm be same to the device when connected with
power and when not connected with power?
If the board is not powered, for a single ESD shock, the ESD protection designs shall be still effective. Especially if there are power planes, since the planes can absorb charges. Am I correct?
If the board is not powered, for accumulated ESD shocks, will ESD protection designs(schottky diodes, TVS diodes and etc.) still be effective? The charge will accumulate on the power lines.


texts:
I'm hoping someone can help me remedy this problem (or at least come up with a temporary solution), as I am a novice in electronic circuits.

The below circuit shows my setup. Vin is my input signal which ranges from 1-5VDC, and it goes through a voltage buffer and then a 250Ω which converts the signal into a 4-20mA output Vout.

simulate this circuit – Schematic created using CircuitLab

This circuit output was working as expected for most of the range for 1 to <5V, but as soon as the signal starts to reach 5V, the voltage stays stuck at ~4.79V (~19mA) and never gets to 5V (20mA). From this, I learned that Op amps have an output impedance which I assume causes this voltage drop problem. I calculated an output impedance of about ~11Ω in the TSV612A which -added with the 250Ω- causes the voltage to max out at 4.79V for an input signal of 5V.

One solution that worked was to increase Vop (Supply voltage of the Op amp) to 5.5V, so that it had a little more voltage to work with in order to compensate this drop.

My question is this: is there another solution that will help to fix this voltage issue without increasing the 5V supply on the Op amp or changing the 250Ω resistor? Are there any characteristics of an Op amp that I could be forgetting about that might help me remedy this problem?

Thank you!


texts: For 3.3V microprocessors, what's the best way to power the gate of a MOSFET?

texts:
The new processors are all 3.3V and dropping.  So while I am used to 5V arduinos being able to power the gate of a MOSFET, at least most of the way, this is not going to be true any more.  And for an IRF630, someone pointed out that I really need to drive the gate to 10V to get the rated on-resistance.  So what's the canonical way to do this?  Do I have a 10V power supply, and drop the voltage for the processor, have a charge pump that generates the 10V from 3.3V?  The current will be very small, because the gate has massive impedance.

Finally, assuming the 10V power supply, what's a good way to switch that voltage to the gate?  Do I have to use a small junction transistor because I don't have the voltage to switch a MOSFET?

The junction transistor is shown in this solution: Multiplying the voltage of an output pin on an Arduino board

I'm just asking if there is another way.


texts: Driving LED with parallel current sources

texts:
I have an LED backlight driver with 2 current sinks.  Each current sink does not sink enough current to reach the max LED backlight current, so I want to combine them.  Is it okay to drive a load, in my case an LED backlight, with parallel current sources?  The circuit would look like something this -

simulate this circuit – Schematic created using CircuitLab

In reality the LED backlight is a bunch of LEDs in series and parallel, but for the sake of simplicity we can treat it as a single LED since the connector to the LED backlight consists of an anode and cathode pin.  Are there any issues with this approach, such as unbalance or what not?  To me I pretty much equate this approach to paralleling load resistors and it is pretty much just an application of the parallel current source concept, so I think it's fine, but I want to see if I am missing something.


texts:
I want to build a custom battery pack / power supply to run a Raspberry Pi.

The board takes 5 volts and I want a 2 amp Max supply.  Does anyone know of a circuit that would help me ensure that the pi always got 5v?

I would be using 9 AA's for my battery pack. The goal would be for it to be as cheap, small, and efficient as possible.


texts: Where does the idea of two port network equations come from?

texts:
When introducing the two-port network models for linear circuits, the texts start with an argument similar to this:

"To characterize a two-port network requires that we relate the terminal quantities V1, V2, I1, and I2, out of which two are independent."

It seems like someone in history had the idea of relating input voltage to input current and output voltage ect. and made a circuit model for his equations.

They relate V1 as a function of I1 and V2.

And I2 as a function of I1 and V2.

And these mathematical equations are modelled as the following circuits:

My question is about the motivation of the idea of writing those two equations at the beginning.

So here we have a network(as in the top figure a) and name the input voltage V1, input current I1; similarly the output voltage V2, and the output current I2.

Question:

The first equation relates V1 to I1 and V2. I have a problem here. I can make sense that the input voltage V1 has a relation to the input current I1. I can also make sense that there is a ratio between the input voltage V1 and the output voltage V2.

But when I think of some one writing the following:

V1 = hi×I1 + hr×V2

my mind gets locked.

Why two independent relations are added to equate V1?

So in a linear system, where does the idea of adding two relations come from? Is there a way to demonstrate it in an easy way?

Edit:

Here is the superposition principle:

But this principle is turning off "voltage sources". But in the equation:

V1 = hi×I1 + hr×V2

is V2 a voltage source(another input) or an output? If it is an output can we still treat it as a voltage source and employ the superposition principle?


texts: What (if anything) are the standards for "generic" part numbers?

texts:
If I buy an MMBT4401 from Diodes, Inc., I get a 40V, 0.6A NPN transistor in a SOT-23 package. If I buy an MMBT4401 from ON semiconductor, I get a 40V, 0.6A NPN transistor in a SOT-23 package. If I buy an MMBT4401 from Micro Commercial Co,... you get the idea. And this is hardly the only case of this; countless companies make 1N400x diodes, 2N7000 NFETs, 2N3904/MMBT3904 transistors...

I'm quite certain that these companies don't all share the exact same silicon (though some of them might be packaging and reselling silicon dice bought from the same source), so what exactly is standardized between them? Is there even a de jure standard (and if there is, who sets it), or is this all just a de facto standard?

In either case, which specific figures of merit are considered "part of the standard"? Can I trust that no 1N4001 will have a forward voltage greater than some standard value, for instance? That one I'd be pretty sure is part of the standard, but what about the parasitic series resistance? I know I wouldn't want a 1N4001 if it had a parasitic resistance of 10 ohms, but could such a diode be made and still bear the mark 1N4001?


texts: Piezo element microcontroller connection

texts:
I have a "noname" piezoelement from Aliexpress:

I'd like to control it via microcontroller. Now I use this circuit to drive the piezo element:

Microcontroller ports produce PWM signals. Everything works fine, the sound is loud enough.

The questions are:

Is this circuit reliable? (can it protect from voltage spikes).
How can this circuit be improved?


texts: Can I power something directly from an IC, for example a little relay?

texts:
I am trying to design a tiny circuit to control a DC motor using buttons.
The motor needs 12 volts to move in one direction and -12 volts to move in the other.
The design I came up with is in this picture:

The special added component is a relay with this lay out:

Vin - NC
GND - COMM
/ - NO

The top left relay is to turn the whole system off. The top right is to prevent short circuits. The bottom 2 special two state relays are to switch the direction of the voltage.
The problem is that I do not know if I can connect the XOR gate on an IC directly to a power using object (the relay.)
Also, do I need to place a resistor in series with the relay becouse it is essentially a coil? (I know that coils act as a short after a long time of DC current.)
If there is a better and easier way to achieve this function, I would be very interested.


texts: What are the reasons for measuring non-zero current under zero bias in a passive device?

texts:
I use a probe station to measure IV curves (voltage sweep) of passive devices (resistors, diodes).

When I sweep from negative to positive bias I often see current well above noise levels (1-10 nA) under zero bias. In other words the IV curve doesn't really pass through the origin. The IV curve does pass through the origin if the voltage sweep starts from zero.

What could be the reasons for that?


texts: Reverse engineering, doubt with value of capacitor

texts:
I want to do reverse engineering of this module (Digital Microphone)

First of all I tried to get the schematics from the supplier but they don't have them.

Finally I starting unsolder each capacitor, as I can see, all are ceramic capacitor (I guess) and measure each ones with the multimeter.

I got the following values.

74 nF    I rounded it to commercial value, 0.068 uF
1,049 uF, I rounded it to commercial value, 1 uF
38,5 nF, I rounded it to commercial value, 0.039 uF
75 nF, I rounded it to commercial value, 0.068 uF
110 nF,I rounded it to commercial value, 0.1 uF

My doubts are:

Are they ceramic capacitors?
Is correct the procedure of unsolder and measure?
Is there another procedure to do it?

I read the datasheet of the principal component (microphone and amplifier) because I want to find some schematics proposal but it doesn't help me. (I am an enthusiast hobbyist.)


texts:
I am a newbie to electronics

I have a sensor that can provide a range of [400 microvolts - 5 Volts]
I want to transform this signal into Digital so that i can read it on computer, I'm seeking a quality information without noise or anythinging that can reduce it quality
I searched into Arduino but it range is between [0.0048V - 5V]
what can I use as materials? procedures? ressources to learn?
any information can Help at this stage.


texts: PCB design for intrinsically safe equipment to 60079-11 standard

texts:
A general question regarding PCB design of equipment to the 60070-11 standard for intrinsic safety type "ib" or better. Often, and more so than ever, ATEX certified electronic equipment requires complex electronics and multilayer, high density PCB design.

The equipment I am currently developing is being designed from the start with it being equally ATEX certified (and eventually IECEx), besides it having the CE and or FCC certification. So on the current PCB design the over voltage Zener protection is included with the correct power ratings, the infallible resistors in series with large inductances, fuses etc. all allowed for from the start. This prevents us from having to re-route the board for an ATEX specific product. For non ATEX the protection components are in most cases left out or replaced by 0 ohm shunts etc.

One issue I'm having with the PCB design to 60079-11 is what appears to be a rather limiting minimum separation distance for the Overvoltage Category, which in our case is 10V, Category I as it is all 3,3V digital and some analogue. One 12V booster charge pump for the OLED display, but this is low current and fused at < 150mA.

In Annex F, "Alternative separation distances for assembled printed circuit boards and separation of components" table F1 - Clearances etc. outlines this, and one can see the lower limit is basically 0,2mm for most cases, including encapsulation, coating etc.

It seems this lower limit is "out of touch" with modern PCB designs that use 0,5mm and even 0,3mm pitch BGAs, or > 10 layer stackups for the PCBs.
In my case, I do have a 0,5mm pitch BGA and an 8-layer 1,6mm PCB. To route the BGA lines I am obligated to have conductor separation to < 0,2mm (0,17mm or so), and in another case, a small analog BGA with 0,3mm pitch, this separation is even lower actually 0,1mm on two or three pins.

The other issue is the layer to layer separation which does not appear to be treated in any way by this standard (other than minimum conductor separation as in table F1). The PCB manufacturers build up the stack-ups with prepregs often less than 0,2mm thick and in most cases even less than 0,1mm. Cores can be 0,2mm readily available... but this again creates a situation with conductor to conductor separation to < 0,2mm minimum as in table F1.

So what gives than ? According to 60079-11 most of these PCBs stacks and BGAs etc. would practically be uncertifiable since the 0,2mm lower limit on conductor separation is clearly unachievable ? Is there a work around that I may have missed in the standard ?

I have seen ATEX certified mobile phones being commercialized, which implies they most likely contain BGA components and multilayers (> 8 layer), high-density PCBs. How do they get Intrinsically Safe certification for Zones 1 and 2 which still require 60079-11 ??

Is pure testing in an ATEX certification laboratory the only way to ensure a pass for intrinsically safe certification in this case ??

thanks in advance for any suggestion or references that may treat this in the 60079-11.

Mike


texts: What type of conformal coating must I use and where must it be applied over the PCB?

texts:
I have designed the layout of a PCB that will have an unique area with crimpage terminal connectors receiving 6KV by an external wire. I have done the shortest polygon (instead traces) for 9 PCB terminal connectors like these:

terminal farnell link

These 9 points must have the same potential. They (1+8) connect 6KV with 8 wires coming from contact relays (flying lead contacts). So doing this way, coil (low voltage) contacts can be separated from 6kV contacts (and 6 6KV polygon) using bigger distances. Finally, I will have a board with 24 HV relays so, 24 coils pads at 12V by one side of the board (middle), traces will go from them to the left corner of the board. HV polygon will be allocated at the right upper edge, with some slots (air gaps) that I made and adding more than the minimal distance that calculations give me using CTI0, conformal coating, etc.. (i.e.: minimal d + 50%(d))

I have read that using conformal coating distances can be minimized. So I use clearance and creepage at the PCB design that matches with conformal coating usage tables because my idea is to use conformal coating.

But I sincerely have never chosen conformal coatings neither worked with that. After searching I found that there are various types of products for several application cases. I see that acrylic solution has high dielectric. But I can see that there are many type of acrylic comercial solutions too.

The second chance is that there are several ways for applying the coating. From manual way until automatic one, depending on the number of PCB to produce. I think my case could fit with spraying. And it is said that this brings the need of doing kapton masks for the rest of the board.

So the question are two:

1.- Could anyone share with me commercial acryilic conformal coating solution for good isolation (max high voltage 6kV) of this design?

2.- Where exactly may I spray with solution over the board?
Maybe over the HV connectors and HV polygon after wire connectors being connected/coupled to the crimpage board terminals?
Maybe over the coil contacts, traces and pads?
Maybe over the whole board after soldering all the components?

NOTE:

I have seen this one at farnell web that has 40Kv/mm:

acrylic spray

Or this other one with 70Kv/mm and liquid (but says something about spray gun):

liquid conformal coating


texts: Please explain this formula for the relationship between bandwidth and the temporal response of a photodetector

texts:
I am reading "Optoelectronic Sensors" by Didier Decoster and Joseph Harari.

At section 1.8.2 they start explaining the relationship between rise time and bandwidth, and they give a very weird formula that I don't understand:

That's the whole thing, they don't explain anything more. Then they move on to some very interesting things about noise, but they mention BP in there and I don't understand what it is.

Now, my understanding about bandwidth and rise time came from this website, specifically equation 18 that basically says:

$$
t_r = \frac{0.35}{B}
$$

where \$t_r\$ is rise time and \$B\$ is bandwidth.

With that in mind, here is what I don't understand about the equation 1.7 in "Optoelectronic Sensors":

What is BP and how is it different from BW?
Is \$\tau\$ (tau) the rise/fall time? Or is it something else?
What are \$\tau_m\$ (tau_m) and \$\tau_d\$ (tau_d)? They didn't mention them anywhere before.


texts: Current decrease in a lamp due to the change in scale of an analog ammeter

texts:
I do not understand what happens in the following situation regarding internal resistance of an analog ammeter. The internal resistance of analog ammeter changes if the scale is changed.

For example if the ammeter has a scale such that the max current is 50 mA and then I switch to another scale, where the max current is 500 mA, the internal resistance will be different because changing scale is equivalent to add or remove shunt resistances.

Consider the circuit in picture, where the lamp is a tungsten filament lamp (the resistance value is at room temperature and rises with temperature). I represented ammeter and voltmeter and their internal resistance next to them. Consider the two scales 1. and 2. of the ammeter:

The maximum current is i=50 mA and internal resistance is Ra=6 omh
The maximum current is i=500 mA and internal resistance is Ra=1 omh

simulate this circuit – Schematic created using CircuitLab

Now suppose that I set AM1 to scale 1., I measure the voltage difference across R with VM1 and I find a certain value.

If now I switch  AM1 to scale 2. what does happen to the current I and to the voltage V across R?

I tried this with a real circuit and I found that the

Voltage V across R increases
Current I decreases

How can this be explained? In particular why does the current decrease?

I tried to give me the following explanations: Ohm law states

V=I*R|| =R||*10/(Ra+R||) (where R|| is the parallel given by the lamp and the voltmeter which is almost equal to the resistance of lamp)

I see why V should increase if Ra decreases but, looking at the formula, the current I should increase too!

I think that the problem is to consider the rise in resistance of the lamp, hence R|| increases if V increases and this would explain why current I decreases.

But at the same time, following this reasoning, R|| should also increase when current I increases (since more heat is produced by the lamp and it should get hotter)..

I don't see how to get the explanation right and I do not understand how to "prove" that the current must decrease, just starting from the fact that the lamp has a resistance strongly dependent on temperature.


texts: Do they make LEDs that have a resistor built-in on the anode? If not, why not?


texts: What happens for the SCR if I connect gate with ground when it is turned on?

texts: When I connected a silicon control rectifier by applying positive voltage in anode and negative voltage in cathode, after that I triggered the gate by pulse voltage and it connected, after that I want to connect gate with ground and I want to know what happened.


texts: Long term stability of 1602 LCD contrast calibration?

texts:
When setting the contrast on a 1602 or similar LCD module such as this one does the contrast remain relatively constant over the lifetime of the display or would it require periodic recalibration as the LCD slowly fades over it's?
I am considering using something like this in my application - the user would only need to read it once in a blue moon (providing WIFI IP address to access devices controls using a mobile device) but if the product needs to be opened up every year for maintenance just to calibrate the display then obviously this is not a solution.


texts: I'd like to know if there is some magnet in the rotor or in the stator of the generator? Or neither of those (rotor & stator) need a magnet for the current to flow?


texts: Circuit for determining the dc mean of a wave-form

texts:
I need to find the DC mean of a waveform whose maximum and minimum values will vary. The input signal has a frequency range of 0 - 3Hz, and will have a voltage range of 0 - 5V. I would like to find the DC mean of the waveform after the waveform has gone through three cycles. The waveform I want to find the DC mean of is shown below:

Can anyone suggest a circuit for me to implement this solution please?

Edit - RM::
I'm adding this "description". Please delete/ amend as appropriate.

The requirement relates to blood pressure measurement.
 Each cycle is a pulse or heartbeat period long - typically around 1 second / 60 BPM (Beats Per Minute) but can be as long as 2 seconds / 30 BPM or as fast as 1/4 second / 240 BPM (although values at either of those extremes would be very rare.) (eg Super athlete resting and super athlete under utter extreme exertion.)

Ideally the system will acquire the mean value after a single valid cycle and,
 chose 1 -

Update it on a cycle by cycle basis thereafter
Track it continually over the last single whole cycle so it is up to data instantaneously for the last pulse period.
Track it continually over the last N whole cycles so it is up to data instantaneously for the last N pulse periods.
Other ...


texts:
I am trying to measure pulse length, with ICP (input capture pin) on Atmega8, coming from this circuit:. PINB0 is ICP pin on AVR.

This is (most of) the code:

volatile uint8_t num_interrupts = 0; //number of input capture interrupts.
volatile BOOL write_glcd = FALSE; //write to LCD.
volatile uint8_t tim1_num_ovf = 0; //number of overflowes for timer1.
volatile uint16_t test[50]; //holds time elapsed since last TIMER1_CAP interrupt

int main(void)
{
    DDRC |= (1<<PINC3);
    PORTC &= ~(1<<PINC3);
    DDRB &= ~(1<<PINB0); //icp pin as input
    PORTB |= (1<<PINB0); //pull-up on icp pin
    TIMSK = ((1<<TICIE1)|(1<<TOIE1)); //enable timer1 overflow and input capture interrupts.
    TCCR1B = (1<<CS10); //1x prescaler, input capture on falling edge.
    cli(); //disable interrupts.

    start_LC();

    while(1){
        if (write_glcd) {
            cli(); // disable interrupts

            for (uint8_t i = 0; i < num_interrupts; i++) {
                glcd_clear_y((uint8_t[]) {4, 5, 7}, 3);
                glcd_write_num_xy(test[i], FALSE, 8, 0, 4);
                //glcd_write_num_xy(((test[i] & 0xFF0000) >> 16) * (UINT16_MAX + 1UL), FALSE, 8, 0, 5);
                _delay_ms(1000);
            }

            _delay_ms(2000);
            write_glcd = FALSE;
            start_LC();
        }
    }
void start_LC(void)
{
    PORTC |= (1<<PINC3); //pull output high, it induces some oscillations in LC tank circuit.
    num_interrupts = 0;
    write_glcd = FALSE;
    tim1_num_ovf = 0;
    _delay_ms(10); //wait for oscillations in LC tank circuit to dissipate
    TCNT1 = 0;
    sei(); //enable interrupts.
    PORTC &= ~(1<<PINC3); //induce oscillations.
}
ISR(TIMER1_OVF_vect)
{
    tim1_num_ovf += 1;
}
ISR(TIMER1_CAP_vect)
{
    test[num_interrupts] = ICR1;// | ((uint32_t)tim1_st_ovf << 16UL)); //commented out, just for now, timer1 ovf interrupts doesnt happen, so its ok.
    num_interrupts += 1;
    tim1_num_ovf = 0;
    TCNT1 = 0;
}

The problem is, I get some relatively random data written to LCD. Something like this:

55
48
42
39
16
12
22
65

write_glcd gets set in TIMER2_OVF ISR after every second (which is based on number of TIMER2 overflow interrupts), the code is not included here.

As I understand these numbers were suppose to be time in TIMER1 ticks it takes between TIMER1_CAPT interrupts, so between two falling edges of the signal. But as I measure the frequency on the oscilloscope I get around 370kHz (constant), so, why do the values differ so much? I understand they differ by a small factor, but those values below 30, just dont make sense...

Thanks in advance!

P.S.

Sorry for the bad schematic, but I cant use the inbuilt schematic editor for some reason...


texts:
During my commute every morning in the bus with nothing else to do, I have a strange tendency to notice antennas on the roofs of buildings. Almost every building has a Yagi, which I've been told is for TV reception.

Another one which I see that quite many buildings (mostly larger office buildings rather than homes) have is a monopole antenna with radials. Like the one in this picture, except with a longer radiating elements:

Image from Wikipedia.

I'm curious, what is the purpose of this antenna? And I am familiar with the characteristics of this antenna (such as the radiation pattern, etc.) but I am curious as to what they are used for. I see them alot and they all appear to be for the same purpose as they seem to be approximately the same size (thus intended for sending/receiving on the same frequency band). It's difficult to estimate the length for distance as they are quite high but they are maybe somewhere between 4 and 6 meters.

Do they maybe have something to do with TV, telephone or Internet (seems unlikely). I have only limited experience with telecommunications engineering so if anyone knows the purpose of the antennas, if there is a probable common purpose, I would be interested to know.

EDIT: One of the buildings that has this antenna is the offices of a government agency that deals with people's pensions. Another building with this antenna is a construction company.


texts:
Here is TTL NAND circuit:

My task is to calculate max. number of circuits of same type it is possible to connect in parallel at output of this circuit. It is known R1=4k, R2=1.4k, R3=1k, Vcc=5V, Vce_satuartion=0.2V, Vbe=VD=0.7V, beta_reverse=0.1, beta_forward=40.

What does parallel connection of TTL circuits look like? Maybe like this?


texts: Electrical schematic symbol help(looks like an or gate)

texts: I'm wondering if that little dot represents anything?


texts: Where break loop in Sallen-Key active filter to measure phase margin

texts:
I have designed the following Sallen-Key high pass filter (see image below). I would like to verify its stability using the phase margin of the open loop transfer function.

Inserting a voltage source at -IN  does not break the feedback loop due to R1. So where do I have to insert a voltage source in order to get a good approximation of the open loop transfer function? Or is a more involved method such as the General Feedback Theorem needed? And if so, how to apply this here?


texts: 660 Mbits per second photo-diode amplifier on 3.3V rail

texts:
I've got a 10mW laser diode that can transmit at 660 Mbits per second, I've got the laser driver circuit that can do this, I've got a photodiode from Hamamatsu that looks good for this speed (-3 dB ~1 GHz) but I'm struggling to design the photodiode preamplifier.

In my innocence I thought I'd find an op-amp that will do this. I've seen a document posted by Spehro in another answer (question wasn't totally relevant) that gave me some clues and, I came up with a circuit that kind of works (in simulation) based on those ideas but I'm pushing my own limitations now and I don't feel confident so I need advice on the best approach to take. What I have come up with so far is

Ignore op-amps and
Use a 9 GHz BJT common-base and an emitter follower.

Am I missing some fundamental approach that could pay better dividends?

Hamamatsu are profoundly silent on the way they coupled photodiodes with a transconductance amp despite the device I'm trying to emulate being discontinued and Hamamatsu say they are moving away from this wavelength photodiodes and lasers. I'm trying to emulate that Hamamatsu device from their now apparently defunct range of 1.3\$\mu\$m products. (G10476)

My question is am I taking a reasonable approach?


texts:
I'm experimenting with writing a software UART on my microcontroller using GPIO pins. This is to temporarily add a UART channel on a project until we get the new design implemented that uses a uC with more UART ports.

What I'm having difficulty with is correctly detecting a start bit in a serial stream. The source of the stream is external and doesn't care when my device powers up. So it's very likely that my device will power on and start seeing data bits in the middle of a byte transmission. Undoubtedly, that will cause my software UART to read erroneous values, as it won't be able to tell the difference between a start bit and any other high-to-low transition.

Is this an inevitable issue with a UART channel? Or is there some clever trick that the uC manufacturers use in their hardware UARTs?


texts: An op-amp connected to another op-amp, the one with ground and the other with virtual ground

texts: When I have two op-amp circuits, the left one is connected to real ground and the output of this circuit is connected to the input of the right op-amp circuit which is connected to the virtual ground. How do I calculate Vo ?


texts:
LTC6102 is a shunt resistor current sensor with the following datasheet:
http://cds.linear.com/docs/en/datasheet/6102fe.pdf

The package Description has come on page 24. If everything is in mm, then it must not match the size of breadboard pins. Is it? If yes, how can I use it on breadboard or prototype PCB boards?


texts: Linear technology power supply, question about a transistors

texts:
On page 12 of this journal there is a power supply design by LT. On page 14 there is a complete schematic.

I understand everything but these two parts:

There is a negative supply of -5V connected at the output and it draws, through a resistor, 8mA so LT3081 can function normally and output near 0V. Voltage drop on the resistor is 4.4V.

Q1:  What purpose does this transistor have? Could one use a slightlly bigger resistor to achieve 5V drop on it and do the same thing?

Q2: Why is this transistor here? Would it be the same without it?


texts: Soldering to PCB edge connector coated for FPC contact

texts:
Figure 1. (1) Lenovo keyboard controller (upside down), (2) keyboard membrane lower layer and (3) upper layer. The spacer layer is just about visible around the contact dots.

I'm building a footswitch PC controller with four momentary pushbuttons, up, down, PageUp and PageDn. I've found an ideal controller in a Lenovo USB keyboard with some missing keycaps and figured out the matrix. Pins 1 - 18 are the "columns" and 19 - 26 are the rows. http://keyboardtester.com has a simple online app which shows the "pressed" key as I short out the rows and columns. I will dump the flexible membranes and connect my footswitches directly to the green PCB.

The FPC\$^1\$ keyboard membranes are clamped against the PCB edge connector which appears to be coated with a dark grey material that looks like graphite. A quick test with the soldering iron on the inner edge of pin 26 failed to wet the pin.

Does anyone know what the correct term is for this edge connector coating material and can anyone suggest a means of attaching wires to the green PCB pins?

\$^1\$ FPC = flexible printed circuit.


texts: What is a good way to test maximum current?

texts:
I am building a device that can power other devices (it has a voltage regulator, battery controller, etc...).

What is a good way to measure how much current it will provide, and/or test if it will provide a specific maximum current?

Normally, my device will be asked to provide 100-200 mA, but, I would like it to be able to provide 1000 mA max.

I can try to power another device like an Arduino (50-100 mA) or a 1000 mA motor I have, but I am thinking there should be a better way.

That wouldn't test intermediate levels like 200 mA or 500 mA. Plus the 1000 mA motor produces feedback which could be bad.


texts: Guided propagation in transmission lines

texts:
Can you help me on understanding why we may say this transmission line the propagation is guided and there is not any radiation?

It is a 2-conductors transmission line, in which the conductors are assumed to be at a very low distance. My textbook assumes that the line is open, and says that, since the currents on the wires are opposite, the EM fields cancel each other.

But, I do not understand some things:

1) How can I "see" (graphically) that tue EM fields cancel each other?

2) And if was the transmission line connected to an impedance Zl?


texts: Estimating gate or transistor count for an IC

texts:
I'm messing around with calculating predicted failure rates using MIL-HDBK-217F.  For microcircuits (depending on linear or digital) you need to come up with a gate count or a transistor count for the piece part.  Does anyone have a rule of thumb or quick and dirty way to come up with this for some of the more complex circuits short of finding a schematic and counting?

It clearly doesn't need to be super precise given the ranges in the handbook.  For example for something like a B/P Digital Gate the ranges are 1 to 100, 101 to 1000, 1001 to 3000, etc.  So you just need to land in the ballpark.

For example, if I'm looking at a 74ALS193A, looking at the TI datasheet it's simple enough I can count out 48 gates and some change because of the flip-flops.  All in all, for this specific case I can be confident it's less than 100.  That said I can't dig up a mfg schematic for everything.  Some piece parts only give block level or simplified diagrams...or no diagrams.  It'd be nice if I could apply some kind of axiom without reviewing the piece part schematic.  I'd thought about maybe looking at propagation delay and dividing by the typical delay for a NAND gate for that device's logic family but couldn't figure out a good way to apply that to the aforementioned binary counter.

Anyway, hope it's not a dumb question.


texts:
im new in electronic.

i don't know 2 this component:

maybe this is Diode Marking ST S56 Z424

i can't found reference this part. can anyone give me a link reference or similar part?

Transistor, Marking  FR5505 P417D

i found referensi this part 55v 18A, but in my country nothing shell this item. can i replace with IRF9Z34N 55v 19A?

thank you for all the help


texts: Assuming a coaxial cable is matched with the load antenna, what is the DC voltage at the entrance of the cable if the length of it goes to infinity

texts:
This is a question from a previous year's exam which I'm having difficulties solving.

Given a load impedance of Zl = 48-i14 [ohm], we want to plan our coaxial cable with an impedance that gives a minimum SWR.

I understand that the min VSWR is 1 when there is no reflection and Vmin = Vmax, so the coaxial cable impedance has to match that of the load.

Now, the question states:

"If you take a voltmeter on DC, and attach it at the entrance of the coaxial cable to the inner conductor, and to the outer shielding, what will you read on the DVM if the length of the line tends to infinity?"

Now my attempt is this:

Since we're dealing with DC, we know that the DC resistance of a conductor increases linearly with the length of the line, which means we have infinite resistance, meaning all the voltage will fall on the line and not the antenna.

The second part asks what happens if we were to remove the load.

This is the same as asking what if Zl =infinity, which means that we should be getting max voltage on the load.

Somehow neither of these answers are sitting well with me, and I'd appreciate some input


texts: Can faster processors/clocks execute more code?

texts:
I am writing a program to run on an ATmega 328 which runs at 16Mhz (its an Arduino Duemilanove  if you know them, it's an AVR chip).

I have an interrupt process running every 100 microseconds. It's impossible, I would say, to work out how much "code" you can execute in one loop of 100 microseconds (I'm writing in C which presumably is converted to assembly then into a binary image?).

Also this would depend on the complexity of the code (a giant one liner might run slower than several short lines for example).

Is my understanding correct, in that my processor with a clock rate or 16Mhz performs 16 millions cycles per second (this means 16 cycles per microsecond 16,000,000/1,000/1,000); And so, if I want to do more in my 100 microsecond loop, buying a faster model like a 72Mhz version would give me 72 cycles per microsecond (72,000,000/1,000/1,000) ?

Currently it runs just a bit too slow, i.e. its taking a little longer than 100 microseconds to do the loop (how long exactly is too hard to say, but it gradual falls behind) and I would like it to do a little more, is this a sane approach getting a faster chip or have I gone mad?


texts: Measured Drain to Source Peak Voltage seems very high on PoE circuit

texts:
I am looking at TI's PMP20878 test results found on their website. Based on the schematic I am very confused how the Drain to Source peak voltage can be much greater than the typical PoE input of 48V.

Full Schematic

For example:

For Q16, how is the peak drain to source voltage 126.7V??

For Q13 how is the peak drain to source voltage 90V??

Am I missing a principle related to the transformer T2??


texts:
So, I have some 1mm2 (cataloged in the USA as 17AWG) fine strand (259 * 0.07mm) test lead wire that I am trying to adapt to Eurostyle terminal blocks (which I can then adapt to other things, such as header pins or barrel plugs).  Since this is normally done with ferrules, I got some uninsulated ferrules for 1mm2 wire (said to be for 18AWG in North American catalogs) and tried fitting them to the wire.

However, they simply will not go on cleanly -- if I force them to go on all the way, several strands (at least a dozen) do not make it into the ferrule barrel, flying out instead.  Is this an issue with technique, or a sign I need to go up to a ferrule made for 1.5mm2 (16AWG) wire?  Should I just clip the loose strands, even?  Or are ferrules simply not made for wire this size with this fine of a stranding?

The ferrules I am using have a nominal barrel ID of 1.4mm and a flare diameter of 2.5mm -- these seem to be standard dimensions for 1mm2 uninsulated ferrules.  I cannot use insulated ones, either, for the insulation barrel on them (at 3mm ID) is too small for the 3.7mm diameter insulation on my test lead wires.


texts: Optimal Capacitor Placement on DC/DC Convertor

texts:
I'm trying to decide on the best layout for caps on a DC/DC converter.
Which of the following options (or another, unlisted option) is the best choice?

GND Out plane with 5V Out going the opposite direction of the caps.
GND Out plane with 5V Out going the same direction of the caps.
GND Out and 5V Out both going the opposite direction of the caps.
GND Out and 5V Out going the same direction of the caps.

Or does this even matter?

Other details:

There are less than 5 components on the output side so a ground plane may be overkill?
Caps are 1uF


texts: Do long transmission lines degrade rise/fall times, and if so, by what mechanism?

texts:
I remember someone telling me long ago that if a voltage step is sent down a transmission line, the step will become smeared as it travels down the line, and the rise time will become degraded. I'm not referring to degradation caused by signal reflections, but rather some other limit on \$dv/dt\$ imposed by the transmission line that increases with length, regardless of the termination.

Is there such an effect? What's it called, and what causes it in practical transmission lines?


texts: Changing AA batteries for rechargeable Li batteries

texts:
I want to change 2 AA batteries in series for rechargeable batteries. The specs of the device are the following:

-Input Vcc: 1.8-3.3V (It seems to support 3.5, not sure if it can be an issue)

-Consumption: Sleep 5uA, running 1mA, transmitting 450mA.

The device runs around 10 times per day, the running mode lasts for around 3 seconds each. I expect it to work for about a month before having to recharge it, can anyone suggest me a way to find this out or a straight forward battery?


texts: What component is represented by reference designator GT?

texts: I can see that G represents a generator/oscillator, and T represents a Transformer, but what does GT represent?


texts:
I am thinking of using MAX1709ESE step-up converter in my DIY project, and from the datasheet I have found that the chip is manufactured in SOIC16 case without a thermal pad (as opposed to MAX1709EUI+).
There is no PCB design example in the datasheet, and so I would like to ask if someone has any experience in creating a PCB with good power dissipation for chips without a thermal pad?


texts: The explanation about why do we define the formula of Characteristic impedance,propagation constant and Velocity propagation

texts:
There is a long transmission line

1.Characteristic impedance \$Z_C=\sqrt{\frac{z}{y}}=\sqrt{\frac{impedance}{admittance}}\$,and in the  lossless line,\$Z_C=\sqrt{\frac{L}{C}}\$

2.propagation constant  \$r=\sqrt{yz}=\sqrt{admittance \times impedance}\$

3.Velocity propagation \$v=\frac{1}{\sqrt{LC}}\$

We will learn these formula above when we are learning the long transmission line,and i have three questions about these three formula.

Q1:

The definition of Characteristic impedance:the ratio of the amplitudes of voltage and current of a single wave propagating along the line,i know the ratio between \$A\$ and \$B\$ means \$\frac{A}{B}\$ ,but i still don't understand why can we define the Characteristic impedance \$Z_C=\sqrt{\frac{z}{y}}\$ according to its definition,can anyone tell me why?

Q2:

propagation constant  \$r=\sqrt{yz}=\sqrt{admittance \times impedance}\$,why can we define that?because i don't think that there is any relation between "propagation" and " admittance and impedance" ,i think it is unreasonable when \$r=\sqrt{admittance \times impedance}\$ when there is no any relation between "propagation" and "admittance and impedance",why don't we just define \$r=\sqrt{y+z}\$ ,so can anyone know why can we define propagation constant like that?

Q3:

Why can we define Velocity propagation \$v=\frac{1}{\sqrt{LC}}\$?what is the relation between "Velocity  or propagation" and "LC",L is inductance ,and C is capacitance.


texts:
I am trying to build a circuit that will allow my arduino board to be turned on by a button (switch). Much like a power button on PC. Here is my schematic.

In real life I used a phone charger instead of the battery.

And here is arduino code.
void setup() {
 pinMode(11, OUTPUT);
 pinMode(11,HIGH);
}
void loop() {
  // put your main code here, to run repeatedly
}

The setup should work like this.

The user press the button
Arduino GND pin is connected to phone charger GND
Arduino starts
Arduino pin 11 goes high
The pin activates the 2n2222 transistor
The transistor connects other arduino GND pin to ground
User releases the button
Arduino stays on

The problem is, when I plug in the charger, arduino turns on without user pressing the button! I found the transistor to be guilty because if I disconnect the transistor collector from arduino gnd pin, arduino shuts down. Tried changing the transistor and no luck. Same thing happens if I put pin 11 to LOW in the code. I have no idea what's happening here and how is this possible. I'm relatively new to the electronics. Are there any possible workarounds that don't involve complicated circuitry? Also bare in my that I have only 2N2222 NPN transistors, so solutions involving FET, MOSFET, PNP and other transistors won't help me. Thank you in advance!!


texts: What is the difference between Continuous-Time and Continuous Value in signals?

texts: I do not understand the difference between Continuous Value and Continuous-time. Discrete-time and discrete value. Can anybody offer a clearer explanation?


texts: Why don't Inductors have voltage ratings, but transformers do?

texts: Inductors don't have voltage rating, but transformers do... why is that? Why not just put a current, frequency, and turns ratio for transformers and be done?


texts: Want to create a box that allows speaker switching with my amp

texts:
I came up with an idea that is likely not worth the trouble, but I love tinkering so I'm curious to see if it's possible.

In short:
I have a guitar amp head. It requires 16 or 8 ohms speakers. For sake of simplicity, I'll just focus on the 16 ohms. I have a  4x12 speaker cabinet. All speakers are 16 ohms. I would like to wire them all in parallel within the box so I can toggle them on/off individually. Any combo between 1 and 4 speakers. So I was wondering if I could put a box between the amp head and the cabinet that would have a 4 position switch. One speaker, two speakers, three speakers, four speakers. And each of these positions activates a different circuit of sorts in the box that would keep everything working with what the amp head needs. So position one would basically just pass through. But the others, I'm not sure what they would be. Is this even feasible?

Appreciate any help you may have!


texts:
I'm finding some JTAG documentation a bit lacking in examples of what I call "typical sequences." My goal is to wiggle a GPIO pin of my device using the JTAG interface. Using the BSDL file for my specific device, I have identified the correct CELL index in the boundary scan register for my pin-of-interest's output3 cell (let's call it index j), I have identified the "output disable" control CELL index for the same pin-of-interest (let's call this index k), and I have identified the "disable" bit polarity required to enable/disable the GPIO output driver (assume a logic '1' puts the pin into high impedance). I have identified the total length of the BOUNDARY_REGISTER (let's call it length N), and identified every single "safe" default bit polarities for every single CELL (let's assume all safe values are a logic '1').
Question Number 1: To drive the output high, would this be the basic sequence of JTAG flow?
Step 1) Send the "SAMPLE/PRELOAD" command to the Instruction Register (IR) ("sending" implies walking through all the JTAG TAP controller states and ending back at the RUN/IDLE state). Step 2) Shift N bits to the Data Register (DR), with all bits being the "safe" logic-1 except bit number k, since a low in this bit will enable the output for the pin. Step 3) Send the "EXTEST" command to the Instruction Register (IR), the output pin will update upon completing the Update-IR state. To then change the output to a low state, I would repeat steps 1, 2, and 3, except I will now also set bit number j low in the DR as this sets the output low.
Question Number 2: When sending the N bits to the DR, is it sent LSb first (cell index 0 is sent first), or MSb first (cell index N-1 is sent first)? Or is this manufacturer specific?


texts: Insulation resistance tester: orders of magnitude difference in measurement depending on connection polarity

texts:
https://youtu.be/eGjd7HoYyz8?t=115

The man on the video is measuring a transformer's insulation resistance, the resistance measurements are very different depending on how the meter is connected:

When the positive lead of the meter is connected to the chassis of the transformer and the negative lead is connected to a low side winding the resistance measures as 30MOhm
When the positive lead of the meter is connected to the low side winding and the negative lead is connected to the chassis the resistance measures as >1GOhm

The question is what is causing such a behavior of the tester.


texts: Where exactly do the electrons go in the circuit once they traverse the circuit elements?

texts:
From my understanding, when a voltage is applied to a circuit the free electrons in the circuit elements start moving towards the higher voltage potential. So what happens once the electrons reach the the higher voltage potential? It doesn't make much sense that all the electrons would build up as there are a discrete amount of particles in any given physical object which I assume would cause the circuit to eventually not work. Not only that but I also would assume that once there were a sufficient build up of electrons they would start to repel further electrons. I would think that there would be some sort of mechanism to come back into the circuit from the voltage source but as I understand it you would either need to heat the voltage supplying material enough that they can break free or have a particle/photon break the bond.

Any help in understanding this is much appreciated


texts: Add constant current to an XL6019 module

texts:
I need to add a circuit to an XL6019 module to get a constant current (adjustable) source to drive some SMD LEDs. I'm no expert in complex circuits and my level of knowledge in electronics is basic.

I've found a tutorial to add the same feature on a LM2587 module (https://www.instructables.com/id/Adding-a-Current-Limit-Feature-to-a-BuckBoost-Conv/) and used it as a reference for my project (I've actually just changed a resistor with a lower power rating one and the package of the voltage regulator).

The modules should have about the same specs and differ only by the main IC pinout. I can't understand if there is something wrong with my circuit or if I have to check the components for a failed one.

This is my schematic. The Wago connectors are used to connect the XL6019 output and the main 12V power source to the circuit. The JST-SH connector goes to a 3296w 10k trimmer with the same pin numbers as the port.


texts:
I have these circuits:

Their goal is to protect the +vcc and -vcc pins of an opamp. They limit the voltage  to +30 V (-30 V) and 25 mA in normal conditons.
The 1200 ohm resistors act like 25 mA load at 30 V.
When there is a short on one rail, this circuit drops the Vout voltage. Which means that the supply isn't "symetric" anymore. And i don't think thats good ( more about that here and here). So what I would like is that when a short happens on one rail the other one is also shutdown until the fault is adressed and cleared.
I was thinking of some sort of voltage monitor that would trigger a BJT or MOSFET on one rail when the votlage on the other rail is not high enough. But the negative rail makes thing a bit more complicated for me.
OPA445 datasheet


texts: Confusion about Ohm's law and electrical power (basics of electrical engineering)..?

texts:
I am studying electrical engineering, but I still have some doubts about Ohm's law and electrical power.

According to Ohm's law: \$I=\dfrac{V}{R}\$
So that means voltage is proportional to current.

Higher voltage = higher current.

Now I was taught that in order to transmit on power lines, the voltage needs to be transformed higher so that according to \$P = U * I\$, current decreases and there is less heat loss.

But wasn't current proportional to voltage? How can a higher voltage not induce a higher current?

For another example let's take a 100 W light bulb. I was told that if I have a 10 V Voltage, the light bulb "will drain" 10 Amps in order to function.

Is this wrong? Is 100 W the amount of maximum power the light bulb can handle or the power it needs, and how can it "take" 10 Amps if current depends on the applied voltage and bulb resistance?

I don't understand how current doesn't depend on the applied voltage according to Ohm's law.


texts:
I have seen many articles that tell me I should be using RTOS for time management and resource management. My time has not permitted my own research, so I come to chiphacker for advice.

I use low resource microcontrollers(MSP430, PIC) and was looking for RTOSs I can use.

To the point:

Resource cost of system
Advantages of system
Disadvantages of system
Implementation Tricks
Situations the RTOS should/should
not be used in.

I do not use systems like the arduino, the projects I work with cannot support the cost of such a system.


texts:
I'm building up a project to transmit data from one computer to another computer from a wireless media and I have to use LEDs for this purpose (As per the requirements of the project, so I can't use laser diodes). I'm thinking about using the USB to RS232 module, an Op-amp, a schmitt trigger and a SHARP IR sensor to send the light signals and a photo-transistor.

I'm going to do it like this:

1. Connect a serial monitor to the PC
2. Use RS232 module Tx pin to drive a switching transistor which is connected to the SHARP
   sensor's Vcc Pin
3. In the receiving circuit, get the light coming from the IR Sensor IR LED using the
   photo-diode and connect it to a schmitt trigger
4. Connect the schmitt trigger output to an Op-Amp
5. Connect the Op-Amp output to another RS232 module Rx pin and read data from a
   serial monitor

I'm just wondering if the above selection of items are the appropriate ones. The receiver has to be 1m away from the transmitter. So are there any other options I can use other than the SHARP IR sensor?


texts: How to detect an I2C slave presence/ absence as an interrupt?

texts: Involved in a task to build a test equipment with a ARM M4F microcontroller for the purpose of testing various PCBs. One of the PCBs has I2C compatible current/voltage monitoring chip on it. Is there a possibility to detect this PCB using the I2C communication on plugging it to my test equipment? just like an external interrupt to the microcontroller for example?


texts:
I am in the process of hooking up the ratsnest in pcbNew, in KiCAD.
I finished with the process, except the last connection.
Here it is:

The upper copper layer is set to Vdd. As you can see, the barrel jack connector is in contact with the upper layer, thus providing Vdd across the upper copper layer.
The pin of the IC is where Vdd should connect. As you can see, it makes contact with the upper copper layer. But the ratsnest remains.
I checked around to see if a trace is blocking the upper copper layer, but as you can see, it is connected.
I tried connecting the Vdd directly with the Vdd of the IC, but the line remains. What is causing this?
EDIT:
If i select the upper Vdd trace with Control+click (thanks to Pete W advice) i get this:

When i do the same with the trace that connects to Vdd, i get this:

EDIT2:
If i remove the trace that connects to Vdd, then two ratsnests show up:


texts: Power a coil with a MOSFET driven by a BJT in ground

texts:
I am trying to do something something maybe trivial. I have little to no knowledge in transistors so bear with me.

I want to power a high voltage coil with a low current switch using transistors I have at hand.

The working circuit is simple with a high current switch:

simulate this circuit – Schematic created using CircuitLab

My idea is to drive it with an n-channel e-MOSFET I have at hand, a CEP83A3, but since the switch has to be in the negative side of the circuit, I thought that with an PNP transistor I could make it work with no success. This is my basic idea:

simulate this circuit

I tried with voltage dividers in different places to lower the input to the MOSFET but had mixed results, none of them worth showing. I have seen the push pull output configuration, but not sure if it will work with my setup having the switch in the negative side.

I did search here and Google but found nothing with a switch in the negative side.

Could someone help me with this? Maybe with a little explanation to know what is going on.

Thank you for your time spent reading this.


texts:
I was wondering if I could get some critique on my first PCB layout.

I've tried to isolate the 240V side from the 3.3V side as best as I can.

Only thing really concerning me is if I there is enough distance between my tracks on the 240V side and if the track widths are enough?

I am trying to keep the PCB as compact as possible. At the moment it measures about 46mmx39mm.

The PCB is to wirelessly control lights with a regular light switch as the input, 240V connected to the IRM-02-3.3 with the 3.3V then powering the ESP8266-01.

Got an optocoupler and Triac in there to switch the light load.

Schematic:

Thoughts and feedback greatly appreciated :)

UPDATED PCB:


texts: Aperiodic lattices and beamwidth of reflectarray antenna

texts:
This question is about reflectarray antennas.  In the paper below, it is mentioned that:

  "A second useful rpoperty of aperiodic arrays is the possibility to reduce the number of elements in one assigned aperture without major impact on the beamwidth."

Viganó, M. C., Toso, G., Caille, G., Mangenot, C., & Lager, I. E. (2009). Sunflower Array Antenna with Adjustable Density Taper. International Journal of Antennas and Propagation, 2009, 1-10.

I understand that aperiodic lattices are able to reduce sidelobe levels by suppressing grating lobe formation.  However, why does the periodicity of the lattice affect the beamwidth of the antenna?  I am hoping to get an answer on this that includes a qualitative explanation in addition to any math that is required.  Thank you!


texts: Should I worry about the risk of tombstoning?

texts:
A colleague has (apparently unsuccessfully :-)) tried to convince me of the risk of tombstoning

in the following situation:

He claims pad 1 for R55 and R59 will lose heat faster during soldering because they have two traces leaving, while pad 2 only has one, and that this would cause tombstoning. Frankly, I've never noticed anything like it, even these 0402 resistors lay perfectly flat on the PCB. Am I too careless?

(The traces are 0.2mm wide)

edit
I could also have shown 0402 parts with one pad connected via 4 spokes to a copper pour, which should be even worse, but again no problems whatsoever.


texts: Is case grounding compulsory in typical 32.768kHz crystal for Real Time Clock?

texts:
Pictures shown below is a typical 32.768kHz crystal, commonly use in Real Time Clock circuit (e.g: DS1307 & DS1337)

Referring to an earlier question posted here, it is a good practice that ground planes should be beneath the crystal. But is it compulsory that we should ground the crystal's body/case too (like what they did in these pictures)? And if yes, what happens if we didn't grounded the case?