texts:
I have built a sine wave oscillator circuit that outputs 3V@1Khz peak to peak, I am trying to connect the circuit output to a transformer(TRIAD-vpl2-4000) in order to amplify the voltage, I connected a buffer(OP07C8  manufactured by ST) between the circuit output to the transformer input in order to push more current to the transformer.circuit output below

When I connect the transformer to wave generator with output impedance of 50[Ohm] I get a clean sine wave on the transformer output, but when I connect the transformer to the circuit the output gets distorted, can anyone please explain what is the reason for that ?

I measured about ~65mA(pk2pk) at the transformer input when is connected to the circuit and 50mA(pk2pk) when connected to the wave generator (assuming the voltage output from the circuit and generator is the same, 3V)
So, I don’t think it is an issue of input current to transformer since generator and circuit provide similar currents.

Is this setup can even work ? or should I start look for a different transformer?
Any help would be much appreciated

ido

EDIT: Updated out waveform when not connected to a transformer:


texts:
Suppose I had a unit that could accept DC power between 6 and 14 volts, and the choice of using either a 7.4V 1000 mAh or 11.1V 1000 mAh battery.

Do either of these choices offer a clear advantage?  What are the tradeoffs involved?

update: I have not selected the device yet. It will be a small monitor (3-5 inches) to display telemetry data from an RC plane (which explains the battery voltages -- it's convenient to use either a 2S or 3S LiPo pack).  Now I've got a better understanding of the principles involved, and know the main thing I need to check; whether it has a linear or switching power supply.


texts:
I found an old box with 4 ESP8266 module.  I initially thought they were ESP8266 -05, but this chip only has 4 pins (with a separate ground) instead of 5 pins (with a separate ground).  This is pretty old, so I'm wondering if it was a difference chipset before they upgraded it?

If anyone could give me any information (specifically schematics) for this thing, that'd be great.

Thanks!


texts: Differences between ripple counter (e.g. 74LS161) and CMOS 4040

texts:
I have been using the 74LS161 for some tinkering, and then switched to the CD4040 because it had 3 times as many counter stages in the same package size, and I don't need preset for my purpose.
Early on I was intrigued though by how much it is different. A 74LS161 increments on the rising edge of the clock input. Whereas the CD4040 increments on the falling edge of the clock, thus effectively making the clock itself another, the "zero-th" counter stage. This is a nice feature.
However, now I have a problem where the 74LS161 was really good for: the Ripple Carry Output, it's missing with the CD4040. I need something to trigger an S-R-latch, resetting it when the counter overflows. And I do not want to now hook up 12 lines to a 12-input NOR gate cobbled together from three chips that I might need for that. If I could just have that ripple carry output, which is exactly one clock pulse wide. Is there any way I could derive that?
I'm thinking of a falling edge of the last counter stage. How do I make the falling edge trigger an SR latch? Maybe instead of the SR latch I use a single edge triggered D-flip-flop, invert the last counter stage so that have a rising edge with which I can trigger the flip flop while holding D high. Then I could use an asynchronous reset and clear which most of them have, including the 74LS74 that I have on hand.
So is that the way to go or is there any other way of deriving a ripple carry like single pulse from a 4040 counter? Or a general technique to turn a binary counter into a Johnson counter?


texts: What is the difference between F5AL250V and F5L250V fuses?

texts:
In the glass fuses' code F is for fast blown the second number is the current, but I ignore what is the difference between L an AL (if there is any).

Could someone explain this.


texts: Constructing a simple emergency light kit

texts:
This is my first adventure in the electronics world and, as I'm a CS student, you can expect a lot of associations that maybe aren't that right.

The main feature of my circuit is:

If there isn't energy coming from the transformer (220v to 9v), turn on the leds (using a 6v battery), else, let the leds off.

Recently I met transistors and it seems to me that a pnp transistor would do the job. You can see a diagram that I'm going to use to explain what I thought (to make it simple, I'm not showing the transformer and the rectifier bridge):

So, if there isn't energy coming from the transformer part and, as I'm (trying to, actually) reducing the voltage from the battery in the base of the TIP127. The voltage in the base will be lower than the emitter, which will turn the leds on.

Doubt

Unfortunately, I discovered that the idea of using a resistor to reduce the voltage from the battery won't work. Do you have any suggestion to put me in the right direction?

This is my first circuit. I'm pretty sure that it have a lot of design problems. Any kind of suggestion or critic will be appreciated!


texts: What sensor(s) to detect (frozen) steamed up mirros?

texts:
I am trying to build a (solar powered) device that heats up a mirror a bit until all steam/mist that was on it is gone. In the winter, the water is frozen. This is to remove any visual obstructing water.

I have so far strapped some thin wires on the mirror and when I run some current through them, they heat up and after a while the mirror is clean. This is basically the same way things in a car work like.

Now since heating eats up lots of precious energy, and since I would like to run this from solar mostly, my plan is to run this only if there actually is something.

When there is enough moist, I can misuse the heating wires to measure resistance, but this won't work so well when things are frozen, or when the mirror is already partially dried.

I was thinking about some capacitive sensing, but I am not sure if it will work, especially when things are frozen.

This thing will run based on some microcontroller, so calibration data or so won't be a problem.

What is a good way to reliably detect "water based visual obstruction" on a mirror?

Note: The mirror in question is in some area outside where there is very little space to drive (so you can see around the corner) so I have very little space in front of it (otherwise I would hit it with the car). So stuff that looks at the mirror from a meter away or so is not wanted.

For the more visual people, it is similar to one of these:


texts: What does Boost Converter With 2-A Switch mean?

texts: I am new to boost converter technology. All i want to know is what does switch current indicate.


texts: How does data rate change when Wifi channels overlap?

texts:
Let's say there are two wifi access points close to each other, both uses the same channel and the same protocol, with the maximal theoretical data rate of 54Mbit/s. I understand that in case both of them want to stream data they will be able to do that by using the CSMA/CA mechanism.

My question is, how much will the throuput be if both of them want to stream a big amount of data? Will it be 27Mbit/s?

Thank you very much in advance!


texts: Buck Boost Driver to switch 2 LED chains

texts:
simulate this circuit – Schematic created using CircuitLab

I'm working on a project to turn 2 LED strings (each containing 6 HB LEDs).
Here is my question.
The Buck Boost driver I'm using is an ZXLD1371.
Connecting one chain is pretty straight forward. But if I wanted to connect two chains to the circuit, Can I use 2 Series pass transistors (FETs) to connect each cathode of the LED chain to the Supply?

The Pass transistors will be interfaced to a micro controller and Will be made sure that they don't both turn ON at the same time.

Can you think of any issues with this setup? TBH, I think this will work. But its good to get a 2nd opinion :)

Please see the circuit included.
P.S. Values not actual.

Datasheet of BB controller : http://www.diodes.com/_files/datasheets/ZXLD1370.pdf

Cheers
Labmat


texts: Analog to digital controller-Sampling rate

texts:
One method to design a controller for a digital control system is to first design it in the s domain and then convert it. However, choosing a suitable sampling period is important.

In most problems I've faced up to this point I first find the smallest time constant c of my system. Then I choose the sampling period so that 0.1c< T <0.5c.

I just came across a problem in which the transfer function has two poles at the origin and I can't find a time constant. How should I choose my sampling period?


texts:
I have the following code running on an atmega328 (ArduinoUno).
#include <stdint.h>
#include <avr/interrupt.h>
#include <stdbool.h>
#include <util/delay.h>

volatile bool receiveQ = true;
volatile bool transmitQ = true;

ISR(USART_RX_vect)
{
    uint8_t byte = UDR0;
    if( !receiveQ && byte != 19)
    {
        return;
    }
    switch ( byte)
    {
        case 19:
            receiveQ = true;
            transmitQ = false;
            break;

        case 17:
            receiveQ = false;
            transmitQ = true;
            break;

        // process incoming data
        default:
            break;
    }
}
void transmitByte(uint8_t byte)
{
    while( !(UCSR0A & 1 << UDRE0));
    UDR0 = byte;
}
void transmitString(char *pstr)
{
    while( *pstr != 0)
    {
        transmitByte(*pstr);
        pstr++;
    }
}
int main(void)
{
    UBRR0H = 0;
    UBRR0L = 103;
    UCSR0C |= 1 << UCSZ01 | 1 << UCSZ00;
    UCSR0B |= 1 << RXEN0 | 1 << TXEN0 | 1 << RXCIE0;
    sei();
    while( 1)
    {
        if( transmitQ)
        {
            transmitByte(19);
            transmitString("data");
            transmitByte(17);
            transmitQ = false;
        };
        _delay_ms(1000);
    }
    return 0;
}

I want it to implement XOnXOff handshaking, and my question is if I am doing it correctly.
When I set up communication with PuTTY, I first see "data" that is sent by the Arduino. I then send XOff (Ctrl+S), some data, and XOn (Ctrl+Q), following which the Arduino sends the next "data". And I can keep doing this again and again.

The reason I am wondering if I'm doing this correctly is because I have to manually send the XOff and XOn bytes from PuTTY when transmitting data, although I have set the flow control to be XOnXOff.

However, PuTTY strips the XOff and XOn bytes and only gives "data" when it is receiving data.
Update
The secnario is for real-time feedback control. During each time period, the serial input to the atmega328 is the reference signal. (If no new data is received it uses the previous data.) The serial output from the atmega328 is the sensor value (which is also used by the controller.) I am using the XOn and XOff characters to signal when to start sending the data and when transmission is complete.


texts: PT1000 2 wire probe. Can I add third wire?

texts:
I'v got 2 wire (81 cm) PT1000 probe which I want to utilize in a project.
I would like to use current source and couple of opamps to make the measurement through ADC (uC) just like described here: link1.
The point is I need to reach measurement spot which is 5 meters away. I will  measure added wire resitance by multimeter and substract it in uC.

As I understand from link1 PT1000 3 wire probe has been used there (first image on the top). Can I modify somehow the schematic to use my 2 wire probe or can I attach third wire [link2 in comments] (I understand disadvantages of this setup)?


texts:
I stumbled upon a very badly drawn      circuit on the interent which must be good .    I have not been able to figure out how a series of transistors work in this circuit. It is depicted below.

When this circuit powers, the leds turn on and stay on one by one until the last led is turned on, and then they all go off and the cycle starts over again. My question is in regards to if someone could explain to me why this behavior happen with the transistors. I am not sure how an astable pulse to this array of transistors would cause this cascading behavior.


texts:
I've recently acquired a lpc1313fbd48 microcontroller and I was looking around on newark.com for a bluetooth module that I could use to connect my microcontroller with my phone. I then began to if certain microcontrollers can accept certain bluetooth modules.

So my question is:
How do I pick a bluetooth module for my microcontroller? Are there certain pins or frequencies that I should be aware of when searching for a module?


texts:
Is there such a thing as a low pin-count eeprom IC that can be used to replace logic circuits with just a couple of inputs and outputs? I'm thinking of DIP-16 or smaller, but it needs to be parallel.

I'm aware of DIP-8 serial eeproms but unless I'm missing something, this would make things more complicated than using dedicated logic ICs.


texts:
I am trying to work around a circuit and my requirement is as follows: -
There are two inputs and two outputs. Each input controls an individual led. I am writing a code for this requirement using a Nuvoton MS51 based controller (Which itself is 8051 based controller). The software used for the same is Keil. Following is the code I have written-

#include "MS51.h"
void main (void)
{
    P01_INPUT_MODE;
    P03_INPUT_MODE;
    P10_PUSHPULL_MODE;
    P00_PUSHPULL_MODE;
    while (1)
    {
        if (!(P0 & SET_BIT3))
        {
            while( !(P0 & SET_BIT3));
            P0 ^= 0x01;
        }
        if (!(P0 & SET_BIT1))
        {
            while (!(P0 & SET_BIT1));
            P1 ^= 0x01;
        }
    }
}

The problem I am facing is that both the switches are not working simultaneously but only in a sequence. The first switch will work, then the second (I am not able to use the first switch again).
Is there anything wrong that I am doing in the code?

Solution: I have found the mistake I was doing. The mistake was of pull-up/pull-down of the switch. My switch is pulled down and the code that I had written corresponded to the case of a pull-up. Hence my code was being stuck in the while loop again and again, hence stopping the flow of code to the next line.


texts: What exactly is the need of Back and Front poch delays in VGA ,TF,LCD Timings?

texts:
I am trying to interface a 24 Bit TFT screen.

But I am having a hard time understanding the need for Back and Front poch delays and how to calculate these ?


texts: Is the SPBT2632C2A compatible with a 3.3v Logic System? I was thinking of using it with a BeagleBoneBlack, Absolute maximum rating is rated for 5.5v, So i can feed the module power from a LM1117-3.3 and drive the Tx/Rx Pins directly from the beaglebone's gpio??


texts: How to calculate maximum effective radiated power in any direction for Galtronics small cell site

texts:
Answer Calculations from PE commissioned by AT&T: the GQ2410-06621 antenna does have 10 total input ports, however, our analysis of the AT&T DAS node includes only the frequencies and power levels at which AT&T proposes to operate.  For this site, three Ericsson radio units are proposed to be installed - two Model 2203’s, which will operate in the PCS (1950 MHz) band, and one Model 2205, which operates in the unlicensed 5 GHz band.  Each unit is connected to the antenna by two ports, and the four remaining CBRS band ports are not proposed to be used. As the report states, the maximum effective radiated power in any direction would be 85.4 watts.  This ERP value includes the antenna gain, so it would be the output value of the calculator you linked to, rather than the input.  We calculated the ERP as follows:

Each Ericsson Model 2203 has two ports, each with a maximum Transmitter Power Output (TPO) of 5 watts.  The maximum TPO in the PCS band is therefore 20 watts (13 dBW).

The connections between the Ericsson radios and the Galtronics antenna result in power losses that we estimate to be 0.55 dB.

The maximum gain of the GQ2410-06621 antenna is 8.9 dBi (6.75 dBd) in the PCS band.

The ERP in the PCS band can therefore be calculated as 13 dBW - 0.55 dB + 6.75 dBd = 19.2 dBW = 83 watts.

Unlicensed operation in the 5 GHz band is limited to an ERP of 2.4 watts in order to comply with FCC Title 47 §15.247.

Original question: For their 5G rollout, AT&T plans to erect a small cell site in my neighborhood. Based upon information provided by AT&T, the Galtronics Model GQ2410-06621 will be installed.

Looking at the specifications sheet for the Galtronics Model GQ2410-06621, it has 4 ports for AWS/PCS/WCS Band at 1695-2360 MHz, where the maximum power per port is 100 Watts. This Galtronics model also has 2 ports for 5 GHz WiFi (2x ports for U-NII Band 5150-5925 MHz), where the maximum power per port is 1 Watt.

My question is, how does one calculate the maximum effective radiated power in any direction for this Galtronics small cell site? Professional engineer consultants calculated the maximum effective radiated power in any direction would be 85.4 Watts, representing simultaneous operation of 2.4 Watts for 5 GHz WiFi and 83 Watts for PCS service.

Here's a quote from the Site and Facility Description: AT&T is proposing to install one Galtronics Model GQ2410-06621, 2-foot tall, cylindrical antenna, on a cross-arm to be added to the side of a new utility pole. The antenna would employ no downtilt and would be mounted at an effective height of about 24 feet above ground. The maximum effective radiated power in any direction would be 85.4 Watts, representing simultaneous operation of 2.4 watts for 5 GHz WiFi and 83 Watts for PCS service.

For the Galtronics Model GQ2410-06621 (https://galtronics.com/wp-content/uploads/2019/10/Datasheet-GQ2410-06621-Rev_1.0.pdf), I have attached the specifications.


texts: microcontroller with buttons/LEDs -- fallback when Hi-Z

texts:
I'm designing a circuit with a fallback function and would like to know whether it's flawed or can be done with less components.

The MCU here starts a motor in "up" or "down" direction. (Only "up" is shown).

If the top end switch is touched, then positively, definitely do not go further up.
The MCU needs to know if the end switch is touched, not only for the sake of stopping.
The push button is multi-purpose, including the menu navigation and alike.
However, if the MCU is down (a firmware update went wrong etc.), the push button starts the motor.
As long as the MCU is running (signalling this fact with a logic "1" at a push-pull output), the push button is solely for the MCU and should not start the motor.

Answering @Bruce Abbott 's question. I had VDD=5V in mind. D1 protects the opto-isolator U1, which might have a maximum reverse voltage around 5V. Without D2 the BtnUp input would always read "1". Both D1 and D2 could probably be omitted with VDD=3.3V?

D3 is green or longer wavelength but good that you asked. I ought to count p-n junctions in this path.

R1 and R4 might become MCU's internal pull-down resistors, but they might be too high-ohmic from EMI perspective.

Partially inspired by this Tri-State post and lednique.com


texts: Shared via on 22pF cap only used to smooth differential clock signal?

texts:
Google's so cluttered these days, it's hard to find simple answers.

I've got differential clocks running around 500MHz (1000Ms).

There's some optional 22pf caps on each Address line, going to the dram.

It's Micron's DDR2 recommended layout.

It's so crowded, I'm sorely tempted to share vias between them.

No more than 2 to a via.

And they're only 22pf.

But I sure would like to crank that clock up to 800MHz later on (1600Ms).

Could sharing a via on 22pf caps make any difference?  The vias are tiny (6 mils).

And, anyone have the common sense to know the cutoff point for sharing vias?

Like, anything under 1nF, don't worry about sharing the vias?


texts: Where can I find XT-IDE (8bit IDE, XTA) specifications?

texts:
I have an old hard drive and would like to try to read the data from it. The hard drive is IDE, but it is the old version of IDE, called XTA and it is only 8 bits wide (compared to "normal", 16bit IDE). It is also incompatible with the modern version. 8 bit controllers sometimes show up on ebay, but they are very expensive.

So, I decided to try to create an adapter from parallel (a PC is easier to program than a MCU, for me anyway) port to 8 bit IDE. For that I need specifications (timings, registers, commands), but I cannot find them anywhere. googling for XT-IDE finds lots of pages about a reverse project - a modern IDE controller that can be used in a 8bit ISA slot (on old PCs), but I want to connect an old hard drive to a newer PC. Wikipedia says that the registers have different meanings on XTA than IDE.

Can anybody share the specifications, or at least tell me where to find it?


texts:
I want to make a simple rs232 to parallel (8 bit) converter.

I would like the input to 1 wire and the output can just be 8 bit with no strobes etc. and run at high speeds (ideally up to 1Mbps, put ~100kbps would be ok)

Ideally, what would be simplest circuit to achieve this? I tried to work it out but it ended up being quite complex, multiple cloks/monostables, shift register, decade counter.. So, I thought I'd post here as I thought there may be a trick to simplify it or a specific chip. Ideally CMOS.

Thanks :)


texts: LED : calculation of optical power[mW] from luminous intensity[mcd]

texts:
I have an application with LED with given optical power.
I found on ebay some LEDs but it appears just intensity [mcd]
How can I determine optical power of LEDs in mW ??
Please, mention some clues.
link with characteristics of LEDs, below :
https://www.ebay.com/itm/200Pcs-3mm-5mm-LED-Light-White-Yellow-Red-Blue-Green-Assortment-Diodes-DIY-Kit/123476752059?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20131231084308%26meid%3Da49075803d31408b809647367f4bebbd%26pid%3D100010%26rk%3D6%26rkt%3D12%26sd%3D292715528268%26itm%3D123476752059&_trksid=p2047675.c100010.m2109


texts:
Iam trying to power the circuit mentioned here (v4.3),
Will this schematic work?

I would like to be able to use a single power supply that can provide both 5V and 12V DC circuit. I have the following requirements:
(1) The 5V and 12V supply must be isolated
(2) The 5V rail needs to power the RPI and can work with 2A current rating
(3) The 12V, however, must power 12 pumps with a max rating of 1.2A each for a total of 14-15A current rating (the circuit shows only 5 pumps, will be adding in the additional pumps in future)
(4) Want only a single AC input in to the enclosure. This must get converted to the two independent DC power rails.

Any suggestions? A off-the-shelf PSU would be great too, but I could not find any that matches my requirements.


texts: Ripple filter @ 2 amp without breaking the bank?

texts:
I'm trying to create a +160v and +/- 100v supply that with idle at 2A.
The problem I'm having is I can't find capacitors that can handle the ripple currents for the prefilter. I need to order like $200 worth of caps to keep the ripple currents barely within spec.
LC and RC filters don't work because without a capacitor before them the DC loss is too great.
Is there a sane way to filter at these currents?
A few volts of ripple is fine, I just need the caps to not die after a month.
Any ideas?


texts: Why does my D Flip Flop Circuit have an X output?

texts:
I'm working on one of my projects and I'm having trouble with my flip flops. The project is to design the circuit for a gas pump that has a handle and a sensor. When the handle is down, the pump pumps, but when the sensor is activated, the pump shuts off. It will pump again until a second high pressure is read, at which point the pump shuts down completely until a manual reset is done (not part of the project). I'm working on the Mealey design since it's a little smaller.

Essentially, when my handle is high and my sensor is low, I'm getting an X for my output and I don't know why. I hope someone can provide some input:

Here is everything I have for it:

Alright, I added the reset. Now I'm getting that my states change every time my clock changes. Any ideas?:


texts: RFID antenna beam direction and how to control it

texts:
I've been working on some RFID stuff lately and I'm wondering if someone could help me understand how the beam direction works?
I'm having problems with my RFID reader picking up signals from tags that are behind it. From what I understand, the beam that powers the passive tags should be a cone and therefore it shouldn't be able to reach tags that are behind the reader, but this is being done by both of my RFID readers (the readers are Chafon UHF high performance integrated reader, model CF-RU5309). I did some more digging into my RFID reader and it's apparently omnidirectional but I'm not sure if this is possible. Does this mean it can read any tag within a circular area around it?
I've tried to put up some aluminum shielding on the wall behind where the reader is installed but that doesn't seem to have done much other than stopping tags that were really far back behind it from being read, while close ones can still be read. The shielding is a 3ft square placed at the center of the reader, with another rectangle of aluminum shielding that covers up to 2 ft above where the tags sit behind the reader. The tags being read are xerafy microX ii and are set up so that there's two tags on a large aluminum piece of metal. I've included a quick sketch of my setup and a link to the products I'm using. The tags being read are about 3 feet off the ground while the reader is about 10 feet above ground.

http://chafonrfid.com/productdetails.aspx?pid=692
https://www.atlasrfidstore.com/xerafy-microx-ii-rfid-tag/
The antenna is claimed to be a 9dbi circular antenna. Not sure if this means it can't be omnidirectional but I'm pretty sure that I found online that the reader is stated to be omnidirectional.


texts: MOSFET switch between parallel batteries for dual charging

texts:
UPDATED:

I am developing a wireless device composed of :

2 Varta CP 1654 A3 Li-Ion 3.7V 120mAh (supporting 2C charge) with protection circuit module
2 MCUs that can handle Li-ion CC/CV charging

My wireless device is composed of 2 earbuds connected with a cable, I can't use any other type of battery. There is a Protection Circuit Module (PCM) on the board where each cell is mounted in each earbuds (PCM recommended by Varta).
Correct me if I'm wrong but fast charging at 2*2C of parallel cells seems to be problematic for this reason:

If during charge cell_A reaches 4.2V before cell_B, cell_B could either receive a dangerous current > 2C if PCM_A triggers overcharge or ultimately both PCM_A and PCM_B would prevent the charging.

My GOAL is to have the fastest charging device possible while being safe and the fact that I have two ICs able to manage CC/CV charging makes me wonder if I could trigger switches between the batteries when the device is connected (Vcharge available) so then I could manage a 2C fast charge independently for each cell :

I am trying to find a circuit that could act as a switch between the two cells. I thought at first about two MOSFETs in parallel but the body diodes will prevent the use that I want.

LOGIC_A represents if Vcharge is available to the device

The switch should be closed when no charge and open during charge.

I know this is unusual and most designs have single cell battery while some others have parallel batteries but with slower charging current than 2*2C. Please my question is not about modifying the design of my product, I just want to know if there is the possibility of such a "switch" circuit that could allow me to use the two chargers at fast charge instead of just one at slower charge.


texts: What about variable frequency switching power supplies?

texts:
Maybe this question is perhaps too broad for the site: however, after looking on Google, searching the literature and asked to a friend who's a specialist in the design of SMPS without getting any useful answer, I decided ask it here, apologizing in advance if it is "Off-topic".

Question: do there exists switching power supply topologies which do not rely on the standard PWM paradigm but work, for example, by producing a variable, voltage controlled, frequency sine oscillation? And in case the answer is yes, what are their most used structures?
A little bit of background

I got interested in the topic after seeing the timeline of the switching power conversion as given in the wikipedia:
it spans at least 50 years, so it seems plausible that a great deal of different ideas have been developed. So why focusing on designing fixed frequency PWM modulators/demodulators?
In general manuals and application notes and about switching power supplies, it is occasionally said that "the frequency is kept fixed in order to improve the EMC compliance". However, it seems more that this is a design trend and not a design requirement imposed by deep physical limitation, as it is seen for example in [1], so why always choose the PWM way of design?

References
[1] Mikko Kuisma, "Variable Frequency Switching in Power Supply EMI-Control: An Overview"
January 2004IEEE Aerospace and Electronic Systems Magazine 18(12):18 - 22, DOI: 10.1109/MAES.2003.1259021.


texts:
I'm working on a circuit that will have a current shunt before a device connected to a truck's 12V system. This system can have voltage drift, and large transients during operation. The connected device has several switching regulators on-board, and the current shunt needs to be connected in front of the device. I'd like to have a digital representation of the voltage at either end of the current shunt. I really don't need fast sampling, even 10Hz would do. Preferably the output would be in I2C or SPI.

Would an ADC be the correct device to use in this scenario? How would I protect it from the voltage spikes and drift?

Additionally, what are some components that I could place before the device in order to suppress the voltage spikes and other noise, to assist the regulators?


texts:
I have a cable with 3 X 10 AWG stranded conductors, L1, L2 and Earth. This cable will need to pass 32 amps of continuous current for 24+ hours at a time. I have this contactor:

As you can see, the contactor has box screws (is that what they are called?) and I intend to use them as the UL standard for "faston" (quick connect) crimp terminals won't allow for more than 25A continuous through a yellow terminal. Actually, maybe someone could confirm this for me?
I feel a bit cheap shoving the AWG 10 stranded wire into the hole and clamping it down with the screw. I realize this may actually be the best method, but I am wondering if there is a cleaner, safer alternative.
I thought of using something like this but for the life of me, I can't find a current rating. I can't even find a confirmation that it will handle as much as the conductor it's crimped to. Also, I'm not sure that this would create a better contact in the contactor than just bare wire...
I would appreciate any insight! Thanks!


texts: 2 coil latching relay IC control: part number or type of IC

texts:
I got a wall switch for a water heater from a Chinese supplier.

In the power board they used 2 latching relays with two coils for each others.

I want to redesign this board for my DIY project.
Here is the schematic for the driver IC controlling the two relays.
I don't know what the IC or MCU is - there's nothing written on it. It's has 8 pins, SOIC 8 package.

It receives a logic TTL input at pin 3.

If the input is high level --> Generate 100ms pulse at pin 5.

When input is low level --> Generate 100ms pulse at pin 7.

Does anyone know what kind of IC or MCU this is?


texts:
so I've been trying to create a circuit with a PIC16F917, a button, and three LED's, where upon a button press the LED output changes, like the button press cycles through different modes. I've been trying to do this utilising pointers, in a way like a multiplexer, where the value of an integer depicts the certain output mode (interpreted by outputconfig()), and the push of a button increments that integer by 1; but don't really know what's going wrong.

Also, why does XC8 say upon the build, that the use of "delay()" and "outputconfig()" within main() is a "function declared an implicit int"? And why does it still work?

Any help and/or guidance would be much appreciated. Below is the code I am working with. Thankyou!

#include <xc.h>
#include <pic16f917.h>
#include "configbits.h"
#include "definitions.h"

int value;
int *output;
int result;

int main()
{
    TRISEbits.TRISE0=1;

    TRISDbits.TRISD5=0;
    TRISDbits.TRISD6=0;
    TRISDbits.TRISD7=0;

    while(1)
    {
        if(1==IN1)
        {
            delay();
            if(1==IN1)
            {
                output=&value+1;
                result=*output;
                outputconfig();
            }
        }
    }
}

int delay()
{
    int i;
    for(i=0;i<1000;i++){}
}

int outputconfig()
{
    if(0==value)
    {
        OUT1=1;
        OUT2=0;
        OUT3=0;
    }
    if(1==value)
    {
        OUT1=0;
        OUT2=1;
        OUT3=0;
    }
    if(2==value)
    {
        OUT1=0;
        OUT2=0;
        OUT3=1;
    }
    else
    {
        NOP();
    }
}


texts: MOSFET always slightly on (with Pulldown) and other strange behaviour

texts:
I'm trying to control my RGB LED strip with my arduino, using IRLZ34N MOSFETs according to this schematic

simulate this circuit – Schematic created using CircuitLab

I tried it out, everything worked. I soldered it to a circuit board just like that, except for that I used 4 copper wires on the Arduino connections. Everything worked, I unplugged the copper wire from the Arduino and checked back ~3 Days later, then this happened:

The strip was slightly glowing, even when the gates of the MOSFETs are directly connected to ground. Connecting a Gate to +5v made that color glow fully though. That's pretty much my problem, some deeper examining got me those Results:

I desoldered the mosfets and my multimeter reads a resistance of ~290;310;350Ω between Drain and Source. Another strange behaviour is that the conduction seems to go from 0-100% really fast. My LED strip goes from the constant "slightly on"-State to 100% brightness in a matter of some mV. Also strange is that this happens at ~4.7V on the Gate, while my fully functional IRLZ34N gives the strip 0-100% brightness at around 1.5-2V. I also tried to shorten Gate-Source and Gate-Drain, booth changed nothing. So my conclusion was that I probably destroyed the MOSFETs, but still the question is: How? Because I want to do the setup again (of course with new MOSFETs) but without killing the MOSFETs.


texts: What's the purpose of a tactile switch with GND pin?

texts: Some 5 pin or 3 pin tactile switches have an extra GND pin such as this Omron B3W-1150. What's the purpose of this pin?


texts: Disambiguation of AC Analysis and Small Signal Analysis

texts:
I am trying to understand Small Signal Analysis (SSA) for Diodes and BJT transistors through different textbooks but I have some issues.

Is AC Analysis the same as SSA? I have seen hints that imply this but most textbooks say that SSA is about small signals so what I understand is that it is for both AC and DC signals as long as they are small enough. But if that is the case then why in SSA we have to short DC voltage sources?


texts: IC 558 Quad timer chip, single timer in monostable mode

texts:
I'm looking at the datasheet / Application Notes for the 558 Quad Timer.
Specifically, Figure 5.a Monostable Operation (One Shot)

I want to drive a LED with the output. I see from the notes on data sheet that the out pin is, "Note: 3 The NE558 output structure is open-collector, which requires a pull up resistor to Vcc to sink current. The output is normally LOW sinking current."

I have connected the -ve side of the LED to OUTPUT A, pin 1 on the 558, the LED +tive side connects to Vcc via a 220ohm resistor.
 Is my output correctly configured?

From TIMING A pin 2, I have a 10M ohm resistor connected to Vcc and a 0.01uF capacitor between pin 2 and gnd.  I'm looking for an on time of 0.1sec for the LED.
Is my timing correctly configured?

Lastly the TRIGGER A, pin 3.  I'm using a SPST Normally Open push button wires as follows.  One side of the push button is connected to gnd. The other is connected to pin 3.  Pin 3 is also connected to Vcc via a 10k ohm resistor (Pull Up Resistor).  Is my trigger correctly configured?

Pin 5 is connected to Vcc and pin 12 to gnd.
When powered up the LED remained off regardless of the state of the button. As well the chip quickly became very hot.   Fortunately, i have two spare 558 chips.  Any assistance would be greatly appreciated.


texts: UART ESD protection, and is it necessary on inter-board connections?

texts:
This is probably a straightforward question, but I wanted to ask just to be on the safe side. I have a Wifi Module that I'm connecting to an ARM Cortex M4 uC, and it interfaces via UART.

Since I tend to throw on ESD and EMI protection on any lines communicating with the outside world, I figured I would add it to the UART lines. Typically, though, the two UART lines, TXD and RXD are purely inter-board - meaning that the only connection is between the module and the uC. In this case, I typically forgo the rigorous ESD protection and simply use a series resistor.

However, I've also added headers on these lines so I can use a logic analyzer and an FTDI chip for programming. This being the case, should I add additional ESD protection? Or could I add switches to disconnect the lines from the uC while programming the module?

If I should add extra protection, could anyone suggest any devices to do so? I've used a few ICs for SD Card interfaces and USB lines, but I have yet to come across one for UART.

Any input is appreciated.


texts: How is this series series feedback topology forOPAMP?

texts:
This is stated as series series type of negative feedback but why.

Whereas this one is series shunt topology


texts: Why are the junctions where ADC pins connect to PCB board ignored in thermocouple cold jucntion conmpensation calcutaions?

texts: Why are the junctions where ADC pins connect to PCB tracks ignored in thermocouple cold junction calculations?


texts: What is wrong with this XOR gate built with four transistors?

texts:
I try to undestand how to build an XOR gate using discrete transistors.
I checked this question with an extensive answer

Howerver the xor gate there and also on Wikipedia seems needlessly complicated.
I simulated the following circuit in Logisim and it seems to work. It is based on the idea that input B switches between A and not A.

Since I did not find this circuit documented as an XOR implementation, I expect it is not feasible. Please explain why.


texts: Running a 230V heating element using 120V

texts: Would a heating element that is rated at 3000W at 230V actually heat properly if the element was powered by 120V only? My hope is that it will just take longer to hear up, but worry is it can't get hot enough.


texts: Using a reed switch with safety in failure

texts:
I'm planning on building something similar to this project to be used as an alarm for when a stair gate is forgotten open.

Image above taken from this link:
https://www.electronicshub.org/arduino-based-door-monitoring-system/
I have a question about the reed switch.
Using a reed switch seems like a good idea. But I want to make sure that my circuit is protected against possible failure of the reed switch. So I was thinking, should I go for a normally closed one instead? This way, if the reed switch fails or the wiring gets detached, the alarm will trigger.
Is my thinking correct?
Thanks in advance.


texts:
Consider that we have compressed camera output video by JPEG using a Cortex-M4 MCU (Like STM32F407xxx that has a DCMI unit).
I want to know, Is it possible to stream a live video by JPEG and NRF24L01P?

I can show it theoretically by an example:

Expected resoulation is: 240x160 = 38400

Size of each RGB image (in bytes) = 38400 x 3 = 115200

Accoring to the JPEG wikipedia:

  JPEG typically achieves 10:1 compression with little perceptible loss
  in image quality.

So, Comperssed size will be (in bytes) = 115200 / 10 = 11520

And, According to the nRF24L01+ product specification:

  It has user configurable parameters like frequency channel, output
  power and air data rate. nRF24L01+ supports an air data rate of 250
  kbps, 1 Mbps and 2Mbps.

Assume we working with 2Mbps. But due to packet headers and noises and... We consider that data rate value will be 1.5Mbps( = 196608 Bps).
So, FPS  of this video stream will be : 196608 / 11520 = 17 That can be acceptable.

Did I forget something? Is it possible in practice?
Thanks in advance.


texts:
I'm trying to implement an RC debouncing circuit into a design I'm currently working on, and I have been using this PDF as a reference: https://my.eng.utah.edu/%7Ecs5780/debouncing.pdf
In the PDF, the math is described on how to obtain values for R2 and C. I want to account for a button that has about 10ms of noise, so using the formula in the PDF I get that my values for R1, R2, and C should be

R1 = 10Kohm
R2 = 160Kohm
C = 0.1 uF

The Schmitt Trigger inverter that I plan to use is the 74HC14D. Its datasheet is found here: https://www.nexperia.com/products/analog-logic-ics/asynchronous-interface-logic/buffers-inverters-drivers/74HC14D.html
And the following circuit setup is from the PDF as well:

However looking around, I find that there are people similar to me who also want to implement a debouncing circuit for their buttons as well. Most of the time, I am finding that the following values for R1 and R2 and C work as well:

R1 = 10Kohm
R2 = 10Kohm
C = 0.1 uF

The only difference between my values and the above is that my R2 is really high. Looking around on the EE stack exchange, I've also found that R2 should not be too high, or else the voltage at point A on the diagram will not be low enough for the inverter to register the voltage as LOW. Do I trust my calculations, or have I incorrectly done my calculations somewhere along the way/misinterpreted the PDF?


texts: When connected an external voltage to vout of this 5v regulator, the chip get very hot. I connected a 4v to its Vout, and it draws 500ma. The protection diode from vout to vin doesn't help. My doubt is that I also have 3 different labels for this voltage regulator: They are AMS1117-1225L, AMS1117-H505KE and AMS1117-H1418. I have tested all three. Only the 1225L will over-heat and draw 500ma. Other 2 are just okay. WHY!? is this 1225L an older device? I can't find any datasheet about it either. another question is, I want to add a 5v input to the vout of the AMS1117 5.0v, do I need a protection diode between my 5v input and this vout?


texts: Detection of FM transmitter carrier phase

texts:
I would like to detect the phase (only) of a standard FM transmitter carrier over the air while it is modulated, while at the same time avoiding receiver threshold effect.

Typical commercial FM transmitters use +/- 75 kHz carrier deviation and modulating frequencies of 15 kHz or higher.  I need to lock to the FM carrier and track it while it is modulated, and recover just the steady-state carrier phase.  I'd also like to avoid the usual 10 dB threshold effect in order to achieve maximum sensitivity under weak signal conditions.

Can I do all this using a PLL detector and an SDR?  If I understand correctly, the loop bandwidth would be made narrow (say, 1 Hz), therefore removing the modulation and leaving only the carrier itself.  Eliminating the limiter should eliminate the threshold effect and allow the PLL to track the carrier down into the noise for maximum sensitivity.

Any thoughts or suggestions will be appreciated.


texts: I have a multi-tester. And its model name is J0411A. And it looks like thisYou might see that this multi-tester includes a resistor tester. When I set the tester to x1 of Ohm section and connect + to - directly, I get about 2.6 Ohm. When I set the tester to x10(other things are same), it points 1.8 which it means 18 Ohm. Why two numbers are different?


texts: What is the problem with my switching circuit?

texts:
Firstly, I used TIP120 for switching. There was a problem of leakage current may be, so I had one out of four panels glowing. So I decided to switch to MOSFET IRF510. I soldered my circuit from scratch, but the problem remains. Is there something wrong with my circuit?

VERY IMPORTANT NOTE: It works fine on a breadboard!


texts:
I'm struggling with the concept of floating voltages.

For a grounded supply I can connect one side to an effectively infinite ground and get full power.  It may vary depending on its construction, but if the grounded supply provides X volts then it is necessarily true that:

[A] (V+ to G) - (V- to G) = X, correct?

Now suppose I want to "ground" a floating supply.  My understanding is that the supply's V+ and V- separated behavior with respect to some "ground" of practically infinite capacitance must be characterized by the source of the voltage:

A floating driven power supply cannot send power through a path that does not directly connect its V+ and V- terminals, as roughly explained here.
A chemical power supply, like most conventional batteries, cannot send power that doesn't connect its V+ and V- terminals, because the driving chemical reaction will not occur without electron transport exactly matching the needs on both terminals simultaneously.
But a capacitor should be able to send power from either its V+ or V- terminals, right?  It depends on the charge of the G, but not only does the relationship [A] above hold, but also the capacitor can dump all of its power into an arbitrary ground if V+ and V- are independently and separately connected to that ground.  I.e., there is no such thing as a "floating" capacitor?

(Evidently I'm assuming that a "floating" supply is defined to be one in which power only flows between V+ and V-.  Is that accurate?  And are there any other "floating" power supply categories than #1 and #2.)


texts: Are induction stoves considered inductive loads?

texts:
I know a washing machine and a coffee grinder are considered inductive loads so when doing math for wiring you would multiply wattage by 2x to be on the safe side. Just one plate of my inductive stove, apparently, is the biggest load in the house. It says 2100W on it. I wonder if I should treat it as a 4000W load when doing wiring. I have a strong grid connection so it was not an issue so far, but I am planning to add some batteries and the difference between 2KW and 4KW would be a major issue.
So the specific issues I'm concerned about:

Power factor. Do typical induction stoves have a power factor close to a washing machine?
Inrush / collapsing flux when you turn it on/off. I wonder if that might be even worse than in a washing machine. Once I had a plug come loose on that stove and before it switched itself off, it arc welded a few square millimeters off the plug and blackened the wall outlet.

Are there any rules of thumb about how to treat induction stoves when doing wiring?


texts: Components calculations for this circuit. Is my reasoning right?

texts:
In order to review some concepts, I decided to solve the circuit below that I found. It looks like a homework, but actually it's something I'm doing by my own. Below the circuit you can check my calculations and correct me if I'm wrong.

This is the statement: The circuit shown can be used to monitor the voltage of the source VCC. Determine the unspecified components in order to: a) turn D7 on when VCC >= 13.5V, b) turn D2 on when  12V =< VCC < 13.5V, and c) turn D1 on when VCC < 12V. Assume that:

Diodes voltage drops are 0.7V
VCE_sat = 0.2V
Pz_max = 500 mW
Iz = 20 mA
V_LED = 1.2V
I_LED = 10 mA
Hfe = 100
VBE = 0.7V

This is what I have:

I'm going to start with LED D7 which is going to be driven by Q3. Let's assume VCC = 13.5V, minimal condition for case a). Voltage at node n1 is 11 + 0.7 + 0.7 = 12.4V. LED current has to be set at 10mA, so minimum base current for Q3 is 10 mA/100 = 100 uA. Say 130 uA to ensure saturation. Voltage drop across R7 is ((13.5 - 0.7) - 12.4) = 0.4V, this yields R7 = 0.4V / 130 uA = 3.08k.

Zener current is 20 mA. This means that Q3 base current plus current through R8 should be equal 20 mA. So IR8 = 20 mA - 0.130 mA = 19.87 mA. Voltage drop across R8 is (13.5 - 12.4) = 1.1V. R8 = 1.1/19.87mA = 55.36 ohms.

Assuming Q3 is saturated, then voltage across R6 is VR6 = VCC - VCE_sat - V_LED = 13.5 - 0.2 - 1.2 = 12.1V. As D7 current is 10 mA, then R6 = 12.1/10 mA = 1.21k.

When Q3 is ON (VCC>=13.5V), voltage at node n4 will be almost the same than VCC, so LED D2 will be off. When VCC goes below 13.5V, let's say 13.4V, would that be enough to turn Q3 off? For LED D2 to turn on, Q3 must be OFF so voltage at node n4 drops. Imagine now that VCC drops to 12V. Q3 and D7 are OFF and D2 should be ON. Voltage at node n3 should be Vn3 = 12-0.7-0.7-10 = 0.6V. Does not this look insufficient to turn Q2 on?

The only component missing now is R1. Below 12V, D1 and Q1 have to be ON. Q2 and Q3 should be OFF. But here is where I'm stuck. Does this mean Q1 base is being pulled up through R3 and D2?

I appreciate any input on what I have so far.


texts:
I made a USB port in a gas detector prototype. I plan to keep a USB cable attached to that USB port forever. I silicone conformal coated the USB port pins on the PCB.
Can the USB head of the cable cause a spark when current runs through it, or is the spark expected to happen in the USB port pins only (which I already coated?)
Note: This port will turn on only if a gas is detected, rather than that it will keep off


texts: Does current flow from the emitter through the base in this circuit?

texts:
The datasheet says "Css is charged via a PNP transistor that is connected to the error amplifier." Does this mean that current flows from the emitter through the base?
I have drawn on this diagram to show what I think must be happening:


texts:
There are many guides to using chip antennas, with and without baluns, PCB layout considerations, etc., but I've been unable to find any information on how chip antennas work at a fundamental level, and how they're manufactured.

Can anyone provide any insight, or links to more information?


texts: How Single Pole Switching of Circuit Breaker can improve the transient stability of the Power System?

texts:
There are numerous methods we can use to improve the transient stability of the power system.
Visualization of methods like using fast excitation system, High-speed governors or using dynamic resistance switching is easy.
But, How the implementation of single pole circuit breaker can increase the transient stability?


texts: how to derive the ac emitter resistance of transistor amplifier biasing?

texts: I went through many textbooks and websites and I found out the derivation for AC resistance for diode which is \$r_d=26mV/I_{F}\$ where as for ac emitter resistance it is \$r_e=25mV/I_E\$ for which I didn't get any derivation or explanation. So, I wanted to request the forum for mathematical derivation or are they same with a valid reasons.


texts: What is the current in a FET as gate voltage is increased towards large voltages?

texts:
I know that beyond a threshold voltage VGS, increasing the gate-source voltage VGS in a field-effect transistor (FET) increases the drain-source current IDS quadratically. I've looked on the web and in textbooks, and I don't see any explanation for what limits the quadratic growth.
Assuming that I have plenty of source-drain voltage VDS, what is the limiting behavior for very large gate-source voltages VGS in a FET?
Some thoughts:

Increasing VGS continues to open up the channel, and the resistance continues to decrease, causing quadratic growth in the current indefinitely until either the device burns up and you reach for the fire extinguisher, or the extreme electric field causes a breakdown between the gate and the channel. See dashed line in attached figure.
Increasing VGS beyond a certain point gives diminishing returns. The maximum current is limited by some (??) physical effect (e.g., maximum electron velocity in the semiconductor). See dotted line in the figure.

Does anyone have any good references for this? Is the behavior drastically different between MOSFETs, JFETs, MESFETs, HEMTs, and other transistors?
Hand wavy explanation < Physical intuition < Physical intuition with mathematics (scientific papers / references preferred).


texts: I need to control a 12 V 5 A (or 3 A if need be) with an Arduino UNO which has 5 V and 40 mA. Unfortunately I don't know how to read transistor data sheets. What NPN transistor should I get for this project?


texts: Finding the Mid-Band Gain of a Transistor

texts:
I am studying for an exam working on the current problem:

simulate this circuit – Schematic created using CircuitLab

I have already found:

$$Q-Point = (I_{DS},V_{DS}, V_{GS} = (.783mA, 1.32V, 14.21 V)$$

Givens:
$$V_{TN} = 2V$$
$$K_n = .001 mA/V^2$$

Current question: Find:
$$A_{vin} = V_o/V_{in}$$
$$A_v = V_o/V_s$$

My work:

$$A_v = -g_mR_D(R_{in}/(R_{in}+R_i)$$
$$R_{in} = R_1||R_2 = 750k$$
$$I_{bias} = V_{DD}/(R_1+R_2) = .005mA$$
$$I_{DQ} = 5I_{bias} = .025mA$$
$$g_m = 2\sqrt{K_nI_{DQ}} = 3.16*10^{-4}$$
$$A_v = -g_mR_D(R_{in}/(R_{in} + R_i))$$
$$A_v = -1.31 V$$

Is my logic to find Av correct? How would I start to find Avin?


texts: Why short 3 terminals per contact on a membrane keypad?

texts:
What is the purpose of a three-terminal momentary contact in a matrix keyboard?

The motivating example is that I have a damaged membrane keyboard where some of the keys do not work.

At first I thought it should be easy to rig up a matrix of keys to replace the damaged board, but as I was trying to determine the wiring, I realized that there are three terminals in each button pad.  If you look carefully at the scan below, you can see the two distinct layers and, on the top layer, either interleaving traces on the top layer, or a fully connected grid on the top layer.  Where the top layer isn't interleaved, the bottom layer is interleaved.  All the circuit examples of matrix keyboards I've seen have a simple row/column grid, and does not have the extra contact in the button.

With the three terminals per pad, hooking up a standard 4x4 matrix doesn't seem reasonable -- it would require pushing adjacent pairs of buttons simultaneously.  I eventually rigged double-pole momentary buttons to bypass the keyboard but...

My question is why would they design three-terminal momentary contact keys like this and what are they used for?

Actual Membrane Keyboard with 3 Terminals/Key:

This is the left keypad from a ProForm Sport 1200 Treadmill, Model PFTL59506.  The membrane has some identifying numbers: "LUXE ETPF51105,LEFT#222227.

I think that traces 1, 2, and maybe 7 are damaged as in Fixing/Replacing Conductor Ribbon Cable .

From close visual inspection of the membrane and some continuity checking, I found this:

From the bottom-right and proceeding clockwise, ending on the small center pad, the terminals shorted together are:

3-6-8 - No Label/hidden -- ??? / Rings
3-7-8 - Trainer Program -- dead
2-1-4 - Incline Up    -- dead
2-1-5 - Incline Down  -- dead
2-1-6 - Fan           -- dead
2-1-7 - Calorie Program --dead
3-5-8 - Weight Down   -- Works / Rings
3-4-8 - Weight Up     -- Works / Rings


texts:
Is there a specific bluetooth module for FTP? Or any bluetooth module can be used for FTP.. Because when i see the modules they are specified as being Serial. Will HC 06 be to  FTP? If not to what to use with STM32F4 to receive a file from android device via Bluetooth?
(Q2) i am getting modules which say stereo audio transmission, can these be used


texts: Guitar Dual Volume Control Not Working Correctly

texts:
I'm not sure if this is the correct place to ask this, please notify me if there is a better place.

I have just created my first guitar pedal and thought i would go simple with a basic passive circuit but it doesn't work correctly.

If I am switched one way both potentiometers control the signal volume but if i am switched the other way there is no signal but there is a noticeable change in noise as i turn the potentiometer.
The footswitch is supposed to switch the signal between the two potentiometers to have 2 selectable volume levels

This is how i have it wired currently:


texts: What is the difference between a solar system battery and a normal battery?

texts: I want to design a solar powered system but I am puzzled by the type of battery which I should use. I am aware that for solar applications special batteries are available but I could not find any in my locality. Please guide me as to what differentiates a solar battery from a normal battery. And in what way the characteristics of charging and discharging circuit differ for both batteries.


texts: Passive switch that detects when a door is opened

texts:
Background In my school, we are assigned lockers and I am trying my best to make mine as impressive as possible, at this point I've build a custom shelf for it and put up some LEDs. The problem is that I manually have to reach for the on/off-switch for the lights, and let us be honest, that is not really something you should have to do in 2019. Hence, I'm trying to figure out how to make the lights go on when I open the locker.

Current progress Firstly I though about automating the process using an Arduino and motion sensor/distance sensor to see whether the door was open, but since the whole apparatus would have to be turned on 24/7, even the 50mW that I calculated that it would require was to much for two AA batteries in series. Then a friend suggested that I put in a button that would be pressed when the door was closed, opening the circuit with the LEDs, and closing the circuit when the door was opened. This would be very battery effective, but it is hard to place a button correctly, and it would propably come off if I accidentally closed the door with to much force. Today, I thought about using a LED as a "solarpanel", detecting that it was dark when the door was shut, and detecting increased luminosity when the door was opened, activating a transistor and closing the circuit. Problem is that a) I tried to build a prototype, but I didn't succed in powering the transistor using two different power sources, and b) the corridor that my locker is in is quite dark anyways, and would probably not be able to power the transistor.

Question Is there some way I can detect if a door is opened or closed without using any power?

I'd be grateful for all suggestions


texts: Can current absorbed by a shield of a cable be harmful to a human?

texts:
I wonder if I should isolate shielding everywhere throughout the system. It is a bit costly because shields are on the outside and tend to touch a bunch of outer metal parts. But then humans can touch those parts too.

For example here is a GX connector I am using:

I just let the shield go through the outer metal casing here. So I, and others, will touch the shield every time we connect/disconnect this plug. The maximum voltage on the system this connects to is 12V and the shield is not connected to anything within the system (the ground is separate).

I keep wondering if that is a good idea. What if:

a high voltage cable falls down on this cable and charges the shield?
a lightning strikes the cable while someone is holding it? (there is a very small probability of that)

Those are outside/third-party threats so should I consider them? Are there any rules regarding selling a system that has this potential vulnerability? Should I invest in a 5-pin connector instead an run the shield inside through a pin? But then wouldn't that expose the wires within the connectors to noise?


texts:
How analog & Digital Communication Can be through same 2 wires?
Which protocal is used in 2 wire communication and how it will fetch information from signals?


texts: Changing the full scale deflection of an analogue volt meter

texts:
I've bought an old pocket style (think of an old pocket watch) analogue volt meter and the full scale reading is 6V.

I would like to change this to 3V, however I have opened it up and there is no (multiplier?) resistor - or any resistors at all.

I've measured the coil and it is approx 52ohms.

How can I modify this meter to have full scale deflection at 3 volts?


texts: How do I communicate with an ATtiny85 development board that has V2.2 bootloader?

texts:
I'm very new to this so go easy. I'm trying to download a program to an ATtiny85 development board with a microUSB connection. All the posts I've read keep referring to a much older IDE version. I eventually caved and installed said version (1.6.5r2 I think). I spent a heap of time setting it up as per the various posts, only to have an error message:

This tool doesn't know how to upload to this new device. Updates may be available.
> Device search timed out
Device reports version as: 2.2

I found some help at
 https://kovo-blog.blogspot.com/2019/01/how-to-upgrade-bootloader-on-digistump.htm
 but the instruction

git clone git@github.com:micronucleus/micronucleus.git

caused an error.

daniel@pop-os:~$ git clone git@github.com:micronucleus/micronucleus.git
Cloning into 'micronucleus'...
Warning: Permanently added the RSA host key for IP address '13.236.229.21' to the list of known hosts.
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
daniel@pop-os:~$

and that was that.

Help to get up and running with these micros would be well appreciated.


texts: Inverting Amplifier Not Applying Gain to Bias Voltage

texts:
I am simulating an inverting amplifier circuit (Page 3 in this app note) with LT spice.  The amplifier has a gain of 10 V/V and since I am using a single rail supply, I am applying a bias voltage at the non-inverting input of about 0.113 V.
I expected the bias voltage to be amplified to about 1.25 V at the output but it looks like this is not the case.
Below are the amplifier circuit and simulation results.  It is connected to a series of sallen-key filters not shown.  The filter output rides on a 1.25 V bias which should be removed after passing through the 1uF coupling capacitor.

The output shows that that bias voltage does not get amplified and so the amplified signal clips at the negative swing (green plot).  The blue plot is the output just after the coupling capacitor.
When I increased the bias voltage to 1.25 V, the output had the correct bias voltage.  This seems contrary to what's suggested in the application note.  Am I missing something?
Edit
When I simulate a circuit like this, I get exactly what I expect.
The only difference is that there is no coupling capacitor before the op-amp.  Why does the removal of the capacitor cause such a difference?


texts: I know slip in induction motor determine the current and torque but the point I want to ask, when controlling with vector control it is said stator and rotor flux is always kept with 90 degrees apart but if stator and rotor is always kept at 90 degrees their speed should be same and it means no slip there. if no slip no torque exists. So there should be a speed difference between rotor and stator but how is that possible to keep 90 degrees between stator and rotor and in the same time having slip (speed difference between stator and rotor) ?


texts: Problem generating square wave using IC555

texts:
I'm having trouble trying to build this circuit:  (Step 5) - (diagram below).

I built it, and everything works fine, but the coil doesn't spark.
I then used a scope-meter to check, and there is a almost perfect square wave outputted from pin 3, but after the resistor, the wave gets messed up, reduced to almost just background.


texts: Two phone batteries connected in series not working

texts: I have two, fully charged, 3.7V standard Nokia phone batteries, that I want to connect together to use as a 7.4V battery, I connected the (+) of one to the (-) of the other, and then tested it but it does not seem to be working, what am I missing?


texts: Why can't normal single-use alkaline batteries be recharged?

texts: What is the electrical/chemical mechanism that prevents them from being recharged? If recharging is possible in a narrow circumstance, what are the constraints and drawbacks?


texts:
I am learning about headphones and microphones and I have 2 questions.

I bought a few pairs of headphones from the dollar store and took one pair apart. There is a weak little magnet in the center with very thin insulated wire coiled around it and there is a very delicate plastic sheet covering this little assembly. Now, the headphones worked before I took them apart so it's very exciting to see the guts. I've also studied this design and I think I understand the physics of it.

My questions are:

Should I be able to use these kinds of headphones as microphones? I've thus far been unsuccessful.
The headphone jack is tip-ring-sleeve. If I connect sleeve (which I think is common ground) to either tip or ring (and thus completing the circuit), can I use my multimeter to measure the current/voltage if I yell into the headphone?

My goal is to see (detect) this thing at work. I've learned a bit about op-amps too, and I wonder if I cannot do what I want without making a slightly more advanced circuit.

Kindly,


texts: How exactly do inground electric dog fences work? I need help making a square perimeter with one side that dose not trigger the collar

texts:
I need help laying out an in ground electric dog fence in a square formation with one side of the square not triggering the collar. The issue it that the manufacture says that inorder to do that we need to make a double loop in which the wires are 5 feet apart, that will not work for our property. I'm willing to do any solution, I was thinking about maybe using shielded coax something. I'm sorry if this seems like a nuisance question but I would really appreciate feedback.

I did some research and its a 10kHz system, also i should have specified this originaly but its a PetSafe PIG00-1077. Also we can put the transmitter box pretty much anywhere.
Double Loop Diagram on p.9 And as for a diagram of my yard i count find any, but the side we want to not affect the collar is the side yard so its only about 5' wide so if we where to make it a full perimeter the dog would probably not be able to go down the side yard. We also have 2 front gates meaning if we to do a double loop the wire would need to be underground but then we would run into the issue of putting the cable under the driveway.

[![fenceDiagram][1]][1] The red and yellow show where the collar should trigger. The yellow is where the front gates are and the green shows where the collar should not be trigger.

https://imgur.com/a/THyxf4H
Also here are some pictures of the sideyard i'm referring to.


texts: Building a decent 12V power supply from batteries

texts:
I'm currently building a flyback transformer.

As you can see, the power supply is 12-15V, 3A. Up until now I've been using a 12VDC power supply from batteries. I guess I should have realized sooner that this would be insufficient for something requiring so much power - when online, the PD across the batteries drops to ~9V, and the current is in hundreds of milliamps. Clearly insufficient.

My question is, is it possible to somehow modify this to run on batteries? I was thinking perhaps to use capacitors to store charge to allow for a greater output current, but of course only intermittently to allow them to charge.

Since I need this to be portable, a mains-run power supply is sorta' out of the question. I'm sure there are ways round it though.


texts: Why do we need more voltage levels to drive a dynamic multiplexed LCD?

texts:
https://www.nxp.com/docs/en/application-note/AN3412.pdf
Dynamically driven LCDs require more than two voltage levels to drive segments. The different voltage levels to drive a dynamic
LCD must be at least 0, 1.6, and 3 volts, so the required voltage levels are generated with external resistors. The voltage levels
are called bias, in this case ½ bias. To turn any segment on, the voltage applied between the desired frontplane terminal and the
appropriate backplane must be 3 volts. To turn any segment off, the voltage level applied between the frontplane and backplane
terminal must not be higher than 1.6 volts.


texts: W5500 with POE functionality Link status ON with nothing plugged in?

texts:
I am working on a design that uses a W5500 for networking. I followed a reference schematic and believe all my connections are correct, however I am facing issues with the network connectivity.
Basically, the device thinks that the link is always on. The Link LED turns to yellow about 1 sec after booting and stays on, even if I plug in an Ethernet cable from a router or if there is nothing plugged in.
Schematic:

Wiznet W5500 Reference Schematic:

I've included the schematic here. I am using a Chinese HANRUN RJ45 connector with POE functionality.
RJ45 Connector
Does anyone know why this is or could be happening? I have followed the reference schematic and the only thing I can think that is different from the reference is the reset and the RJ45 connector.
I checked reset. It's sitting HIGH at 5 V. It needs to go low for >500 us to reset. Hitting the reset button correctly resets the device.
I should mention I did my testing with Arduino software. I used Examples -> Ethernet -> Link Status. Even when there is nothing plugged in, I get Link: ON.
Thanks for any help in advance. I will be checking back and trying to answer as many questions as possible


texts:
I've been trying to understand how a circuit becomes digital. I understand the different between an analog signal and a digital signal, but I don't see where digital circuits come from if all the components are analog.

For instance, this quote from one article:

  Most of the fundamental electronic components – resistors, capacitors, inductors, diodes, transistors, and operational amplifiers – are all inherently analog.

Followed by this quote from the same article:

  Digital circuits operate using digital, discrete signals. These circuits are usually made of a combination of transistors and logic gates and, at higher levels, microcontrollers or other computing chips.

But logic gates and microcontrollers are made from combinations of the components named above-- analog components.

Do you see my confusion?


texts: I need some really basic help here. Can I use a 4bit adder chip as a subtracter by using the 2's complement for the number to be subtracted?


texts: How to drive a 10 Watt LED from an Arduino?

texts:
I wired a circuit using the NPN transistor 2N2222.

An active HIGH is maintained at Arduino Pin 7 connected to the base of the transistor. The LED lights up but the brightness is considerably lower than when powered by a 9V battery directly. From the datasheet of 2N2222, I learnt that it can handle a max collector current of upto 1A. So why doesn't the LED glow brightly when the transistor is in saturation?


texts:
I have a signal that goes low for about 0.2μs or faster and i want to create an active low pulse about 1.8μs every time the input pulse goes low. How could i do that?

I want it to drive the !WAIT pin of a cpu to give time on a slow peripheral to latch the input.

Also, it would help if the output didn't pull high before and after the pulse so i can use multiple circuits tuned for different peripherals.

Also, every component needs to be through hole


texts: Peak open-circuit current and applied voltage of transformer function

texts:
I know that the back-EMF equation tells shows that the peak flux density is proportional to the AC supply voltage. But what is the explanation for that the open-circuit current increases non linearly whereas the applied voltage increases linearly (I did notice this while I was performing an experiment)? Does it have to do with the B-H curve  or something?

As a consequence (I guess), the magnetizing reactance did change with the change in voltage. What physical effects cause this?? Shouldn't it be constant?


texts: Small axial inductor for piezo disc buzzer?

texts:
I'm planning to operate a 15mm piezo disc as a buzzer at about 5 KHz. Can I use a 5mH 0.5W axial inductor for this? Peak current through the inductor is 70 mA, average current 22 mA, average dissipation is 2.3 mW (as per LTspice; with 1 Ohm resistance, I don't know actual resistance of inductor).

The inductors look something like these...
https://i.stack.imgur.com/we1zc.jpg

update: This is the one I'm considering https://www.ebay.com/itm/50PCS-0410-Color-Ring-Inductance-4-7MH-472K-1-2W-Axial-RF-Choke-Coil-Inductor/351831546222 And a related datasheet https://www.taitroncomponents.com/catalog/Datasheet/TIA0204.pdf lists 85mA max and 20 ohms for the 1mH inductor.

Found another one http://www.mantech.co.za/Datasheets/Products/ECXX_3L.pdf This one says 30 ohms, Isat 120mA, Irms-max 100mA for 4.7mH inductor.

So, I should be safe, right (and can maybe get rid of the additional 20 ohm resistor I have)?


texts: 21V power supply -- 26V output with different mains?

texts:
I have an AC/DC power supply (from the UK).  It is labelled 230V/50hz. As far as I know, electric in Mainland britain is 240V/50hz.  Indeed, the unit did correctly power the Korg keyboard in the UK. The DC output is labelled 21V / 1.2A. (The Korg piano is indeed labelled 21V input on the back.)

Now I have the same power supply in France.  As far as I know, France is also 230V/50hz. When I plug the power supply in the wall in france (obviously using a 50 cent plastic plug adaptor - of course NOT using any sort of transformer, etc).

Using a good multimeter, in France the output from the power supply is 26 volts (around 25.9 to 26). Is that normal?  Why not just 21?

(Unfortunately I never tested the output, in the UK.) Now, the electric piano is actually not working.  ie, I did plug the power supply in question in to the Piano and no result, nothing comes on.

Does anyone know:

Why is it showing 26 rather than 21 as labeled?
Do you reckon I may have blown a fuse in the piano, due to the 26 versus 21? Or, perhaps not a fuse, just permanently ruined it?  Conversely, is it likely just some other unrelated problem with the piano?
To rephrase: If the piano says 21V on the back, would 26 V be too hot, or no problem, typically?

It's an expensive pro piano and a real nuisance! It is a mystery that it is showing 26V. It's almost impossible to find a replacement power supply, and, that may well not be the problem.

A further question for you experts:
would an alternate supply, eg,
http://www.webducommerce.com/alimentation-21v/chargeur-alim-secteur-21v-1-7a-36w-p-3485.html
with a HIGHER amperage rating, actually be OK??  Should you try to match the amp rating, or us the point that it must be "at least" 1.2A in my example?  Thanks again, pro geniuses!


texts: Buck - Boost converter inductor selection

texts:
Hello i am creating a circuit that uses the TPS63070 buck-boost converter. As i was looking at its sample circuit and application in the datasheet on page 18 (under Inductor Selection), i am given 4 suggested inductor values.

I dont really understand on how to use the formula given in order for me to determine what is suited for my use.

my applications is for this to control 2 motors that may draw 0.5A - 1A (variable speed) at 7.5v each.

here is my circuit. Also maybe for consideration is i made the circuit so that i may adjust the under voltage cutoff protection and the output voltage. Output voltage maybe adjusted by +- 0.75v during application and undervoltage maybe adjusted by +- 0.5v.

So of the recommended 4 inductors

- 1.2 μH    Coilcraft,    XFL4015-122ME     4.5 A / 18.8 mΩ
- 1.5 μH    Coilcraft,    XFL4020-152ME     4.6 A / 14.4 mΩ
- 1.0 μH    Coilcraft,    XFL4020-102ME     5.4 A / 10.8 mΩ
- 1 μH      Murata,       1277AS-H-1R0M     3.7 A / 45 mΩ

which one should i pick? and if you can tell me how did you compute for it, it would greatly help me in future endeavours. Thank you.


texts:
I need switch which is normally closed, but when I press it, it goes to off state. As soon as I move finger from it, it must go to default state (normally closed). Which type of switch is this? I need two of them, for limit switch control of DC motor when it reaches full travel in either direction.
Thanks in advance


texts: NAND gate output doesn't change to logic 0 when expected

texts:
I have this circuit:

I'm powering it from an Arduino but that's inconsequential to the operation, it's simply a convenient source of +5v. The orange line is +, black to gnd.

If it's not clear from the picture (the lines got a little messy, sorry), the basic idea is I have 2 switches connected to ground, both attached to a 10k ohm pull-up resistor from the +5v side. The resistors are connected to the input gates of a 74LS20 quad input NAND gate. I've tried to pair the inputs together as I want it to function as a dual input gate. I'm using a quad input due to lack of components.

When I throw the switches to the up position, as pictured, the circuit is shorted to ground, which should pull the input pins low, meaning the output pin is high and the LED lights. This works fine.

However, when I open the switches, the input pins are high (I checked this with a multimeter, they're at +4.98V), but the output doesn't change, the LED stays on.

I've tried the same circuit with a couple of IC's in case one was faulty, but the same behavior is exhibited.

Have I wired this wrong? It's been a very long time since I've messed around with this stuff so maybe I've forgotten something fundamentally intuitive about electronics, apologies if that is the case.


texts: VHDL: Can't give a std_logic type a value of 0 or 1 (on or off)

texts:
I have the following code from one of the files in a project:

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
USE ieee.numeric_std.ALL;

entity twoplayermux1 is
    port
    (
        --inputs:
        show                 :  in std_logic;
        set              : in std_logic;
        input                : in std_logic_vector(7 downto 0);
        try                  : in std_logic;
        player               : in std_logic;

        --outputs:
        show_out             : out std_logic;
        set_out          : out std_logic;
        input_out        : out std_logic_vector(7 downto 0);
        try_out          : out std_logic;

        show_out2        : out std_logic;
        set_out2             : out std_logic;
        input_out2       : out std_logic_vector(7 downto 0);
        try_out2             : out std_logic
    );
end twoplayermux1;

architecture Behavioral of twoplayermux1 is
begin

process (show,set,input,try,player)

begin

case(player) is
        when "0" =>
            show_out <= show;
            set_out <= set;
            input_out <= input;
            try_out <= try;
        when "1" =>
            show_out2 <= show;
            set_out2 <= set;
            input_out2 <= input;
            try_out2 <= try;
        when others =>
            null;
        end case;

    end process twoplayermux1;

end Behavioral;

However, because player is an std_logic, the compiler gives me the following error:

Error (10515): VHDL type mismatch error at TwoPlayerMux1.vhd(36): std_logic type does not match string literal

The error is in the case statement where I wrote when "0" => and when "1" =>.
If I change playerto an std_logic_vector of 2 bytes and write when "00" => or when "01" => then it is being compiled without any errors. However, I do not want a std_logic_vector of 2 bytes. It needs to be 1 byte like so: player : in std_logic_vector(1 to 1); , but that doesn't work either.

NOTE:

It is a project for an FPGA board.


texts: With Lilypad boards, whats the best way to put them into clothing so they can be easiy taken out?

texts: I want to make a vest that has LED all over it (for the purpose of night time cycling) but i want to be able to easily wash it.


texts: How does this RC pulse generator circuit work?

texts:
In this video from Ben Eater, he uses an RC circuit to create a push-button "write-pulse" generator for his EEPROM (discussed around the 14 minute mark) that ensures the write pulse fits within the timing requirements from the datasheet.
The schematic for the circuit is:

simulate this circuit – Schematic created using CircuitLab
However, I am at a loss understanding how this circuit works. Ben states in the video that the 1k resistor is to allow the capacitor to self-discharge, but to me it looks like there is no way for current to flow out of the capacitor when the push button is open, as both ends of the capacitor are tied to +5V through the resistors. I also don't understand how the capacitor gets emptied for the next time the button is pushed.
So how is it that this circuit is able to create the single inverse spike for the write-pulse that is seen on the oscilloscope in the video, and what exactly does the 1k resistor do?


texts:
I need to operate a peripheral chip via bidirectional I2C across a significant air gap (30mm) and powered wirelessly. Has anyone done the I2C to IrDA? Any problems? Any better solutions?

I want to connect with a remotely powered board carrying the chip. Air gap is what it says - no wired connection for power or signals


texts: USB-C PD, Voltage and Current of Power Adaptors

texts:
I have a rather basic question... but I don't want to take chances.

I have two MacBook Pros, one which ships with a 87W power unit, and the other a 96W power unit.

Now, I understand that a device won't draw more current than needed. I also believe I understand that voltages are negotiated and that using too high a voltage is dangerous.

Furthermore, I expect that USB-C, as a 'smart tech' should be more controlled than just hooking up 'raw' electricity to a device.

That said...

When I inspect my 96W charger I see:

Output Voltage: 20.5VDC/4.7A or 15VDC/3A or 9VDC/3A or 5.2VDC/3A

When I inspect my 87W charger I see:

Output Voltage: 20.2V/4.3A, 9V/3A, 5.2V/2.4A.

I don't see a clean voltage match for my 96W Mac vs my 87W Mac, there is at least a .3v difference

Is this safe to interchange these devices?

If so, what's insulating me (pun intended), the small voltage difference... or the smarts of USB-C PD?


texts: How can I avoid "Minimum Pulse Width" slack violations in Quartus FPGA synthesis?


texts: Why does this file give syntax error in verilog?

texts:
My original file has the following

module circuit_320a(A,B,C,D,N,F);
    output N,F;
    input A,B,C,D;
    wire w1,w2,w3,w4;
    and #(30) G1(w1,C,D);
    or #(30) G2(w2,w1,B);
    and #(30) G3(w3,w2,A);
    not #(30) G5(N,c);
    and #(30) G4(w4,B,N);
    or #(30)(F,w3,w4);

endmodule

and my testbench has these

`include "ask.v"

module t_circuit_320a_delay;
    wire N,F;
    reg A,B,C,D;

t_circuit_320a_delay M1 (A,B,C,D,N,F);
initial
  begin
     A=1'b0; B=1'b1; C=1'b0; D=1'b1;
  end

  initial #200 $finish;

   $dumpfile("ask.vcd");
   $dumpvars(0, ask_tb);

endmodule

When I try to compile I get syntax errors, why is that?

I have named the original file ask.v and the testbench ask_tb.v


texts: A voltage controlled switch for a single NiMH cell

texts:
I'm developing a small project that contains one AAA NiMH battery that is charged via USB with a MAX DS2711 IC.  The output of the battery is connected to a TPS61006 to boost the ~0.9 - 1.3v cell voltage to a 3.3 usable output.  The problem is that while charging, the MAX chip outputs up to 5V into the NiMH battery, which would be too high of an input voltage to the TPS61006.  I'd like to be able to add a switch between the battery charger and boost converter to turn off the boost converter while the battery is charging, and just take the 5V down to 3.3V via an LDO to run the rest of the electronics off the input charger power.

The rough schematic:

I'm finding out, however, that switching voltages down to 1v isn't exactly trivial.

First thought: Use a PNP BJT.  The problem is that the CE junction drops too much voltage between the collector and emitter for such small voltages as these.  An NiMH battery is fully charged at about 1.3v and completely dead at roughly 0.9v.  With a Vce sat of 0.3 or 0.4V, If the battery is full at 1.3v, the input of the boost converter is seeing 0.9v, which is below it's recommended minimum Vbat in.  One thing I found was these: I'm not sure what the catch is but the Vce for the PNP looks like 60mV at a 100mV output.

Second thought: Use depletion-mode NMOSs.  Unfortunately, finding a surface mount, depletion-mode NMOS, with a low enough Rds(on) is expensive, and these are the only ones that fit the bill, I think.  $10 is too much for this little hobby project.

Third thought: As a noob electrical engineer I saw that there are relays that come in small packages such as these normally-closed solid-state relays.  However once I got my hands on them to play with, there's a drop across the output because the "on-state resistance" (essentially the Rds(on) stackup, I believe) is 2.5ohms.  Too much to use because the voltage drop is too high.

Fourth thought: A coworker recommended just a PFET since the Rds(on) is what dictates the voltage drop across the FET, which is usually milliohms.  This is true, but at a 1V source input, the gate threshold voltage is usually negative unless I'm misunderstanding something, or there's a configuration I'm not aware of.  So at 1V at the source and 0V at the gate, the PNP is already turned off.

Fifth thought: The same coworker pointed me in the direction of JFETs.  However if you just look at the selection of JFETs on Digikey, it seems like there are small SOT packages that handle up to 50mA Id, then it jumps to big TO-247 packages that handle 26A, and nothing really in between.

Other than that, I'm all out of ideas.  To boil the post down, I need a switch with the following requirements, and I have yet to find anything that works:

It is normally on.
It can't drop more than, say, 50mV cross its input to output.
It is controlled by a 0 - 5V input.
It has to handle ~500mA of current.
A small SOT SMD package, but not those tiny, lead-less QFN packages.
I don't want to add additional batteries in series.  That would make the design too easy, and it wouldn't be fun if it was easy.


texts: How to calculate the value of the thermistor based on the output voltage of this circuit

texts:
I recently bought a board that consists of this circuitry. It came without an instruction whatsoever, so I have to figure out how to measure the temperature based on the output voltage at the To.

The circuit consists of a Wheatstone Bridge of R13-R15 and an NTC thermistor TH1. the voltage between point A and B Vd then go through a differential amplifier U3A and then further amplified by U3B. I don't have a volt meter or oscilloscope with me, what I did is read the To using an Arduino ADC and convert it to Voltage output. In order to calculate the temperature, I need to know the thermistor value based on To output voltage, I sort of know the basic theory on how this circuit works, but not quite able to figure out the relationship between To and the resistance of the thermistor yet.

Here are my questions:

1) What is the gain of this overall circuit?
If I read it correct, it has a gain of 12, so Vd = To/12, is this correct?

2) Once I derive the Vd, I assumed that:

Vd = Vref * R14/(R14+R15) - Vref * R15/(R15+TH1)

and further derive from this formula to get the TH1 value. Again, what is the correct formula for getting the resistance value of TH1?

But so far what I get seems to be way off from the correct temperature.


texts: For which frequency is ESR specified by default?

texts:
I'm playing around with an REF5010 voltage reference, and its data sheet specifies an output capacitor with an ESR of 1 to 1.5Ω for best performance. Now when I measure the ESR of electrolytic capacitors it varies widely depending on the frequency (I have an U1733C LCR-meter that can measure at 100Hz, 1kHz, 10kHz and 100kHz).

The Wikipeadia article on ESR says

  If not otherwise specified, the ESR is always an AC resistance measured with standardized frequencies.

but fails to provide details.

Which frequency (maybe depending on circumstances?) is used for determining the ESR of capacitors?


texts: I need a potentiometer controlled by only a 0-10v signal

texts:
I have a PWM control box made for standard 4 pin PC type fans (12v).  It has a potentiometer to control the fan speed via PWM.  It is powered by its own 12v supply.  I would like to exchange this manual potentiometer with one that is controlled by a 0-10V signal.  The 0-10v signal is coming from an aquarium controller and is intended to adjust an LED driver.  I can program this aquarium controller to vary the voltage based on sensor inputs.  Ideally adjusting fan speed based on temp/humidity/pH sensors via the 0-10v output.

My biggest concern is not damaging the expensive aquarium controller (source of 0-10v). I obviously need to crack open the PWM fan controller and measure the potentiometer.

I'm having difficulty figuring out what I need to use or search for.  A digital potentiometer seems close, but needs more inputs than I can provide.

Fan PWM:
https://noctua.at/en/na-fc1


texts: Analyzing LC circuit with multiple inductors and capacitors

texts:
I have a problem understanding what's going on in a more complicated LC circuits with multiple inductors and capacitors

simulate this circuit – Schematic created using CircuitLab

with the two capacitors having the same size and the two inductors different. How can I evaluate the resonance frequency of that circuit?


texts: What is the tiniest, low-power, and efficient am transmitter?

texts:
Here are my constraints:

I need to build an am transmitter, but it has to fit in a 1 inch diameter and ~1 inch height box.
Since the box is very small, I plan to use a CR2032 battery, which is also a considerable limit.
Plus, I plan to use a carrier frequency of 1.52MHz (I can get a crystal to that frequency).
The signal I want to transmit come from an electret microphone.

So far, I have tried to make this work with 555 and a 9V battery, here is what I came up with:

The aim is to mix the 555 output and the incoming sound together, so the antenna goes between R3 and R4.
I had to change a bit the values of R2 and R1 to make the 555 oscillate at 304kHz, so that the 5th harmonic is at 1.52MHz.

Using an old alarm clock, I was able to get a very weak sound.
I added a class A amplifier to get more power through the antenna but I am getting a weird effect.
I can hear a sort of whistle added to the actual sound.
The whistle frequency seems to change (it sweeps slowly) even if I'm not touching anything.
Is it because of the square wave (and not sine) carrier ?

Despite this effect, I was planning to do the following:

Use a flat CR20232 3V battery
Use an ICM7555 instead of a regular 555

At least, it fits in the box...
Any better idea ?

By the way, I'd like to use only DIP packages (max 8 pins) and discrete components.


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I'm about to design a 433MHz transceiver and found a nice reference design using the TRC105 and the RF3608D SAW Filter.

Before designing the circuit I wanted to understand the impedance matching in the reference design, and figure that would be no problem on my smith chart... Now hours later I still don't get it.

In the datasheet for the RF3608D on page 2 is drawn a Application Circuit, which shows matching to a 50ohm antenna.

http://www.mouser.com/ds/2/347/rf3608d-33048.pdf

Looking at page 2 is shown an Application circuit.

I think the 220nH shunt inductor is to cancel the capacitive reactance, which I think is about -5.8ohm (read on page 7).

But I don't understand at all, what purpose is of the series LC circuit (5.6nH || 1.2pF)?


texts: I have an application where I want to pass a current of about 300mA through a load, which should be turned on/off via a 3V/0V signal. I thought of using a 2N7000 as the switch and have it set up on a breadboard. I'm able to turn the MOSFET ON (checked with an LED) and OFF with the 3V output, but the current is much lower than 300mA. What could be the reason? The load resistance is 10ohm and my battery is capable of driving the load.


texts: Can a series RLC circuit have an unstable natural response?

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I'm looking at this exercise in a book for the natural response of an RLC series circuit without a voltage source driving the circuit and they show that the circuit is unstable.

Is it ever possible for an RLC series to be unstable if it doesn't have an input voltage source?  Seems to me the resistor would always bring the voltage down over time without the input voltage to put it back up again.

See example:


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Does anybody know if it is possible to create a true relay in LTspice, one that is a true open circuit when open?  The problem I am having is no matter how big I make the off resistance, there is still current flowing. This causes any resistor in series to drop voltage and mess up the simulation.
I am not sure if this is even possible, since a true open circuit actually changes the net list.


texts: Understanding a simple crystal oscillator transmitter circuit

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I've recently built this circuit: http://makerf.com/posts/mighty_simple_shortwave_transmitter
It works on the desired frequency as you can see from this video : https://www.youtube.com/watch?v=t6nFi7fdoK0 .
Now I'm trying to understand why and how it works, I would appreciate if you can guide me through the circuit in order to understand what each single components do.

This is what I think I've understood:

The oscillation begins in the crystal (xtal) for the reason explained here What makes a crystal oscillation to begin
There is a feedback loop which goes through the transistor Q1. Basically the RF is injected into the base and it gets amplified (and shifted by 180 deg?) by the transistor exiting from the collector.
The L1 - variable capacitor is a tuned circuit but I don't understand why the collector is tapped there and in general what is its purpose.
The L1 - L2 transformer is the way through the RF goest to the antenna and the transformer is required to adapt the impedance of the circuit to the 50 ohm required from  the antenna

Finally, I'm not sure about the two resistor and the 0.05uF capacior.

Also, which oscillator circuit did inspired this design? Is it an Hartley Oscillator?
Thanks for your patience and if you have any good resource (book or website) which could help me in understanding oscillators, please let me know.


texts: Is hand soldering a 48-VFQFN possible? I could not find any videos on this and I guess it must be quite hard.


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I finished laying out HACK, my first RF (2.45 GHz) layout. The sensitive part is the connection between the IC (Atmel SAM R21G18A), the balun (Johanson 2450BM15A0015), and the PCB antenna (copied from a TI app note, thank you Texas Instruments!).

I followed the suggested schematic for the SAM R21 XPlained pro with regards to the connection from chip to balun and from balun to antenna. The schematic part is here:

Before laying out, I used an edge-coupled microstrip differential impedance calculator to find a width of the two traces from IC to balun that was near 100 Ohms, while I used a coplanar waveguide calculator to find a width of the trace from balun to PCB antenna that was near 50 Ohms.
My values are:

Er:4.5 (FR4 PCB)
PCB width: 1 mm
Copper (trace) thickness: 1 oz/ft^2
Traces distance or ground plane distance: 7 mils

And I got 24 mils for the 100 Ohms differential traces from IC to balun, and 55 mils for the 50 Ohms trace from balun to antenna. The layout is here:

I also placed vias to ground near the 50 Ohms trace at 1/20th of the wavelength, then I also stitched the ground planes.

Before I send this out for the first run of prototypes (low budget, so the less revisions the better), can you please tell me if the math I did is correct (did I use the correct formulas?), and if this layout would perform well?

Thanks guys.

Cheers,
Mick


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I spent yesterday opening this fan unit and researching...
I'm looking to reduce the speed by about 25-40%, at the lowest speed setting only.
Please have a look at the photo and let me know what options I have?
Fyi the resistance values is 190, 260, 310
I would prefer not to do the light bulb trick if possible.
Please advise.
Much appreciated
Thanks guys


texts: Log periodic antenna intuitions for its region properties

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a log periodic antenna shown In the diagram shown bellow.
As you can see there are reflective region and non radiative region.
there are phase shift of 180 degrees between neighbor "wings".
I have read that the not radiative region is not radiative because it hase capcitative profile.
I can see why it has capacitate profile?
And why a capacitative profile doesnt allow us to radiate?
Same this for the reflecting region,its says that its reflective because its an inductive profile.
why inductive profile reflects the wave?
Thanks.


texts: How to power schmitt trigger in LTspice with negative voltage?

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I use CD40106 model in LTspice for schmitt trigger, but the circuit I want to simulate has -5 and 0 V levels, CD40106 only accept positive value for VDD and there is no other param to change the value or may be I am mistaken.

Is there any way I could modify the model to simulate my circuit in -5 and 0V?


texts:
I have a question about warning messages from Vivado synthesis tools in VHDL source files. I know for a proper answer I should be providing more information, so I would appreciate just letting me know if this message is what I expect the error to be.
I have components that are 32 bit in size, and are nested inside other components.
I am assuming this error means that I am driving this pin from more than one place at one time in my project? I am using signals inside these components, so maybe they are being multi-driven, or is this to do with the hardware buffers the hardware synthesis tools are generating?.
Below is the warning messages I have in question:


texts: Crystal's datasheet give load capacitance is 20pF, do I need external load capacitors?

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I use external crystal for HSE of STM32F0. I plan to use 8MHz Cylinder Crystals. Datasheet of this crystal below

Datasheet give crystal load capacitance is 20pF

My questions:

1/ Do I need to add 2 external load capacitors? If do not, where is crystal's ground pin like STM32F0's datasheet crystal section below

2/ Can I know crystal's ESR to calculate Rext? Datasheet give maximum ESR value, so how I determine ESR value?

Thanks so much