texts: Two point calibration for analog signal chain

texts:
I am new at this forum, I have agreed to the rules but I have a question that I did not found answered as I would need, considering many hours I spent looking for similar ones here.
In spite of everything I must confess that I have learned a lot during that search because I am a digital guy  and analog electronics is something I would love to learn.
My point is about two point calibration for analog signal chain (Sensor-> OP amp--> ADC) using software methods.
I've read from some other question and answers on this forum (ADC/DAC Calibration?) and (ADC calibration in ATTiny88) that you never should use the bottom 50 mv or top 50 mv from ADC input range to do calibration.
Also I refer to the second link which is related with my questions.

1- Question: How do you account for offset error if you do not consider the bottom 50 mv of FS?

2-Question: Suppose you need a resolution that ask LSB of 31.2mv ( 16 bit ADC, Vref 2.048 v) how you deal with that if you need to keep working with 16 bit, Vref 2.048 v ?

Thank you in advance for some help


texts: Reset and Trigger connected in 555 timer circuit

texts:
What is the effect of connecting Reset and Trigger together in a 555 monostable circuit?

I am  modifying someone else's circuit and don't see why they say a need to connect Reset to Trigger instead of just tying Reset to Supply Voltage.


texts:
Hi I want a current flowing 1A. I don't understand what does it mean to trip?

(Image source - Farnell PTC datasheet)

Does it mean to open the circuit? Should I be looking at a holding current that is 1A and a trip current that is larger than 1A ?


texts:
Are there any practical methods of converting solar thermal energy into electrical power on very small scales, eg: using a 300mm diameter paraboloid reflector with temperatures of approximately 800-1600 °C?

While there are many large scale concentrated solar power plants which use conventional steam turbine engines, I am wondering what other methods there are to produce electrical power from solar thermal energy at high temperatures but using a small solar collector, eg: thermoelectric modules, etc.


texts: Feasibility of 10MHz, 100dB Dynamic Range Transimpedance Amplifier

texts:
I've been asked to produce a photodiode transimpedance amplifier with a 10MHz bandwidth. Current range of 1 nA to 100 uA (5 decades current) -> 100dB Dynamic Range.

Photodiode is a Silicon APD with junction capacitance 6pF.

Logarithmic compression is not suitable since 1.) this is imaging, and 2.) full bandwidth required for all signal strengths.

I believe output referred noise requirement, Vrms is therefore < 1nA * Rf. I understand bias current should be in the 1-10pA range. Other parameters influencing noise/BW are GBW, Input Noise Voltage Density, Input Capacitance.

The problem is, I have not found a single low-bias op-amp that seems capable. Is this performance even possible to achieve with commercial components?

Calculation tool I'm using for bandwidth/total output noise (let me know if this is bad)

Full-scale output of 1 or 2 V is reasonable. For max input 100uA this implies Rf ~= 20Kohm. Therefore, the noise at output should be <= 1nA * 20K = 20uVrms.

For example, I've looked at the following op-amps: ADA4817, LTC-6268, OPA657 all have ~1000 uVrms order noise, but meet bandwidth requirement.

And these lower GBW products: AD8651, ADA4807, AD8655, OPA2301, OPA2365, just barely make the bandwidth, but still show output noise on the order of 100-200 uVrms.

Also, could I possibly use an external input stage? Like some sort of FET buffer to drive the input of a higher bias current op-amp? Discrete transistor circuits are not my forte.

Thanks for any help you can offer.


texts: Any advantage in AC-DC or DC-DC with past, large form factor semiconductors?

texts:
I want to clarify this question with my real-world example:
Say you have a device which contains some AC-DC converter (or DC-DC) for rather high power specs (10 kW  up to 300 kW, not in the same device tho, just to curb the question parameters) and due to some external constraint know that the device will never need to be as-small-as-possible in two of the three dimensions. Smallest envisioned dimension is ~50x50 cm but can be as large as 1m x 2m, acceptable height is I think determined by the necessary active cooling technology, in the 10kW case this shouldn't surpass 10-20cm though. With one word, the device may be large but as flat as possible.
Is there some (any) advantage in sticking to old semiconductor technologies which dropped out of present day electronics due to their inability to miniaturize or other parameters along that line? I am thinking of thyristors (if this is a correct example - I am just a Software guy) which were all over the place in the 60's. Are there past technologies which lend themselves to AC-DC or DC-DC switching with benefits in

price
minimzation of losses
ease of cooling

which are large enough to consider them against present day technologies if above described size is of secondary concern?
Similarly, is there a price/power advantage if one builds the necessary modern semiconductors along these constraints - i.e. their housing may extend more in 2D than usually required? Is there something to be won?


texts: Is my magnetometer calibrated correctly?

texts:
I am calibrating the AK8963 on the MPU9250. The first plot shows original mag readings and the last plot shows readings corrected for soft and hard bias. I am following the guidance of Kris Winer: https://github.com/kriswiner/MPU6050/wiki/Simple-and-Effective-Magnetometer-Calibration.
Do these plots look good enough or are they too flat? Is there a conventional metric to test for this. I was thinking of just plotting a perfect circle and calculating how well it fits.
each axis is in Microtesla


texts:
I have a four PLC with many digital I/O connected similarly to the schematic below. If I use multi meter and measure the voltage between the two points in the schematic, why is it showing 1V? Isn't it supposed to be 0V? The relay coil is not connected. The measurement point is between psu 24V+ and relay's NO. The measurement device is Kyoritsu DMM type KEW 2200R

PLC's schematics.


texts: What is the purpose of the following inverter topology?

texts:
I stumbled upon an Schmitt-trigger oscillator circuit. I can fully understand the principles and its function, but what I cannot fully understand is the chain of inverters after it.

In the above circuit I can understand the functionality of the first two inverters (for regenerative purposes/making the oscillation more "clear") but what is the purpose of the rest of the circuit, and especially of the 6th and the 7th inverter?

EDIT

This is the original image (it is not that detailed, but I hope you can extract some more useful info)


texts:
The dual in-line package was invented in 1964, and it appears that they existed in 14- and 16-pin variants by 1965 (as evidenced by an image in this December '65 article in Electronics Magazine).

My 1976 copy of TI's TTL Data Book indicates that they were manufacturing TTL chips in 14-, 16-, 20-, 24- and 28-pin packages by that time. In later years, 8-bit CPUs were commonly available in 40-pin packages, and Wikipedia's article on the DIP package suggests they got as large as 64 leads.

Can anyone provide a list of dates showing when these various sized packages were first manufactured/sold, to give an illustration of how the technology changed over time?

My bookshelf only goes as far back as 1976. At locations such as archive.org, bitsaver, et.al, so far I have Fairchild's 36-pin 9035 64-bit memory cell from 1969, Intel's 8080 40-pin microprocessor from 1974, and Motorola's 64-pin 68000 from 1979 as earliest examples of each pin count.

As to why I "need" these dates, apart from historical curiosity, I have an old (1970s?) prototyping system that only supports DIP chips up to 36 pin. In the microprocessor boom, 40-pin chips were everywhere, so it intrigues me that this one only goes up to 36.


texts: The inner workings of motors and generators

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Inductive components like motor winding resist sudden changes in current. That's because the magnetic field caused by the current needs time to build up or decrease. That means that when current is flowing and this is suddenly cut off, the winding will try to maintain that current, and becomes a power source generating a voltage to be able to do so. It gets its power from the built up magnetic field.
 At this point what happens to the magnetic field?


texts: motor driver on high resistance power source

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I need to drive a stepper motor powered by a low voltage (12V) source, connected by a thin and long cable (about 15m of 2x0.14mm^2). The voltage drops by about 2 volts, which is acceptable.

Now the motor operation gets extremely noisy.

The driver used is an Allegro A4988 in this case, which automatically limits the motor current. I think this may be the reason for the problem, as the high resistance power source forces the control to constantly change reacting on voltage variations introduced by the whole circuit powered. The constantly adapting control results in wildly meandering frequency and noise sounds. I just wonder why the control frequencies are so much louder than on a stable power supply, where the same meandering occurs, but much more silent.

I tried different capacitors up to 1000u in total, but it seems I would need tons of them to fully stabilise the input.

What could be the exact reason of the noise, and what to do about it?


texts: How does Impedance matching equation work out from original link?

texts:
From this link: L-Pad Impedance Matching Equation

How do you get those two equations? They do not look like a voltage divider formula, do they?

Questions repeated here:

First answer from Adil Malik:

Say
R1=475,R2=56.2,Rload=50,Rsource=500

You simply want from the source side:
R1+(R2∗Rload)/(R2+Rload)=Rsource

So lets try that:
475+(50∗56.5)/(50+56.5)=501.5

So this shows that it works.

But as you can see there are 2 unknowns, ie
R1
and
R2
. So you need atleast two equations. The one I did above was looking in from the source side. You can form a similar equation from the load side and solve simultaneously:

R2||(R1+Rsource)=Rload


texts: Why is the Gray code called a cyclic code?

texts: I understand why it is called reflexive and a unit distance code. I don't see any cyclic pattern which is repeating in the code. Why is it called a cyclic code?


texts: Equation of current in charging of capacitor

texts:
How can I find the equation of current in the following circuit, when switch is closed at t=0. Capacitor is initially not charged.

simulate this circuit – Schematic created using CircuitLab


texts: supposei have 12vac,after rectification my DC voltmeter measures around 15v. my question is why does 12v ac became 15v on the output?


texts:
Modern CPUs are very fast compared to all things external, including memory (RAM).

It is understandable, since CPU clock frequency has reached a point where it takes several clock ticks for an electric signal simply to run from from the CPU through the bus to RAM chips and back.

It also complicates life on many levels: multi-level cache hierarchies are built to deliver data closer to the CPU, which in turn require complex synchronization logic in the chip. Programs must be written in a cache-friendly way to avoid wait cycles while data is fetched.

Many of these problems could be avoided if a significant amount of RAM was located directly on the CPU chip. It doesn't have to an exclusive arrangement: maybe put 1-4 GB on the chip, depending on its class and allow additional memory installed separately.

I'm sure there are good reasons Intel, AMD and the like are not doing this. What are these reasons? Is it that there's no room to spare on the chip?


texts: How to detect and identify multiple points of contact

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I am looking for a way to detect & distinguish multiple points of contact from force or pressure.  I have asked a related question at the URL listed below:

How to encode a large number of digital input signals into a signal result

The answer provided in this was to create a D2A & determine the contact points by extracting it from the voltage level outputted.  I have found this solution to be a bit 'clunky' as I will then be passing the original single into my roughly made D2A, which will then be passed back into an A2D for processing.

I am looking for an alternative solution to this problem.  Any suggestions are appreciated


texts: Can I use Arduino nano's power straight for the micro motors or do I need to use drivers for a drone?

texts: I haven't tried using nano as the primary source for the micro motors as I'm still planning for project. If possible please suggest me any motor driver with less weight or if using any MOSFET would be more efficient ( voltage 3.7-3.3 V)


texts: Practical Considerations of a Butterworth Filter

texts:
I'm trying to design/implement a low-pass filter for the amateur 2M band (144-148 MHz).  To meet FCC regs, I need harmonics to be at least 40dB down, so I calculated a 7-stage Butterworth Filter with a 175MHz cutoff.  This gave me the following component values:

L1, L3 = 56.70371 nH
L2 = 90.94568 nH
C1, C4 = 8.094927 pF
C2, C3 = 32.77569 pF

There seems to be a lot of information on the theory of operation of these filters both on here and on other sites, but I can't find as much on the practical implementation and component selection aspects.  Given that, obviously, you can't buy components with those values, I'm picking "close" values, but I'm not sure to what extent that will affect the resulting filter.  I now have:

L1, L3 = 56 nH
L2 = 91 nH
C1, C4 = 8 pF
C2, C3 = 33 pF

Is there any way I can calculate/simulate what the curve for this filter will look like?  Mostly I just need to calculate it at 144-148 MHz, and 288-296 MHz (the 2nd order harmonic) to make sure I'm not attenuating my pass band and that I am attenuating the harmonics adequately.

Secondly, how can I determine the voltage and current ratings I need for the components?  The transmitter is a mere 1W, which should be about 10V peak, and 200mA (50 ohm characteristic impedance) but I'm not sure if that holds true of the individual components in the filter.

Finally, is there anything else I need to know in actually implementing one of these?  Specific types of capacitors to use or avoid (currently planning on SMD ceramics) and the same for the inductors?


texts: Is a 24V-48V 40A boost converter possible?

texts:
I would like to produce a buck/boost converter that can convert 24V to 48V with a 40A max. output current. It would be used to control a DC motor, specifically the MY1016Z3 DC motor.
I cannot use a 48V source directly because it is for a competition which requires that the battery voltage is 24V.
I have done some testing with the Texas Instruments power stage designer, and according to it, at 20Khz PWM, I would need at least a ~45 μH 100A inductor which I can get.
I would use a 4 switch buck boost converter so that I can decrease losses and also the output voltage.

I just want to check that such a converter is possible with a reasonably high efficiency.


texts: KVL loop current direction convention--should be same in all loops?

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Do we have to take the same sense of direction for loop current, like clockwise, in each loop when applying KVL to a circuit or can we take different directions in different loops?

If we must take the same direction always, please explain why.


texts:
My problem:
I can't configure DMA to working properly on Input Capture event. Data doesn't transfered and error occurs.

static void my_TIM2_initInputCaptureTimer(void) {

  // enable clock source for timer
  RCC->APB1LENR |= (0x1 << 0);
  // set prescaler to 200
  TIM2->PSC = 200 - 1;

  // choose TIM2_CH1 input
  TIM2->TISEL |= (0x0 << 0);
  // set channel 1 as input mapped on TI1
  TIM2->CCMR1 |= (0x1 << 0);
  // digital filter length (0)
  TIM2->CCMR1 |= (0x0 << 4);
  // rising & falling edge
  TIM2->CCER |= (0x1 << 1);
  TIM2->CCER |= (0x1 << 3);
  // prescaler to (0)
  TIM2->CCMR1 |= (0x0 << 2);
  // enable DMA interrupt & Capture/Compare interrupt
  TIM2->DIER |= (0x1 << 9) | (0x1 << 1);
  // capture enabled
  TIM2->CCER |= (0x1 << 0);
  // reset registers WARNING: need for preloading PSC
  TIM2->EGR |= (0x1 << 0);

  // enable TIM3 timer
  TIM2->CR1 |= TIM_CR1_CEN;
  // enable interrupt request
  NVIC_EnableIRQ(TIM2_IRQn);
  // set priority
  NVIC_SetPriority(TIM2_IRQn, 1);

}

DMA configuration:

static void my_DMA_init(void) {
  // enable DMA1 clocking
  RCC->AHB1ENR |= (0x1 << 0);
  // clear EN bit to 0
  DMA1_Stream0->CR &= ~(0x1 << 0);
  // safeguard EN bit reset
  while (DMA1_Stream0->CR & 0x1);
  // check LISR HISR registers
  if ((DMA1->HISR == 0) && (DMA1->LISR == 0))
    printf("status registers is clear\r\n");
  else
    printf("status register is not clear -- DMA wont start\r\n");
  // set peripheral addres
  DMA1_Stream0->PAR = TIM2_CCR1_Address;
  // set memory addres
  DMA1_Stream0->M0AR = (unsigned int)buffer;
  // set total number of data items
  DMA1_Stream0->NDTR = 10;

  // NOTE: configurate TIM2_CH1 interrupt route
  // set DMAMUX to route request (TIM2_CH1)
  DMAMUX1_Channel0->CCR |= 18U;

  // set DMA priority (very high)
  DMA1_Stream0->CR |= (0x3 << 16);
  // set memory data size (32)
  DMA1_Stream0->CR |= (0x2 << 13);
  // set peripheral data size (32)
  DMA1_Stream0->CR |= (0x2 << 11);
  // set memory addres increment  (enable)
  DMA1_Stream0->CR |= (0x1 << 10);
  // set peripheral addres increment (disable)
  DMA1_Stream0->CR |= (0x0 << 9);
  // set circular buffer mode (enable)
  DMA1_Stream0->CR |= (0x1 << 8);
  // set data transfer direction (peripheral to memory)
  DMA1_Stream0->CR |= (0x0 << 6);
  // set transfer complete interrupt
  DMA1_Stream0->CR |= (0x1 << 4);
  // set transfer error interrupt
  DMA1_Stream0->CR |= (0x1 << 2);
  // enable DMA1
  DMA1_Stream0->CR |= (0x1 << 0);
  // enable IRQ
  NVIC_EnableIRQ(DMA1_Stream0_IRQn);
  printf("DMA1_Stream0 %u \r\n", (DMA1_Stream0->CR & 0x1));
}

Interrupt routines:

void TIM2_IRQHandler(void) {

  InCapTick = TIM2->CCR1;
  // reset interrupt flag
  TIM2->SR = 0;

  tick = systick_ms;
  flag++;
}

void DMA1_Stream0_IRQHandler(void) {

  printf("within\r\n");
  printf("LISR: %u \r\n", DMA1->LISR);
  // clear interrupt flag
  DMA1->LIFCR |= (0x1 << 3) | (0x1 << 5);

}

Full compiled project (gcc-arm\make) for thoose who interested:
https://drive.google.com/open?id=1fwns5fKexGWJl64UDeYfDyFmSFA9BURZ

(stm32h743zi-nucleo board)
expected behaviour: (when you press user button (the blue one) ->PG0 pin get SET (1) state -> so input capture pin (PA5, they should be connected via jumper) get low-high transition and capture first value (output it via com-port) when you free button, input capture pin get high-low transition and capture another value(output it via com-port), but none of this events do not kick start DMA request.

Data will be outputted via com port with 115200 speed.


texts: Wiring an electret condenser microphone?

texts:
I'm trying to make a simple microphone circuit using this microphone:
http://www.cui.com/product/resource/cma-4544pf-w.pdf

I am connecting a 3V supply to a 2.2k Ohm resistor which then leads to terminal 1 of the microphone. I have terminal 2 of the microphone going to ground. I have terminal 1 of the microphone also connected to a 1uF DC blocking capacitor with the negative terminal of the capacitor being the terminal connected to the microphone.

I am then attempting to use a Tektronix DPO 4034 Oscilloscope to measure the output of the microphone by probing the positive side of the 1uF capacitor which has been left open.

When I do this, the oscilloscope is only showing the ambient static the probe is picking up. The signal on the oscilloscope does no change if the microphone has 3V power or not.

What can I do to be able to measure the output of the microphone?


texts: Only one attachInterrupt works at a time

texts:
I am using the MSP430f5529 launchpad and coding in Energia.

The goal is to make a program that can detect whether the onboard pushbutton is up or down (as part of an eventual Morse code decoder), which I planned to implement using two attachInterrupts.

If I use one, for example attachInterrupt(BUTTON, buttonPress, FALLING), it works fine and the button press is detected. If I use attachInterrupt(BUTTON, buttonRelease, RISING), the button release is detected.

However, if I have bothattachInterrupts in the same program, only one of them works; based on trial and error, it seems whichever interrupt was declared last takes precedence.

In the below code, for example, only buttonPress fires. If I swap the order of my attachInterrupts, only buttonRelease will fire.

#define BUTTON PUSH2

volatile int buttonDown = 987; // set to an arbitrary value so I can tell if the functions changed it at all

void setup() {
  Serial.begin(9600);
  Serial.println("Test code for buttons");

  // Enable internal pullup
  pinMode(BUTTON, INPUT_PULLUP);
  // attaching release before press
  attachInterrupt(BUTTON, buttonRelease, RISING);
  attachInterrupt(BUTTON, buttonPress, FALLING);
}

void loop() {
  Serial.print("buttonDown: ");
  Serial.println(buttonDown);
}

void buttonPress() {
  buttonDown = 1;
}

void buttonRelease() {
  buttonDown = 0;
}

How can I make both buttonRelease and buttonPress work at the correct times? I tried to just check if the button state changed using a single interrupt (that detected CHANGE, not just RISING or FALLING), but that seemed to lead to even more problems down the road, since the hardware would sometimes register a change in the middle of running the code needed to process what to do with that change.


texts: What determines the transmit frequency in this 555-based transmitter?

texts:
I'm a general class ham, and am just starting to do my own homebrewing. I was planning on basing a QRP transmitter off of this instructables project,  seeing as I have a veritable plethora of 555 ics in my shack toolbox.

The problem is, this transmitter is designed to operate a bit below the commerical AM band. How is the general operating frequency being set? I'd like to get it set around the 1.8 mhz band (160 meters).

Help is much help appreciated, as I'm going to use this to teach the other kids in the ham radio club at my school how to build basic transmitters. Picture of circuit:
http://www.instructables.com/image/FD38QHUGIKL42D3/Schematic.jpg">


texts: How does one charge a 37-volt lithium battery?

texts:
I have removed a 37-volt lithium ion battery from a self-balancing scooter for a robotics project. I retained the PCBs of the device for charging the battery. Unfortunately, the electronics appear to be as dead as the battery now is. However, my search for an external charging solution (short of buying a lower-voltage battery or a new set of hoverboard PCBs) has been unfruitful. Below are my searches and their results (or the lack thereof).

[Lithium Battery Charger]

Li-Po Chargers that max out at 22.2 volts.
AA/AAA battery chargers.
12-volt Lithium-Ion chargers.
Balancing Circuits.
Power Tool batteries and chargers.

[37 Volt Lithium Battery Charger]

Chargers of all sorts, but left out the decimal in "3.7" in the title.
Hoverboard, Scooter, and Bike chargers that must plug into an assembled unit (not the lone battery).
Balancing Circuits.
Individual 3.7-volt cells.

The battery is a "Smart Lithium Ion Battery Pack" Model KY01, 37VDC 4Ah, 148Wh. It only has an XT60 connector; no balancing cord.

What solutions exist for my charging of this battery without any of the (functioning) original electronics?


texts: What is the shortest range radar system?

texts:
I've been reading up a bunch on radar and most applications exploit the long range capabilities (rightfully so), but I'm wondering what is the smallest range a radar system can operate at?

I'm interested in synthetic aperture radar on small scales. Specifically, I would like to measure the ocean waves over a 5m radius (yes 5m, not 5km) and build a "depth map" showing the "instantaneous" wave heights and surface currents (maximum frequency is 10Hz). I know this is done from space satellites, so why can't it be done from a pier or drone?

I'm not a radar person, so excuse my ignorance, but doesn't the concept of radar scale? I would imagine you can build a miniature antenna array that scales to the range of interest? So if my range of interest is 0-100m (yes meters), couldn't the antenna be as simple as a wifi antenna?


texts:
Usually on the breadboard i power the microcontroller and then power all the other devices through the microcontroller.
Now i want to move my project to an enclosure, and i'm consedering to power all the devices directly from the power supply, is this possible / correct to do?


texts: Should dielectric constant be high or low for high-speed design? And why?

texts:
I'm very confused that dielectric constant should be selected high or low to design high-speed boards.
It can be compared with FR4 material, dc ~4,6.


texts: How do digital oscilloscopes achieve such high sample rates?

texts:
From the perspective of data capture, how is this achieved? If I wanted to implement a home-made digital device to capture high frequency analogue signals, what are my options? So far, I've only come up with some fairly useless ideas for designs!

Using a PIC microprocessor, the A/D sample rate on a 18f series I believe works out to be in the order of 1Mhz at 10 bit accuracy if I'm correct (?) And I can't imagine dedicated A/D chips being much better, how do modern scopes achieve frequencies in the GHz?


texts: Channel separation on a 3.5mm audio jack

texts:
I read an article regarding the removal of the 3.5mm audio jacks on phones.
It quoted this:

We chose to discontinue the 3.5 mm audio jack in our second-gen phones to create
a better quality audio experience for everyone to enjoy. With the 3.5 mm audio jack,
the stereo sound was compromised due to poor sound channel separation and the
sound quality was compromised due to a mismatch between phone and headphones.

    — Liang Jun

I could buy the argument of a mismatch between phones and headphones with impedance mismatch since it seems to vary quite a lot from one headphone to another one.

But I do not understand the issue with channel separation. Can someone explain it to me?


texts: ratiometric hall effect sensors outputs at high RPM

texts:
Im using an allegro A1308 linear ratiometric hall sensor to measure the rpm and angular position in a shaft rotating at 20K rpm. My magnet is a 2mm dia 1120 mT magnet placed at around 15mm from the shaft. The TEAG(total effective air gap) of the sensor and the magnet is 1.5 mm. I notice that the output voltage of the sensor falls dramatically as the RPM increases, and by 10000rpm falls to such a level its indistinguishable from the sensors no-flux output. Im trying to figure out why exactly this is -

is this because the magnet flux experienced by the sensor at such high speed is actually less,
or is this because the sensors output cant rise fast enough?

any thoughts will be welcome
thanks
harsha

Edit After Sunnysky and Andy s answers below :

3.If I used 2 latching hall effect sensors -the ones that go high when it sees a N pole and stay high till it sees a S pole, with two magnets 180 degrees apart and with opposite poles facing the sensors - would that work? The frequency then should be just double the rps and well within the sensors bandwidth. Thanks


texts: How can I Improve the quality of an amplifier?

texts:
I amplify using LM358 Op-amp and 2 resistors.

I played a song on my mobile. The output of the Mobile is the input of my circuit.

The output of my circuit is connected to 8 ohm speaker.

I hear unclear drums, Low volume and I can not hear the singer.

I tried to change the gain 101 , 50 , 10 and 2.2 but It gives almost the same result.

Is it possible to make the volume higher with not too bad quality?

What about using transistors ( common emitter for example ) is it better that LM358 ?


texts: Negative voltage from multi-tap transformer

texts:
If we have a multi-tap transformer like this:

Is it possible to use two of the taps to generate negative voltage and use other taps for positive voltage?


texts: Whats the difference between one terminal power source vs. two terminals power source in circuit simulators?

texts:
I found a step down voltage regulator circuit online and tried to simulate it and noticed that it runs when I use the one terminal power source and it doesn't run when I use the two terminal power source! Can anyone explain why is that!

Here is the circuit where it regulates 40 volts into 5 volts using one terminal power source:

Here is the same circuit using two terminal power source:


texts: How can I maximize the amount of energy an antenna is receiving?

texts:
Bear in mind that I am very new to electrical design and have only a beginners level circuit course under my belt.

I am trying to build an AM radio and although there are a lot of tutorials out there for this, none of them answer this specific question about designing a receiver. The best resource I have found so far is: http://www.antenna-theory.com/basics/gain.php, but it seems to be talking about sending (not receiving) signals.

I would like to know how I can make/modify a receiver so that I can maximize the amount of energy it will get from the carrier wave.

Is there a very good resource on making receivers that will explain the math and theory? Please point me in the right direction so I can gain some understanding and get through this project.


texts: How do I build the current regulator circuit referred to on the LM337 datasheet?

texts:
What I would like to accomplish: I am trying to add current regulators into a home built dual rail linear regulated power supply.  I previously asked this question about transformer fusing and received useful responses from the EE Community.  The supply is mostly complete now and I also added a current source using the following schematic off the LM317 datasheet:

I adjusted the resistor values though to ensure that the current source stays well below my max current (.35Amps on each secondary of the transformer).

I would like to also build a current regulator on the negative rail using either Figure 12 or Figure 15 from the LM337 datasheet:

Problem: I may not understand exactly what is going on with the LM337 schematics, but I cannot figure out how to connect this circuit up correctly, especially after the LM317 current regulator was straight forward.

Where do I place the load?  I think this is supposed to be a Current Source where the load goes between V-in and V--.  I appreciate any help you can provide in understanding how the LM337 current regulator configurations are supposed to work.


texts:
Is my interpretation of the circuit with N-Channel MOSFETs correct?

When IN = 1, MIDDLE = 0 and OUT = 1?
When IN = 0, MIDDLE = 1 and OUT = 0?


texts: The STM32L431 EXTCLK MCU pin 14 and 15 need to be conected or not

texts: Is there a way to make the internal MSI (RC) clock recalibrate itself (automatically in hardware) onto the LSE 32.786kHz clock input, effectively reaching the same precision as a sealed-external oscillator? the slow speed clock (LSE) cannot be fed into the PLL circuitry which provides e.g the 80Mhz core clock.


texts:
I have a 24 volt relay that starts a 220 volt pump motor for a sprinkler system.  The relay and pump are about 800 yards from the 24 volt signal generator.

I have had four relays go bad and fail.

I am thinking that a voltage spike gets into the line - but I do not know from where it occurs.

I would like to fuse the whole system so I can find where the voltage comes from.

Do you think 250 volt AC fuses are sufficient for the pump lines and automotive fuses are good for the signal?  Should I use fast or slow blow?  Will a Zener diode offer any additional help.

I am a mechanical engineer and know just enough to be dangerous.  I would really love to have someone design or even build this for me.  $$


texts: Safe voltage drop(due to line length) for laptops and router?

texts: Ahead of working from home this winter, we bought a 2000W inverter/generator to get us through a season that normally has a power outage, or a few.  Attaching this to a couple extension cords, if I have done my AWG/length calculations correctly, the furthest outlet in my setup should drop by 2-3 Volts (out of a standard ~120 AC) in addition to whatever (hopefully)minor variations come out of the inverter.  Mainly I want to make sure this is safe for the laptops/phones (claimed AC-adapter acceptable input voltage is 100-240 on all), but there will also be a router and mini-fridge, perhaps a cheap TV plugged in.  The amperage rating of the cords are well above these loads, I am mainly concerned about the sensitivity of the electronics.  I think this setup will be safe for them, but wanted to run it by those with more EE experience than me!  thanks!


texts: IR transmitter connected to phone audio jack

texts:
I took an IR LED transmitter, and soldered it to a mono audio jack (positive pin to the left channel, negative to mass). Now, the LED is quite small, and I'm pretty sure that the phone audio output voltage is enough to power it on.

If I connect a multimeter to the jack and put it on the diode check mode, the LED turns on (I can see it glow violet using a camera). However, if I connect the jack to my phone, turn the volume at 100% and play a WAV file, the LED doesn't light.

I have searched the internet, and found that some other people had my same idea, however most of them used a stereo jack and soldered the LED pins to the Right and Left channels of the jack connector, and left mass unused.

I don't understand why is that, and why my LED doesn't work. Did I miss something?


texts:
This question pertains to the N-channel MOSFET Fairchild FDBL0065N40.

While extracting the Rds(on) values from figures in the datasheet, I came across a discrepancy I can't explain away. Here's the \$I_D\$ vs \$V_{gs}\$ figure.

From eye-balling it, you can see the \$I_D\$ at \$V_{gs}=5V\$ is about 300A (at \$V_{DD}=5V\$). That results in a Rds(on) of:
$$Rds(on)=\frac{V_{DD}}{I_D}=\frac{5V}{300A}=16.67m\Omega$$

Next, this figure of Rds(on) vs \$V_{gs}\$:

Which shows an Rds(on) of about \$2.75m\Omega\$ at \$V_{gs}=5V\$.

To summarize, in the first chart, I calculate Rds(on) to be \$16.67m\Omega\$ and the second chart, I get \$2.75m\Omega\$ at the same \$V_{gs}\$. Can someone help me understand this apparent discrepancy?


texts: Why does the capacitor start to discharge from peak and not from V(input<0) in a peak detector?

texts:
My university asked to my do a report about a practice in the lab. One of questions  it asks to us to describe the  working of a peak detector, it's exactly like this:

The output is like this:

For me it's strange this output behavior, I expected that the capacitor would only start to discharge when the input was below zero. Can someone explain why this thing is happening?


texts: I am trying really hard to understand the way SR Latches and D Latches work.I've realised that in a SR Latch we got a current state let's say Q(t) and Q'(t) and we want to predict the next state let's say Q(t+1) and Q'(t+1) by changing the inputs R and S.My question is : Do Q(t) and Q'(t) work as inputs as well? I've studied the NAND and NOR implementations for SR Latches and the NAND implementation for D Latches.Any help would be appreciated.Thank you all in advance.


texts: Looking for Honda SPDIF connector information

texts: Does anybody know what this connector is and perhaps where to find one?  It's used on a 2016 Honda Civic carrying SPDIF.  It goes into a plastic connector.  It has a metal tube and pin that goes inside the tube so it's a male connector goes into a female connection on the radio.  The scale is in cm.


texts:
I've been researching power supply design techniques and information for the last few days and feel like I have a good understanding of how this is to work, but I can't seem to get my simulation to fruition.

The PS needs to have maximum of 5% error and .5% ripple. Current output isn't an issue, just something usable. SO basically the idea is I need something very smooth at 10V with basically no ripple. The other trick is that I can't use a solid state regulator, I have to design my own circuit.

So What I know is that I need a transformer to step down the ac voltage. Which then goes through a rectifier to convert to DC which steps down ~1.4 V if I use a full wave bridge rectifier (which I understand is the best for noise reduction)? Then I need a filter capacitor, which goes into a regulator circuit.

I have a design that simulates correctly on SPICE with a 12v rms transformer, but I don't actually have one. I think this would be cooler if I could use my 5V rms cell phone charger to get the 10V DC final result. Is this possible in a simple sense? This project is supposed to be fairly simple and I have most of the quirks figured out, I just can't produce the voltage I want with the 5v transformer.

BTW the regulator circuit I created is a shunt regulator just using a reference zener and some resistors to create feedback. I will post my circuit, any help is greatly appreciated!

Also the circuit is a complete rough draft which works for a 17v output from a transformer, but I would like to do it with a 7v if possible. Really Im just going for simplicity but need to meet specs.!


texts: Driving DC motor using a single MOSFET, why does the motor spin without applying a gate voltage?

texts:
The arduino drives the gate of the mosfet (irf540n) just fine (I've tested it with an led + 100 ohm resistor) and now I want to drive a small dc brushless motor. I've connected everything properly but it works not quite the way I want it to.

The drain and source are supposedly not connected if there is no gate voltage applied and thus the motor should not spin but it does spin (I've connecting it correctly, just the standard way that is found all over the internet).

When the gate voltage is made high by the arduino the motor spins a little faster.

My question is thus: why does the motor spin when there is no gate voltage applied?

Difference with the above schematic is:
- No diode
- Mosfet is irf540n
- Motor is driven by 9V

Other than that the configuration is the same (connected ground of arduino to the - side of the 9v battery, the - side of the battery is connected to the source and the + side of the battery is connected to one terminal of the dc motor while the other terminal of the dc motor is connected to the drain)

EDIT: I got it working when I tried it again (using another irf540n MOSFET). Diode in parallel with the dc motor is indeed a good thing. Placing a resistor as you guys said is also needed indeed so that the capacitance of the MOSFET is able to discharge I think. Btw drain & source mixing up isn't that big of a deal is it? Thanks everyone.


texts: While I understand how GPS receiver finds its distance from GPS satellites and exact position using trilateration, I still do not understand how is GPS system able to find the latitude and logitude coordinates(for example X:6274419 Y:650167)? How does this work?


texts: How to determine parasitic capacitance of a diode according to the datasheet?

texts:
In order to do simulation, I would like to determine the parasitic diode capacitance of a diode according to this datasheet, when the information is not present into the datasheet... (Simulation model does not always include the parasitic capacitance of the diodes and all diodes are not present or cannot be imported in LTspice (if LTspice is used)

Here is the datasheet of the following component. It is a power diode.

https://www.kynix.com/uploadfiles/pdf65976/STTA512B.pdf

Thank you very much


texts: Flashing LED circuit using Flyback Topology Flickering Problems

texts:
Background: Design an LED circuit that alternatively flashes 40W LED strings approximately 45 times per minute.

Approach: I began by getting my hands on Linear Technology's LT3799-1 - Offline Isolated Flyback LED Controller with Active PFC Demo Board DC1947A for initial testing. The circuit for that demo board great when lights are in steady state. The strings consist of 14 LEDs with a Vf~42V, being driven at 900mA, this I assume I good starting point for my project.

I prototyped a simple flashing circuit by adding two external BUK9616-75BN Channel FETs with the LEDs, the circuit below shows just one, but it would be the same for two strings:

The BUK9616 receives sufficient Vgs~10V from the function generator, therefore it operates in full saturation. The flashing circuit works well when not connected to the demo board.

Problem: When the flashing circuit is added to the demo board and I vary the duty cycle of the wave, just as I did without the demo board, as the LEDs transition from Off to On, there is a slight noticeable flicker. I suspect the issue may be in the 'Open Circuit Protection' of the board as I see a slight hiccup in the gate of Q1 on the demo board (10V), corresponding to the light flicker that looks like this:

I believe this suggests that the voltage divider formed by R3 and R4 have reached a voltage > 1.25 triggering an open circuit fault and essentially stopping all the switching in Q1, entering hiccup mode to clear the fault once a load is "detected", and this very same hiccup is causing the flicker.

I would like to essentially de-activate this open circuit protection, however, these boards are very expensive and I'd hate to damage one. Here are the possible approaches to solving this issue:

1) Remove R3: This "cuts" the feedback from the third winding and forces FB to be 0V, therefore FB will never reach 1.25V and Q1 will never stop switching.

2) Increase the value of C7: This capacitor also charges up to 1.25V when there is an open in the secondary, both the CT and FB pins must be at 1.25 for switching to stop.

3) Using a Triac dimmable LED driver, like the 3799, although I think the flickering associated with triacs in LED drivers is not the issue here. Could the PFC circuitry be causing this as well?

Suggestions/feedback on the three proposed approaches is highly appreciated!


texts:
I have a cheap wireless pool thermometer (AcuRite 617 1) and I'd like to intercept the temperature data at the receiver and use it with a computerized data-logging system.

Conveniently, inside the receiver is a small break-out board that is connected to the antenna and has digital "V", "G", "D", and "SH" pins:

Here is a segment of captured data from the "D" pin during a transmission (these happen once per minute). Before this segment, there is what appears to be much-higher-rate data, but I believe that might be noise -- this is the beginning of the 1.36kHz / 680Hz data.

I've googled a bit and can't find an encoding that looks quite like this, but if I were to guess what's going on, here's what I'm thinking:

the initial 4 cycles of 680 Hz are to synchronize the clocks but contain no data
the 13 cycles of 1.36 kHz (2x the initial rate) that follow appear to have one of two forms: they either drop low before the midpoint of the cycle or after it -- i'd assume one form is a logical one and the other is a zero.
after that, there appears to be a weird gap, but if you discount the part of the low that is part of the preceding "1", then the remaining gap is 735 µs, which is a (phase-correct!) continuation of the 680 Hz preamble.

Am I looking at this correctly? Is there a name for this encoding?

Some further notes on the break-out board:

the board is marked "RF211" and looks remarkably consistent with the MICRF211 "general purpose, 3V QwikRadio Receiver that operates at 433.92MHz"3
the MICRF211 data sheet has the following figure (with very little explanation), which looks tantalizingly like what i'm seeing except for the double-data-rate square wave as compared to my capture:

2016-02-14 Update: I've revisited this project and appear to be getting a clean 64-bit stream between a 4-cycle preamble and a 1-cycle "postamble", after which the display board shuts down the RF module by pulling ^SH low (top line):

According to Micrel's "33/66% PWM" scheme (which appears nowhere else on Google), that's

-_-_-_-_0000011110011000110000000000000000000000100011101000010010101010-_

So now I have to start manipulating the temperature to decode the bits. Here ("x") are the bits that seem to change without any apparent change in the display:

0000011110011000110000000000000000000000100011101000010010101010
------------------------------------------------x----xxxx----xxx

I assume these are either least-significant bits or battery-level (which is only shown as "Low" when it drops significantly).

2016-02-15 Update: I'm taking the show on the road to give the new "Reverse Engineering" stackexchange a crack at determining meaning: https://reverseengineering.stackexchange.com/questions/12048/what-is-contained-in-this-transmission-rf-pool-temperature-sensor-base-unit-re


texts:
Electronic newbie here.

I'm trying to use a TLP222A as a remote switch for a small signal (3V and about 150-200mA at most).

It's super simple, but I can't understand why the following happens:

I'm powering the TLP222A connecting pin 1 and pin 2 (anode and catode) directly to a power supply that provides 5V and 40mA, connecting and disconnecting the anode with a momentary switch.

First, I have tried to turn on and off a led connecting it to the same 5V and ground through the TLP222A and it works perfectly. The led turns on when I connect pin 2(anode) to 5V and it turns off when I disconnect it.

simulate this circuit – Schematic created using CircuitLab

(D1, D2, D3, M1 and M2 are part of the TLP222A)

Then, I have tried to connect two cables to pin 3 and pin 4 to check if I have conductivity when pin 1 and 2 are connected to the power supply. The tester never indicates conductivity.

I have also tried to connect the cables to the device that I want to control remotely and nothing happens.

simulate this circuit

Could someone help me to understand what is wrong in my approach?

Thanks


texts: Resetting 555 via Transistor (optionally driven by Touchplate/Piezo)

texts:
Right now I am using a 555 circuit to generate a 1kHz square oscillation (not displayed below). Generally the reset is pulled down, but through a button I drive a transistor to output the square oscillation when the button is pressed.

I now want to achieve two things:

Instead of activating the signal by setting the reset to Vdd, I want to deactivate the signal by pulling the reset down to ground, when pressing the button. I tried several things but none worked.
I noticed that when I touch the base of the transistor the 555 outputs something ( a strangely distorted 50Hz signal). So it seems to be possible to drive the transistor by a touch plate (plain metal (cu) plate) for example. How can I achieve that the transistor is driven by a Piezoelement or a touch plate?


texts:
I'm worried if someone charges my single-cell lipo with an Apple USB power supply that it'll get damaged.

Is there documentation on Apple's USB chargers?

I'm imagining I want to be able to support old apple chargers as well, so well-managed documentation on all the different ones out there and their versions would be nice (e.g. iPhone, iPad, other ones...).  Haven't found anything yet.  Is this just something people hack to find out and Apple never officially tells anyone what they do?


texts:
Another question I have asked made me ask this question.. The previous question was about fitting Linux into Cortex M3. A few well answers proved that it is not feasible. SOmebody suggested ucLinux. I have been researching uClinux as an alternative.

I have one critical question, the footprint of uClinux. I have looked around to find a breakdown of requirements, there is no nice info on the net. The modules under interest are:

Core kernel
TCPIP stack
Serial Driver
DHCP
WiFi Support (any of the stack from vendors is ok)

I am looking for RAM/Flash breakdown. I don't need a filesystem however there is a chance that I need it due to the driver model of Linux.

Bonus question:
- Porting drivers from Linux to uClinux. I know the memory architecture is different. Considering driver doesn't do anything special wrt memory, could I just recompile the driver and expect it to work under uClinux?


texts: Can the range of a monostatic RFID antenna be increased using an amplifier?

texts: How does an RFID reader monostatic antenna both transmit and receive at the same time, are they CW or pulsed? I would like to extend the read range of a reader by using an amplifier between the antenna and the reader. Is that a feasible way to increase the range?


texts: Acceptable imbalance at starting of a 3-phase motor (480V)

texts:
I've read several places that the maximum acceptable imbalance of a 3 phase motor is 10%, but that's of a currently running motor.  However, I have a 90kW motor that is tripping and to determine if it was phase imbalance I measured the peak currents on each phase.  I found 200A, 422A, and 438A for A,B, and C phases.  I was surprised to see such a dramatic differential.  We tried it several times and even confirmed it with another motor, so possibly it is typical.  Is this typical for a full volt 3 phase motor?  What would not be acceptable?

Thanks


texts: What component should I use to represent a solenoid valve in multisim

texts: I'm trying to model a 12V 500 mA pilot assisted solenoid valve in NI Multisim, but it doesn't have any solenoid components that I see. I thought I could just model it with an inductor or relay, but I don't know what component to use or what values to give it. It doesn't need to be exact, just something vaguely approximating the electrical characteristics of a solenoid.


texts: What does short to ground mean? How to do that?

texts:
I've just started a simple project using raspberrypi and a capacitive touch sensors breakout board. I had a few problems using I2C, but after some time of research I managed to get stuck on one only... On one of the forums I found an answer that solved the same issue for another user, so I'd like to try it out:

  Turns out I forgot to short the ADD to GND to set address 0x5a.

The thing is, I don't really know what that means... Am I just supposed to solder ADD to GND? There's GND already on this board (apart form ADD). Do I just connect them both to GND? What does shorting to ground actually mean?

Thanks a lot for your help and sorry for the trouble :)


texts: What does the GSM AT+CSQ command output signify?

texts:
So the command returns the received signal strength(RSSI) and bit error rate(BER). I see that the RSSI is obtained even if the SIM card is not inserted in the GSM module. So what does RSSI signify?

AT+CSQ

+CSQ: 25,6

OK

Also how can we check if the network signals are available or not, when the SIM card is inserted in the GSM module?


texts: Is AC relay "inrush" current caused by more than the mutual inductance effect?

texts:
My interest is in the "inrush" current of an AC relay. I took apart a 24VAC one. It's energized current was about 40mA but when I removed the plate that is pulled by the electromagnet, the current doubled (roughly). This leads me to believe that part of the inrush is at least due to fact that the plate has not been pulled into the closed position.
I'm curious as to why less current flows through the coil after the plate is pulled against the electromagnet.


texts: How to go from specs/requirements to design, architecture, code, tests, documentation for embedded systems?

texts:
How do professional embedded systems engineers design, architect, code, test, document systems?

Any good examples, libraries, resources that showcase the process of going from specs/requirements to system design, diagrams, architecture, coding, testing, documentation?

For RTOS versus no operating system code? So we can see the difference and thought process?

Ideally it would showcase things like: a hardware abstraction layer, modularity, classes, different types of tests - from mock tests, whitebox, blackbox, integration tests, security tests and so on?

And perhaps can be compiled, tested on a computer before porting over to the end platform (ESP32 or STM or Arduino .etc.)

Any examples for safety critical systems, medical devices? Versus less critical systems so we can see the difference in rigour or tests?

I'm trying to improve and got sick of hacking things together and not understanding how to properly engineer reliable embedded systems...

Thanks for helping a junior embedded systems engineer!


texts: Is it OK that I solder inside my bedroom?

texts:
I'm a hobbyist solderer using tin lead solder to occasionally repair broken electronics. As I don't solder all day every day, I use my normal writing desk in my bedroom, which stands next to my bed, for soldering, cleaning it afterwards with soap and water to remove flux residue, etc. As solder pops and splashes, there may be some little solder leftovers lying around in the room.

Is this safe?


texts:
Is there a maximum length for USB 3.0 cable? I couldn't find anything in USB 3.0 specification document.

Also, how do you check for errors while doing USB SS data transfer?


texts: Why would you need both a pullup resistor and a capacitor to ground on an IO pin?

texts:
I was looking at a board schematic and noticed something odd. All the IO pins are identical in function. But for some reason, there is one IO pin that has both a pull up resistor and a capacitor to ground connected to it (while all the others have nothing). Why is this?

(The IO pins come from a CycloneII EP2C5 FPGA if that's relevant info. I've looked at the pin out documentation for the chip but there's nothing particularly special about this pin. The FPGA is mounted on a bare bones general purpose development board, and as such has no specific intended function. And all the circuitry on the board is just supporting circuitry like power.)


texts:
I am trying to make a 27 MHz carrier wave transmitter from a crystal oscillator and a secondary amplifier. Thi is the complete circuit:

simulate this circuit – Schematic created using CircuitLab

The first part, left of C6 is a colpitts crystal oscillator. And on the right side of C6 is the common emitter amplifier. Colpitts crystal oscillator that I've built can be found here.

Q1 and Q2 datasheets can be found here.

The problem is the following. If I have CE amplifier disconnected, and measure the voltage with oscilloscope at O1, I get expected 150 mV peak-to-peak. But as soon as I connect the CE amplifier and measure the voltage at O2, I get around 300 mV peak-to-peak (note that antenna at this time is not connected), which is far less than I was expecting.

Values choosen for colpitts oscillator are the same as on that website I posted a link to. For the CE amplifier I calculated the values my self, here's how I did it:

\$\beta=100\$
I chose: \$I_C=I_E=1mA\$
I chose: \$V_E=1V\$, so \$V_B=1.7V\$
\$R_6=\dfrac{1V}{1mA}=1k\Omega\$
\$I_B=\dfrac{Ic}{\beta}=10uA\$, \$I_{R5}=100uA\$, \$I_{R4} = 110uA\$
\$R_5=\dfrac{1.7V}{100uA}=18k\Omega\$, \$R_4=\dfrac{9V-1.7V}{110uA}=66k\Omega\$
\$R_7=\dfrac{9V-4.5V}{1mA}=4.7k\Omega\$
For \$C_4\$ I read somewhere: \$X_{C4}<=\dfrac{1}{10}\times R_6\$, and I get \$C_4 >= 60pF\$

C5 and C6 were chosen arbitrarily, If someone could tell me how to precisely calculate their values I'd really appreciate it.

So shouldn't the gain of the amplifier be:\$r_e=\dfrac{25mV}{I_C}\$ \$A_v=\dfrac{-R_C}{r_e}=-188\$?, while I'am getting gain of only 2.

What could be the problem? I read somewhere that impedence missmatch can affect the power of the signal transmitted, could this be the case here, since the output impedence of colpitts oscillator is relatively low, while the input impedence of the CE amplifier is relatively high?

Any help is greately appreciated!

EDIT:

I know I havent explicitly stated, but I would really appreciate it, if one could also suggest a solution to this problem.

EDIT2:

What if I were to use BS270 MOSFET in common gate mode instead of 2N3904, would the gain increse? I've read somewhere that MOSFETs are faster and seen them used in HF applications. Because I have them at hand and can't buy any components at the moment.


texts: Formula of snubber capacitor capacitance for SCR dv/dt protection

texts:
I have a formula here for finding the suitable value of shunt capacitance to be put on an SCR snubber.

\$C=\frac{1}{2L}(\frac{0.546V}{dv/dt})^2\$

where L is the snubber inductor, V is the DC supply voltage and \$dv/dt\$ the maximum allowable surge voltage. My question is about the derivation of the said equation\$-\$if it is a correct one. The formula looks bizarre to me when considering the equation for getting the right inductor, \$V = L\frac{di}{dt}\$, which is more straightforward. Moreover, I'm puzzled why choosing the capacitor value would depend on the series snubber inductor.


texts: Why is there a need to use a transistor or an op amp in a sensor?

texts: I am trying to design a proximity sensor that works only in the dark using LDR and IR transmitter and receiver. I have looked at some circuits (this tutorial and this video) and some people have used MOSFET or om-amps in their circuit, is there a voltage signal that has to be amplified? I am still confused why do we need them? Why can't one just make a circuit with few resistors and a potentiometer that will control the sensitivity of the circuit?


texts: Why cannot I edit MOSFETs in LTspice by "nmos"

texts:
update: I edited question so that it will be mainly related to LTspice

OK, now I have used irfz44n for an example model, I realized that, by using the directive above(nmos), I am not able to modify Vto value. However if I use the second one(vdmos), I can control the Vto value. But while choosing the mosfet from component selector, I get it from "nmos" option. I wonder why this is the situation? Should I use vdmos instead of nmos all the time?


texts: Non-zero primary current under open-circuit test

texts: Ideally the primary current should be zero under the open-circuit test. Could someone explain to me what are the physical effects corresponding to the two equivalent-circuit parameters that cause the primary current to be non-zero when the secondary winding is open-circuited? I was told that it isn't due to loss in the copper windings!!


texts: I am new to FPGA use. While I can find considerable information on programming them, I would like to know how FPGA manufacturers decided what elements to include? I.e., how is the internal design of the FPGA determined?


texts: What's the idea behind this, assuming it is ideal?

texts:
The circuit is a biased push-pull. The diodes keep the input signal above and below the input signal so it is always conducting. The problem is that I don't see why one of the two transistors would not conduct in a semicycle.

If the input is \$5.3V\$ then above D1 the voltage is \$5.9V\$. The output after the drop is then \$5.3V\$. On the other side, below D2 the voltage is  \$4.7V\$, which is below the output voltage, making the php transistor Q2 conduct. I know I'm missing something, but I don't know where. In the book (The Art of Electronics) it says that in the positive swing Q2 shouldn't conduct, but I can't figure out why.

simulate this circuit – Schematic created using CircuitLab


texts:
I am designing a PCB based around the STM32H7 MCU, which is a LQFP144 package. I'm designing in Altium and was using the Altium vault to find components.

I noticed my specific MCU isn't on there, but other variations e.g. STM32F7 with a package size LQFP144 are.

Just starting out in PCB design, I'm looking for some advice.

Is it more common for me to just choose the other variation on Altium vault and then adjust the pinout and design my own schematic symbol considering the package type is the same, or is it more common to start designing a footprint from scratch?

I appreciate any advice or tips!


texts: Two multiplexed 7-segment displays flickering

texts:
I'm working on a temperature sensor.
I've got:

LM35 (Sensor)
LM741 (Op-amp to amplify LM35 Vout to 5V)
PIC 14F458

The temperature is shown on two 7-segment displays with only one BCD converter (4511). Therefore I multiplexed these two displays.

The problem is that my 7-segment displays are flickering a lot and I don't know why.

If you want to see the simulation on Proteus: LM35 - SSD

Here's the schematic diagram on Proteus :

And here's the C code on CCS.

#include <sonde2.h>
#include <math.h>

#define CONV_CST 0.48875855327
#define TRESHOLD 25
#define TENS_DISPLAY PIN_E0
#define UNITY_DISPLAY PIN_E1
#define GREEN_LED PIN_C0
#define RED_LED PIN_C1

int simpleBCDConverter(value) {
   // Shift tens from 4 bits to the left
   // So we have ([Tens] [Unity]) XXXX XXXX
   return ((value / 10 % 10 << 4) + value % 10);
}

/**
 * Convert a number of 10 bits to its BCD equivalent
 */
void bitsToBCD(int value) {
   int tens = value / 10 % 10;
   int unity = value % 10;

   output_high(TENS_DISPLAY);
   output_d(tens);
   output_low(UNITY_DISPLAY);
   delay_ms(10);

   output_high(UNITY_DISPLAY);
   output_d(unity);
   output_low(TENS_DISPLAY);
   delay_ms(10);

}

/**
 * Check temp level, and switch on the right led
 */
void checkLed(int temp) {
   // If temps is greater than treshold
   // Blinking Red LED with 555 (astable)
   if (temp > TRESHOLD) {
      output_low(GREEN_LED);
      output_high(RED_LED);
   } else { // Otherwise, green LED
      output_high(GREEN_LED);
   }
}

void main()
{
   setup_adc_ports(AN0);
   set_adc_channel(0); // A0 connecté à l'entrée analogique
   setup_adc(ADC_CLOCK_INTERNAL);
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1|RTCC_8_BIT); // 51,2 us overflow
   setup_timer_1(T1_INTERNAL|T1_DIV_BY_1); //13,1 ms overflow

   setup_low_volt_detect(FALSE);

   int temperature;

   while(TRUE) {
      //delay_ms(10);
      // Read the value from A/N converter (10bits [0 => 1023])
      // And convert it to a range from 0 to 100 (°C)
      // 0.48 => (5 / 1023) * 100
      temperature = read_adc() * CONV_CST;

      // Check temp level
      checkLed(temperature);

      // Convert bits to BCD
      // And show temp on 7 segment displays
      bitsToBCD(temperature);
   }

}

Thanks.


texts: What is the DC behavior of the switched BJT emitter follower configuration

texts:
There is a circuit shown below where we have a sub-circuit I marked in red.
I know that it is a source follower with the AC behavior shown below.
As you can see the circuit has DC voltage input only.
What is the DC behavior of the part I marked with the red arrow?


texts: My multimeter probes are too big to measure a laptop battery

texts:
I'm having laptop battery problems, and the hardware manual gave diagnostic instructions involving measuring the voltage in the battery. So I bought a multimeter (never used one before in my life) and had a go... but the probes are too big. The pins on the battery are tucked into little slots that the probes can't fit into.

What should I do to measure the voltage?


texts: Comparator circuit undesirable fluctuations

texts:
I have designed a comparator with hysteresis and rail to rail operation and my output depicted in figure1.The inputs of the comparator is a sine wave signal and a triangular waveform as shown below.Vdd is 1.2V and the transistor technology is 65nm.I am little confused about the reason for the small undesirable fluctuations as shown with the red arrow in figure 1. Which is the reason of these fluctuations? How I can improve my output PWM signal to look like the figure2.

Also in figure 3,4,5 depicted the comparator circuit with the hysteresis. The input of the left transistor is the sine waveform which shown in figure 1.It's the output of the rail to rail circuit as shown in figure 6. DC analysis is shown in figure8,9,10,11,12.

Furthermore in figure 7 depicted the output sine waveform of the rail to rail circuit with small also fluctuations when I connect the rail to rail amplifier with the hysteresis circuit. Why its appear?

Thanks in advance!

figure 1

figure 2

figure 3

figure 4

figure 5

figure 6

figure 7

figure 8

figure 9

figure 10

figure 11

figure 12


texts: Altium - design rule check does not match with signal integrity for impedance

texts:
I have designed a 2-layer PCB with Altium Designer. I placed an impedance rule of 50 Ohm in trace width rule section. When I run the design rule check, there is no impedance error.

However, when I run signal integrity and calculate impedance, the values around 250 Ohm is displayed.

Does anybody know the problem and its solution?

Please consider the screen shots of the Altium Designer:


texts: How to set Rin & Rfb to optimize input impedance / Johnson noise of an opamp circuit?

texts:
This question follows great answers I got for my previous question about GBW. It teaches me I should use two stages in my microphone preamp project. This leads me to this question:

Considering the following sketch:

How do I choose the type (inverting or not) of opamp and resistor values to get 15dB & low noise without affecting input impedance of 2nd stage. Formulas (like Rfb/Rin) works with 43K/7K5 or 4K3/750R.

I understand that the lower the resistors, the lower the Johnson noise, but what is the ballpark? Does it affect impedance?

Thanks to you, knowledgeable people!

Please note that  I don't care about phase revert since I can wire my input backwards.


texts: Looking for a device to "pass through" or "make high impedance" 8 bits based on one control bit

texts:
I need a thing (preferably a single IC) that has 8-bit input, 8-bit output and a control bit, with this behaviour:

If the control bit is active, set output bits to the inputs (no need to actually conduct through, as long as they have the correct (0-5 V TTL compatible) signals.
If the control bit is inactive, set output pins to high impedance so they don't interfere with other stuff.

So essentially a "bus output enable/disable gate".

I don't seem to find any; maybe I'm searching for the wrong keywords.
Anyone have an idea?


texts:
I have two Arduino UNO, two Xbee shield, and two Twi Xbee (type XB24).

I am very new to xBee and my question is: Can I communicate each other via Wi-Fi ?


texts: Matching transistors for discrete opamp (audio use)

texts:
I am building some GAR2520 discrete opamps that require a matched pair of BC550(CTA) NPN transistors. I built a simple emitter follower with a 15V supply, biased at about half that. I input a 1khz sine wave from a signal generator at 500mv amplitude. I measured the average DC voltage, and AC amplitude across the emitter resistor, in hopes to grade them for matching. I have made a plot of AC voltage and a scaled-for-convenience DC voltage per transistor:

How important is it to consider both the DC and AC response of the transistor when matching for use in a circuit where "hfe-matched" components are specified? I can provide more information on the test circuit if needed. The discrete opamp is going to be used in a microphone preamp, where I obviously don't need DC capability, but I am still not sure in what way to weigh these parameters in the quest for matched transistors. Thank you.

Edit: Since it has been brought to my attention that I should not see gain from an emitter follower (duh), I realize that there was in fact no gain, the reality being that a 1000mV Peak to Peak input resulted in an emitter follower output of ~840mV Peak to Peak, depending on the transistor of course. Obviously the transistors still performed to varying degrees, but this was not the best circuit to check such a specification. I think I will build what was suggested by @Dave Tweed, and plot those results. Thanks for the input so far everyone.

Here is the ill-fated transistor testing schematic:

Multisim doesn't have a BC550 model, and from a very cursory look at the spec sheet it seems the BC547 is a good approximation. In the simulator of course the output is just barely lower than the input, as expected for the topology in the ideal case. It should be noted that the wave generator and the oscilloscope are both from an Analog Discovery USB unit.


texts:
I'm working on a project that uses light as a medium for data transmission. I would like to achieve about 2-3 MB/s. It suppose to virtually behave like any LAN cable. I would want to know if it is suitable to build a device around a microcontroller like Arduino? I have been searching around the stack and found about how 32-bit ARM processor is favored over 8-bit Arduino in WiFi technology (here). I am not sure if this applies to light communication too.

By the way, I have experimented with FTDI microcontroller before, and it cannot achieve above 200 KHz without generating a lot of errors. I tried to connect a loopback (output directly to input), and found out that there are still reading errors at 300 KHz. Therefore, I assume that microcontroller is not suitable for this experiment. Thus, what would be the suitable hardware for this experiment?


texts:
Emergency lighting solution

Continuing from the previous post above. Firstly I know how to calculate current in a DC situation.

However, since I am using an inverter that produces 220V at its output I would like some assistance in calculating the current consumption of a 30W LED and NOT a 50W LED. The specs given from the box for the 30W LED is 30W LED website:

Supply voltage: 200-240AC
Power: 30W
CRI: RA>70.PF>0.9

Is it possible to determine the current consumption of the 30W LED from the specs given above?

Is the current consumption of 151mA correct, assuming a supply voltage of 220V AC? Using the following site of rapid tables

If it is correct then using a 18A-h is an overkill and since I will be running the light for only 2 hours(duration of the black out) a 3.5A-h will therefore suffice. Is this assumption correct?

The smallest SLA battery is 3.5A-h battery in my region.


texts:
why voltage fluctuation happen in houses when we connect heavy load ?
since all the houses are in parallel,so all of them recieve same voltage..then why voltage fluctuation is there? and why not current fluctuation?
why voltage stabilizers are used not current stabilizers ??

I mean it is the Property of parallel connection that it doesn't matter how many load you add in parallel, all of the load share same voltage


texts: The Deutsche 9 pin(gree,type2) connector in heavy-duty vehicles outputs the following protocols. Connector pin C,D is used for J1939@500kbps, pin F,G is used for J1939@250kbps and H,J is used for CANH&CANL. Since J1939 is a higher layer CAN protocol, does it mean that all these pins are connected to a single BUS?


texts: Static noise when electric guitar plugged into amp

texts:
I have an Epiphone Wilshire that is producing a "static" sounding noise when plugged into an amp. I removed the cover plate and found a loose, black wire (ground?). It looks like the wire is connected to the back of one of the tone knobs.

I suspect a grounding issue, but I'm not familiar enough with guitar wiring to know where this wire should connect.

https://imgur.com/a/TQsQo6M


texts: Calculating the smoothing capacitor for a power supply

texts:
Trying to build a simple 9V power supply using a 7809 voltage regulator and full wave rectifier. The load current from the regulator is 1A. So I = C*dv/dt, therefore,

C = I*t/(delta V)

To my understanding t is the time between the two peaks or the time the capacitor supplies the load. So if t is reduced, shouldn't the ripple increase ?, so isn't ripple (delta V) dependent on t ?, if so then why is delta V just arbitrarily chosen without considering t ?


texts: getting noise when connecting speaker out of sim800l to raspberry pi

texts:
i was trying to make a roaming device which helps me route my calls through internet, to save my bills while on international roaming.

my setup goes like this:

gsm module sim800l, raspberry pi4, a usb audio adapter Quantum-QHM623 and an android app to get calls redirected.

basically this setup routes all my calls from my simcard to my phone app via the internet

the project is almost complete but the only issue i am facing is, the speaker of sim800l when connected to mic of usb audio adapter, i get a whole lot of background noise,
these are the trouble shooting steps i followed which might help you assess the situation.
1) i can hear the voice with a lot of interference only when i connect speaker +ve from 800l to the +ve of mic in the usb adapters +ve side. if i connect -ve of speaker out to the mic ground of audio adapter, all i hear is noise alone, no voice.

the other audio line which is mic  from 800l < ---- > to speaker of the usb adapter works absolutely fine,

I tested the modules this way and they seem to work fine
audio usb adapter:
to see if the audio adapter is working, i tested shorting out the mic and speaker and simulated a call from the android app, and it worked fine(i was able to hear own voice after i speak some thing, and the voice quality is too good)

sim800l:
ATcommands work fine, was able to send and receive messages, able to call receive calls and hang them up using minicom

audio lines of sim800l:
i shorted the mic and speaker lines and made a voice call to my mobile number, and i was able hear my voice fine but the quality is ok.

any help with this noise issue is very much appreciated.

EDIT: I can work around this issue using a different power supply. I had previously used the same raspberry pi to power the sim module, but now I have used a different power supply to power the sim800l module, and now it's working quite well.

Is there any solution to use the same power supply and not get the noise?


texts: Is it possible to use multi gigabyte DRAM modules with a microcontroller?

texts: I have two leftover 2GB RAM modules that I removed from my MacBook Pro when doing an upgrade. I was just wondering if these were usable with, for example, an Arduino. I'd be too much of a beginner to actually try to do this now anyway, but I'm curious if it is at all possible, or if that's just way too much memory for a microcontroller to address.


texts: How to determine if a button would work with Arduino?

texts:
I want to get a push button that looks cooler than the one that came with my Arduino Starter kit, but I'm not sure if any kind of buttons will just work. The button came with the Starter Kit looks like this:

I went to a local electronics store and they had different kind of buttons. Many of them are way larger than the one that came with the Starter Kit.  The button that came with the Starter Kit has 4 leg pins, but I usually use only 2 of them. The buttons I see in the store have a variety of number of pins. Some buttons have 2 pins, some have 4 and some have more than 4. Some buttons are huge and I'm worried that they are not compatible.

I'm new to electronics. How do I determine if a button would work with Arduino? Would something like this one work?

Is there anything I have add or take note of for these buttons to work?


texts:
In the question above I was asked to solve the general shape of Vout, and the exact values in t=0.5ms,1ms.

My question is - can I approximate a constant virtual ground in the negative input of the opamp?

From the one hand, it's an ideal opamp with negative feedback
But from the other hand, there's finite supply voltages, so it's not that simple to use the infinite gain argument (the relation Vout=A(V+ - V-) is no longer valid outside the linear regime of the opamp)

*Except the finite supply voltages, the opamp is ideal


texts: Static in earphones when scrolling with mouse

texts: Why do I sometimes hear faint static in my headphones when I scroll with my mouse? I have noticed this on multiple(4) computers, with Windows 7 and 8. Does anybody else notice this? It happens when I have programs running that make noise, and when there are no programs running that generate sound, such as browsing a web page. Does anybody have an idea where this comes from? It doesn't bother me, because its so faint, but I am very curious.  I'm guessing that it is a hardware issue of some kind.


texts: 12V battery choices (powered LEDs and piezo buzzer)

texts:
I need to power two 12 V LED lights (1W - forward current @ 0.083 A) and a small piezo buzzer all in parallel (unsure about the current, tried to measure it with multimeter, but get nothing...).

Originally, I tried to build the battery with eight 1.5V AA cells, but it turns out to be too big for my use. I'm looking for another compact, lightweight battery to power the circuit and two possibilities come to mind:

One cell 12 V A23 Energizer
Stack of four Coin Lithium 3V Batteries, 2025

They have pretty much the same size and price. Which one would be able to power my circuit the longest, and for how long? I didn't get much from the datasheet.


texts: UART adapter to... what is this connector's name?

texts: Any idea of what the connector from the right is named?


texts: LDO 3.3V Overheats on DC input and no load

texts:
XC6206P332MR 662K 3.3V 200mA TOREX LDO Voltage Regulator SMD SOT-23

The capacitors on Vin and Vout are not too close, maybe 1cm away from the pins,
I've tried anything from 0.1uF to 22uf, Im powering the LDO from a 4.2 Lipo,
It's the second LDO from a second supplier I'm trying.

Considering my input is DC, I'm a little confused why it's overheating. It appears to be drawing 200ma.
Behaves the same with no load or if I connect a 1k resistor for some load.

I haven't tried an oscilloscope yet though to see if there's some instability.
It is my first SMD circuit, I've used non SMT 3.3v regulators before without any issues.

Ordered and soldered two new 1uf ceramic capacitors as advised, did not change the outcome however. my caps could definitely be placed a lot better.


texts: What is the difference between PAM and PCM?

texts:
What is the difference between Pulse Amplitude Modulation (PAM) and Pulse Code Modulation (PCM)?

Both seem to be effectively sampling an Continuous Time (CT) analogue wave and converting to a Discreet Time (DT) wave.

Images & animations would be super helpful!

Related question: link.


texts: What does it mean for amplifiers to be stable only down to N gain, where N > unity?

texts:
This is related to

What's special about "unity-gain stable"?

which is about unity gain stability.

But what exactly does it mean if some op-amp is said to be only stable to, say, gain 3 rather than all the way down to unity gain?

Guesses:

Does this gain 3 refer to open-loop gain? (The amplifier has an adequate phase margin at the upper frequency where open-loop gain is 3, but not beyond?)

Or does it refer to closed-loop gain? (The amplifier will be stable up to its unity open-loop gain frequency, if the closed-loop gain is not less than 3?)


texts: AT89C2051 IC crystal and crystal oscillator connection

texts:
I am referring schematic for AT89C2051 IC and 4 AT89C2051 IC's are used for motor application as shown.

(Pls note there are total 3 IC's where XTAL2 pin of first IC is assigned to XTAL1 of other 3)

Now, I want to replace crystal with crystal oscillator, IC datasheet suggests following configuration as per datasheet's page no. 4

So, I am thinking to add below configuration in design.

Is it correct approach  OR I need to do some changes, if so please someone help.

Thank you in advance.


texts:
I have read from some book that: "The voltage quantity symbol V sometimes has subscripts to designate the two points to which the voltage corresponds. If the letter a designates one point and b the other, and if W joules of work are required to move Q coulombs from point b to a then, \$V_{ab}=\frac{W}{Q}\$. Note that the first subscript is the point to which the charge is moved"

While Wikipedia (http://en.wikipedia.org/wiki/Double_subscript_notation) says: "\$V_{CB}\$ means the "\$V\$" from \$C\$ to \$B\$."

Can you help me with the true meaning of the first subscript?


texts: I recently bought a nice RGB Led Controller with a very nice design and i want to know what technology is used for recognising the touches on this thick plastic layer. It works absolutely reliable and is very sensitive. I wanted to integrate exactly something like that in my arduino project. Anyone an idea which companies are making such capacitive touch panels and do i need some kind of controller? (Note: i am very new to electronics)


texts: Why do most Arduino boards need a USB - serial adapter?

texts:
I know that some Arduinos have built-in USB functionality which means they can act as USB devices as well as being programmed directly.

I also know that most Arduinos use an additional microcontroller to convert USB to serial.

Why is this needed?

Is this a limitation of the microcontroller that does not support USB?

Can some only be programmed using serial?

I am particularly interested in the difference between the Arduino UNO which uses an additional microcontroller (ATMega16U2) for USB conversion and Arduino Leonardo which does not have some middle layer controller.


texts: How can I use a build server with Keil uVision4 (MDK-ARM), script a build, use a makefile?

texts:
I would like run daily builds, or check-in/commit triggered builds of Keil MDK-ARM based projects. So far I've gotten things going with the batch file feature of the IDE. This does require you to build the project at least once with the IDE, then check-in the batch file and associated .__i and ._ia files created by the IDE.

Additionally, the IDE puts lots of user specific things into the batch file like the Windows PATH variable. This could become a problem with multiple developers, because the batch file for building could be changed at each commit from a different developer.

Ultimately, one just needs to keep track of the various switches for armcc, armasm, and ArmLink.

Is there a way to use a more standard makefile to build Keil uVision projects?  Is there a method of translating a uVision project file into a more maintainable build script?


texts: Precisely drawing component footprints in EAGLE

texts:
Whats the recommended way for placing components accurately and quickly when creating EAGLE parts?

For example in the drawing below, using grids with 0.01 grids will give us the control needed for components with separation such as 10.16 but scrolling 1000 0.01 grid spaces is quite tedious.

Source: http://www.mouser.com/ds/2/400/cc-e-524996.pdf


texts: Why can I put an electrolytic capacitor on AC?

texts:
I have seen here and there schematics with electrolytic capacitors put on AC. And this sounds weird to me.

Electrolytic capacitors have a polarity, right? If we invert the polarities on DC, bad things happen. As far as I understand, AC inverts polarity every now and then (commonly 50Hz). Why can we put such capacitors on AC without damaging them?

Example:

from demonstration here: http://youtu.be/qdXbnhb1bVo?t=5m57s


texts: Ways to lay this cyrstal out without increasing the PCB footprint?

texts:
I am trying to follow the best practises in laying out a crystal.
Namely:
1. Keep traces short and direct
2. Keep it as close to the pins
3. Keep-out region under the crystal
4. No vias
5. Isolate the crystal

However I cannot fit my bypass caps near the pins.
Before I change the footprint of the PCB to accommodate the requirement, is there anything I can do to make my current design work?

[update]

The MCU is ATMEGA34U4. Crystals is this

Matching capacitors are 18pF (as per the datasheet in the link).

[Update #2]
The following is what I came up with. Thank you all for your eyes on this!


texts:
What's the purpose of the BJT pair on the output of this regulator?  Note: +VD is used to power several IC's.
It almost looks like a way to power +VD from two separate sources.  If so, I guess I'm not clear on what happens with the BJT's when both sources are applied.


texts: connector recommendations for CAN bus and power supply to distributed PLCs

texts:
I'm looking to build a distributed PLC system with up to 20 devices spread throughout a building, controlling lights, HVAC, irrigation, security, etc, and want recommendations on what connector to use for CAN and DC power.

The power (24VDC, 1W/device max, 50mW/device typical) and CAN will go in the same cable.  While M12 connectors seem to be "common" for CAN, they're not very easy or cheap to buy.

RJ-45 looks like the all-around cheapest option and the quickest to terminate cables, but I'm concerned about reliability and power handling with 20-40 plug/socket pairs in series, before you even consider copper loss and unclean/non-office environmentals like heavy dust and insects.  I could use two pairs for power to improve matters but it's still marginal.

I could use Molex or Camden style power connectors but they have other issues, like the time taken to terminate cables and increased likelihood of transposed conductors.

What standard connector, perhaps commonly used for building management and/or industrial automation, am I missing?  I don't need 1Mbps; 100-200kbps should be plenty so impedance control isn't real important.

Background: I would like to avoid a star topology and the central switch or controller that it implies.  Running one CAN cable adjacent with the power distribution cables also reduces the installation cost dramatically, especially for retrofits.

Edit: does anyone know what is used in vehicles?  They'd have to be plentiful and reliable.


texts: Automating music box with electric motor

texts:
I recently purchased a DIY music box kit from a website which I will not link to here. If you watch this video you can see that it has a serious design flaw: it has a tiny hand-crank, and it's thus next to impossible to play your custom tunes at a constant rate. The thing sounds like crap for this reason alone.

I'd like to automate the crank with an electric motor, since I am under the impression that it's pretty hard to make your own wind-up music box (difficult to get the wind-up mechanism to turn at a constant rate, involves fans and other intricate timing mechanisms, etc).

So it doesn't take much torque to turn the crank, but it needs to be turned approximately 100-150 times per minute in order for the music to sound decent. What kind of motor am I looking for? It should be relatively small, so I can fit it in the wooden music box I'm making along with the musical mechanism itself and whatever other contraptions I need to put it all together. I'm also pretty noob with electronics, so I'd prefer not having to put together my own circuit board or anything; at most I'd like to just make a few solders and hook up the battery, then snap on a few widgets & gears and pump out those tunes.

What kind of motor should I use?


texts:
Consider the below circuit :

According to my textbook Vs will be

However I have another solution which is different from this.

Using superposition, we will first find the drop due to the voltage source and due to its polarity, Vs will have a positive terminal on the bottom of the resistor and negative terminal on top of the resistor.

So due to this source we will have a drop of (50/50+150) * (j26.6m.) For the current source, due to its direction, also the positive terminal of Vs will still be at the bottom and the negative terminal will be at the top, so the drop will have the same sign and will be equal to (50*150/50+150) *(j0.1168m) and the total drop due to these sources will be +j11.03mv not with a negative sign as the answer.

Can someone explain why my answer is different from that of the solution?


texts: Are there any sensors out there that detect how tightly a particular object is held by a human hand?

texts:
I'm trying to find a solution for quantitatively measuring the amount of tightness with which a smartphone is held by a human hand.
Is there any way of using the current sensors in an Android phone to achieve the said requirements? If not, is there any external sensor available that can be used with a microcontroller like Arduino to do a similar thing?


texts: Identify object that pass through a hole?

texts:
We have small bags in 2 different colors that pass through a hole of about 40cm. The bags can be dropped and so they pass very fast.
We have to know which kind passed through the hole.

I was looking for many ways that will keep the bags passive without batteries.

This is commercial and many bags will be manufactured.

Here are the ways I see, would be happy to hear your opinion.

Bad: color identification which will not be accurate at sun/dark.
Ok: RFID passive tags inside the bags and a coil around the hole, problem is that the coil used to detect them has to mechanically be installed very precisely into the hole. Also, the speed of identification is slow(?) and the tech is pretty old.
ok: Bluetooth beacons inside the bags which will require battery inside the bag, and the tags are pretty expensive.( Estimote, Kontakt)
NFC which is still new and there are not many solutions ready yet.
Camera with advanced AI .

Which seems reasonable? any specific manufacturers for these?


texts: Potential lose of time-dependent currents in presence of static magnetic fields

texts:
A time-dependent current (either DC or AC) that creates a changing magnetic field around the wire, in absence of other materials, only lose current in heat proportional to ohmic resistance of wire itself.

In our paradigm there are several nearby permanent magnets that constantly keep a magnetic field perpendicularly and parallel to copper wire which their strength is greater than magnetic field generated by changing current.

Hence changing magnetic field of time-dependent current might lose some potential by inducing eddy currents on nearby permanent magnets (which is trivial in nonconductive ferrite magnets) or hysteresis on magnet body's crystal structures. But does the magnetic field of permanent magnets also enforce moving current inside the wire creep and lose more potential to overcome applied field? or current loses because of nearby permanent magnets in general is much lower than ohmic resistance of wire and we can ignore it?

Are there equations to accurately calculate total current lose due to presence of permanent magnets in such circumstances when we know applied flux density by magnets and current density inside wire?


texts: Voltage drop in Vin of 7805 regulator when used with a Bridge rectifier and CT(Current Transformer)

texts: I have a voltage regulator circuit powered by a CT. I rectify the output AC voltage to DC voltage and provide that as an input to the regulator L7805CV. My input voltage is about 7.20V When I connect the regulator, the input drops to 4.6 V and the output is only 3.3 V instead of 5V. When I try it with another regulated voltage of about 15 V, the output is fine to 5V and there is no drop from the input side. I tried the regulator circuit with appropriate capacitors at input and output side still makes no difference. Why is there a drop only when I connect it to the CT?


texts: Need help interpreting a printer PS label

texts:
I have an HP OfficeJet 8600 that won't power up.  First it wouldn't turn off, but after doing a standard partial reset described on several websites, it now refuses to turn on.  Took the CMOS battery out, verified it was good with a multi-meter, and had it out a good 45 minutes, so anything that can be reset/cleared by removing it for a few minutes definitely was.

Took the power supply out to meter it, and that's where my confusion begins.  If you look at the label on the PS in the attached image, you'll see that it accepts anything from 100 to 240 volts AC and puts out either 32v DC or 12v DC.  The power supply connects to the printer's mobo with a 3-pin molex connector, and its pin config is diagrammed on the label (top right corner).  It shows both voltages being delivered on the right pin, ground on the middle pin, and a crescent (sleep mode?) on the left pin.

This would make sense to me if each voltage was delivered on a separate pin, but I wasn't aware you could have more than one on a single pin, which apparently is the case here.  When I meter the pins, I get 32.5v across right pin and ground (middle).  I get 30.3v across the right pin and the crescent (left) pin.  I get 2.2v across the crescent (left) and ground (middle). I don't get 12v anywhere.

Does this make sense to anybody, and if so, can you explain to me how it works?  I don't think I can declare my PS good or bad w/o first testing the 12v path to see what it reads, but how to I do that?

Thanks,
lunchbeast


texts: VHDL: Real addition leads to 'bound check failure'

texts:
After a year's hiatus, I returned to learning VHDL. I'm working on the exercises on Peter Ashenden's book Beginner's Guide to VHDL and I'm stuck on exercise 11 of chapter 3.

The goal is to write a module, that will perform basic arithmetic operations on two real numbers. Here is my module:

-- floating point ALUish thing

entity FPALU is
    port ( x, y : in real;
           f1, f0 : in bit;
           z : out real );
end entity FPALU;

architecture behav of FPALU is
begin
    fpalu_behavioral : process(x, y, f1, f0) --is
        variable result : real := 0.0;
    begin
        if f1 = '0' and f0 = '0' then
            result := x + y;
        elsif f1 = '0' and f0 = '1' then
            result := x - y;
        elsif f1 = '1' and f0 = '0' then
            result := x * y;
        elsif f1 = '1' and f0 = '1' then
            result := x / y;
        -- else null;
        end if;
        z <= result;
    end process fpalu_behavioral;
end architecture behav;

And its test bench:

-- test bench for floating point operations

entity FPALU_test_bench is
end entity FPALU_test_bench;

architecture test_FPALU of FPALU_test_bench is

    signal x, y, z : real;
    signal f0, f1 : bit;

begin
    dut : entity work.FPALU(behav)
        port map ( x, y, f1, f0, z );

    stimulus : process is
    begin
        x <= 3.4; y <= 5.8; f1 <= '0'; f0 <= '0'; wait for 20 ns;
        x <= 3.4; y <= 5.8; f1 <= '0'; f0 <= '1'; wait for 20 ns;
        x <= 3.4; y <= 5.8; f1 <= '1'; f0 <= '0'; wait for 20 ns;
        x <= 3.4; y <= 5.8; f1 <= '1'; f0 <= '1'; wait for 20 ns;
        wait;
    end process stimulus;

end architecture test_FPALU;

This code will analyze and elaborate fine, but once I try to run the test bench I get this error:

ghdl -r FPALU_test_bench --vcd=FPALU.vcd
./fpalu_test_bench:error: bound check failure at FPALU.vhdl:15
./fpalu_test_bench:error: simulation failed

Line 15 being result := x + y;. This question seems to be similar, but since packages haven't been introduced yet in the book, I assume it should be possible to do without. Also, I added two real numbers in a similar fashion in another module and it worked fine. So, why won't this simulation run? I guess it's an "overflow issue" from what I have found here and on Google, but no definite answer.


texts: How to calculate the segment array resistors in a multiplexed display array?

texts:
The situation:

Four seven segment displays are multiplexed by a 16F648A. Now I need to calculate the required value for the segment resistors.

Supply voltage 5V.

Datasheet:
Segment voltage 1,8V.
Segment current 30 mA cont.
Segment peak current 80 mA (1/10 duty cycle, 1mSec pulse width).

Circuit:
Segment array resistors 180 ohm.
When displaying 4x8 supply current 60 mA
When displaying 1x8 supply current 15 mA (cathode removed from the other 3)

Assumptions not sure:
Display duty cycle 25% (4 displays).
Display segments all on at once. ( one instruction in the pic)
Actual segment current  60 mA/7 = 8,6 mA.

How to calculate the segment resistors value for the max. permissible current.?
The 80 mA peak might be to high for the pic. But first I need to find out how to calculate.

Resulting from the answers and comments I have continued as follows.

While multiplexing still active I selected only one digit to be active and connected the oscilloscope over one segment resistor. The outcome of this was that the voltage drop over the resistor is between 1,7 and 1,9 V. So let us take 1,8 V over a resistor of 180 ohm. Resulting in an I/O current of 10 mA. Far within the reach of the 16F648A. I decreased the resistor to 68 ohm and found that the voltage dropped to about 1,2V resulting in an I/O current 17,6 mA. The brightness of the display only increasing very little.

I measured also the duty cycle and it is indeed 25%.


texts:
I recently took an oscilloscope to a reset circuit on a new board I am working on (derivative of WildFire). Nothing earth shattering here, U6 is an Atmel ATMega1284P (VCC=5V), and U8 is an FTDI FT231X (VCCIO=3.3V, 5V-tolerant). The relevant parts of the schematic are:

and

and here is a scope trace of what happens when DTR goes low on the FTDI chip.

The blue line is DTR, the yellow line is RESET (never mind the labels). When DTR goes low, it looks to me from the scope, that the RESET signal doesn't get all the way to GND, reaching a minimum at the cusp of about 1.72V before 'discharging' back to 5V.

The thing is, the ATMega1284P is certainly resetting as intended, but I'm concerned that it's not reaching a low enough voltage to be in spec for a reset. The datasheet says that Vlow for RESET is 0.1*Vcc, which would be 0.5V @ Vcc=5V, and I'm a good 1V above that apparently.

So, (1) can you explain why RESET doesn't get all the way to GND, and (2) can you suggest a fix, without changing the design fundamentally, that will get RESET to drop below 0.5V when DTR transitions from 3.3V to GND? I'm imagining the shape of this fix to be something like change R11 to a different value, or change C24 to a different value. Or some combination theretofore.

Or am I just seeing a measurement artifact? You can't really see it behind the cursor bubble on the scope trace, but when DTR transitions from GND to 3.3V, it looks like RESET exhibits an inverse signal, rising to about 6.48V and then 'discharging' to 5V. I'm not seeing how that is a predicted outcome of the circuits in play here.

EDIT
Writing a question down thoughtfully makes it stare you in the face sometimes. It's because DTR is at 3.3V and RESET is at 5V. So the most that C24 can pull down reset is by 3.3V, which leaves a residue of 1.7V.

So the updated question is how would you fix this? Pull the ATmega1284P reset up to 3.3V instead of 5V?


texts:
I'm trying to work on UART for AVR. After setting the baud rate registers UBRRnX, I'm trying to configure the UCSRnA register.

I'm trying to set the 2nd bit, U2XO. Which is the right way to do it?
UCSR0A = (1 << U2X0)

or

UCSR0A = UCSR0A | (1 << U2X0) (Notice the OR operator in the 2nd statement)