texts:
I am trying to learn a simple LED circuit here.
First, I am trying to light the LED with 3V and 20mA. Based on what I've learned, R1 should be 100ohm. (5-3)/0.02 = 100ohm.

simulate this circuit – Schematic created using CircuitLab
I think I get it right so far (I hope.)
Now I am trying to turn on/off the LED using a 2N2222A NPN transistor:

simulate this circuit
I looked it up online and find most people referring to the hFE as 100, therefore I plug in the 100 to the current gain formula hFE=Ice/Ibe => Ibe = 0.02/100 = 0.0002A. I then use the Ohm's law again to get the value of R2 for the transistor based on the Ibe I found early. (5-0.7)/0.0002 = 21500ohm => 22kOhm.
I am able to light up the LED but can an expert here validate if I am doing it correctly. In addition, can someone clarify below confusions for me?

I am not sure if I am using the correct current gain (hFE) value for the Ibe.
Am I using the correct formula hFE=Ice/Ibe to calculate the resistor R2 for the transistor base?


texts:
I have searched across web, but I am unable to find such a circuit.

I am looking for a circuit of a AC nano-voltmeter in range 5-10 to 100 nV which output is suitable to be handled by some precise ADC like ADS1252 ( which will be later interfaced by Arduino or ESP8266 or ESP32 ).

The signal is in frequency range of 10 to 4000 Hz.

A precision of 2 to 5 nV would be sufficient.

The signal is coming from a coil without core, it gain signal from another coil, which change frequency. (I can make it static frequency on about 1000 Hz if this makes the things easy.)
The impedance of the source coil is about 1-2 ohms. The current is considerable small - a few nanoampers I presume (I am unable to measure it).


texts: How does the "rubbed" coating of an LCD align liquid crystal molecules?

texts: For many LCD applications the liquid crystal layer's relaxed state is a "helix" twisting the alignment from one direction at top to another on the bottom. Obviously, within the liquid crystal layer itself the "aligning" force is the same that causes the molecules to align along a director in general. My question is about the bottom and top layers whose direction is forced by a "rubbed" polyimide coating (additional link) (or similar mechanism). What's the nature of how this coating encourages the molecules to have a certain orientation? Does the rubbing cause microgrooves that the (usually elongated) liquid crystal molecules naturally fill? Is the force electrical in nature? Chemical? A combination? The picture from the first source implies grooves, but I haven't found any explicit answer.


texts: Can I replace this oscillator circuit with oscillator IC?

texts:
Disclaimer: I am programmer and when it comes to analog circuits I have no idea what I am doing.

I have a board with STM32F103 that uses external oscillator made by crystal and two capacitors:

The crystal is CD05M008000RD1 / 49SMD-8-20-20 described as 8Mhz, 20pF, 20ppm, ESR 60Ohm.

Everything seems to be working fine, but I am trying to reduce the board size and the crystal is rather big. I am looking for either smaller crystal or a complete oscillator in small package.

I found for example this: O 8,0-JO32-B-1V3-1-T1-LF described as XTAL OSC XO 8MHZ HCMOS SMD, 50ppm.

Can I use it so that it will look like this?

I see that it is less precise (20ppm vs 50ppm), but for my use-case it should be well within the limit. It is still way better than the internal oscillator. Are there any other differences that I am not seeing?


texts:
Recently I bought an ethernet switch controller based on the Realtek RTL8305NB chip. It was bought as a proof of concept for my robot. Unfortunately, the board is too big and I want to design my own 2-layer PCB (also to learn new stuff). I would like to use the same chip, but finding its datasheet is almost impossible (I even contacted manufacturer and few shops - no result). Does anybody know a similar chip? Why is the datasheet for RTL8305NB so hard to find?

What I need:

10/100 MBPS,
at least 3 ports,
package for 2-layer board (not BGA).

I am new to the ethernet technology and I will appreciate any help and piece of advice.


texts: Capacitors in parallel without resistance

texts:
For the following circuit, at time 0, the switch switches from A to B, figure out the voltage wave form at B.

The question I am concerned with is whether the voltage across the capacitors will change instantaneously or not? Will the output waveform at B be a step function? (0 for t<0 and C1/(C1+C2) after t>0).


texts: loop gain, open loop gain of op amp in inverting configuration (feedback capacitor)

texts:
I was trying to understand the 2nd answer from this post here, with the circuit of the post shown below.  The 2nd answer has equations including open loop gain I wasn't able to understand (1st question).

It has the following equations:

Loop Gain =  \$ A_{ol} \frac{R_1}{R_1 + R_F} \frac{1}{s/w_p +1}\$ and \$A_{ol} = \frac{A_{DC}}{(S/W_1+1)(S/W_2+1)}\$

The original post tries to explain why one may want to have a capacitor in parallel with the feedback resistor.

I know that it is to kill the high frequency noise generated from the op-amp.

But if you look at the output of the op amp and see how it would go to the inverting input through the feedback resistor, doesn't the feedback resistor and the parasitic capaitance, Cp, form a low pass filter? (2nd question)


texts: What component is a VZ reference designator for

texts:
The board I'm looking at is a modem board from a fax machine.

There are 2 identical components labeled VZ1 and VZ2 on the board, both components have F175 on the face and have 2 SMC leads.

One of them has a resistor across the back pins, and they look like they might be part of the power circuitry.


texts:
While building some small (single digit wattage) inductive power transmission systems, I wondered if a larger one could be build using an induction cooker as transmitter.

What would be the mandatory properties of an inductive receiver to please an usual household inductive cooking plate and make it engage in power transmission? Would the coil and capacitor of an equal plate make a good resonant receiver?


texts: Powering multiple ADCs from a single power supply in bipolar mode

texts:
I am making a PCB with 10 analog to digital converters, which each ADC needs 5v as analog supply and 10 mA as current.
I found a tutorial that uses 2 common 9v batteries for only one ADC for the bipolar mode, but I  need to feed the 10 ADCs simultaneously.
Can you help me to fix the needed battery, and how I can feed all devices without damaging the PCB?


texts: Any regulation needed when powering an AVR MCU from USB?

texts:
I know that USB PSU's are regulated but does that mean I really don't need anything at all in my circuit to have reliable operation?

Now my circuit will be running 24/7 and should be as reliable as possible. The most sensitive part and also central part is an ATMega MCU.

I'm still fairly a noob and would like know if there still could be any hazards coming from USB PSU's and what would you do to avoid them?

There are several questions about USB PSU's already but some of them have answers that give me some doubts about the general short "yes, this will work" answers.

For example I read in this answer that a charger might actually disconnect you at some point, is that true? If yes, can I do something to prevent it?
https://electronics.stackexchange.com/a/99187/17371


texts: Can I drive a stepper motor with a regular MCU?

texts:
If we just focus on the signals and not the power, will an ordinary MCU like any of the ubiquitous Atmel 32-bit controllers be sufficient to drive a step motor?

What are the benefits of prepackaged special purpose motor driver chips apart from the simplified PCB layout?


texts: Step down converter LM2596 with voltage spike on output when powering up, destroys subsequent circuits

texts:
I use this step down converter with input 30V DC and output set to exactly 5V.  At the output I connected an ESP8266 (WEMOS D1 mini, has 3.3v regulator on its board) and an MP3 player module (DY-SF5W.)
One thing is, I experience sparking on the input side of the step down converter module  whenever applying power to it. But more concerning, I destroyed my load at the output (the MP3 player module DY-SF5W.)
I set the output to exactly 5V and connected the ESP8266 and the mp3 module to the output of the step down module. After powering up the step down converter 2 or three times (30V DC at the input), the mp3 module was destroyed. The microcontroller on the mp3 board smoked and you could see it glowing. The voltage was definitely set to 5V, and the ESP8266 was still working ok. I then connected another MP3 player board/same model, which first worked ok, but again after 2-3 times powering up the input of step down converter, again the uC of MP3 player board smoked exactly as the first one. The ESP8266 again survived.
I then monitored the output of the step down converter closely with oscilloscope, all looked fine, but after setting time base to 25ns, I could see that at the moment when connecting the input voltage to the step down regulator, its output VCC spikes to plus 18V and down to minus 10 volts, but only 25-50 ns in length, and then back to 5V. The question is, is it possible that this very short Vcc change is dangerous to certain parts, and why I do not find more results when searching google for damages due to that? Even with a 4700uF cap at the output of the step down, I sometimes get those spikes.
Another step down converter module of same type shows the same spikes.
How can I securely get rid of them?


texts: How to create a complex transfer function amplifier bjt based

texts:
I need to create an amplifier as shown in the first photo bellow, where we have a 20dB/dec rise  and at the end of transfer function -40db/dec decline.
I see we have a zero and then a double pole.
A basic bjt amplifier was created with 2n2222 in PSPICE shown bellow,Its transfer function in the last photo is far from the transfer function i need.
I can add another stages and mosfets or feedback to my bjt frst  stage.
could you recommend a structure which structure has a similar transfer pole zero transfer function structure as shown in the first photo bellow?
Thanks.


texts: Unknown source of noise when measuring with oscilloscope

texts:
The original question was how to decrease power supply noise, but after discussion it seems to be just a measurement problem.

Case 1: When I short the ground lead to the probe, I read about +-2mV rms - acceptable by me.
Case 2: When I connect the ground lead and the probe to the 0V of the power supply, I get a lot of noise with spikes up to +-50mV - not acceptable.

Common sens and several people say that in both cases, I should have a reading as in the case 1. What could be wrong with the oscilloscope?

The oscilloscope has an earth ground pin in the AC power cord. The power supply also has the ground pin in its AC power cord. I do not connect power supply's negative negative terminal to the earth ground (the green connector on the front panel). Even if I do, it does not seem to affect the measurement - I still get the same random noise.

Please, help me to find the source of this noise.


texts: Is it possible to redesign a portable electronic device such that it can be charged by a domestic microwave oven?

texts:
Soon after iPhone 6 was introduced there was a prank claiming that the smartphone can be charged by leaving it in a running domestic microwave.

TL;DR don't do it, it is very, very unsafe. There's a number of videos showing how a lot of things goes wrong, don't do it anywhere.

So a portable device such as smartphone as it's shipped cannot be charged by a domestic microwave.

Could it be redesigned so that such charging becomes possible? I've read a number of publications about distant future concepts where you have a number of large solar panels on Earth orbit and they capture energy and then beam it to Earth surface as microwave radiation where the beam hits some cleverly designed receiver and the latter converts microwaves to electricity. Perhaps something like this can be done for charging devices.

Suppose the following limitations apply:

it must support typical domestic microwave ovens, no adjustments of oven must be required
the portable device may contain any new or altered elements unless those significantly impair its usability or make it unsafe

Is it doable?


texts: Diagnosing LCD backlight inverter problem

texts:
I am having problems diagnosing the error with a notebook LCD display inverter.

Symptoms: After switching the notebook on, the LCD backlight comes on but the intensity oscillates rapidly (flickers). After about 1 second the backlight turns off completely. Once the backlight has turned off, the AC output of the inverter measured with a DVM is 0 Vac.

I visually checked the inverter board and there are no obvious faults.

Given the symptoms, can anybody venture a guess at the problem?

On the one hand I am tempted to say that the backlight is ok (after all it ignites) and the problem is more likely to lie with the inverter.
On the other hand I am wondering whether the flickering of the bulb (faulty bulb?) causes a open-circuit protection of the inverter to kick in after 1 second.

So in summary I am not quite sure whether the fault is more likely to lie with the bulb or the inverter.


texts:
I would appreciate some help solving the following circuit.  I've been trying for a very long time and can't get the same answer the book has.  I'm trying to get \$ V_o \$ in terms of \$ I_{os} \$.

The answer is \$V_o = I_{os}R_2 \$ when \$ R_3 = R_1 || R_2 \$.

My attempt is simply:

$$ V_+ = 0.5 I_{os} R_3 \\ V_- = -0.5 I_{os} R_1 + V_o \frac{R_1}{R_1 + R_2} $$

since \$ V_- = V_+ \$,
$$ 0.5 I_{os} R_3 = -0.5 I_{os} R_1 + V_o \frac{R_1}{R_1 + R_2} \\ V_o = (R_1 + R_2) R_3 I_{os} $$

But this is wrong. Even in the simulation that I conduct, I see that \$R_1\$ has no baring on \$V_o\$. What am I doing wrong?

simulate this circuit – Schematic created using CircuitLab


texts: 2 pole single phase induction motor appears to have starting capacitor permanently connected (no centrifugal switch)

texts:
I am trying to repair and rewire an AC induction motor from a small  compressor. From what I can tell it's a 24 slot, 2 pole single phase induction motor that has main coil and starting coil. The wires for both coils are 24 AWG but the main coil has twice as many loops and the wires appear to be doubled up (A pair of 2 wires connect to power on main coil and a single wire pair for the start coil). There is a thermal overload box connected inline to both the start coil and main coil but what I wasn't expecting is what looks like a start capacitor connected directly from mains to the start coil, no centrifugal switches or timers. This compressor has a low duty cycle but it must run for longer than is healthy for a start capacitor when building pressure.

It looks like a start capacitor to me because it's not in an oil filled tin but could this be a run capacitor and there is no start capacitor?

What am I missing?


texts: USB battery charger noise in an audio amplifier

texts:
As the title says, I'm having some issues with battery charger noise and an audio amplifier.

The PCB with the charger and amplifier is connected to a GSM device, and that's where the audio signal for the amplfiier comes from. The amplifier itself is a class D TPA2000D1. A USB connection charges the battery via the AAT3681A-1 charger IC. The battery voltage is used to power the rest of the board (i.e. not the 5V directly). The amplifier gets its power through a low noise, high PSSR LDO, the ADP150.

Now, the issue I have is that when the USB and the battery are used during a call, clirps / bursts of noise about a second apart can be heard on the speaker. If I remove the USB power and use only the battery as the power source, the amplifier is silent! This means, for me, that the noise is somehow caused by the USB power and presumably because of the switching nature of the charger IC.

So I tried to measure this: although I see ripples on the V_BATT line when the USB is connected, the TPA_VDD line is silent and looks exactly the same with and without the USB connection. Although I measure there about 30mV peak-to-peak noise, the oscilloscope alone shows about 25-28mV peak-to-peak noise when nothing is connected.

I also tried other 5V sources (external power supply) with the same results.

My questions are: what am I doing wrong? What can I do to reduce this noise (e.g. filters, other charger IC)? How can I measure this noise anyway? I hear it but I can't see it.
Any ideas are highly appreciated!

Thanks!

EDIT
Here is the layout. There is a ground plane over the board, which is not visible here, so all components share the same ground.


texts:
Why doesn't the Inductance/Capacitance of Laptop charging wires and other appliances effect the performance of the devices/ power supplies?

An inductance would be introduced if the wires are lying in a loop or mixed together.


texts: Differential vs non-inverting op amp advantage

texts:
Assuming I need to measure and amplify a voltage drop over a resistor that is connected to ground on one side (no negative voltages, since current flows always in one direction), is there any real, practical advantage of using differential op amp over a simpler non inverting one?
Non-inverting config:

Differential config:


texts: Is there a difference between rise and fall time and modulation frequency

texts:
I was wondering if there was a difference between modulation frequency and rise and fall times of a laser diode or LED? If a laser had a modulation frequency of 100MHz would that be the same as a rise time of 5ns and a fall time of 5ns as 100MHz is equal to 10ns?

Thanks


texts: VHDL does not connect output of a device to the input of another device in structural architecture

texts:
I am a newbie in VHDL. I have the following structural top module that I am trying to synthetyze.
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

-- Uncomment the following library declaration if using
-- arithmetic functions with Signed or Unsigned values
--use IEEE.NUMERIC_STD.ALL;

-- Uncomment the following library declaration if instantiating
-- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;

entity nodoA is
    Port ( data : in  STD_LOGIC;
           clk : in  STD_LOGIC;
           rst : in  STD_LOGIC;
           start : in  STD_LOGIC;
           data_tx : out  STD_LOGIC;
           data_rx : in  STD_LOGIC);
end nodoA;

architecture Structural of nodoA is
    component Transmitter is
        Port (
        data_in : in STD_LOGIC;
        clock : in STD_LOGIC;
        load: in STD_LOGIC;
        reset: in STD_LOGIC;
        data_out : out STD_LOGIC;
        count_max : in STD_LOGIC;
        reset_counter : out STD_LOGIC;
        en_counter : out STD_LOGIC
        );
    end component;

    Component Contatore_mod3 is
        Port (
        reset : in std_logic;
        enable : in std_logic;
        count_max : out std_logic
        );
        end component;

signal temp_count_max : STD_LOGIC := '0';
signal temp_reset_counter : STD_LOGIC := '0';
signal temp_en_counter : STD_LOGIC := '0';

begin
    tx : Transmitter port map(
        data_in => data,
        clock => clk,
        load =>start,
        reset => rst,
        data_out => data_tx,
        count_max => temp_count_max,
        reset_counter => temp_reset_counter,
        en_counter => temp_en_counter
    );

    contatore : Contatore_mod3 port map(
    reset => temp_reset_counter,
    enable => temp_en_counter,
    count_max => temp_count_max
    );

end structural;

I tried to syntethize it and in the rtl schematic I get the following output (even if I asked to the compiler to not trim the logic for optimization purposes):
As you can see, wires from Transmitter to Contatore_mod3 are not connected, even if I used some internal signals to connect them. Does anyone know how to solve it?


texts: Why do tantalum capacitor datasheets only quote endurance at their max temperature? How does it change at room temperature?

texts:
I'm on my first large board design, and it's only begun to dawn on me how infuriating capacitors can be to design with.

Exhibit A: I need 100uF for a simple circuit to keep my FPGA on for 1ms after power is cut. This is hard to find in a cost-effective ceramic, but because it is just being used for energy storage I can deal with tantalum. So I start looking for a 100uF tantalum that's good to 25V, should be easy right?

It probably is, but I've noticed that all tantalums quote endurances between 2000 and 10000 hours. This seems terrible, that's barely a year of continuous operation. These numbers are quoted at Tmax, so how do I derate for a lower temperature? For example, at 55 °C I imagine the lifetime is more reasonable, but I can't find any resources on this. Is there any way to know? Is it a crapshoot? If so, isn't designing with tantalum caps incredibly risky in something that expects to be used on the order of years? How do you deal with this conundrum?

Edit
I've since come across two resources that helped my comfort level with tantalum lifetimes, which I'll add here to help anyone else who comes across this question. AVX has a useful primer on tantalum derating that goes over the MTBF calculations:

Voltage Derating Rules for Solid Tantalum and Niobium Capacitors

Better still, Vishay has a very simple "FIT calculator" that does easy MTBF calculations for all of their tantamlum families. Playing around with this was super useful for framing typical MTBF values in my mind:

Vishay FIT Calculator

Bizarrely, Kemet only has such a calculator for aluminums, and while I can find references online to an AVX calculator I can't find it on their site as of Sept 2017.


texts: Confusion about accuracy vs tolerance of an operating resistor

texts:
Let's say I bought a 100 Ohm resistor from a manufacturer with a tolerance of 10%. What I understand from the term tolerance here is that: it is the amount that a resistor may initially vary from its "stated nominal resistance". So in our case when I have this resistor in my hand I can say this can be between 90 to 110 Ohm.

But imagine I have a good ohmmeter and I measured this resistor as 98 Ohm.

If I install this resistor to a circuit, what can I say about the variation or accuracy of this resistor by time? Can it still vary between 90 Ohm and 110 Ohm during its operation or it will be around 98 Ohm always? Im a bit confused between tolerance and uncertainty accuracy/uncertainty here.


texts: What is the exact difference between SGMII and 1000Base-X?

texts:
I was wondering what the exact difference between SGMII and 1000Base-X is, because both seem very similar. Is the "big" difference only the physical medium they are supposed to be transmitted on?
Both standards transmit Ethernet frames and use the same medium access method (CSMA/CD), so what's the crux here that justifies to use two names for basically the same thing?


texts: Why does last data of I2C DMA transfer break?

texts:
I used DMA to transfer I2C data, but I always lose the last data. hardware configuration is shown below:

  DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)I2C1_DR_Address;
  DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)I2C1_Buffer_Tx;
  DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
  DMA_InitStructure.DMA_BufferSize = 2;
  DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
  DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
  DMA_InitStructure.DMA_PeripheralDataSize = DMA_MemoryDataSize_Byte;
  DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;
  DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;
  DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;
  DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
  DMA_Init(DMA1_Channel6, &DMA_InitStructure);
  DMA_ITConfig(DMA1_Channel6, DMA_IT_TC, ENABLE);

The data to be transfered is:

  I2C1_Buffer_Tx[0] = 0xF0;
  I2C1_Buffer_Tx[1] = 0x55;

When a data frame has been sent, an interrupt of DMA is generated:

void DMA1_Channel6_IRQHandler(void)
{
  if (DMA_GetFlagStatus(DMA1_IT_TC6) != RESET)
  {
    DMA_Cmd(DMA1_Channel6, DISABLE);
    DMA1_Channel6->CNDTR = 2;
    DMA_ClearFlag(DMA1_IT_TC6);
    switch (mode)
    {
      case 1:
        I2C_GenerateSTART(I2C1, ENABLE);
        mode = 2;
        break;
      case 2:
        I2C_GenerateSTOP(I2C1, ENABLE);
        mode = 3;
        break;......

When I set a breakpoint at I2C_GenerateSTART(I2C1, ENABLE):

I get SDA signal from oscilloscope in this pattern:

It shows that two data have been sent through SDA:0xF0 and 0x55, however, when I set breakpoint after that code:

 and I got following data:

it shows that only one data has been sent through SDA: 0xF0 and then a restart condition. so, I will lose the last data if I let the whole program run as usual.

I can only explain the phenomenon like this: DMA has already sent two data(0xF0 0x55), and then it generates an interrupt. However, those two data are still in I2C's buffer, then, in DMA's interrupt, it generates a start condition. For some reason, it breaks the final data.

Can any one give some suggestion to fix this problem or I can only set buffersize of DMA n+1 if I want to send n data.


texts:
Three "simple" questions here:

1-I know the diferencies between linear and switching DC-DC converters/regulators. Are there any applications where the disadvantages (specially noise and ripple) of the buck and boost converter that you can buy on Aliexpress or such webs are really a problem?

2- If so, how clean is the output of a linear regulator in comparison with a buck/boost converter of that kind?

3-Would it be possible to step up first the voltage and then use a LM317 to regulate it down a bit and having a very clean output?

I have a 12V supply and I need 30 to closest to 0V I can go. So that idea came to my mind to combine both boost regulator and a LM317 to get the benefits of both and I think it would be the cheapest solution and with the lowest ripple/noise at the output (if my thoughts are correct).

EDIT1:Of course the boost will be manually regulated to have an input voltage of 2-3V above the output of LM317.
EDIT2: The point is to make it as simple as possible so if the LM317 could reduce the noise sufficiently for no filtering in the output to be required. Also, if a commonly available boost/buck converter will be enough for everything I will go for that option. I don't know what uses are the SMPS not recommended for, because everything a could read is "not suitable for not sensitive applications" but it never specifies what are those.


texts: I want to generate a narrow pulse of very small duration. How can I implement it using PWL function. Or is there any other method for this.


texts:
When doping a PNP bipolar transistor, does it matter which parts are doped by what amount? The picture below will show my question. Am I right in saying that the Emitter is connected to one P region, the Base is connected to the N region and the collector is connected to another P region?

The confusing part in the question is that it says "not in that order". So can I just use the values given to dope the regions in any random way. Or does the Emitter area require the highest doping amount or the base area the lowest amount etc.

Thanks


texts: What are the typical paths of holes and electrons in an unbiased PN junction?

texts: Can anyone tell me the typical paths of holes and electrons in an unbiased PN junction at equilibrium?  In terms of diffusion currents, is that only holes (majority carriers in the the P-Type) traveling exclusively within the valence band and electrons (majority carriers in the N-type) traveling exclusively within the conduction band, both remaining in their respective 'lanes' even across the PN junction and both due to concentration of charges (the coulomb effect)?   And in terms of drift currents in the opposite direction, is that minority carrier holes traveling exclusively in the valence band and electrons traveling exclusively in the conduction band with both traveling due to the charge imbalance created by the diffusion current?


texts: When I googled about skin resistance I find people mentioning values as low as 500ohm but usually around 10-100kohm. When i measured the resistance of my own skin by putting the probes on the inner side of my forearm(just below the wrist) with 1-2cm between the probes, the resistance is so high my multimeter can't even measure it. I tried wetting my arm with some saliva and got a resistance above 1000kohms, and yes, I mean 1 million ohms. So to assure that I didn't misinterpret the numbers on the multimeter, I measured a 100kohm resistor on the same setting and it showed me "100" and then my skin again and it showed me about "1487". Is this possible?


texts:
In my truck a warning light comes on when I go to take off if a passenger is sitting there but the seatbelt is not secured. After some research and thinking it may be their weight, capacitance or maybe an infrared beam (although I cannot see a sign of that). Maybe other things I haven't thought of?

I am a furniture manufacturer and would like to incorporate a night light into furniture to have a light come on at night automatically when someone stands up. The truck gave me the idea and I was thinking because they sell so many they have probably put a lot of thought into how they work. Does anyone know the solution the auto industry uses or have other good ideas on ways to go about it?


texts: Grounded Common AC-DC Power Supply Simple Circuit

texts:
I need an AC to DC converter circuit where it is safe to connect common to ground.

My situation: I have a remote 120v->24v transformer. The 24v neutral is grounded. The DC circuitry is the only load on the transformer. The common node must be grounded for a communications bus.

What AC to DC converting circuits will allow you to connect common to ground?


texts: More advanced magnetic breadboard with software defined wires

texts:
Since we could compile the netlist on a typical x86 like computer
and download it to a FPGA chip so everything is connected and functioning,

Why can't we extend the same idea to Mix Signal engineering with bread boards.

I mean SMD magnetic devices could easily mount on the breadboard surface using
magnetism , and wires could be connected as the same way that connections were made
in FPGA chips?

My question is do you know such kind of device? What it named ?
If such device do exists.

And also why current breadboard technologies are not based on magnets?
What are the technological limitations why what I dreamed breadboard is not
in the radio-shack?

--Thanks in Advance --


texts:
I am running in to a problem when working on 3 phase problems. I don't really know how to determine if the voltage given in the question statement is the line or phase voltage.

  The magnitude of the phase voltage of an ideal balanced three-phase Y-connected source is 4000V. The source is connected to a balanced Y connected load through a distribution line that has an impedance of 1+j8 per line. The load impedance is 119+j27 per phase. Using the source voltage Van as the reference, find the following phasor quantities.

For me when I see the Van as reference I think that the 4000V is the phase voltage and the line voltage will be sqrt(3)*4000.

Am I right in this assumption?


texts: I'm trying to design a linear power supply to provide 32V and up to 10 amps from a 50V source. Is this the correct way of using multiple LM338 regulators to achieve this?


texts:
I'd like a simple switch that triggers when a flashing light is detected. Purpose is to open gate by flashing car headlights (say 3 times).

I have looked at comparators and photoresistors and various MOSFET devices that compare ambient light to further input (point photoresistors in different directions so headlights will trigger a detectable difference even in daylight - they are very sensitive), read about optocouplers and many other devices but get lost in it all and no solution yet for how to accomplish this.

I've looked at comparators the most and they have become really sensitive and cheap, and are adjustable to trigger at determined millivolt difference. They have a lot of use in quality control devices.

Switch would have to be tolerant of different light intensities and flashing rate, basically just measuring 3 discrete voltage differences within, say, 5 seconds as a trigger and then sent to a relay, I suppose. I'd adjust the comparator until I found the sweet spot between noise and intentional flashing.

Seems like there's got to be similar devices for momentary switches; push once for one action, twice for another, etc, within a given time. Seems so familiar but I can't remember a specific device. Many small things (like my circuit tester, mp3 player) scroll through a menu with each button push (which would be like the comparator sending a signal). I could leave the first couple menu items blank, have 3-4 signal events (like button pushes) have the open gate command. But what CMOS or MOSFET can be set up for that?

I would like it to be simple and rugged for outdoor use on the gates. I've heard of strobe detectors used by emergency services to change traffic lights but only word of mouth on that. Security isn't an issue as this would be an additional switch that could be turned on/off and mostly the gates are used for animal control.

Oh, and purpose is also to not have to give everyone an RF module and to allow guests to use it without anyone else activating gates or having to get out of car (some places are quite muddy, narrow, dark, steep edges, no good place for input code box to be mounted). Motion detectors or garage door type light beam won't work because animals can trigger it.

I'm a novice but have repaired many devices, built LED drivers, battery chargers, RC vehicles, large & small appliances, heavy equipment. I was inspired it was doable when we built a game device (Family Feud style with two buttons, first to press activates lights and buzzer and locks out the other button) and the plans online were very complex with multiple transistors and CMOS chips but we did it using just two off the shelf automotive relays.


texts:
I have a board I am trying to debug and it has a Mitsubishi 4-bit CMOS computer on it of type M34225M2-163SP:

http://pdfs.datasheetdirect.com/view/2994013/M34225M2-XXXSP.png

I assume the instructions are burned into the ROM. Is there any way to read the contents of the ROM and figure out what the computer does?


texts: IR range problem after coding burst/gap rate and ratio for TSOP1236

texts:
I programmed an ATTINY13 to drive an IR led on 36kHz with this code:

void setup(){
  DDRB |= (1<<PB0); //Set pin PB0 as output
  //DDRB |= (1<<PB1); //Set pin PB1 as output
  TCNT0 = 0;
  TCCR0A = 0;
  TCCR0B = 0;

  TCCR0A |=(1<<COM0A0); //Timer0 in toggle mode Table 11-2
  TCCR0A |=(1<<WGM01); //Start timer 1 in CTC mode Table 11.5
  TCCR0B |= (1 << CS00);// Prescaler table 11.6
  OCR0A=110; //CTC Compare value, 36khz
}

void loop(){ //cycle = 1/36 = 28μs

 for (int i=0; i<10; i++) { //burst of 10 cycles
  TCCR0A |=(1<<COM0A0); //on for 14μs
    delayMicroseconds(14);
  TCCR0A &= ~(1<<COM0A0); //off for 14μs
  delayMicroseconds(14);
 }
  delayMicroseconds(392); //gap of 14 cycles
}

The loop function is based on the TSOP1236 datasheet on burst/gap rate and ratio:

  • Carrier frequency should be close to center frequency of the
  bandpass (e.g. 36 kHz).
  • Burst length should be 10 cycles/burst or
  longer.
  • After each burst which is between 10 cycles and 70 cycles a
  gap time of at least 14 cycles is necessary.
  • For each burst which is
  longer than 1.8 ms a corresponding gap time is necessary at some time
  in the data stream. This gap time should be at least 4 times longer
  than the burst.
  • Up to 800 short bursts per second can be received
  continuously.

I'm getting readings now on the receiver's end, using Arduino and an attachInterrupt().

I posted a question here about this. It won the tumbleweed award, but I seemed to have found the answer.

However, the range went down significantly from a couple of meters, when I was overdriving the LED and wasn't using gaps, to about 30 centimeters now. It's also not very steady; sometimes it doesn't report a beam break, sometimes it does.

I only need about a meter.
What am I doing wrong?


texts: Proper use of CD4504BE Level Shifter IC for SPI

texts:
CD4504BE Datasheet: http://www.ti.com/lit/ds/symlink/cd4504b.pdf

I've been searching all over the web for a proper example of the use of this IC, but I haven't found anything. My basic application is to shift the 5V SPI signals from ATmega328P (Master) to the 3.3V ESP8266 (Slave).

The below diagram shows how I believe it should be connected:

Questions:

Are these connections correct? If not, how should these be connected?
Regarding the MISO line, I show it as connected directly from ESP8266 to ATmega328P. This works, but ideally I would like to shift this 3.3V signal up to 5V. Is this possible with a single IC? My assumption is no, I would need a second CD4504BE. If it is possible, how should it be connected?


texts:
I am planning to use TDA7498E in one of my projects and was going through the datasheet of the same and got confused at one point. In the absolute maximum ratings, it is written that the INPA, INNA, INPB, INNB have the maximum input ratings of -0.3V to +4V.
The thing which got me confused is that since the analog audio signal is more or less like a sine wave with equal peaks both in positive and negative, then how are we supposed to provide the input to the TDA7498E?
Any audio source will at one point give an audio signal greater than -0.3V (In absolute terms).
Please let me know if I am thinking in the wrong direction.
Absolute Ratings
Datasheet


texts: Sensible standard wiring type for long-range I2C

texts:
I'm planning on interfacing with some sensor devices via I2C over a long bus, with devices chained every 2m or so, up to 16m in total. I've seen other questions here referring to this from the "which protocol should I use?" angle, but I'm more interested in the actual wiring.

My main requirements are:

The cabling must be something that a non-technical person can acquire from a general retailer like Amazon or eBay. Preferably something obvious and well-known like USB, CAT5, or S-Video.
Connectors should be as cheap as possible - I'm trying to make the individual sensor boards as low-cost as possible.
Maximum stability, if possible.
Trying to avoid adding extra parts, so cases where I need things like differential line drivers should be avoided if possible.

The devices will probably run on 5V logic.

Is there an ideal cabling type for this kind of thing?


texts:
How is it possible to modify this reverse polarity protection circuit, to switch off when more than 5.5V will be applied.
I was thinking about voltage divider, and zener diodes, or voltage comparator linked to gate of MOSFET, but I'm not sure which way is better one.
I have DDS generator which requires 5V , 100mA and I'd like to avoid using voltage regulator due to voltage drop. So I could power it up from 5V and in the same way it will switch off if reverse polarity connected or more than 5V was provided.

Thank you


texts:
I've got a plan for a large electroluminescent display.  EL panels are typically driven with a sine wave at around 1kHz, and I want to use mains power for this.  What's the best way to convert mains power from 60Hz to 1kHz?  I don't need a whole lot of current - 500mA RMS should be plenty.

I've been thinking converting to DC, then back to AC again would be the simplest way to do this, but I'm concerned about the efficiency of such a system; is there a better way?  I also don't know how I'd produce a clean sine wave (EL is quite picky) at the output.

EDIT:  I'm in the US, so this is 120V at 60Hz.


texts: Transistor count of floating point multiplier

texts:
I'm trying to figure out just how expensive floating point fundamentally is, at the hardware level. For example, how many more transistors does a 32-bit multiplier cost in floating point compared to integer.

To be specific:

A 32-bit floating point multiplier, versus a 32-bit integer multiplier.
Both have a throughput of one clock cycle.
The FP does not need IEEE semantics; it can make the simplifications typical of GPUs e.g. no exceptions, rounding mode is not configurable, denormals flush to zero.
The integer multiplier only produces 32 bits of result and throws away the rest.
If it matters, say the target clock speed is 50 MHz and the implementation technology is CMOS.
I'm just considering the arithmetic hardware itself, not other issues like control logic, register renaming etc.

Roughly how much more expensive is the floating point circuit? For example, twice as many transistors?


texts: How to determine the operating voltage and current of a laser diode?

texts:
I have harvested several laser diodes out of old 16X to 22X DVD writers. I used a driver circuit based on LM 317 but  I was not able to reach the lasing current of the diode. I do not have the specs sheet for any diode. I did experiment with various resistors to control the laser current but with no luck.

  How can I experimentally determine threshold current of laser diode and the operating voltage of a unknown laser diode?

This driver is the one that I used.


texts: how to know how many bits a microcontroller has?

texts:
How can I know what kind of architecture a microcontroller has?
For example where can I read in the datasheet of the pic 16F873 how many bits architecture is? 8, 16, 32?

Next question what does:
What does mean:   Up to 256 x 8 bytes of EEPROM Data Memory.
Mean that there are 256 slots of 8 bytes? Or (256 x 8) bytes? So 256 slots of 8 bit each?
I don’t think it’s explained really well :S.
Thx for answers :)


texts:
I need someone to check my understanding of Nyquist frequency. I understand it in the following manner.

$$F_{nyquist} = ( F_{sampling}/2 ) * n$$
where n is an integer (negative and positive). For instance:

$$ F_{sampling} = 10 kHz $$ then $$F_{nyquist} = [-10, -5, 0_{(?)}, 5, 10] kHz$$ I am not sure, whether 0 is a nyquist frequency (Question 1). Then the mirroring a.k.a detected alias frequencies can be found at the following locations:

(\$F_s\$ in the picture is \$F_{sampling}\$)

green - signal being sampled (original signal)
red - alias frequencies
yellow - is it alias frequency ? (Question 2)

Questions:

1) is F = 0 Nyquist frequency ?

2) does the mirroring happens around F = 0 ?

3) is my understanding correct ? Are the red circles alias frequencies ?
The problem is, that I cant replicate all of the alias frequencies in matlab. I can see alias at $$ F_{alias} = F_{sampling}*n  + F_{signal}$$. For signal at $$F_{signal} = 3 kHz$$ I can see aliases at $$F_{alias} = [13, 23, 33]$$

 , but I DONT see it at $$F_{alias} = [7, 17, 27]$$ as expected due to the mirroring.

The following MATLAb code should illustrate the process I understand as "looking" for aliases.

clear all;
clc;

% sampling rate
F_sample = 10000;
T = 1 / F_sample;
% time range
t = [0:T:T*10];         % asmpling time - 10 samples
t_x = [0:T/100:T*10];   % smooth "time" to see the sinusoids of F_aliases signlas

% nyquist frequency
F_nyquist = F_sample / 2;

% arbitrary signal within sampling range (F_signal is less than F_sample / 2)
F_signal = 3000;

% when the following frequencies are sampled, they should appear as the
% F_signal
F_alias_1 = F_nyquist*2 - F_signal; % 1st mirroring - Zone 2
F_alias_2 = F_nyquist*2 + F_signal; % 2nd mirroring - Zone 3

% from F to w
w_signal = 2*pi*F_signal;
w_alias_1 = 2*pi*F_alias_1;
w_alias_2 = 2*pi*F_alias_2;

% calculate signals
x1 = sin(w_signal*t);       % samples (red circles)
x2 = sin(w_alias_1*t_x);    % blue signal
x3 = sin(w_alias_2*t_x);    % green signal

plot(t,x1,'ro');      % Sampling (red circles)
hold on;
plot(t_x,x2,'b');     % 1st frequency that SHOULD be sampled the same as original signal
hold on;
plot(t_x,x3,'g');     % 2nd frequency that SHOULD be sampled the same as original signal

xlabel('time');
ylabel('amplitude');

This is the outcome:

red circles - samples of 3 kHz signal at 10 kHz sampling rate (original signal at 3kHz is not depicted, just its samples)
blue - alias at 7 kHz (1st above 5 kHz (Zone 2), half of sampling frequency)
green - alias at 13 kHz (2nd above 5 kHz (Zone 3), half of sampling frequency)

Obviously, the blue doesnt "fit" the samples, while the green fit them perfectly


texts: Flush/slotted actuated rotary switch knob?

texts:
I'm thinking of using the R10015RS02Q SP10T rotary switch for an upcoming project I'm working on.

It's marketed as having a flush/slotted type actuator which I think requires something like a flathead screwdriver to rotate.

What I'd really want is for it to be hand actuated, however all the knobs I've found are meant to be used for a shaft-type rotary switch. I know it's possible to get a shafted SP10T rotary switch, but in my research it's cheaper to get these flush/slotted kinds.

My question is are these flush/slotted actuator devices ever intended to be used with a  knob/hand actuated, or am I looking in all the wrong places for a knob?

As a side note, what are these slotted rotary switches usually used for/with (if anything)?

I know this is awfully close to a shopping-type question, I'm justifying it as valid because of this question which asks what type of knob to use with a round shaft potentiometers.


texts: When is a charge controller NOT necessary?

texts:
A pratical/theoretical question.. is a charge controller always necessary?

Example: A ventilation fan needs to run when the sun is out.

Can I directly connect a 12v solar panel to a 12v fan?

Will it just run in proportion to sunlight?

Will it burn out if too much/little sun?

More generally, to what degree can one build a super simple solar system?

Fridge, fan, and other devices, each with their own simple PV panel?


texts:
I'd made this LED organ (schematic below and here):

And one of the filters are not working. On the opamp's inverting input, there's a small sin signal, and I don't know where it comes from.

I measured these with my scope on the filter. This is the (audio) input signal from the function generator:

This is the output one of the filters:

This is on the inverting input of the opamp without an audio input signal:

I don't know which component is causing this. I replaced the opamp IC and the transistors are working too, but I get the same problem.


texts: Why does a capacitor charge and discharge?

texts:
I know that a capacitor would resist a change in the voltage across its two ends. Assume that the capacitor in the diagram is a fully discharged capacitor( 0v across its ends). Now if I connect this capacitor to a DC source, and if it has to maintain the same voltage as before, shouldn't the capacitor act like a short circuit throughout(so that the voltage =0v)? Why should it build up its voltage to be equal to the source/battery voltage?

Similarly, why should a capacitor discharge when disconnected from the power supply? If it has to maintain the same voltage (say V) across its ends, it shouldn't discharge right? Shouldn't it just hold the potential within it so as to avoid a voltage change across its terminals?


texts: How to make my difference equation make the deadline constraint?

texts:
Back at it again.

STM32L43KC Datasheet:

The question this time is I am finally starting to implement my digital filter which can been see as:

Z - Transform:
$$LPF_D=\frac{Y}{U}=\frac{0.3957z^2+0.7914z+0.3957}{z^2+0.3848z+0.1979}$$

Difference Equation:

$$Y_i = 0.3957*U_i + 0.7914*U_{i-i} + 0.3957*U_{i-2} - 0.3848*Y_{i-1} - 0.1979*Y_{i-2}$$

With a sample of \$T_s = \$ 15uS. Created with the Tustin Method. With a Pre-Warp frequency of 20kHz.

Code architecture:

The ADC is sampling at 66kHz.

System clocked at 4MHz

Using a DMA to tunnel the ADC's sample into a short type array that can store up to 2000 samples called:

"short adcValues[2000]".

I have two interrupts:

Triggers when the DMA fills half of the array "The Half Transfer Interrupt"
Triggers when the DMA complete the transfer to the array " The Complete Transfer Interrupt"

This allows me to process the top half first while the bottom half is being processed and vice versa.

I have measured the time I am given to be in each interrupt which is 15mS for both the half transfer interrupt and the complete transfer interrupt. So essentially I would need my difference equation to be executed within 15mS.

With the current solution It gets executed in 188mS. I know you can do a lot of things such as used fixed point, DSP, FPU, however I am very new to this and have no idea which approach should I try.

Is my implementation even correct without the optimizations? Is it even possible to execute the code within 15mS when it needs to run 1000 times?

Code updated: Thanks to awjlogan. I got the code down to 25mS still not quite < 15mS. I guess the only thing to do is to increase the clock speed?

Second Update: Changing the clock speed to 80MHz got the code to 1.1mS! Thank you everyone for helping and giving their input.

short adcValue[2048];

uint32_t U_i[3] = {0,0,0};
uint32_t Y_i[3] = {0,0,0};

//16.16 Format
const uint32_t COEFF_0 = 0x654C;
const uint32_t COEFF_1 = 0xCA99;
const uint32_t COEFF_2 = 0x6282;
const uint32_t COEFF_3 = 0x32A9;

    void DMA2_Channel3_IRQHandler(void){

    if (((DMA2->ISR) & (1<<10)) != 0){
        halfTransferComplete = 1;
        DMA2->IFCR |= (1<<10);
    } else if (((DMA2->ISR) & (1<<9)) != 0){
        transferComplete = 1;
        DMA2->IFCR |= (1<<9);
    }
}

   while (1) {
    if (halfTransferComplete == 1){

    for (int i = 0; i < 1024; i++){

         U_i[2] = U_i[1];
         U_i[1] = U_i[0];
         U_i[0] = adcValue[i];
         Y_i[2] = Y_i[1];
         Y_i[1] = Y_i[0];
         Y_i[0] = COEFF_0*U_i[0] + COEFF_1*U_i[1] + COEFF_0*U_i[2] - COEFF_2*Y_i[1] - COEFF_3*Y_i[2];
         DAC1->DHR12R1 = Y_i[0] >> 16;
    }
        halfTransferComplete = 0;

}

    if (transferComplete == 1){

     for (int i = 1024; i < 2048; i++){

         U_i[2] = U_i[1];
         U_i[1] = U_i[0];
         U_i[0] = adcValue[i];
         Y_i[2] = Y_i[1];
         Y_i[1] = Y_i[0];
         Y_i[0] = COEFF_0*U_i[0] + COEFF_1*U_i[1] + COEFF_0*U_i[2] - COEFF_2*Y_i[1] - COEFF_3*Y_i[2];
         DAC1->DHR12R1 = Y_i[0] >> 16;
    }
         transferComplete = 0;
      }
  }
}


texts: For power gain , we simply could do like this output power/input power in an amplifier, then what is the reason behind taking logarithm of it making it into decibel? Is there any advantage or is it just a convention?


texts:
Several years ago I attempted to build a coil gun, but gave up in frustration after burning out several SCR's when designing the trigger circuit. The SCR is used as the switch that dumps the energy stored in the capacitor into the coil.

I've since brushed up on my fundamentals and tackled the problem once more. Below is the circuit I've come up with.

V2 applies a 3.3V, 10ms pulse to the gate of M1. This pulls the gate of M2 low and causes current to flow into the gate of the SCR. Since V2 is a logic-level signal, I used this configuration so I could drive M2 without needing a level-shifter. R1

R3 is a current limiting resistor used to limit the gate drive current to 40mA, which is the rated maximum gate current required to turn on the SCR.

R4 is used as a pull-down resistor to prevent spurious signals from triggering the gate of the SCR.

Since C1 is charged to 200V, I've included D1 to prevent the drain of M2 from seeing large voltages when the SCR is triggered.

L1 is the coil and D2 is used as a flyback diode to prevent reverse charging of C1.

I know I've left out some details, but is the overall design of this circuit good practices?


texts: If you put a MOSFET in backwards does the impedance change?

texts:
if I stick a MOSFET that should be going (S-D) to positive in backwards, and make it (D-S) to positive, all the current drops across the diode instead. This diode then approaches an impedance of 0.

Technically the current wouldn't go through the higher impedance S-D capacitance, and wants to travel through the diode instead.

Can I ignore the capacitance of source-drain while the voltage drops across the diode?

(I know this is not a ~practical~ thing, but I'm wondering more about the diode versus S-D capacitance than the practicality of backwards FETs)


texts: question about transistor matching circuit

texts: I'm studying this transistor matching circuit provided initially by Bob Moog. I think I mostly understand how it works, the op amp, bjt not under test and resistors form a current source, which stays constant for each transistor Vbe is measured for. What I'm a bit unclear on is the purpose of the 10k between the two transistors in the NPN measuring circuit, and why it's not needed in the PNP measuring circuit.


texts: How should I layout voltage regulators (VRs) to separate Analog and Digital?

texts:
I need to create two power and ground domain: Analog and Digital. I've a common power supply that I'll call VCCBattery that power 2 voltage regulators. Since each voltage regulator have decoupling Caps and GND pin, on which plane should I connect this GND pins?
After that, how should this 3 planes (Battery GND, Digital GND, Analog GND) shoul be connected together? (like first Digital and Analog and next to Battery, or a star joint between them)

Here's voltage regulators that I use and their Pinout with essential capacitors:


texts: Basic question I would like to be solved

texts:
Can someone please solve this for me, telling me what's the right option and why? I will translate for you the question:

"What is the reading shown by the voltimeter inserted in the circuit of figure 2".

R stands for resistence and V for volts.

It wasn't me that selected the option B and I am not sure if it really is the right option.


texts: Connecting a Raspberry Pi to a 220V switch

texts:
I have a switch that works at 220-230V AC and I'd like to link it to my Raspberry Pi and I want to know what I have to do from an electrical point of view.

So my switch, when switched on, places 220V AC on a wire, which somehow I'd like to transform it to 3.3V DC so I can react from software when the switch is on.

I should mention that the switch may stay switched on or off an indeterminate period of time (which of course I will handle in software) and I wouldn't like to damage my raspberry.

How do I do this? Is a transformer the solution here?


texts:
I am trying to get a deeper understanding of sine wave inverters (like this one) and thereby came across different topologies like a Push pull inverter with a center taped transformer or a full bridge configuration as seen in a class D amplifier.
I think that the center taped transformer setup requires less transistors but a bigger transformer whereas the full bridge option gets along with a smaller transformer.
Nonetheless I am not able to find more details or an overview of maybe other different existing topologies e.g. When to use which topology for a special power rating.
Am I looking for the wrong buzzwords or can somebody help me out with a link to books/application notes/etc describing inverter topologies and their characteristics?


texts: Does a soldering iron tip consist of multiple parts?

texts:
I recently purchased a new soldering iron and read here that it is good practise to tin the tip before actually using it. As I turned on the iron and applied solder to the tip, I noticed the very top of the tip accepts solder perfectly fine, but the lower parts have solder just run off.

When the iron cooled back down, I noticed the top of the tip looked nice and shiny, whereas the lower parts of the tip have blackened. I am unable to remove the blackened color with a damp sponge.

The separation between the top of the tip and the blackened part is a distinct straight line, so I assume it is made of a different material or coating.

I am therefore wondering whether what I observe with this new tip is normal? I'd like to maintain this tip as well as possible, so am wondering whether it is good practise to store the tip like this (top part tinned, lower part blackened)? Or do I need to maintain it in a different way? I have read through the questions on tip maintenance but could not find anything similar to what I've observed here.

The soldering iron works perfectly fine, I am just worried about the blackening of the base of the tip.

The soldering iron is a TS100 and the tip is a B2. (https://www.amazon.de/gp/product/B072LR7DV6/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1)


texts: Do barcodes allows to uniquely identify production items?

texts:
I hope this is the right place to ask.  I'm trying to learn about barcodes, I did some research and I wonder if, I can uniquely identify production patches (not just products).

For example, is it possible, given 2 Aspirin boxes, to differentiate them via barcode. It's not enough for me to just detect them as Aspirin, I need to uniquely identify each box.

Can this be done via barcodes?


texts: If I have two aligned PCBs with pads touching each other, will they bind if I reflow them?

texts:
I have a design where two boards of the same size will be stacked like pancakes and physically touching. I want to electrically connect them, and I thought of just adding matching solder pads and putting the boards on a reflow oven. The idea is that the pads will melt a bit and form an electrical bridge across them, permanently bonding the boards and making a durable electrical connection. Here's the type of pad I was thinking of using. Is my idea crazy or will it work?

The manufacturing process also requires me to put it in a reflow oven anyway, so I thought I would save some effort by using this technique instead of something like a pin header or a board-to-board connector.


texts: Where are document options in altium 2020

texts:
I switched to altium 2020 and I can't find the document options dialog that was previously available  in "design / document options". I want to set parameters like in the screenshot (altium 2017).
How should I do?


texts: Questions about NFC's card emulation mode

texts:
NFC has a mode called "card emulation" in which it can communicate with an RFID reader because it acts as an RFID card. All the literature I have and the web searches I did only got me so far as with card emulation the device should at least "emit a unique ID". But I would like to know if:

it is possible, according to the NFC definition, for such a card
emulation information to be configured completely free (probably
going as far as emulating a RFID card with a java routine on with its
top limit being the maximum of bytes allowed on a RFID card in the
RFID protocol), and;
such a unique ID (if not freely configurable) is hardcoded by the
manufacturer or dependent on the SIM card.

On a side-note, it probably would be interesting to know what manufacturers enable you, as a user, to do and what should be theoretically possible because of protocol definitions.

For example, the Nexus S's NFC chip is read only and does not offer any card emulation mode.

I thank you in advance for all answers.


texts: Output capacitance of H-Bridge IC (DRV8432DKD) for snubber design

texts:
all. I have implemented a hydraulic pump driver circuit using a DRV8432DKD (36-HSSOP package).  I provided pads for an RC snubber on my PCB, but I am having some trouble coming up with the values for the snubber's parts because I cannot find any information in the datasheet for the output capacitance of the IC's output FETs.  Most (if not all) discrete FETs list a dynamic output capacitance (Coss) in their datasheet, and then a good starting value of the snubber capacitor is (Coss + mounting capacitance) * 2.

My initial thought is to survey a few of discrete FETs in similar packages with similar current ratings and use their values of Coss.  Any guidance in this area would be greatly appreciated.


texts: Control theory: What is the relationship between the number of elements in your system, and your diff'eq IO model and the dimension ABCD Matrix?

texts:
From my understanding, the order of your system is directly proportional to the number of elements in your system.

Suppose I have a circuit containing 6 capitors/inductors

Then the order of my model is 6

To write the relationship in a differential equation, I need:

$$y^6 + a_1 y^5 + a_2 y^4 + a_3 y^3 + ...+ a_6 = u^6 + b_1 u^1 ... +b_6$$

In terms of ABCD matrices

A is of dimension 6 (i.e. a 6x6 matrix)

Can someone verify whether my understanding is correct?


texts: What does schematic of a transceiver equalizer and transceiver preemphasis circuit look like

texts:
I have been reading about transceiver basics and was wondering about how 3 circuits look like:

Receiver equalizer.
Transmitter preemphasis.
Clock data recovery.

Where can I find a circuit diagram and detailed explaination of their working, more like a "white paper".


texts:
I am trying to design a gps data logger. I am not able to comprehend the chip antenna layout given here.

The pads 1 & 2 in the layout share the same terminal? Isn't it same as connecting the feed line to GND?

Thanks


texts: MicroSDHC "WP_VIOLATION" recurring Error

texts:
I have a few 8 gigabyte MicroSDHC cards that are being used as the nonvolatile storage in a data logging hardware application. The data being stored is going to be in a raw format, rather than in a standard filesystem.

Anyways, in the process of developing this system, some of our MicroSDHC cards have gotten stuck in a read-only state; all write commands return a WP_VIOLATION flag, windows reports the cards as read-only, and hdparm on ubuntu agrees. hdparm is willing to (attempt to) clear the flag, but subsequent writes continue to fail although hdparm will report the card as not read only until it is remounted, at which point the read-only flag is once again raised.

Basically, some of our cards are stuck in bizarre write protect states that we did not (intentionally) trigger and we can't come up with any way to get them out of it. Are there any esoteric SD commands that may be of use?


texts: understanding charecteristics of transistors

texts:
While plotting input characteristics of a transistor, we choose to keep output voltage constant and plot the variation of input voltage and current. Why do we choose to keep output voltage constant and not current?
While plotting output characteristics of a transistor, we choose to keep input current constant and plot the variation of output voltage and current. Why do we choose to keep input current constant and not voltage?


texts: Iellegible JFET name, seems to be HEPxxxxx

texts:
I have this poor scanned schematic on which there is a Motorola P-channel JFET, labeled as Q5, and I can't read the name. It seems to me that the 2nd note is written "Q5 is HEP*1036" where * represents an unknown character. So, does anyone know what it could be? Is there a HEPxxxx series of JFET's?
On this other datasheet there is the same circuit using the 2N5461, but I can't find those down here in Brazil.
https://datasheetspdf.com/datasheet/MC1315P.html


texts: Converting hexadecimal digit to two's complement

texts:
So I have the number 'E' which is 14 in decimal and 1110 in binary. To get the two's complement I first get the one's complement and add 1, so I get:
One's complement: 0001
Two's complement: 0010
So the answer in decimal form is 2, but the textbook says the answer is -2. What am I doing wrong here?


texts: Don't know which transistor I should use

texts: I am new to transistors. I want to know which transistor I should use which will suffice for my H bridge. My motor draws 1.2A at 6V when stalled.


texts: Switching circuit for driving LED at different current values

texts:
simulate this circuit – Schematic created using CircuitLab
Above schematic is for limiting current to 4A when battery is connected to LEDs.

Datasheet of LED(BXRA-56C5300H 50W) are 23.5 Vf and 2.1 A typical current.
Led max rated current is 4 A @ 28.5 V only for pulsing at 10% duty cycle.
My actual project has 64 such LEDs

Current design

Powering 32 such LED with DC power supply of 24V 67A. Limiting current to each parallel connected LED to 2.1 A using current limiting resistor of 1 ohm 5W rating. LEDs are mounted on heat sink

New design

Requirement is to drive each LED string at Max rated current of 4A when required and then switch back to regular operation which is described in current design above.This switching should be digitally controllable.I understand my current DC power supply cannot supply so much of high current.So I was thinking to use another power source.I have in mind to use SLA(car batteries).

Since LEDs are connected in parallel each LED will required its own current limiting circuit so equal amount current is supplied to each LED.

Can anyone suggest me circuit for achieving this digitally switching between current limiter circuit of 4A(shown above) and 2.1A?

I simulated this circuit in proteus and I was getting 3.8 A flowing through LED string. But I am still figuring out how can I switch between this limited current to my current setup of 2.1 A . I need to run entire array of LEDs @2.1A most of the time and only on requirement need to switch to 4A . So I need to switch between two these two power supplies.


texts: Arduino IR Transmitter & Receiver w/ LEDs Flickering Issue (What's wrong with this circuit?)

texts:
I have an Arduino Uno connected to two IR transmitters and respective receivers. Basically, when one of the receivers detects a beam break, I have a strand of LEDs display a pattern. This all works in principle, but the problem is that when the IR transmitters and receivers are connected to the Arduino, the LEDs flicker with random colors.

The specific parts I'm using:

Adafruit 36mm 12V LEDs (http://www.adafruit.com/products/683)
12V 5A power supply for the LEDs (https://www.adafruit.com/products/352)
Two IR transmitters (https://www.sparkfun.com/products/10732)
Two IR receivers (https://www.sparkfun.com/products/10266)

Here's a video of exactly what's happening. At first, the IR transmitters and receivers are disconnected and everything is fine, then I connect the IR receivers and the flickering begins at around 8 seconds. http://www.youtube.com/watch?v=REAp5rODYUs. The flickering will continue even when I disconnect the IR receiver, albeit at a reduced rate.

Here's my wiring diagram:

In the above diagram, the Arduino is powered via USB (I tried with a 12V power supply too), and the LED strand is powered from an external 12V power supply (I couldn't find a diagram for an LED strand).

If it matters, I should mention that I'm using the IRremote library to control the IR transmitters (http://www.righto.com/2010/03/detecting-ir-beam-break-with-arduino-ir.html) and the strandtest example from the Adafruit WS2801 LED library (https://github.com/adafruit/Adafruit-WS2801-Library) to test everything right now.

The strange thing is that I also have another strand of similar LEDs (http://www.adafruit.com/products/322) and they do not experience the flickering regardless of if the IR transmitters and receivers are connected or not. So the only thing I can think of is to use an external power supply for the IR so as it avoid connecting them to the Arduino. Is that a valid solution? If so, how do I got about determining what power supply I would need (in terms of voltage and amperage output)?

Finally, I'm more of a software engineer (ie, spend most of my time on StackOverflow) so laymen's terms are better if it all possible. Thank you!


texts:
I have a project, using a temperature sensor, TMP36 and Arduino. Basically its a bluetooth thermometer. Everything worked fine at breadboard and connected and energized by my notebook. Now I connected it to a 4 x AA recharchable batteries and I started to get wrong temperatures (running on USB, I get 22 degrees, running on batteries, I get 44 degrees).

As formula to get the temperature, I'm using this one:

\$\text{Temp in °C} = \dfrac{Vout(\text{in mV}) - 500 }{ 10}\$

My debug info follows:

UPDATE

USB (5v)

voltage read from TMP36 = 147

voltage converted to 5v arduino

(147 * 5.0) / 1024  = 0.71

temperature = (0.71 - 0.5) * 100 = 21.78

Battery

4 x reachargable AA = 1.2v (voltimeter says 5.6v)
not enough energy to turn it on the BT module, but the board was turned on
(power light was on)

Recharged Battery

4 x reachargable AA = 1.2v (voltimeter says 6v.7)

voltage read from TMP36 = 171
voltage converted to 5v (I assume, that the arduino has a voltage regulator to limit the input to 5v, right?)

171 * 5.0 / 1024 = 0.83
temperature = (0.83 - 0.5) * 100 = 33

my questions are:

Is there a way to correct it via software or should I drop the voltage, using a diode/resistor?
At the datasheet its written that the input voltage range is from 7v to 23v. Does it means that it has a regulator to 5v internally to regulate my arduino to 5.5v? Does it means as well that I will need more battery to put it to work?

Arduino used is the Iteaduino BT

schematics
data sheet


texts: drawing flipflop after statement table and kmap simplification

texts:
I try to make counter using flipflop.

15-0-1-2-8-7-5-13-6-9-15 synchronous counter using D flipflop

Here is table:

Kmap simplifications:

After the steps, I don't know (what I do) how to draw and connect flipflops. I know I will use 4 D ffs.!


texts: How to charge Laptop Li-ion Battery cells manualy?

texts:
I have received some Li-ion batteries which were originally used in Asus A2 Laptop battery original one and I would like to know if it is possible to charge each cells independently with some device or just normal universal charger.

I Apologize if i asked in wrong section.


texts: One-Wire data transfer with a DS2401 via AVR

texts:
I've an ATMEGA32 and a DS2401 (64 bit ROM - Silicon serial number). I want to read its contents.

Can anyone help me giving me a clue, sharing a pdf tutorial link for One-Wire communication or a sample code or something else?

Note: I use Codevision.


texts:
I have a 25AA160 wired to a PIC24FJ64GB110 (100-pin):

SO -  RD3 (pin78)
SI -  RD2 (pin77)
SCK - RD1 (pin76)

SS is not used. CS\ is wired to GND and WP\, HOLD\ are wired to VDD.

I copy/paste code from Microchip and modified few lines to accomplish my hardware configuration.

This is the code (sorry a bit of long):

#define EEPROM_PAGE_SIZE    (unsigned)64
#define EEPROM_PAGE_MASK    (unsigned)0x003f
#define EEPROM_CMD_READ     (unsigned)0b00000011
#define EEPROM_CMD_WRITE    (unsigned)0b00000010
#define EEPROM_CMD_WRDI     (unsigned)0b00000100
#define EEPROM_CMD_WREN     (unsigned)0b00000110
#define EEPROM_CMD_RDSR     (unsigned)0b00000101
#define EEPROM_CMD_WRSR     (unsigned)0b00000001

#define EEPROM_SCK_TRIS     TRISDbits.TRISD1
#define EEPROM_SDO_TRIS     TRISDbits.TRISD3
#define EEPROM_SDI_TRIS     TRISDbits.TRISD2

struct  STATREG{
    unsigned    WIP:1;
    unsigned    WEL:1;
    unsigned    BP0:1;
    unsigned    BP1:1;
    unsigned    RESERVED:3;
    unsigned    WPEN:1;
};

union _EEPROMStatus_{
    struct  STATREG Bits;
    unsigned char   Char;
};

#define Hi(X)   (unsigned char)((X>>8)&0x00ff)
#define Lo(X)   (unsigned char)(X&0x00ff)

void SPI2INTInit()
{
    IFS2bits.SPI2IF = 0;    // clear interrupt flag
    IEC2bits.SPI2IE = 0;    // enable interrupt
    SPI2CON1 = SPI_MASTER;  // select mode    SPI_MASTER = 0x0120
    SPI2STAT = SPI_ENABLE;  // enable the peripheral  SPI_ENABLE = 0x8000
}

void __attribute__((interrupt, no_auto_psv)) _SPI2Interrupt()
{
   IFS2bits.SPI2IF = 0;
}

void EEPROMWriteEnable()
{
    unsigned char Local_8;
    Local_8 = writeSPI2(EEPROM_CMD_WREN);
}

void EEPROMWriteDisable()
{
    unsigned char Local_8;
    Local_8 = writeSPI2(EEPROM_CMD_WRDI);
}

void EEPROMWriteByte(unsigned char Data, unsigned int Address)
{
    unsigned char Local_8;

    Local_8 = writeSPI2(EEPROM_CMD_WRITE);

    Local_8 = writeSPI2(Hi(Address));
    Local_8 = writeSPI2(Lo(Address));

    Local_8 = writeSPI2(Data);

    // wait for completion of previous write operation
    while(EEPROMReadStatus().Bits.WIP);

}

unsigned char EEPROMReadByte(unsigned int Address)
{
    unsigned char Local_8;

    Local_8 = writeSPI2(EEPROM_CMD_READ);

    Local_8 = writeSPI2(Hi(Address));
    Local_8 = writeSPI2(Lo(Address));

    Local_8 = writeSPI2(0);

    return Local_8;
}

union _EEPROMStatus_ EEPROMReadStatus()
{
    unsigned char Local_8;

    Local_8 = writeSPI2(EEPROM_CMD_RDSR);
    Local_8 = writeSPI2(0);

    return (union _EEPROMStatus_)Local_8;
}

void main()
{
WORD rxData;
    WORD txData = 0x5AAC;

SPI2INTInit();

    // Write MS byte into EEPROM address.
    EEPROMWriteByte(Hi(txData), 0x10);
    // Write LS byte into EEPROM address.
    EEPROMWriteByte(Lo(txData), 0x11);

   // Now Readback one data from the serial eeprom.

    // Read MS byte from EEPROM address.
    rxData =  EEPROMReadByte(0x10);
    rxData = (rxData<<8) & 0xff00;
    // Read LS byte from EEPROM address.
    rxData |= (EEPROMReadByte(0x11) & 0x00ff);
    // verify write and read SPI EEPROM (single byte)

    if( rxData != txData )
    DebugMsg("EEPROM error");
}

I always got "EEPROM error" and I could not see any pulses on SO, SI and SCK on oscilloscope.

I think somewhere in my code I have to tell SPI2 to use these three I/O lines as SO, SI and SCK:

#define EEPROM_SCK_TRIS     TRISDbits.TRISD1
#define EEPROM_SDO_TRIS     TRISDbits.TRISD3
#define EEPROM_SDI_TRIS     TRISDbits.TRISD2

but, how? Am I right?

Many thanks

Wei


texts:
this is the designed pid controller and i am using TL084 op-amps which has +15 volts and -15 volts as their supply. when the error is generated, due to integrator the control signal(Vc) output is going to saturation point of nearly 15 volts. I want Vc to be in the range of (0.85-3.8 volts), so that i can give this to SG3524 PWM IC to generate constant duty ratio PWM pulses. I tried by putting zener diode of 3.3 volt rating, but now Vc is coming upto 3.5 volts(basically saturation limit has come down to 3.5 volts) . The problem is how to limt the Vc to the specified range.
Can any one please suggest modifications for proper design of anti-windup  working scheme of this.
Here VFb=-3 volts and VRef= 3 volts


texts: Kirchhoff's Law - Finding i in non series/parallel circuit

texts:
I am trying to solve this setting up equations to each node.

Node A: 10A + i5 = i
Node B: i + 4A = i3
Node C: i3 + i2 = i4
Node D: i1 + i4 = i5

I am lost from here. I don't know Vcd or Vad in order to define the respective currents i4 and i5. I am trying to solve this only by using KCL. Are there any other efficient methods?


texts: Some questions about a servo motor driver input ratings

texts:
A servomotor drive input can be supplied either 3-phase or single phase.
The photo of the driver nameplate is shown as follows:

Does that mean in full/nominal load if this drive is supplied single-phase, it will draw 9.9 Ampere rms current through line? This makes sense to me because I=P/V so I = 2.38KVA/240 is around 9.9A. I might have ignored power factor(?)

But FL current is written as 9.9/4.6 A. Does that mean in case of three-phase power input the total current drawn will be 4.6 A. How can we calculate 4.6 Ampere from 2.38KVA?

motor nameplate:


texts: How to remove gain and offset errors from ADC logic?

texts:
I have a 3-bit converter with ideal LSB of 50 mV. The following table shows the non-ideal logical values.
I need to remove gain and offset errors from the codes below.
I read on the internet that one step to remove gain error is to calculate a new LSB, by doing an average:
AVG_LSB = (363 mV - (-2 mV)) / (8-1) = 52.14 mV
If I calculate the table using this new LSB (NEW gain) I get table 2 shown below.
Did it remove the gain error? If so, then why is it called removing gain error?


texts: I don't mean LEDs for indication, debugging, etc. I mean LED effects like on the MSI Z370 Motherboard, where entire sections of the board are illuminated by continuous strips of light. How is this accomplished?


texts: Getting bad square-wave from the function generator

texts:
I have a small function generator:
http://www.velleman.co.uk/contents/en-uk/p371_hpg1.html

And using the following device for DAQ:
http://www.mccdaq.com/PDFs/manuals/USB-1208LS.pdf

I hook up the generator output directly to the daq board. At 1Hz output I see he following plot(sampling rate is 500Hz):

It doesn't look like a nice square wave. When I increase the freq. it gets a little better.

What can be the problem?


texts:
After several failed attempts to buy simple rabbit ears for FM tuner I decided to make my own. Now, I have zero knowledge in RF circuits. While finding the formulas for pole length wasn't hard, I could not find much on toroid chokes. Or rather, I found too much of it.

So, I decided to look at manufacturer's datasheets (e.g. here) and found this: "43 Material is used for EMI/RFI suppression in the 20 MHz to 250 MHz range". Hurray! In another place: "Common ferrite types used for HF baluns are 43, 31 and 61". So I go to digikey and none of those materials there, even though there are thousands of toroids and dozens of core materials.

Question: What common ferrite materials are suitable for a choke with 3-4 turns of micro coax, for 88~108 MHz range?

UPDATE:

From the document reference kindly provided by @jonk it seems ferrite cores #31, #43 and #61 are indeed good fits for this application. Here are some examples from different (not Amidon) manufacturer:

FT82-43 RFI Suppression 5 - 500 MHz, 21.0 x 13.2 x 6.35 mm
FT82-61 RFI Suppression 20 - 500 MHz, 21.0 x 13.2 x 6.35 mm

UPDATE:

I removed images irrelevant to the question.

Also, there seems to be a confusion about my goal. Here is an explanation of what I am trying to do: from many different sources like this one it is recommended to have RF choke (also called feedline choke) added to coax cable to suppress signal pickup by coax braid. Since I am making antenna from scratch anyway, why not make it right, right?


texts: DIY battery Pack Cell amperage difference

texts:
I have individually tested the capacity of ten 18650 batteries with my iCharger 4010. My question is, how much ampacity difference is ok when packing them in parallel ? The following are the readings from my batteries. I was thinking arraigning as below:

1970mAh
1876mAh
1796mAh
1783mAh
1635mAh
1596mAh
1497mAh
1457mAh
1158mAh
800mAh

Will test the 800mAh again.


texts:
I'm trying to step down my source voltage of 4.5V to a 3.3V suitable for the MPR121. The chip has at the best settings a typical current of 393μA. The 3.3V has to be quite accurate as to not damage the keypad. When researching, I've come across two possible solutions that could achieve what I want to do:

Voltage Divider
In this case, can the output be stable and accurate enough to be able to step down and voltage and if so, what value resistors would I use?
Voltage Regulator
This is then another IC just to step down the voltage (footprint wise), any suggestions on which regulator I would use (linear, switching)?


texts: Can you identify this crystal oscillator?

texts:
I've always used the internal oscillator in my AVR microcontroller projects, but have discovered that I need to use an external oscillator to increase the clock frequency. I have some of these 20MHz crystals in the spare parts bin, but I can't find a datasheet.

Searches for "MPC" and "970T" aren't providing any useful hits. I'm brand new to using crystals, and as such I am going to have a bit of work ahead to learn the ropes. Before I can get started I'd like to at least try using the ones I have on hand.

Do you recognize the logo or markings on this part, and if so can you point me in the right direction?

Edit:

This is a 4-pin device which is why I believe it is a crystal oscillator rather than just a crystal.


texts: Is it possible to make an SR latch using XOR gates only?

texts:
Due to certain rules, I can only use components available to me, so I cannot implement an SR latch using the standard NOR or NAND configurations readily available online. If it is possible, please may you explain how one might go about doing so.

Thank you.


texts:
I got a bunch of electronic components from someone, but some of them came without any ID. The one below is a relay, but I think the upper enclosure is missing (containing the model/type).

It looks like a relay and the upper part can move, connecting the two metal parts at the left top and right top.

As you can see, it has 6 pins, 4 on the left side, 2 on the right.

Does anybody can give some more information about this relay?


texts:
I want to use a switching boost converter that has 3.3V output in order to power an SD card. Also, the input voltage is a CR2477 battery, with voltage ranging from 2 to 3 volts. I have seen that an SD card may require up to a maximum of 100mA during writes.
As a result, I found this boost converter: TLV61225DCKR  .

As you can see in the link above, the output current is said to be 400mA on the site. However, by checking the datasheet of the converter, I found out that 400mA is the switch current limit. Furthermore, from the datasheet, I saw this figure:

This figure was the only reference I could find for output current, and the problem is that the efficiency falls dramatically at around 100mA, where the axis ends. I do not understand why on the farnell site the output current is rated as 400mA. Is this an error of the farnell site? Also, could you explain what exactly is the switch current limit "Isw", as mentioned in the datasheet?

Lastly do you have any recommendations for such a boost converter? The important aspect is to be as efficient as possible during those 100mA peak current writes.


texts:
OK so I've been asking around and reading how to connect ground pins to ground. Some said create vias to the ground planes. But should I do that for every pin? Because sometimes when I create via  to each component then route their connection on the ground plane, the net line doesn't disappear all the time.

Then other sources say create polygon pours after the connection is done. Sounds fine.

Honestly I'm a bit confused, can anyone just clarify how to route ground connections? I have tried connecting initially but I feel that something is not right about it.

Note that the ground pins of each of the boxes are connected


texts: My attempt at designing a voltage regulator - will this work?

texts:
I am recently getting into electronics design and learning about all this fascinating stuff.
I wanted to challenge myself to build a voltage regulator that can take the output from a series of solar panels (18-28V) and regulate it so I can charge a lead acid or NiMH battery (in essence using the circuit as a voltage source).
I wanted to know - would this circuit work? I recently learnt about opamps, they are cheap and hectic so I thought it would a great opportunity to use them in a circuit.
I wanted to avoid using a regulator chip, but I cannot think of a way to do so which would not require more components. Components = moar soldering time.

Thanks!!!!


texts: Are there ways/technologies to use High negative voltages in flash memories?

texts:
I am using an FGMOSFET with tunneling gate and control gate as an analog memory for simulation in SPICE. I use -25V to inject electrons into the floating gate and 25V to remove electrons. Everything was going well until I read this paper:http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.27.7816&rep=rep1&type=pdf

and it says

  Bidirectional tunneling can be used to add or remove
  electrons from a floating gate. This solution, however,
  requires either dual polarity high voltages, or a single
  polarity high voltage and a means for pulling the
  floating gate to this voltage when adding electrons, and
  pulling it near ground when removing them. Both
  approaches are unattractive. The dual polarity solution
  has a negative voltage much lower than the substrate
  potential; the single polarity solution does not support
  simultaneous memory reading and writing.

With the current technology we have, is this still valid. Are there technologies that allow a higher negative voltage than the substrate. I would really appreciate any help to point me in the right direction. Thanks


texts:
For my project, I would like to design my own SATA->USB-C adaptor.
For this, I'm using the Odroid schematic (here), and also the schematics of Cubieboard (here).
My question is about the JMS539 datasheet, more precisely the pin 46. Here is the JMicron explanation :

On the Odroid schematics, MODE_1 is VCC (5V), and on the cubieboard MODE_1 is VCC0 (3.3V).
So, I'm wondering, what is 2'b01 ? VCC or VCCO ? I know that 2'b01 is binary, but it's incomprehensible for me.
Thanks


texts: Question about debouncing - delay of state change

texts:
I have a very simple project where I needed to debounce a button (in software). Logically, my thought process is:

If the state's been stable for a while, and it changes, then immediately signal an event.
Ensure that the next state is stable before allowing another state change.

So if a button isn't pressed and has been that way for a while, but all of the sudden I read a changed input, I don't think I should need to wait to confirm that the changed input has been stable (I know that there has been an actual physical change to the button state). I can simply signal an event, but disallow new events for some set period of time to prevent false button bounces from signaling events.

Here's arduino code for a function getAction() done this way:

static int buttonBounceState = BUTTON_STATE_UP; // "Bouncing" state
static int buttonState = BUTTON_STATE_UP; // Debounced state
static unsigned long lastChangeMillis = 0; // Time of last state transition
unsigned long currentMillis;

buttonBounceState = digitalRead(BUTTON_PIN);

if (buttonBounceState != buttonState) {
   // Only allow state change if it's been 20 millis since last
   currentMillis = millis()
   if (currentMillis >= lastChangeMillis + 20) {
       buttonState = buttonBounceState; // Change state
       lastChangeMillis = currentMillis; // Only update timings at state transition
       // Button state has changed, so return an action
       if (buttonState == BUTTON_STATE_DOWN) return ACT_PRESS;
       else return ACT_RELEASE;
   }
}
// No button state change. Return no action.
return ACT_NONE;

However, it seems that everywhere I look, the way debouncing is done is that the initial state transition needs to become stable before actually performing a software state change/event signaling. For example, the bottom picture here: https://www.baldengineer.com/arduino-de-bounce-a-button-with-micros.html

My question: is it better to do debouncing this way? Is there something about my method that might fail that I'm not thinking about - i.e., some sort of noise while button is stable-open or stable-closed? If not, it seems that my method would give more accurate timings; and I don't miss very quick button taps (but delay until stable would). Also, how do these two software methods relate to hardware debouncing. How would a hardware debouncer be implemented that can time things similar to my method?


texts: How well would cat-5/6 work as a multi pair audio cable?

texts:
I'm looking at a situation where I'd want to connect a number of devices together to pass line level analog audio signals around. For the connections in question, there will always be small groups of channels (I've been assuming groups of 4) that go together. So rather than require a big mess of patch cables, I'm wondering what existing off the shelf items would work. 1m Cat-5/6 patch cords are easy to get and would have the correct number of conductors and meets the mechanical requirements but how would it do for signal quality?

Edit 1: I'm not sure that I didn't introduce some confusion here. I haven't settled on what kind of signaling I'm going to be using other than that it doesn't inherently need to deliver any power (the component at the other end will have whatever amps are needed to avoid that).

Edit 2: In the case I'm considering, I would be building the devices at each end and one of the advantages I'm seeing to using Cat5 is that I can use a single RJ-45 jack rather than four 1/4in TRS or XLR jacks (one of the devices could easily be limited by panel space for  jacks).


texts: How to convert current obtained from CT to precise voltage applied as input to ADC?

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My aim is  to convert current obtained from CT  to precise voltage that can be applied as input  to ADC.

As shown in the diagram , a conductor carries current of up to 63 A passes through the Current Transformer(CT) .The CT CT 1273-A1-RC has turns ratio as 1:2500 and current range of 0 to 100A . I have made one simple circuit in which there is shunt resistor in parallel and a diode in series with CT. The current passing through CT is from power distribution unit i.e. used in server rooms. So it is ac current .
$$I_s=(I_p)/2500$$

I_s=(63/2500)=0.0252.
My requirement is minimum-maximum voltage at the input of ADC should be in the range from 0 to 3.3 V . So for shunt\burden resistor
R_shunt= 3.3/0.0252=50 ohm,

Problem I am facing is how to obtain precise voltage (DC value) and also is there any need of additional circuitry in the circuit should be made so that it can be applied as input to the internal A to D converter of STM32L011x3  and display on seven segment display .So can anybody help me regarding it?

NOTE: I have done few calculation please see 1,2,3 for the selection of components. Can anyone crosscheck the values and tell me whether am I going right or wrong?


texts: Biasing using a Current Source in NMOS Common Source Amplifier

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I see that there are multiple ways to bias a simple Common Source NMOS transistor but I want to understand about biasing using current source.

I put up this circuit in SPICE:

The above is simple Common Source Amplifier biased with help of current source without a constant gate voltage. My first question is, "is this really biased with current source? or is it biased with -1.4V below the current source?"

I called this "biasing using current source" because changing the current value changes the operating point and Source potential is not fixed (while operation).

Well, now arises an interesting observation. I see that this circuit amplifies the voltage variations at Gate (which is what i wanted).
However, the source potential varies with gate. (acts as source follower).
But to amplify, shouldn't the source potential be fixed? Only then Gate-Source potential would vary and produce the output right? So, I wanted to know how current variation happens across the resistor to amplify the signal? (shouldn't the current just stay constant?)


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I'm looking for a logic gate IC that implements a set of AND gates with one leg that is common to all AND gates and one that isn't. To create a "group enable" function where if the common input is low, all outputs are 0 and if it is high inputs on the non-common input are passed through to the output.

Anyone know if such a thing exists (before I go an implement it with AND gates)?

Thanks in advance


texts: Can you explain the performance of a (Bluetooth) antenna?

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I have got this pcb with a Bluetooth antenna and the electrical engineer who did the job gave me this chart :

My questions :

what does decibel loss means in reality ? My guess : the antenna is supposed to emit at power 100% but there are some losses in the pcb and the actual signal strengh is of 100-x%, hence a loss of x%. Correct ?
At the Bluetooth frequency range, my antenna is -13db. Is that good or not ?


texts: Step-down as LED driver leads to flickering

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I received a LED driver board that uses an A6902D step-down as regulator.
Here the schematic of the driver section:

PWM_3 is the signal from the MCU: 500 Hz (tried frequencies up to 15 kHz) 0..100% PWM, 5V
C is the output signal where the LEDs are connected. It's a series of 6 LEDs with a total forward voltage of about 19V. The power supply is 24V but I tried to lower it down to 20V without any change in the behavior. Here the datasheet of the LED.
The problem is the LED flickering at almost any settings of PWM. Most at lower intensities, but also over 75% you can see the annoying flickering.
Checking with an oscilloscope I see that the input PWM is correct: clean and stable signal, while the output (pin 1) is interrupted here and there. I mean there are fraction of seconds where the A6902D keeps the output low, even if the PWM is still present at the input.
I guess it's a sort of protection, but I'm not able to find out the root cause.
Of course feel free to ask any specific measure I might take to help to better understand what's going on.
Another thing that may be useful. These drivers are very sensitive and burn too often. I destroyed several boards (the A6902D smoked) just keeping those in my hand, even without the LED connected. So I'm afraid there are some caveats in the design.


texts: How does this MOSFET with the configuration of its gate work?

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I'm seeing the schematic of a Notebook HP Pavilion dv9000 (download). On page 33 you can see this part:

Take a look at the configuration of PQ37. I mean its gate. the gate is connected to PC170 and PC117 and PD15 and PD21. why? what and how does this configuration do/work?


texts: Is this resistor needed in this opamp circuit?

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I'm looking at the datasheet of the MCP6241. There's this schematic:

The op-amp has a input bias current of 1 pA, and \$ 10^{ 13}\Omega\$ input impedance. Is resistor Rz still needed then?


texts: Is it a problem to connect a controlled current source in parallel to a voltage source?

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Does a similar connection cause conflicts or damage?

An example of situation in which it's used. I've seen it's common practice in RF to put an inductor (RF Choke) between the drain of a MOSFET and VDD like in the following picture:

At DC, VDS is set equal to VDD. But between D and S there is a voltage controlled current source, since the MOSFET is biased between gate and source so that it can provide a proper drain current. So, current source in parallel with voltage source.
How can the MOSFET current source react when there is something that forces its voltage? In non-RF class A amplifiers, usually there is a resistor instead of an inductor and so this situation doesn't occur.


texts: PCB layout for high side switch (high current)

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I'm working on a PCB layout for two high side switches. You can see below a picture of my current layout.

The copper weight of the future PCB will probably be 2 oz/ft² (double sided).
I use two p-channel MOSFET(IPB180P04P4). I expect 10 Amps for the MOSFET on the right (I choose to be very close to the minimal footprint, Pd about 0.2 W) and 15 Amps (U2, peak at 30 Amps, Pd about 0.45 W, max 1.8 W) for the MOSFET on the left (U1, 8 cm² of copper).

IC1 is a current sensor.

The terminal blocks (U15, U16) are of this type: WM4670-ND on Digikey.

To draw that much current on this type of PCB, one of the calculator online told me I needed 20 mm traces. To save some space, I decided to split this large trace into two traces (one on the top, one on the bottom). I connect both traces with a pattern of vias (drill size 0.5 mm on a grid of 2x2 mm²). I don't have any experience in this kind of layout so I looked at other boards and picked up a dimension which seemed fair to me. Is this via pattern the right way to go ?

Under the MOSFETs, I use the same kind of pattern but with a smaller drill size 0.3 mm to make the thermal junction. Does the solder will flow better with this size ? None of the vias are filled so far...

I'm also thinking about not having any solder mask on these traces, that would be to apply some solder on the copper.

I'm also concerned about the pads of the MOSFETs. I did choose not to cover them with copper. I thought the device could self-centered this way but that may probably increase the resistance...

Please feel free to comment the layout !
Thank you !

EDIT 1

I slightly improve the design. I added more vias under the thermal pads of the MOSFETs. There is some bare copper under the MOSFETs (if I want to add a heatsink in the future).

Please feel free to comment ! Thank you in advance !

EDIT 2

A new update to this design. I increased the copper area around the leads of the MOSFETs. That should decrease the resistance of these traces.

I added more vias between the top and bottom layers to improve the current distribution in these layers.

I asked the manufacturer if I could have plugged vias under the devices to improve the heat dissipation. He told me that was duable.

I don't think I will change anything else. That was kind of my best guess so I may give it a go if nobody has any comment.


texts: Implementation of Adjustable Current Limiting Circuit

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I have a circuit that can deliver 0-10V and 0-100mA to a load, and want to have an adjustable current limit that will limit the current delivered. To do this I have a current shunt that I monitor, and when the shunt voltage exceeds a threshold a error amplifier starts to turn off a NMOS transistor M1, that behaves as an adjustable resistance. The NMOS drops the voltage at the load to the desired value. When the current is underneath the threshold, U1 is saturated on and M1 is completely on.

This circuit works, but has to have compensation that slows down it's response, or else I see oscillations due to the feedback loop. The real problem is that the circuit takes too long to kick in, and lets the current pass through for a time.

The load current is limited properly eventually, but before that it receives all the current the source can provide. The voltage at the gate of the NMOS slowly ramps up until its DS resistance provides the correct voltage drop to pass only 50mA.

Ideally I would like to see a damped response where the current ramps up, and if starts to exceeds the limit it stops. Is there a good way to implement that with this circuit?

I have looked into NTC/PTC, but due to the fact that if the user wishes the current limit can be changed to arbitrary values I don't think they will work as intended. For example, if the current limit is 5mA, receiving 10mA delivered is a failure. But if the current limit is not set, any current from 0-100mA is acceptable. This means that the temperature isn't really a good indicator of if the circuit needs limiting or not.

My current thought is to use a comparator that will control a transistor that will steal all of the current from the load until the value is stabilized. This means that during over current events, the load voltage will temporarily drop to ~0V until the voltage ramps back up to the limit.

Additional notes: I can't change the supply rails of the error amplifier U1.
U1 and M1 don't need to be the OP07 or FDR84OP, I just used them for testing.