texts: How to go from a development board to a production board?

texts:
Ok, I am a software guy and new to electronics. My product needs a small computer and currently I have developed everything on development boards like raspberry pi and such. As the development board does not have all the hardware that I need, I have added the missing hardware through USB and GPIO's but obviously the production board can not be like that.

So my question is how do I go to the next step to come up with the production version of my hardware? In other words, what would a hardware specialist do to turn its development board into a production ready product? These are what comes to my mind

1> Get the schematic of current development boards like the pi (or any publicy available schematic that is close to my basic hardware requirement like the cpu type and such) and try to find some one to add the missing pieces to it and re-organize the position of the ports (like usb port and such) to your desire and make it the production product. This is possible because CAD software like Eagle are very powerful and adding a couple of more hardware chips (say like a temperature sensor) and changing the locations of ports is fast to do.

2> Are you stupid? The design of such board is very complex, specially a computer like pi and you have to hire a board design consulting company (or whatever they are called) to design this production ready board for you. If so, how should I talk to? US or China?

3> If your are building a production level hardware, you need to have the design team in-house and you need to hire the right ppl with such expertise to do so. This is not something that you want to contract out. you must have it internally as practice has shown. If it was a simple board you could have done yourself, but a computer needs a lot of work (although there are many commonality among them) and you have to start from scratch as there are so many details involved.

Oh, my production size is not big. I need 5,000 units every 6 month. The main thing is the a good reliable final board design with my requirements to get it to a PCB manufacturer.

As you see, I am sort of lost in this hardware manufacturing space and your insight and personal experience will be very valuable to me.

Many Thanks!


texts: Should a linear amplifier be considered as a current source or a voltage source?

texts:
Linear amplifiers such as class A, B, and AB can deliver current to the load. Then should it be regarded as a current source?
However, a current source should have a high output impedance while a voltage source should have a low output impedance. Now consider the following class B amplifier. It is in the emitter follower configuration. The impedance looking into the emitter is low and hence the output impedance should be low. So in this case, should this linear amplifier be regarded as a voltage source instead of a current source?

Source: https://www.electronics-tutorials.ws/amplifier/class-ab-amplifier.html
Consider another class B amplifier configuration in the following diagram. Now it is in a common source configuration. The impedance looking into the course is high and the output impedance is also high. So in this case, should the power amplifier be considered as a current source?

Source: https://www.sciencedirect.com/science/article/pii/S0026269219304719?casa_token=r_fOAPtZPQEAAAAA:1msPiihOEI1AHetzlhnBU4VSO_zqVF2TYRrsCU39GQ73phPj05mjhYxolI9JbNH2DCQJs6s8
So as a whole, can we say that a linear amplifier can either be a current voltage or a voltage source depending on its configuration?


texts:
I am using this circuit with a BTA16 TRIAC:

The load is a 110/12 V transformer. I am getting spikes in the output.

Note: CH1 is the secondary of the transformer (load), CH2 is the MOC3021 input.

How can I get rid of the spikes?


texts: How do I improve and isolate from mains ground my Tesla coil control circuit?

texts:
I made this circuit for my tesla coil. It is a glorified slayer exciter. I based my circuit one the one shown here

Both the coil supply and the control circuit supply come from an appropriately modified microwave oven transformer. The transformer core is grounded, and I noticed some sparks going from the 12V secondary to the core. These sparks only happen when the control circuit is activated and the secondary is generating high voltages. I suspect the diodes used to clip the input for the MOSFET driver are transferring the high voltage to the supply rail and thus to the transformer winding. Is there any way to prevent the MOSFET driver from frying and at the same time prevent high voltages in the supply rail? Can you suggest any improvements to the control circuit?

From what I gather high voltages in the mains system are very dangerous for appliances connected to the same network, so the transformer arcing is very bad news. I'd prefer not to switch it on until this is fixed.

simulate this circuit – Schematic created using CircuitLab

Here is the transformer with a resistive ballast, the bridge rectifiers and the capacitors.


texts:
I am am new to RF design and I need to place a chip antenna due to space limitations. The only antenna that is easily available to me has a very weird layout. There is no physical connection from the feedline to the antenna and also the dimensions of this gap is not clearly mentioned. Can anyone please explain what is going on in this layout?

The link of the datasheet. https://datasheet.lcsc.com/szlcsc/Huaxin-S-T-RFECA3216060A1T_C127620.pdf


texts: Understand average time current curve of a fuse

texts:
When I made my buck-boost converter (12v input) (1-20v 4A output max) I choose a 7A fast blow fuse at the input in base to the calc 80w/12V = 6.66A.
Suppose my dc-dc converter drives 5A to output (cause the current control pot is not exact to 4A, maybe 4.5-5A max), did the fuse survive to that output current?
I look at the average time current of the fuse but I not understand very well. In the curve regarding to 7A in the "x" of the graphic the curve is marked 100A and that's what confuse me.

Datasheet: https://www.mouser.com/datasheet/2/240/Littelfuse_Fuse_251_253_Datasheet_pdf-522535.pdf


texts:
Here's a schematic of the VCXO oscillator section from a Siemens S55 mobile phone. AFC signal coming from the processor tunes the crystal via a varicap. There's also a thermistor going back to the processor for temperature compensation. It looks like a Colpitts oscillator,  but I have no idea why there are two transistors. The upper transistor base is AC-coupled to ground, which hints a cascode configuration.

Why did they choose to use such two-transistor configuration?
What is the role of R955 if AC is shorted to the ground anyway - or rather why is the upper transistor base polarization connected with the signal path?
What do C958 and C952 do?


texts: I am not able to program the PF3000 IC. I have customized the voltages, when I program and put the IC in my other product, I am not able to get the programmed voltages. I followed the video shown. But still OTP programming is not happening. So, I am suspecting the problem with the OTP programming.


texts: Can I find out how much heat in temperature can a resistor give if I know its wire and its resistance value?

texts:
Wire :  nichrome 80:20
Ohms per metre : 750 ohms per metre
Resistance value : 5k ohms
Resistors dimensions : 8mm diameter and 50mm.

Voltage I am going to pass is 240v.

How much heat does Resistors dessipate ? (Can I guess the temperature or do we have formula for calculating heat in temperature)


texts: How are the individual homes connected in a 3 phase power distribution system (power grid) so that they have correct voltage?

texts:
For a single phase distribution system it's simple, each home has one wire coming from the neutral and one from the live, in turn each outlet has a live and a neutral wire. The live is 120V relative to earth, which is the neutral wire's voltage (ignoring ground because that is just there as a safety feature).

For 3 phase (I am talking about standard North America three phase where two phases are given to each house, not industrial 3 phase motors) there is a neutral wire, but it is thinner than the live and meant to simply carry away current from unbalanced loads, not used under ideal circumstances, so since it is not a main source being used to carry the electricity and I will assume this is an ideal circumstance so we can ignore the neutral wire. I would then think that this would mean that two live wires would need to feed to one outlet, with one of the live wires in place of the neutral, creating the circuit. But the standard voltage of a wall outlet is 120V, and two live wires makes 208V because they are only 120 degrees out of phase. From my research I know that the 208V is used in some appliances, but most use 120V.

So my question is this: How do you get 120V from a wall outlet without using a neutral wire, if each wire individually is 120V relative to ground, and two lives connected makes 208V? This diagram may help you understand my question.


texts: Is the denominator of the passive high pass filter given wrong?

texts:
Circuit can be found here

The following section from a book called AOE shows the Vout/Vin for a high pass filter:

But shouldn’t the denominator be square root of the sum of squares of R and Xc? But above the denominator is given as the algebraic sum. Is the above equation wrong? What is the meant by approximation here?


texts:
I think I have understood Carry Lookahead adders.
However, I don't really understand how parallel prefix adders evolve from carry lookaheads. Can someone explain to me the difference between PPA and CLA?


texts: Simulate Gyroscope through MEMS accelerometer

texts: Is possible to simulate the Gyroscope using Accelerometer values? I would like to make that in Android Context so using MEMS smartphone accelerometer.


texts: What are Fuses in Atmel microprocessors and when I should or need to change the default settings?


texts: Why is there a resistor inline with switch in blender motor?

texts:
Our hand-held blender stopped working and I took it apart to see if I could fix  it (no, as it turned out).

The circuit was simple; a switch and a 0.47 Ohm (R47) resistor in series with a full bridge rectifier whose DC output was connected directly to the motor.

The wattage is 200 W and the voltage 120 V, so the voltage drop across the resistor is small.

Question: Why bother with the resistor?

Note: I am not looking to fix the device, I know one of the windings is burned out, but I am curious about the resistor! (I am an EE, and 'should' know these things,  but...)

Added: The labeling is R47 10%, and UTM 206-8. A quick look at the Jameco catalog gave me 'Power Wirewound Ceramic Resistors, axial'.


texts:
I'm trying to send SPI data to a MAX7219 from an STM32F042 (the protocol is one-way without MISO). I must be missing something very obvious. With the code below, the only visible side effect is the GPIO nCS line wiggling. Neither clock nor MOSI show any activity.

What am I missing?

#include "stm32f0xx.h"

int main(void)
{
  RCC->APB2ENR |= RCC_APB2ENR_SPI1EN;
  RCC->AHBENR |= RCC_AHBENR_GPIOBEN;

  // SCK
  GPIOB->MODER |= GPIO_MODER_MODER3_1;  // alternate function
  // GPIOB->OTYPER default push-pull
  // GPIOB->AFR[] default AF 0: SPI1_SCK,

  // MOSI
  GPIOB->MODER |= GPIO_MODER_MODER5_1;  // alternate function

  // soft nCS
  GPIOB->MODER |= GPIO_MODER_MODER4_0;  // GPO
  GPIOB->ODR = GPIO_ODR_4;              // deselect

  // SPI configuration
  SPI1->CR1 |= SPI_CR1_MSTR;            // master mode
  SPI1->CR1 |= SPI_CR1_BR_1;            // spi_sck = SystemCoreClock / 8 = 6 MHz
  SPI1->CR1 |= SPI_CR1_SSI;             // software CS
  SPI1->CR2 |= SPI_CR2_DS_3 | SPI_CR2_DS_2 |
    SPI_CR2_DS_1 | SPI_CR2_DS_0;        // 16 bit format

  SPI1->CR1 |= SPI_CR1_SPE;             // SPI Enable

  // transmit test packet
  while(!(SPI1->SR & SPI_SR_TXE));      // make sure TX buffer is empty
  while(SPI1->SR & SPI_SR_BSY);         // make sure SPI isn't busy

  GPIOB->ODR &= ~GPIO_ODR_4;            // chip select
  uint16_t data = 0xAAAA;               // test packet
  SPI1->DR = data;
  while(!(SPI1->SR & SPI_SR_TXE));      // make sure TX buffer is empty
  while(SPI1->SR & SPI_SR_BSY);         // make sure SPI isn't busy
  GPIOB->ODR |= GPIO_ODR_4;              // deselect

  while(1);
}


texts: What are these wiggly USB 3 traces on my motherboard?

texts:
I was taking a look at my motherboard, and I noticed the above traces on the USB 3.0 ports. A bit of prior research:

The C34WH IC is probably a SN74LVC2G34 Dual Buffer Gate.
Unclear what chip the top two ICs are, but the markings likely read 1188J.

What is the purpose of making these traces like this?

How is the appropriate shape of the traces calculated?


texts: Half H-bridge using only ntype mosfets or npn transistors

texts:
Would the following circuits work? I keep thinking I need a mixture of ptype and ntype mosfet or npn and pnp transistor for a half h-bridge, but I keep seeing schematics with only ntype mosfets or npn transistors.

My thoughts are:
Case 1: In Q2, since the voltage at D with respect to S cannot be guaranteed to be a constant, the circuit's  behaviour will vary.
Case 2: Similarly, in Q2 the voltage at C with respect to C cannot be guaranteed to be a constant, therefore Ice will vary.

Is this correct? I've kept the schematics simple on purpose to understand it better. I will eventually turn it into a full h-bridge with flyback diodes.


texts: Easiest way to get rid of __clz_tab in winavr compiled code?

texts:
I've ported a program from the arduino environment to a makefile build using winavr, which, in turn, is based on avr-gcc (just like arduino).

However, my program started crashing, and after some investigation I found I was running out of data memory due to a 256 byte increase in the heap, even though I hadn't changed the program at all.

Looking at the map file I see a new table being included, __clz_tab, which is 256 bytes, and resides in RAM.

How do I get rid of this table and reclaim my RAM?


texts:
I am creating a small car that is to be controlled by a small hand held joystick remote.

basically I am trying to find the best option for doing this task.

The vehicle has two 24V motors, one for driving forwards and backwards movement, the other is for left and right steering. The motors need to be able to be analog controlled in the sense that their speeds can be varied. The handheld control remote is to have one 2-axis joystick, one axis correlates to the steering motor and the other axis to the driving motor.

In order to properly answer the question, you'll likely need to know what I've done so far. I have managed to do this by using simple RF transmitter and receiver modules from ebay. As seen here, http://www.ebay.com/itm/433Mhz-WL-RF-Transmitter-Receiver-Module-Link-Kit-for-Arduino-ARM-MCU-Wireless-/380717845396?hash=item58a48d4b94:g:x9cAAMXQigBSMp4X I have been using two arduino MCU, one in the remote which is needed to read the joysticks axis values and then send those values via the transmitter unit stated above. The second MCU in the car is used with the RF receiver module to obtain the joystick readings from the transmitter and then accordingly control the cars motor driver board.

This is working exactly how I need it to, however.... is it the best way of doing it?

These are my questions:

1) Do common RC cars perform this analog type control without MCU? If yes, how?

2) The remote I have created, is just a nano, 2-axis joystick and transmitter module but the battery drains very fast. What is the best option for a low power remote that is capable of sending 2-axis joystick readings. I ask this as I feel the nano is high in battery requirements.

3) lastly, The cars are to be used around each other and the RF units I am currently using are all on the same channel and therefore I get interference. How can I pair a transmitter and a receiver so that they will only work with each other? Preferably I would like to be able to use dip switches to set channels so that there could be say 100 of these cars each on a different channel.

P.S. hopefully not, but I get the feeling all of this can be done without 2 MCU, meaning the circuitry will do what my code is currently doing. If this is the case where do I start to learn how to build a circuit that can do this? eeek! way over my abilities!


texts:
simulate this circuit – Schematic created using CircuitLab

Why might one use a delta-wye transformer with the delta configured in Dab rather than Dac, or vise versa? Will this cause a difference in phase sequence? In Dab, coil A's non-polarity side is connected to coil C's polarity side, and in Dac coil A's non-polarity side is connected to coil B's polarity side, as shown in the schematic.


texts: Calculating things inside a circuit with resistors (parrallel and series)

texts:
I have gotten the flowing practice exercises that I need to do:

I have done 3 and 4, but I don't understand exercise 5. I have calculated the amperage that goes trough R1 (I think):

R1 = 50 Ohm so the remaining is 65 Ohm

R1 can let a maximum of 230/65 = 3,5384 A flow, so there is an amperage of 3,5384 - 2,0 = 1,538 A flowing to the rest of the circuit (if I am right).

Then I am stuck. The formula of the resistance in parallel is 1/Rt = 1/R1 + 1/R2 + 1/R3 and so on. but I don't see how you can calculate the amperage flowing trough R2.

I am very keen to learn the basics of resistance, and it would be great if somebody could help me out.


texts: How to connect photo diode to trans impedance amplifier?

texts:
transimpedance example here

I need to design a trans-impedance amplifier to amplify the signal from a photodiode to make a PPG sensor
I need a signal to acquire from the wrist.

photodiode I am going to use is SFH 7060

I don't understand how to connect anode and cathode of SFH 7060 to the amplifier input pin.

is it as follows?

connect pin 6 of SFH 7060 to (photodiode anode) inverting input of opa170?
and connect pin 7 to GND

do I need an instrumentation amplifier for this?

SFH 7060 data sheet


texts: Optocoupler/relay type for isolating two DC circuits

texts:
I have recently started experimenting with an Arduino and would like to control a seperate circuit (for example, a small and cheap digital video camera powered by battery) from my arduino.

Basically my plan is to solder two wires to either side of a tact switch on the target device's PCB. Since I am new to the world of electronics and do not wish to risk any possible damage to my Arduino, I would like to isolate the two circuits from one another.

I have done some research to figure out how to switch one circuit from the other and the options I have come across are relays and optocouplers. I think I prefer the idea of using an optocoupler because they are small and completely separate the two circuits. I can also order some free samples to try them out.

My understanding of optocouplers is that I would not need to connect the ground of the arduino to the ground of my target device (operating on it's own battery source). Is this correct?

Also, considering I plan on using this to control only low voltage DC circuits, what would be a good choice of optocoupler? I plan on ordering several so that I can use them for various breadboard experiments where needed.

Thanks


texts: Choosing a power transistor with low dissipation

texts:
I need some advice about how to provide a DC voltage (between 0 and 24V, tunable) with high current (about 8A) to a motor.
All the times I have done this, I have used a BJT Darlington pair like this one, with BDX53C and BUV20:

At left we have a tunable biasing network which provides a voltage between 0 and a bit more than 24V (to get exactly 24V at the emitter of the BUV20.)
My problem with this type of configuration is heat of BUV20: it becomes too hot and it is difficult for me to keep it cool although I use a 100x100 mm heatsink and an 80mm fan (with also thermal paste.)
What I need is another final stage which generates less heat. I was thinking of replacing my Darlington pair maybe with a power MOSFET, but I do not know how to choose it regarding its "thermal behaviour." In other words, I do not know how to quantify (with datasheet parameters) how much a certain transistor generates heat at a certain biasing condition.
Which configuration and which transistors do you think may be good for my purpose?


texts:
I've recently realized that I can't do everything easily in ngspice, mainly because analysis has to be performed through the interpreter. I'm considering switching to a new SPICE simulator.

I'd like a list the advantages and disadvantages of the following SPICE simulators as well as experiences with the various simulators:

HSPICE
LTspice
ngspice
PSpice

I'm well aware HSPICE is an expensive proprietary simulator, but I am able to get access to it, problem is I'd have to access it on a sever via SSH.

LTspice is already free, but not installed on my Windows 7 machine.

Already using ngspice in Fedora Linux.

PSpice available to me on my university's computers. I refuse to install it on my own computer, because it messes with the registry a bit too much.


texts:
I've just gotten into STM8 programming and am trying to figure out how to read voltages with its ADC. This was one of my first forays into embedded C programming, so "nooby" code mistakes aren't completely out of the question here. I've already had success getting UART and basic GPIO functionality working, but I just can't seem to figure out what's going on with the ADC. For some reason, as the title implies, I keep getting the maximum ADC value (Vdd = +3.3V), and the data registers read 1023, with a bit of fluctuation. I've tried different voltage sources (potentiometer, function gen. and even directly tying the pin to GND) to no avail. The particular device I have is the 20-pin STM8S103F3, and I'm using SDCC+STM8Flash to program the device. I'm using a custom header file defining register addresses, and have double-checked that they match the datasheet. My configurations are as follows:

//Code from an example I found online, modified to fit my device
//On the STM8S103F3, AIN0 and 1 are not physically mapped to a pin
//so I'm using AIN2 (PC4). I'm just trying to poll the ADC without
//interrupts. Just reading the values directly.

//***This isn't the entire code here. Just the parts pertaining to the ADC.***

PC_DDR = 0b00000000; //Setting all of Port C to input
PC_CR1 = 0b00000000;
PC_CR2 = 0b00000000; //GPIO config registers set according to the datasheet
ADC_CSR = 0b00000010; //Set ADC channel to 2 for AIN2 (lower 4 bits set channel)
ADC_TDRL = 0b00000100; //Disable Schmitt trigger for channel 2
ADC_CR1 = 0b01000000; //Frequency prescaler = f/8
ADC_CR2 = 0b00001000; //Right-aligning data
ADC_CR3 = 0b00000000; //Disabling buffer

//Then, to poll the ADC by enabling the ADON bit
ADC_CR1 |= 0x00000001; //This was from the example code, what's the difference between 0x and 0b?
ADC_CSR &= 0x01111111; //Not entirely sure what's going on here, but maybe clearing the EOC flag?
while ((ADC_CSR & 0b10000000) == 0); //Waiting for the EOC bit to be set?
result = ((unsigned int)(ADC_DRH * 256) + (unsigned int)ADC_DRL); //Concatenating the upper and lower bytes to form a 10-bit value

With the above ADC configurations, I've only gotten values ranging from 1023..1016 or so, no matter what voltage I apply to the input. Any thoughts? Thanks!


texts:
I'm working with a device that has an array of 102 sensors(link here). For each low-high transition detected on one of its inputs, it outputs an analog level according each sensor respectively. Once this occurs 102 times, you must wait a short period and can then begin again.

I was thinking of using a timer interrupt to generate each transition and sample the data into an array using the ADC, but am wondering if there is a better way to achieve this using an onboard peripheral (that wouldn't use up as many MCU clock cycles) . I am using a PIC32MX450 currently, but can change MCU if need be.


texts: LED needs a minimum current or minimum voltage to operate in forward bias

texts:
I want to wire up an IR LED on a battery. I've seen many tutorials telling me that I should add a resistor, but none says what resistor to use to maximize battery life. So a 680ohm resistor will do the job of powering up the LED, but will a 47k resistor do the job too and keep the current still running (which will be more beneficial for the battery)?

I wonder if the LED (and all the diodes) need a minimum current, or a minimum voltage to operate, because I want to know how will adding one more diode in series or in parallel affect my choice of a resistor.

Also is my thinking correct? Say I have a 9V battery and a 0.7V drop LED. This means that if I place a resistor in series, the voltage drop through the resistor will always be 8.3V.
So the current through both the resistor and the LED will be determined by the current through the resistor R which will be 8.3V / R.


texts: Howland Current Pump VS Wilson Current Mirror

texts:
I am interested on knowing what would be a better solution to create a current source for low current applications (below 20mA), an opamp based current source such as a Howland current pump (link to PDF) using closely matched resistors, or something like a transistor based current source such as Wilson current mirror using matched transistors in a single package.

I am aware that there are a lot of factors that should be considered, to start with, the types of opamps used, the type of load, bjt vs fet, voltage compliance, etc... So in a general way, what I would like to know is if its worth looking into a transistor based solution, does it offer any advantages over opamp current sources in low current applications?, or should one just stick to opamps for simplicity?


texts: Dependency of Conductivity on Temperature of Extrinsic Semiconductor

texts:
For an Extrinsic semiconductor ,how can we explain the following dependency of Conductivity on Temperature as shown in fig.:

My Thoughts:
At \$ 0K \$ there is no energy available , hence no electrons can flow from valence band to conduction band
\$ \therefore \sigma =0 \$ at \$ T=0K \$
Now as \$ T \$ increases ,energy increases and hence \$ \sigma \$ increases
Now how \$ \sigma \$ decreases as \$ T \$ is further increased from \$ 300K \$ ?please help....


texts: Any suggestion for surface mount oscillator (XO) PCB Layout guidelines?

texts:
I've searched for PCB Layout guidelines related to surface mount oscillator (XO). I only found A LOT of application notes for oscillators based on pierce-gate topology but not for surface mount oscillator unit.
Are they almost the same ? Is a guard ring also recommended ?


texts: Pspice simulation of NE5234 op-amp internal circuit. Currently getting zero voltage gain

texts:
I'm attempting to simulate the NE5234 op-amp via internal circuits. I'm not currently getting any errors, and so the AC sweep simulation does run, but I am getting 0 V on the output nodes. I'd appreciate any insight, or even a direction I should take to try to diagnose the issue.

Schematics of all stages with Volt Bias display ON.

The same schematics from the Analysis and Design of Analog Integrated Circuits text

Thanks for your help.


texts:
I've been trying to reverse engineering a monitoring system and there's a component that I can't understand.

What does these Z symbols represent?


texts:
So I'm still reading The Art of Electronics Third Edition. On P.39, when dealing with inductive "kick", I found this sentence:

  For the fastest decay with a given maximum voltage, a zener with
  series diode (or other voltage-clamping device) can be used instead,
  giving a linear-like ramp-down of current rather than an exponential
  decay (see discussion in Chapter 1x)

simulate this circuit – Schematic created using CircuitLab

Which circuit does the author mean? In fact, neither of them seems to work to me:

In circuit A, when the switch is closed, D2 is actually used as a zener, but it isn't supposed to do this job. Also, after the switch is open, it can reduces the voltage across D1 by its forward voltage drop, but can't clamp the voltage.
In circuit B, when the switch is closed, D1 is forward biased, which may attract the current through L2. When the switch is open, the maximum voltage across L2 would be the forward voltage drop of D2, then why even use a zener? Also, I don't think this structure can be called "a zener with series diode".

So, what do you think the author wants to express by saying "a zener with series diode"?


texts: How to make a fingerprint scanner (UART, Serial) for a headphone jack on Android?

texts:
Square up reads magnetic stripe cards through headphone jack on both Android and iOS. I want to capture fingerprints on an Android phone. Can I develop a hardware to capture fingerprints in the same way using a fingerprint scanner (UART/Serial)?

I want to develop such hardware (like square) which can be used to capture fingerprints through the headphone jack. If it possible?

The fingerprint scanners are available with UART communication protocol. So is there a way to send the fingerprint image through the headphone jack by developing such connector?


texts: Help me identify a component from EAGLE schematic

texts:
Can you help me identify the "L1" component in this schematic? It reads 33R@100MHz and is defined as an INDUCTOR. Maybe I'm reading it wrong (count on it), but I don't know how to deal with the @100MHz tag - resistors/inductors don't have a MHz as far as I know?

The closest I can get is a RC0603FR-0733RL (link: http://export.farnell.com/yageo-phycomp/rc0603fr-0733rl/resistor-rc22h-0603-33r/dp/9238301), but that's a resistor.

Line from EAGLE BOM:
L1   33R@100MHz      L-EUL2012C      L2012C          INDUCTOR, European symbol

Screenshot of schematic:
EAGLE http://f.cl.ly/items/1v2w0r3s0G0i2H1l1g0r/Screen%20Shot%202015-08-11%20at%2020.19.12.png

Thanks a lot


texts: How can I use a 12 V input on a digital Arduino pin?

texts:
I am creating a controller for a 12 V system using an Arduino Uno microcrontroller. For the outputs I am using a relay shield to switch the 12 V components. I have a 12 V toggle switch that turns on some 12 V components in the system and I want to use a trigger signal off of this same switch to send to an Arduino digital input. I know that the Arduino can only handle 5 V max. What would be the best way to step down the 12 V coming off of the switch to the 5 V for the input?

EDIT: The system is for use in a car. Would the amperage of the car battery need to be lowered somehow as to not blow up the components?


texts: Why do the normally closed and normally open relay contacts have different current ratings?

texts:
Please refer to the image below:

Taken from the datasheet:
http://www.songchuan.com/db/pictures/AdminModules/PDT/PDT090410001/201191913495127935.pdf


texts: Current through capacitor, displacement current

texts: How can current flow through a capacitor(open circuit)? Why is there a need of displacement current and why does it exist for a short period of time? Does the displacement current exist in medium between the plates? Why is there a need for charge to flow from battery's terminal to capacitor's plate?


texts:
I have a small demo breadboard circtuit based on this design:

I use this transformer, it's connected for 115V input on primary, and 2x24V output, and I'm using only one of these outputs at the moment...

https://www.hammfg.com/electronics/transformers/power/266.pdf

So, what happens is that for some dummy load that I have, which works on 12v and consume just 130mA, my voltage from this PSU which is adjusted to 12v drop to 2.8V when I attach that load?!

What's wrong with this and how's that I have so much voltage drop?

I triple checked all the parts and connections.

Voltage which comes on rectifier is 27VAC.

Voltage at C1 is 37.4VDC.

Voltage on ADJ pin on LM317 without load is 3.1V, and when I attach load of 130mA it drop to 0.3V.

Voltage on C1 stay still at 37.4V with and without load.

Note, only different part on my breadboard is that I didn't use D1-D4, I used actual rectifier, but that shouldn't make any difference.

And for R2 I used 10k (I didn't have 12k or any other resistor co combine them to actual 12k).

I added these silly breadboard images, maybe someone will see what I couldn't...

I tried to draw how I connected it:


texts: Why is the Voltage only 1.4 for reset input when in high impedance?

texts:
I attempted to make myself a 2-in-1 programmer so I can program both AT89Cx051 and AT89S52 on the same board without having to do so much plugging/unplugging of the port.

The main issue is the strobe pin aka reset (RST in circuit). (pin 1 of the DB25 connector). I tested it with a PC and got no results.

What seems to somewhat work is if I connected RST to VCC via a 1K resistor. It somewhat works because even though the output is only at 3.8V instead of 5 (which VCC is also at), it puts the AT89S52 in reset mode as expected, but I'm not getting 12V at pin 1 of the small AT89Cx051 socket.

If I don't make the manual connection, then I get 1.4V measured at RST, even after I added a 10K resistor between VCC and RST. Without RST being forced to ground, I should get 5V but I'm not.

I have also tested the transistors manually from leg to leg using the diode setting on the multimeter and they turned out fine. The resistors going to the base of the transistors are 2.2K and I used 1K resistors in place of the diodes. All other resistors are 10K. The resistor going into the buffer (74HC125) is 0 ohm.

All capacitors are 0.1uF.

Why would I be getting such awkward voltages for reset pin?
Am I using too weak of resistors or something?

UPDATE

So I ended up making myself an ms-dos 6.22 bootdisk and booted my machine into that with qbasic to test the parallel port (with port at address 278-27AH ) in general with simple circuitry and that seems to work decently.

When I teted only the parallel port on the pc with only a voltmeter with anode lead connected to the strobe pin, I get the following results:

Qbasic code           Result
OUT &H27A, 0          4V output from strobe
OUT &H27A, 1          0V output from strobe

When I plugged my circuit into the port, the voltage dropped:

Qbasic code           Result
OUT &H27A, 0          1.56V output from strobe
OUT &H27A, 1          0V output from strobe

How is it possible I'm only getting 1.56V from that pin?

update 2

I disconnected the 12V line from the circuit and the voltages on the reset line are now 1.52V and 0V


texts: A "fuse" that blows upon liquid exposure instead of overcurrent?

texts:
I have a board that is mounted inside a waterproof housing, but occasionally the housings develop leaks and expose the internal circuits to water.

This can cause unpredictable failures as the corrosion slowly grows until a short or open develops someplace on the board.

I am wondering if there is such a thing as a "liquid fuse"- that is, a component that will permanently fail open-circuit upon exposure to liquid. I'd put one of these right where the power enters the board so it would cut off current to the rest of the board before corrosion could cause a short someplace.

I imagine the component itself could be some kind of conducive powder held together with an easily dissolvable binding agent. Or maybe a jumper compressed by a spring, and the spring is held by some dissolvable material?

This would be going into a mass produced product, so the part would ideally be SMD reflowable, cheap, and commercially available.

I've looked for a part like this, but can't find anything. Any ideas?


texts:
This is a follow up to my previous question regarding USB-C power delivery as a power source. There's been a fair about of development since when that question was asked and since STM have released a chip that will do everything I need in terms of negotiation with the USB-C power supply. (STUSB4500)

The long and short of wanting to use USB-C is that I eventually require 5A @ 5V. I also want to use one connector for both power and data (although bear in mind that these won't be both used at the same time).

I'll be negotiating a 3A @ 20V supply. So I need a buck converter that can fit the specifications. Obviously there's plenty of things around, however the important thing is that the height of the components is less than 4mm.

I'm unclear to the intricacies of buck converter, but they seem to require an electrolytic capacitor and an inductor. Will I be able to achieve a design that can do what I need? Any pointers toward suitable chips would be great.


texts: Can someone explain the workings of this Filter Board?

texts:
I'm trying to understand how the power supply of an analog synthesizer (Roland Jupiter-6) works. It was built around 1983 so some of the part numbers don't yield any relevant Google results. In particular, I'm looking at the "filter board":

What is L1? The schematic symbol looks to me like a transformer, but "L" indicates that it's an inductor.
Also, what is the main function of this board? Obviously, filtering, but more specifically what kind of filtering and how does it accomplish it?
Here it is in the context of the whole power supply:

... and here's a photo of the board:


texts: Is there a data transfer limit for virtual serial ports

texts:
I want to record 5/10 seconds of audio using an electret microphone and an STM32 nucleo development board and send it to my computer in real-time to be processed. I'm a beginner so I'm sure I'm making mistakes, but what limits the data transfer speed for a virtual serial port? I want to sample the audio at 48 kHz, at 12-bits per sample, which by calculation means I need a data transfer rate of  576 kb/s, is that possible via the virtual serial port? if not, is it possible at all with this board?

I have the STM32 nucleo-144 development board, I'm using mbed (https://os.mbed.com/platforms/ST-Nucleo-F746ZG/) and a electret microphone circuit (https://docs-emea.rs-online.com/webdocs/00af/0900766b800affa3.pdf)


texts: Checking CAN Bus load in Vector interfaces

texts: Are there any other ways to check CAN bus load via CANlyzer (other than Statistic window) or CANoe?


texts:
I'm looking to drive 52 LEDs (datasheet), around a large inflatable tent. The LEDs have a forward voltage of 3.3V, at a maximum of 20mA.

I'm thinking of using the NXP SAA1064 I²C 16-channel LED controller (datasheet), which seems to be exactly what I'm looking for, since I can drive one as master and another 3 as slave, giving me a total of 64 channels. All of this will be driven by an Arduino.

Update: After reading the controller datasheet, it seems to be that it's not possible to individually control the outputs - it expects to drive a 7-seg. Is this true? If so, are there nice alternatives?

What I'm not so sure on is how to handle the distance. The tent is around 25ft long, and 10ft high, and the LEDs are placed around the dome. The controller board runs at one corner, which means that the furthest LED will be around 30ft away from the device. The cables to the LEDs have to be relatively thin, since the inflatable tent can't take a huge amount of weight. I can see resistance being a problem.

The way I figure, I'm probably going to end up with ~100Ω on the longer cables, which is going to make those LEDs all but invisible. I considered ditching the controllers for shift registers and transistors closer to the LEDs, but that means more cables, more weight, more complexity, and more cost.

Is there a nice solution to this?


texts:
In Altium Designer standard libraries, parameters PackageReference and PackageDescription are same as Footprint Name and Footprint Description.

I'm also going to have those fields in my new components, I wonder if the above is plain copy or those fields are referencing to each other? Feels redundant to manually copy that two pieces of information.

Can I just create footprint, name it, set description and then somehow reference that information in PackageReference and PackageDescription parameters?


texts: 10-bit digital representation with SPDT switches and voltage division

texts:
I'm completely new to electronics, and have been trying to come up with a way to connect 10 SPDT switches to a single analog pin on my Ardiono Mega 2560 (and off course connected to 5V and Ground). The idea is to enable as many switches on a single pin, to try and free up pins for other uses.

I've put 10 switches in series, with unique resistor values on one pole of each, and in this way, trying to represent the bit values, 1,2,4,8,16,32,64,128,512, which will give me a resolution of 0-1023 integral values, which is the range that I understand the ADC on the Arduino chip supports. The voltage divider works, and gives the correct voltage, but ONLY when a single switch is flipped.

My circuit looks as follows:

Here we can see that the last switch is thrown, and the output voltage is 2.5V, which corresponds to a digital value of 512 as expected. However, when using more than one switch, the voltage drops more, giving me the inverse result of what I'm looking for.

I don't know if what I'm showing here makes sense, but ideally, I want to be able to detect the position of any combination of switches, by converting the voltage to binary and work from there.


texts:
I'm tasked to work for several car manufacturers and would like a system that can work with 'every' car.
For example, I bought the peak system CAN Bus usb, and tried it for Kia e Niro and it didn't get any message, I don't know why still.
Is it possible to have a standard CAN system that can work with every car ?


texts: How to design a power switching circuit using a photo-interrupter

texts:
Okay. I'm completely at a loss here. I was trying to design a switching circuit for a 3A load (Solenoid) using a photo-interrupter. I got to about here:

But I have no idea what to look for in my parts. I plan to use these as the current limiters, and I have to use this as the photo-interrupter. I was thinking I could set one of the current limiters to the specifications of the photo-interrupter, but I don't know if it would work. (I really hope it would.)

As for the transistor, I was thinking of finding an pnp switching transistor that can carry 3A without overheating, but I've never been transistor shopping before, so I don't know what to look for in the specs. Also, I don't know what to set the current for the... Transistor collector? I was thinking of looking for something that switches at the same input current for the phototransistor, so when current stops flowing through the phototransistor, it goes through the collector.

I plan to have a coil of wire as the load, with a total resistance of about 1.213Ω.

Can anyone tell me if my plan will work? Also, if so, where to look for parts? I tried Ebay and Amazon, but neither have any interactive spec chart for Transistors.


texts: i2c 16 channels relay board works wrongly

texts:
I have 6 16 Channel realy boards. I use them with Arduino mega.

Some of works fine, some of not! My code is same.

for example

Wire.beginTransmission(0x20);
Wire.write(0x00); // IODIRA register
Wire.write(0xff);  // set entire PORT A as output
Wire.endTransmission();

if i use this code, all relay closes. if i write;

Wire.beginTransmission(0x20);
Wire.write(0x00); // IODIRA register
Wire.write(0b11111110);  // triggers first relay
Wire.endTransmission();

with this code, you trigger relay 1 on port A. if u write 0b11111101 as address you trigger relay 2.

But in one relay board, some off address triggers another relay too. For example if i want to trigger first relay and write address as 0b11111110 it triggers second relay too. (another relay boards it don't happens)

You will probably say, "check wires", yeah i checked million times, all are true. My code is true, because it works well on other relay boards. And this board runs successfully 1 week ago. and now not!

What am i asking?

I use different function on this relay board several days ago. board i2c address is still same, port addresses are same, but i am affraid, relay address could be changed because of this code? Is there anyway to reverse default case?


texts: Why do we need external pulling resistors when microcontrollers have internal pulling resistors?

texts:
Microcontrollers do have  internal pull up-pull down resistors yet most of the circuits have external pulling resistors.

I looked on Google for answers and a few sites said that those resistors are not that strong but I thought they were good enough to work. I had the thought that they might need external because the internal resistors need to be triggered by programming.

So for some unplanned situation, they attach external resistors as well. But I'm not certain about it.

What is the real reason behind using externals when we do have internals?


texts: MCU + LED + SSR + (how to determine resistor value)

texts:
I am pretty new to electronics and trying to learn some basics. What I am having trouble with is how to figure what resistor value to use. I'll put links in to the data sheets of the parts I am using. If someone could explain the formulas I'd greatly appreciate it. Here is the setup I have... I have an MCU that produces 3.3V and max rating of 20mA. I really want to stay between 5mA - 10mA on each pin. What I would like to do is use the MCU + tinyled + solid state relay (which has small led in it) + resistor (or maybe no resistor?).

So we have 3.3V to work with.

The led I was thinking of using 550-1304 on this datasheet.

Then in series with this solid state relay.

So here is what I got to but I don't know if it is correct or not:

3.3V - 1.8V (Vf of the led) - 1.15V (Vf of led in SSR) = 0.25V (So my resistor needs to handle 0.25V?)

3mA is needed to activate the SSR, and it looks like 2mA is needed to make the led light up, so I am guessing 5mA.

I then took that for the Ohm's law formula, R = V / I which I did this: R = 0.25 / 0.005, R = 50. Is this the correct way to do it? And I am hooking these up in series, how do I know that the led is going to get 2mA and the SSR 3mA and that they don't share it equally i.e. both get 2.5mA? How do I determine how much each component uses? Also is this the correct formula to figure out what I need? I was trying to keep my part count down and not have to throw in a transistor if possible since the pins seem capable of driving the 5mA load. Some insight and general how you figure it out info would be great to see. Thanks!!


texts:
I got this circuit from an automatic lightbulb sensor , it basically turns on whenever the IR sesnsor detects movement, I was able to reverse engineer the entire circuit, however this clever bastards deleted the silk screen of one integrated circuit (as usual), I have all the other values (I can measure the smd caps by desoldering and using an LCR metter, I have yet to do it) however I know the answer... but I want to try anyway

How can I identify what kind of circuit is inside this IC?! (top at the mid of the page)

Also if anyone can see some inconsensitencies in the schemmatic all the feedback is welcome I will go for a round 2 tomorow (to check those inconsistencies)

After desoldering (I made the scratch by mistake) the IC I found a number below it, but still it doesnt fit any schemmatics online

If its any help this is the actual product

http://chinastarlux.gmc.globalmarket.com/products/details/st451-infared-motion-sensor-lamp-holder-pir-motion-sensor-light-holder-439377.html


texts: What's an industry standard in electrical engineering?

texts:
Context: One of my colleague is arguing I can't use one of my baseline equipment for a long lifetime (15years) product because it is not an "industry standard" and might become obsolete and unsupported during that timescale.

Question:
So when should we consider a particular equipment or device is an industry standard? Is there a database? How are industry standards defined?

This is not intended to be an open-ended question: "industry standard" appears to be a well-defined definition and I'm looking for that definition (I've looked at several sources including wikipedia and it doesn't help), guidelines on how to identify them, and explanations of how they are defined


texts: Problem with H-bridge driving a small motor

texts:
I am asking this question because I am literally out of ideas with what might be wrong with my small circuit. It's essentially a 2-channel bipolar H-bridge, that drives two small motors.
H-brige: TB6674PG
Motor: PNN7RE08JD
I have wired the H-bridge like so:

where IN A and IN B are TTL inputs, corresponding to clockwise or counter-clockwise rotation of the motor. I have no resistors between the outputs of the H bridge and the motor.
I have not connected VS1B to anything (but see later). When the circuit is powered, VS1B shows a voltage of 11.4 V.
Problem:
The B channel does work. I can make the motor turn either direction as I change the TTL level. The voltage on VS1A is always 12 V, and the one on VS1B (which I have not connected to anything) is 8.4 V.  (This is not a typo: VS1A has the power, and VS1B has nothing, but the B channel works and the A channel does not).
However, the A channel does not work!  This has happened with multiple H-bridges of the same type now, and it's always channel B that works. My box actually has 4 channels so two H-bridges each, and on the second one I see the same behaviour. Which makes me think it's not just a broken component but something systematic.
What I have tried:

I have tried to give a load to both channels A and B: B works, A does not.
I have connected VS1B to 12 V as well. When that happens, none of the two channels work.

Is there anything blatantly wrong that I am doing?


texts: Powering a 5v relay from a 12v power supply

texts:
I have a relay which is rated for 5v.  My power supply is 12v.

I have measured the resistance across the coil as 400 ohm.

If I place the relay in series with a resistor that is 560 ohm, would it correctly lower the voltage to 5v?

Or is there something more complicated going on, given that the relay is electromagnetic and not a passive component?


texts: Keeping a consistent supply voltage while driving a solenoid from battery

texts:
I am working on a project where I would like to pulse a solenoid using an arduino with the power from both coming from 4xAA batteries.

The project is a puzzle, when you solve the puzzle, the solenoid momentarily engages to open a latch.

The puzzle side of the circuit is pretty simple, an arduino pro mini with various LED's, switches, a buzzer and shift registers.

The solenoid is controlled using an N-channel MOSFET connected to one of the arduino outputs.
The entire circuit is powered by a 4xAA nimh battery pack, to power the solenoid I am using an XL6009 based step up booster obtained from ebay, it's set to about 15V at the moment, there are 2 2200uF on the output of the step up to try and supply the solenoid when it is triggered.

Everything is working well except for one part, when the puzzle is solved and the solenoid is triggered, there is just a very small movement from the solenoid, and the LED on the arduino board goes faint.

I suspect that the step up booster is pulling too much power after the solenoid is triggered and causing a voltage drop from the battery and causing the arduino to malfunction.

I tested this theory by disconnecting the input of the step up after charging the capacitors and it all worked as expected.

So my questions are:
Is it likely my theory is correct?
If yes, is there some way I can protect the arduino from this momentary load? I thought the capacitors would have done this.

Or am I just dreaming that I can run this circuit from 4xAA's?

Here is the solenoid part of the circuit:

Q1 is a STP16NF06
C3, C4 are 2200uF caps
The lead at the top is an output pin from the arduino
The power marked 18V is coming from the step up


texts: could anyone tell me if i can wire the 12V battery to get around 20V out of the whole set? Right now it's wired in parallel which increases capacity but i need around 20V for the amplifier to have enough power (it can work on 12 but at 50% of volume). If i were to wire the battery in series to the charger's + or - that would fry it, right?


texts: Preventing shock risk on isolated transformer secondary circuit

texts:
I fully understand that you cannot get a shock from either phase1 or phase 2 on the secondary of the isolated transformer, however you can be shocked by touching both.
My question is how do you provide protection on a boat whereby the earth wire is disconnected (to provide galvanic isolation) from shore and all metal fittings such as engine and stopcocks are connected to phase 2(N).
if a phase 1 line(L) accidently shorts to a kettle housing and you also touch any phase 2 component you will be unprotected. As far as I can surmise you cannot use a RCD device as the current will be equal.


texts: External Power supply design for driving multiple loads using arduino uno

texts:
In my use case, I need to drive 5 servo motors (sg 90) using arduino uno.  I have a power adaptor rated at 9v 1A DC which i plan to use for arduino uno. For the servo motor power supply, i have a 12V 5A adaptor which i plan to convert to  5V 2A using buch convertors.

From this forum , it seems for servo motors the stall current is ~750mA but while running, i guess current requirement may be higher, So to have safety margin i decided to provide atleast 1A to each of the servo motor.

I have attached the circuit diagram with this post
As the sg90 servo motor 1,2 and 3,4 are connected in parallel to the buck convertor (which is a power source), then we have 5 Volt 1Amp across each of the servo motors. For servo motor 5 we have 5v 2Amp at idle condition.

I have also added a 100uF polar capacitor to "stabilize" the voltage across the motors.

In my case, I may be required to run all the servo motors at a time, Is this power supply design safe for my use case? Please let me know in case something is vague / unclear in my post.


texts:
I'm doing some homework for my circuitry class and I'm stuck.
I have to find the value
\$\frac{V_{in}}{V_{out}}\$ of a low pass filter, the schematic of which I have posted below.

I got the break frequency, which I have shown below, but I do not know how to find the value of \$V_{in}\$ or \$V_{out}\$. I am also confused by what an octave is, but I think it is adding the same frequency per octave.

Any help would be appreciated!


texts: Does an AC-DC adapter draw more current on 110V than while plugged to a 220V supply?

texts: I have a Sony AC 100~240V 0.75-0.4A input and DC 12V 3A output adapter. I connected it to a peltier module that was drawing around 2.9A on both 110V & 220V. Initially I had connected the adapter to a 110V outlet, but there was a small hum from the adapter and it was hot really quick but when I tried plugging the adapter to a 220V outlet there was no hum from the adapter and also the adapter got only warm. So, does the adapter draw more current in a 110V supply? I don't have an AC clamp ammeter with me to measure the current, so there is no way to determine the current draw.


texts: Is the main purpose of cascoding is to increase gain in FETs?

texts: In my recent studies, I have come across the concept of cascoded amplifier using Common Source and Common Gate Configuration. What exactly is the reason of cascoding?


texts: Multiplying oscillator signal with a pulse

texts:
I am trying to multiply my oscillator sine signal with my pulse. But, the voltage of the oscillator is too big so it saturates.

This is the output I am getting from my oscillator. I am getting the required 100kHz frequency for my oscillator by would like to reduce the voltage in order to feed it into my diff amp.

If I just add an 10mV sine input instead of the 300mV that I am getting from the oscillator, the circuit works properly. Can I reduce the voltage in the oscillator so that the output doesn't saturate or is there any way to change my diff amp in order for the output signal to not saturate.

My output when the signal from the oscillator is 300mV

My output when I feed a very small input sine wave into the input of the diff amp and my required output


texts: why does my USB 5V power supply not need a mains ground?

texts:
Every small 5VDC power supply (wall wart style) I see has the standard 2-prong Europlug, i.e. no ground.  Even those with a British 3-prong plug just use a plastic prong for ground.
Background - I am powering a small ARM board with such a power supply (micro-USB plug) and I am getting a mains hum on a microphone. As soon as I connect ground from my oscilloscope though, the hum disappears.  I have also tried using a slightly bigger power supply, in a small metal cabinet, with a mains ground - same result, no hum.
Why does the wall wart not have a ground and is there a safe way around it?


texts: Frequency of audio signals taken from multimeter

texts:
So I grabbed my Fluke True RMS multimeter yesterday and plugged it in to my Samsung Galaxy Note's audio jack, and started to play some music. I saw AC voltage frequency around 0 – 15 Hz (it's way too slow and unhearable). Is that the frequency of the audio signal? Why is it so slow? I thought that audio signals like MP3 music playing comprises of sums of sines and cosines blended perfectly that look like below

Also, why is it that the audio signal doesn't reach 20 Hz – 20kHz which is what I expect to see in the voltmeter.


texts: Is this "lightning storm over a tropical island" a valid electrical symbol?

texts:
This symbol is stenciled on the circuit board for Compaq PS2021 ATX power supplies. I spent almost half an hour on Google trying to identify it, and I haven't even gotten close. I thought it might be an old company logo, but nothing came up on that search either.

Has anyone seen this symbol before? If not, can you hazard a guess as to what it might represent?


texts:
I have heard about Guard Rings many times, and I know they are supposed to avoid currents in places where there shouldn't be no currents, but I never found a good text to read more about it.

Can someone describe them properly or please recommend some material to further reading?


texts: Relay switching off when under load (spot welder)

texts:
I'm building a spot welder. Schematic is under this link here:

It is supposed to give impulse on relay for time determined by 555. On the other side of relay, I attach on one terminal + of 12V car battery (which I also use to supply the pcb), on the other terminal - ground. I use it to spot-weld nickel tape. It is a car relay, so it is a capable of driving high currents.

Everything is working fine when no load is applied to contact side of relay, For example relay contact closes for 0.5s. But as soon as I apply load (a very low resistance one), contact does not close for 0.5s, but it goes quickly on-off. Current does not flow through nickel tape for long enough and welding does not take place.

What might be the possible cause of this?

Because I connect power supply for welding pin by winding the copper cable around relay's contact terminal (on load side, those are also made of copper), I figured out that when high current goes through those copper wires and contact, it induces strong magnetic field (made by high current) that pushes back the contact inside of relay. Does it make any sense?


texts: I have been searching about programmable priority encoder but have not find a good explanation on it. I know about priority encoder. But generally what is 'programmable' priority encoder are? Can somebody explain it?


texts: How/Where to boost voltage in a 555 timer to drive piezo transducer

texts:
I am trying to create a simple and cheap frequency circuit with a 555 timer to drive a piezoelectric transducer.  The transducer I am using calls for a 48v input with 1.66Mhz frequency timing.  I've used a CMOS 555 timer to create the frequency (using 2 trim pots to do some testing).  I don't have an oscilloscope but my multimeter shows I'm right on track.

Now, I am trying to use a 5v USB cable and I obviously need to boost the voltage to 48v.  I'm not sure how or where I should be putting this boost converter, or even if I'm doing this right?

Here's the circuit I'm using for the 555:

simulate this circuit – Schematic created using CircuitLab

Do I just turn the 5v input into 48v input? or do I have to boost it after the output from the 555?

When I measure the voltage with the multimeter (in place of the crystal) I am getting 1.4v.  Obviously not enough to drive the piezo element.


texts: Connecting multiple Fairy lights in parallel to single power source

texts:
The above diagram shows how I'm about the connect the LEDs, info regarding the drop forward voltage been taken from:
Calculating forward voltage for a string of fairy lights: multimeter shows "1"

I'm about the connect the following power source:
https://www.aliexpress.com/item/MS-50-5-50W-5V-10A-Mini-size-LED-Switching-Power-Supply-Transformer-110V-220V-AC/1323532404.html?spm=a2g0s.9042311.0.0.27424c4dHlPdnQ

My question is, should Vin be 5V for the above formulas? If so, how is the 10A of the power source in taken in consideration with the above formulas?

Please let me know if I missed anything.

Update after Passerby corrections!

So as PasserBy mention these leds are connected in parallel uploaded the updated diagrams and added a 3V DC Motor PWM to fine tune the led light.

Dose it make more sense now? open for any additional suggestions and improvement

Clarification for the motor has input -+ and output -+ as agate to the led wire

Thanks!


texts: Infrared LED vs halogen light output comparison

texts:
I am thinking of using a high power ~50W IR led. I am wondering if LED IR is more efficient than halogen as is the case with visible light LED's? I couldn't find the light output of either IR halogen or LED so I can't compare products per watt.

I basically want to determine if using an LED is worth the cost and added complexity versus the power savings if any.  The LED wavelength can be either 840nm or 940nm.


texts: Detecting rising edges from two different inputs

texts:
I want to build a circuit with two inputs A and B and one output Q with the following behavior:

assume A and B are never high at the same time
on the rising edge of A, Q must become low (A means "clear")
on the rising edge of B, Q must become high (B means "set")

Do I need to have a clock for such a simple circuit?
It seems I cannot directly use (A or B) as the clock of a J-K flip-flop and at the same time use A and B as the inputs of the flip-flop because it would violate the setup time.

Is it acceptable practice to just use A as the clear and B as the preset of a flip-flop without using the clock and inputs of the flip-flop?

Finally, let's now remove the assumption that A and B are not high at the same time. How do I detect the rising edges of both inputs, again without a clock?


texts: How to find voltage and current in the given circuit?

texts:
I need to find voltage V(ab)  and current i(0) in the circuit. The task should be solved by mesh-current analysis.

So,What did I try?

Let's notice that there are 3 meshes. It means , using KVL  , I can write 3 equations and find current. My equations are following:

$$20x+20(x-y)+30(x-z)=80$$
$$20(y-x)+20y+30(y-z)=80$$
$$30(z-x)+30z+30(z-y)=0$$

$$where\quad x,y,z \quad are \quad currents $$

After this , I can find z(that is current of right mesh) from systems of equations. And I suppose that z is the i(0). And to find V(ab) , I have to multiply 30 to z. Is my solution right? If not, how to solve this problem?


texts: SMPS: What is current mode instability (aka “sub-harmonic oscillation”)?

texts:
In peak current controlled switching power supplies, there is a phenomenon called “current mode instability” aka “sub-harmonic oscillation”. What is that? Can't seem to get a good explanation of this....

Bonus:
(To mitigate this side effect, they recommend using something called "slope compensation".)


texts: Logical Effort (G) and Effort (H) in Parallel

texts:
I am struggling with this question in which I need to understand what is the route with the least effort (H).
Usually, I'm given a route but it's very simple to calculate, because all the other inputs of the logical gates are regular inputs without any logical gates connected to them, like in this example:

The main difference and what I am struggling with, is in the example above the route is clear, and the legs of the logical gates are just regular inputs..
The circuit which I need to analyze is this:

And the question is which route has the least effort (H) - A,C, or they both the same.
My hunch is that they're both the same, but I can't figure out how to calculate it.
I think the fan-out (f) is the same for both routes - 4/1=4 (I might be wrong here so please let me know if I do).
But I'm not sure how to calculate the logical effort (G) in the routes.
For example, if I look at route A, so the first logic gate is a NOT (g=1), and the next one is NAND2 (g=4/3), but, the other input of the NAND also has a NOT gate connected to it. In my opinion, this shouldn't matter (because again, g of NOT is 1). But when I look further to this route I have a XOR2 (g=4). so far, G=g1xg2xg3=1x4/3x4=16/3, and H=GxF=64/3.
But I don't think it's right, since the other input of the XOR2 is connected to route C, so it has a NOR and a NOT beforehand.
So finally - my question is how do you calculate the effort of a route, if it has more logical gates from the other input?
Thanks in advance!!


texts: What the difference between Ipk and Iout in MC33063A?

texts:
On the first page of the datasheet we are having this statement.

In the equations table with designe procedure we will have this formula.

And all the online calculation tools tells me that I cannot get more than 250 mA of output current without 1.5 A Ipk limit, for Vin = 4.8 and Vout = 12 V. Trying to recalculate it by datasheet's records seems to not going well.

So what the difference between Ipk and Iout? What the actuall transformation ratio? What the maximum output power of this converter? The last question, maybe better describes it's abilities, rather that current.


texts: Antennas- Spacing between Reflectors & Directors in Wavelengths

texts:
I’m building an antenna and I want it to connect to channel 6 on the spectrum allocation chart (2.437 GHz). I’ve calculated the lengths of the reflectors and directors but im just a bit stuck on the spacing between the reflectors and directors.

I’ve came across this table that says the spacing between the reflectors and directors, but it says it in wavelengths. I’m not sure about this measurement means and I was wondering if anyone can help me to shed some light on the spacing between the reflectors and directors from this table.


texts:
I am looking for a display that is 8-10 inches across diagonally, low power, preferably colour and refresh rate isn't an issue.  I would want to display text on it, so I need something with a decent resolution.
I was thinking monochromatic e-ink / e-paper would be the best option, but it looks like they can be quite expensive.  Anyone know of some cheap displays that I could use for a project?


texts: How does a microcontroller drive an LCD?

texts:
I'm not a professional so I'm looking towards a simple answer to this question.

If you want to turn an LED on using a microcontroller, then you have to assign a pin on the microcontroller to the LED. Whenever the microcontroller sets the pin voltage to high, then the LED turns on.

I assume that displays should work with the same principle since they have some kind of a LED for each pixel. The problem is that if it was done the same way we turn an LED on, then for a small 320x240 screen we need 76800 microcontroller pins. It seems that the procedures should be different somehow. So how does a simple IC on an LCD tell each pixel to turn on?!

To avoid confusion I should point out that by mentioning microcontroller above, I mean the chip on the LCD module itself.


texts: Diode circuit analysis with two diodes in series

texts:
simulate this circuit – Schematic created using CircuitLab

In the above schematic the CVD model is being used, with a voltage drop of 0.6 V, for all three diodes. The input voltage sweeps from -10 V, to +10 V. In this homework assignment my task is to sketch a current vs input voltage diagram for all three diodes. In my analysis, I started from the -10V input and did a circuit approximation for that single voltage and tried to find when one of the parameters defining either the voltage or the current for any diode changes its sign, or more precisely, one of the diodes turns off or on. This is my diagram for that specific scenario:

simulate this circuit

The expression for the current is I=(4.4V - Vin)/R1. This current is always >0 for all input voltages that satisfy the inequality Vin<4.4 Volts. However a simulation I performed in LTspice revealed that the diode D1 actually stops conducting much earlier, at Vin=0.6V.

This inevitably led me to seek another analytical way to obtain the same result as above. This is the equation according 3,to KVL:Ud3+Ud2-0.6-Vin=0. Both Ud3 and Ud2 are <0.6V. Rearrangin the previous equation I got Ud2=Vin+0.6-Ud3<0.6, and thus Vin


texts:
I got myself a little button to start playing around with. Attempting to hook it up to a Rpi.

What I wanted to confirm was the purpose and pins for each wire. The button I got is http://www.robotgear.com.au/Product.aspx/Details/782-Button-Module-with-cable

Some confusion was caused for me by G V N S..... I'm guessing G=Ground V=Active N=Neutral S=Dito
Close up with GVNS http://www.robotgear.com.au/Cache/Files/ProductImageOriginals/2233_Button%20module%20with%20cable.jpg

After speaking with a friend who has more experience with this stuff. We're assuming this configuration

G = Pin 6 Ground
V = Pin 4 5V
S = Pin 11 or GPIO


texts: Probing with Oscilloscope Stops ADC Fluctuation

texts:
I've gone back to my constant current project to fix an annoying fluctuation in the required current display.  See schematics below.

The entire circuit consists of a CCS section with signal outs for both the requested current (represented by Vreq) and the actual current (represented by Vact developed across the sense R).

These signals are sent to an amplifier which scales them up x10 and the amplified signals are sent to a uP ADC with an external 2.5V ADC reference.

I'm using a star-ground approach and I keep digital (uP, display driver) and analogue (CCS, amplifier) grounds separate, with a separate ground point for the load return.

Despite this, the required current selected by the 100k POT moves up and down a mA or two on the display.  In preparation for some low-pass filtering, I took some readings with my oscilloscope probe (set to x10) and to my astonishment, the display was rock solid.  No fluctuation, perfectly smooth with the POT turns.

It didn't matter which "Probed" point I tried (see diagrams below), the effect was the same.  Realizing that the probe contains some capacitance and a large resistance, I tried placing a 22pF and 10M in parallel at one of the points probed.  So, far I haven't managed to replicate the "fix" brought about by the probe.  I'll get a chance to do some more this evening, but in the meantime: can anyone tell me why the probe has had such a "beneficial" effect on my circuit?

Thanks!

UPDATE: I should have pointed out that the oscilloscope is mains connected and its ground lead is connected to earth ground.  Also, the circuit itself is floating, that is it's connected to a 5V wall regulator that doesn't use earth ground.  One other thing, in all cases when I probed the circuit ("probed" points), I connected the oscilloscope earth lead to the local ground at that point (not the star ground point) - not sure if that makes any difference.

While I'm updating, another intriguing thing is that if I attach a load (say a 100 ohm resistor) the readings seem to be quite stable.  Not sure if this is related, but I thought it was worth mentioning.

ANOTHER UPDATE:

Well, I had a chance to test things a bit further.  Seems like it's the connection to earth ground that fixes the issue, so @WhatRoughBeast is on the right track.  Unfortunately, the twisted pair trick didn't work.

FINAL UPDATE:

I finally got the circuit to work reasonably well.  I changed the 100k multi-turn pot for a 10k (and the 1M5 resistance to 150k) and the increase in current seemed to cure the flickering, except when the pot resistance was quite high.  I also shortened the signal wires and implemented a simple digital low-pass.  If I had this to do again, I'd use a proper PCB with a ground plane.


texts: Implications of using a 2C-#18 twisted shield pair nec type cmr cable for RS-485

texts:
The cable will be passing modbus and another equal cable will be used for loadshare. The total cable distance will be about 100ft. Its catalog number E2032S.

I notice other threads related to CAT5, but am unsure if I'll be opening myself up to a lot of issues during commissioning if I don't get the correct cable with 120 Ω characteristic impedance.


texts: Effect of changing the length of an inverter's N-mos transistor on the propagation delay

texts:
let's say we want to check the time it takes for our source Vdd to charge a capacitor through an inverter network. changing the width of the P-mos transistor will make more current flow, thus minimizing the charging time. which effect changing the length of an N-mos will have on the propagation delay?
thanks,


texts: impedance matching single vs series capacitor

texts:
Im looking at a impedance matching circuit on a schematic that shows a .75pF capacitor pulled to ground.

With my current board design I have a 1pF and a 3.3pF on the board already so I am thinking of using these two in series to create .75pF.

simulate this circuit – Schematic created using CircuitLab

I am no RF guru so I am curious if this has bad implications at 2.4GHz.

Aside from making sure I am using something that has similar:

type
ESR
voltage-rating
tolerance
temperature coefficient

To Clarify: In the original schematic it shows the single .75pF. I am curious if its OK to switch this out for the two series caps.


texts: Do filter capacitors always have a leftover charge when AC voltage is removed?

texts:
In electronics I have encountered the topic of filters in power supply. One of the concepts mentioned is about the bleeder resistor, where a resistor is connected in parallel to a filter so that the capacitor is able to discharge any leftover charge when the equipment is turned off.
What really questions me is that although I have researched a lot, there is no source that says that there is ALWAYS a leftover charge retained in a capacitor when an equipment is turned off or that a bleeder resistor is always necessary when using a filter. Yes, I know that they are important for safety precautions. I just want to know, is this always the case? Will there always be a leftover charge? Will someone always get a shock or be in a dangerous situation when handling something involving a filter without a bleeder resistor? I want to know if it is something that is absolutely necessary and not it will increase the chances of being safe because I already know that it does.
Sorry if the question sounds stupid, but I am not an expert and just want some sort of precision with this idea explained by someone who knows the concepts really well.


texts: What do I need to create a USB interface between a PC and a board?

texts:
I am making a custom camera that will be interfaced through the USB port to the computer. Currently, the board contains all necessary circuitry to drive the image sensor. It outputs a parallel stream of pixel data and a sample pixel clock. The data is sampled with a NI DAQ board that is in the computer.
I would like to add/create a USB interface to my board, so I do not need to use the NI DAQ.

What options are there to create this interface? What do I have to consider? How complex would it be to write a driver for my board so a computer can recognize it? Any recommended articles to get a general insight on how to approach this problem?


texts: How can a multimeter measure current while being parallel to the element

texts:
An ammeter is a low resistance device connected in series with the element through which we want to measure current However, a multimeter is connected in parallel with the element under observation for current measurement. What mechanism operates there ?

It cannot measure voltage and resistance and then take the quotient as resistance can be measured when resistor is isolated.

Does it first measure the impedance of the element,say it is R and then it varies its impedance between pins to say 1000R , then impedance of this circuit is still nearly R so that we did not disturb original circuit noticeably, then it measures current through itself and multiplies it by 1000 to get the current through R.

Wikipedia https://en.m.wikipedia.org/wiki/Multimeter  says
(Under operation) :

  For analog current ranges, matched low-resistance shunts are connected in parallel with the meter movement to divert most of the current around the coil. Again for the case of a hypothetical 1 mA, 500 Ω movement on a 1 A range, the shunt resistance would be just over 0.5 Ω.

However I don't understand it.

Please explain the solution.


texts: Inverting Op-Amp Schmitt trigger threshold

texts:
I'm pretty sure I found an error in a textbook, and I would like your advice before I send it in.

It's an inverting Schmitt Trigger, built with an Op-Amp. So the Input Signal is on the Inverting Input, R3 is for hysteresis, R1/R2 Voltage Divider determines the threshold.

The textbook implies that to lower the switching threshold to ground, R1 (which goes to Vref, which is positive) should be omitted - (edit: it's not clear whether to remove R1 or bypass it, it just says to use a Resistor from Noninverting to Ground. If interpreted to remove R1, thereby making it infinite, the textbook would be OK, as pointed out by DarenW.)

However, I think R2, which goes to ground, should be omitted, because then the Noninverting Input would see ground and the Op-Amp would compare the Input Signal to Ground, and if it is higher than Ground, it would turn off (as is desired in an Inverting Schmitt Trigger.)

Am I right with my objection?


texts: Are there chips encoded with fixed 8bit values?

texts:
I am assembling a few data acquisition fixtures and would like my software to be able to identify the fixtures programatically. I have a breadboard that I can use for basic circuits. The DUT signals come into the fixture, can interact with the circuits on the breadboard, then from there it is connected to the DAQ hardware.

The DAQ hardware has 16 available digital IO lines I can use. At first I thought I would just pull some of the pins up and down with jumpers to put an 8bit identifier but then I thought it would be cool if there were chips that presented a fixed value.

To clarify, I would like to direct connect a chips pins to my DAQ digital IO pins so that I can read a value encoded in the chip. This is to prevent someone tampering with it and generally raise the level of security for the solution.

I searched for such a chip but cannot find one. I do not want anything I need to program or that requires significant support circuitry; just looking for a super simple, single chip solution to put a fixed value on my digital lines.

BTW, in case it's not obvious: I'm an electronics newbie... big time.


texts: The method and calculation for the total energy that two inductors,which has Mutual inductance, stored in this circuit

texts:
The solution for the total energy that two inductors stored in this circuit is

\$E=\frac{1}{2}\times 4 \times 3^2+\frac{1}{2}\times 6 \times 6^2-1\times 3 \times 6=108J\$

I want to ask two things

1.Why is \$E=\frac{1}{2}\times 4 \times 3^2+\frac{1}{2}\times 6 \times 6^2-1\times 3 \times 6\$,i mean , \$\frac{1}{2}\times 4 \times 3^2\$ and \$\frac{1}{2}\times 6 \times 6^2\$ are both energy calculation because of  \$E=\frac{1}{2} L  I^2\$,but why does \$1\times 3 \times 6\$ is the energy calculation?it just the multiplication of  Mutual inductance and two different current,and there is no \$\frac{1}{2}\$ in it.

2.If i use this method to calculate the total energy that two inductors stored,the answer is wrong,why?

\$L_{eq}=\frac{L_1L_2-M^2}{L_1+L_2+2M}=\frac{23}{12}\$,then \$E=\frac{1}{2}LI^2=\frac{1}{2}\times\frac{23}{12}\times6^2=\frac{69}{2}J\$,why will i get the wrong answer if i use this method??


texts:
I'm going to use a power resistor which needs to dissipate around 2.5W. I will use a resistor rated at 3W.
I have a thermal impedance of 88°C/W. If the ambient is at 40°C, I assume that the resistor will go over 2.5W*88°C/W + 40°C = 286°C

Opening the datasheet, it allow an ambient temperature range -55 to 200°C. Then there is a graph showing the dissipation over the allowed temperature rise, that goes over 300°C.

If the resistor will go over 200°C, is it still ok? Can the resistor handle the temperature? (assuming that the tin will not melt). I should be able, by observing the next graph, which is the derating curve.
In other words, how one should use the Temp Rise VS Power graph? Here an example datasheet: http://www.farnell.com/datasheets/1449996.pdf

EDIT: Searching around and viewing other datasheets, I've understood that one should see only the derating curve. It is considered to use resistor with its stated thermal resistance, while the temperature rise can be used to understand if the temperature achieved is suitable for you. In fact, the derating curve is shaded over the 200°C (max ambient) up to 315°C, because it is not guranteed a well behaviour of the materials. All resistor's datasheet are explained like this.


texts: What options exist to verify Avalon-MM slave component?

texts:
I am writing an Avalon-MM slave. It shall connect to Nios II as master device. What options exist to write testbench for it? I must be sure that an Avalon-MM master can correctly read/write it.

I have come across something called Bus Functional Model but it is not clear how to use it.

How should I start?


texts:
I've got a 3-9W RGB LED (https://www.adafruit.com/product/2524).

It's connected to a breadboard with a power supply that tests as giving 4.9V and 2A on a short circuit.

I've got 5W resistors at 2ohms for the green and blue leads (the datasheet says they have VF=3.6) and a 3.3ohms for the red lead (VF=2.5V).

The datasheet says the max continuous forward current is 700mA, so I'm trying to get as close to that as possible for each color. According to https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-led-series-resistor these resistor values should be drawing ~700mA per die on the LED.

But if I hook up the circuit so the common anode lead goes to positive power, then the individual color leads are connected to their resistors, then the resistors go to ground) and put my multimeter in series with the anode, it shows it's only drawing 0.5A. I was expecting a lot more. I want to get this LED really bright. I mean, it's pretty bright as is, but I'm thinking it could be a lot brighter if it were drawing more current.

I'm trying to understand why it's not drawing the full 2A available... In looking at the datasheet again, I'm guessing it has to do with the forward current curves? For example, the red curve shows that at 2.5V it's only going to draw 200mA. Does that mean that if I take my supply voltage of 4.9V and subtract the VF of 2.5V (for red) that I should look on the curve at 2.4V to see how much forward current it will use? If so, does that mean I need to up my power supply from 5V to something higher to get it to draw more current?


texts: Suitable substitute for a hard to get IRF440 in a switched power supply?

texts:
I am repairing a HP 6023A lab power supply for a friend. The problem was that the power fets had failed. This is what the relevant schematic looks like:

The incoming 120VAC or 240VAC is rectified and the resulting approx 340V (they use a doubler for 120V) feeds the switcher. Here Q3 and Q4 had developed shorts and F1, F2 had blown.

Problem is that IRF440 is a High-Reliability part. MIL std and radiation hardened. The minimum quantity from the distributor is 100 pcs and none of the regular distributors, say Mouser, Newark carry it. It is available from eBay, but I am a bit wary as there are lots of counterfeits around.

The IRF440 is a 500V, 8A N-Channel FET with an Rdson of 0.85ohms. The IRF840A from Vishay has the same parameters or better, with one exception: Eas, maximum pulse avalanche energy. Rest, like diode recovery time is better (5.0 vs 3.5), Qg (38 vs 68) etc and lastly, they are both max 1C/W junction to case, which is surprising as a TO3 part has so much more metal than a TO220. The FETs sit on separate cooling fins and are cooled by a fan.

So, I am tempted to go with the IRF840A as is is cheaper and also readily available. This PSU will be used by a hobbyist and never launched into orbit :)

Is my reasoning sound?

PS. Should F1, F2 be ultrafast, fast or slow-blow? The manual does not say. They are small axial fuses with leads.

The HP6023A has a very endearing feature: A swith on the motherboard isolates the HV supply from the logic supply. You flick that switch and feed mains to two spade connectors. That lets you run the logic without the power part. You then connect a DC lab power supply to the mains input to test in a controlled fashion.

I soldered in two IRF 540 to test and fed in 60VDC. I could verfy that the unit operated properly, ie CC/CV, current limit etc. I am pretty certain that it is just the two FETs and fuses that are faulty.

The service manual also states that they are prone to blowing :)


texts: How to do the bode plot for this function without Matlab?

texts:
I want to plot the bode diagram without any software for
$$G(s)=\frac{(s-2)}{(s^2+4s+15)(s+2)}$$
I do not know how to deal with the factor of \$s-2\$
I will be appreciate if someone can show me your working for the function rearrangement bit.


texts: What is the meaning of "The transistors Q1,Q2 are identical" and of "Q1/Q2 = 10"

texts:
What is the meaning of the given data

  Two transistors Q1,Q2 are identical

Does it mean that they have the same working point (I_C,V_CE), or maybe that only one of these parameters is identical? Or maybe it means that the \beta is also identical? I encounter this data from time to time but I can't find anywher the definition.. i.e.

  "We say that two transistors Q1 and Q2 are identical if: 1)...,2)... etc.."

I have the same problem with the data of sizes relation i.e. I can't find the definition for:

  "We say that two transistors satisfy Q1/Q2 = 10 if: 1)...,2)... etc.."

I would be very helpful for me if anyone would know these definitions or where to find them..

Thanks!


texts: FETs: When does Input Capacitance and Gate Charge matter?

texts:
My question is this:

Besides frequency response (i.e. filter effect), does input capacitance every matter?
When does gate charge matter?

Obviously these have effects on the graphs in the datasheet, but is there any general behavior each has? (i.e. larger gate charge means X, smaller gate charge means Y).

This has come up because I'm doing a lot of load output stuff (i.e. not fast switching, just having a FET for the sake of reverse polarity protection or output OR-ing), and am wondering if these two characterstics even matter if the FET is only really used in a DC, "almost always on" circuit.


texts:
I have a device that outputs 12.4 +/- 0.1 mV when it is inactive and 12.9 +/- 0.1 mV while it is collecting data. I would like to trigger another device that expects 3.3V high and 0V low for it's start and stop conditions respectively. Because of the variability of the first device it seems that amplification (of around 660x) would not work. How can I set up a circuit to detect the very small change in the first device's output and activate a 3.3V source for the second device? A comparator seems like the way to go but I'm not sure how to minimize the size of the circuit.

edit: My two devices are a Force Platform system and an Inertial Measurement Unit motion tracking system. I am trying to use the signal from one to trigger the other so that they start data collection synchronously. The IMU is capable of sending and receiving triggers, but the FP are not, so my idea was to split the digital signal of the FP and use the voltage change on one of the output's pins as the trigger. Both are black boxes for me, the companies that produce them will not give me further information as they would prefer to sell me an interface device that does this for me, however, I'm on a graduate student budget...

Thank you!
-B


texts: Should I inherit from Arduino's Stream or Print when I'm using write?

texts:
I'm submitting a pull request to an Arduino library and want to make sure I'm doing the right thing before I send it. The change allows the dumping of data somewhere other than into a string buffer (in my case sending it to SRAM).

I've implemented this initially by altering the library  to take a Stream object which it will call write on when it's saving data (if the object has been passed). This seemed the most sensible as it's a stream of data.

However, when implementing my SRAM storage class I realised Stream has no write method, and I was pulling in 'using Print::write' to my class to give it that ability. Which made me think maybe I should have modified the library to take a Print object rather than a Stream object, as there's no guarantee a Stream will have a write method.

Would appreciate advice - Print seems wrong as the class, but the API style guide at http://arduino.cc/en/Reference/APIStyleGuide seems to suggest Stream as the way to go though it seems to imply that Stream implements write.


texts: How can I determine the correct voltage connector in an addressable LED strip?

texts:
I found a couple of cheap Addressable RGB strips laying around and they seem to have a different connector that won't fit in the current PC ARGB controller.
I cannot identify what type of ARGB module on each LED, but there are 3 wires on that strip. Since they're addressable, I assume they're 5 V.
Is there a way to determine which is the voltage wire and ground wire without plugging into the controller? I wanted to avoid burning it, which I have done in the past. I used this cheapo multimeter to determine something, but to no avail.
Your help is appreciated.


texts: Burned IC (Has something to do with USB)

texts:
As I was working on a project, I made a short and an IC caught fire and the magic smoke escaped. It was the IC U5 on the schematic (1). I am trying to find a replacement for it but I don't know what it does to search for an equivelant IC.

(1) https://robotdyn.com/pub/media/0G-00005516==SAMD21-MINI/DOCS/Schematic==0G-00005516==SAMD21-MINI.pdf


texts: A question about super-heterodyne receivers

texts:
My question is about the following paragraph:

The text implies that the heterodyning process is basically done to obtain a fixed frequency before amplification takes place. Here I don't understand why. Doesn't the incoming AM signals to the trf receiver already have fixed frequency as well? AM has fixed frequency with varying amplitude.

What am I getting wrong here?
I've read some related question but couldn't find an answer.


texts: Can I mimic Arduino Ethernet library through serial?

texts: I'm ordering an Ethernet Shield for a project I have planned, but before make the investment, I want to make sure the project will work. Eventually it will communicate with a website via ethernet, but I was wondering if I could test this through my PC, using it simply to route page requests, so that I can easily adapt it for the ethernet shield.


texts: Is the transfer function for the given RC network right?

texts:
For the question

I arrived at the following answer
(I have assumed V1 btw)

Is my solution right? I just have a big doubt if whether I can use the voltage division rule at point A when there is an RC network after it.


texts: The maximum voltage the relay contact can withstand

texts:
For some relays they may give a maximum switching capacity graph like below

From the graph can I assume when the current is 0, the maximum switching voltage is also 200V? That is the contact can only withstand a voltage 200V when open?


texts: How to determine DC input voltage of a device without its charger?

texts:
Had a MotoMaster (Canadian Tire) 27/3 LED flashlight for 4 years now.  Model was discontinued 2-3 years ago.  Lost the charger at least 2 years ago and the light's battery FINALLY died today (!!)

I need to find out what is the correct voltage and order a DC charger for it.  Is there a way to determine the values without the charger?

Obviously, I'm asking because absolutely no value is written on the flashlight, except for polarity and a model # that gives absolutely nothing on Google: 037-9405-8


texts: Op-amp circuit with feedback: does the polarity matter?

texts:
Suppose we have the following circuit:

simulate this circuit – Schematic created using CircuitLab

Does the polarity of the op-amp (= which terminal is the inverting and the non-inverting input) affect \$U_o\$? Taking the usual analysis (see below) into consideration it seems like it doesn't matter. This makes no sense to me, because op-amps act as comparators. Can someone please give me an intuitive explanation of why this happens, if it is true? Also, is there any case that the polarity matters when we have feedback?

Analyzing the circuit: suppose we want to find \$\frac{U_o}{U_s}\$:

Voltage law from GND,\$U_s\$ through the inverting terminal(=GND, virtual short): \$-U_s+i_1R_1=0 \Rightarrow U_s=i_1R_1\$ (1)
Voltage law from inverting terminal(=GND, virtual short) through \$U_o\$: \$i_2R_2+U_o=0 \Rightarrow U_o=-i_2R_2\$ (2)
Current law for the node next to inverting terminal: \$i_1=i_2\$ (3)

(1), (2), (3) \$\Rightarrow \frac{U_o}{U_s}=-\frac{R_2}{R_1}\$.


texts:
I am trying to understand a schematic by Espressif for the ESP32 devkit v4.
There are 7 arrows on U1 (CP2102N-A01-GQFN28) and 1 on U3 (ESP32_WROVER(NC)).
Why U1 have a green rectangle?
Link to the full schematic.

Image by Expressif.


texts: Can't find the right power supply - could I use something similar?

texts:
So I've just bought a Behringer MX2642A mixer off eBay, which worked for two hours then promptly shut down. After investigation, it seems that the power supply might have given up - the specs for the mixer are (checked with Behringer):

"2 x 19 volts AC at 2.6 Amps (50Watts)",P/N: W81-19951-02845

However the supplied PSU was:

32VCT 500mA

The connector is a weird screw in-job, with three pins. Two for AC and one for "CT" whatever that is...

Behringer no longer make these PSUs, and I can't find anything remotely similar online. Could I use something like this
http://www.maplin.co.uk/p/3a-acac-fixed-voltage-12v-power-supply-n57dl

...or is the mixer now a brick? :(

Could I even wire two adaptors together?

Any help massively appreciated,

Oliver

Pictures

Mixer:

Supplied PSU:

Couldn't post this as a link, but it's here: imgur.com/n5CY6uM


texts:
I currently work on a sensorbox which needs to measure analog signals (temperature, power consumption,..), digital signals (magnetic contacts, positions,...) and control digital switches (relays). All this magic is controlled by a PIC18F (has an ADC) and interfaced with a larger machine via CAN. This is just a laboratory setup (lots of cables, breadboard), where the controller is programmed using ICSP.

Since the box should now be included in the machine I was wondering how to include the MCU, since the sensors are almost unreachable after the project is finished.

Wire all the cables from the sensorbox to a 'safe' location where the MCU is located
Include the MCU on the box and wire only the CAN to the frontend

Since I am not sure that I have to change the code I would prefer option 1. Here I can reprogram the MCU on the front.

OR

Wire additional cables (the three programmer cables for the MCU) to the frontend.

Whats the conventional method for such a problem?


texts: What is the audio voltage of an android phone?

texts: For a project I am currently working on, I need to use the audio output of an android device. Is there a standard max voltage?


texts: DC or average value of a non-sinusoidal signal

texts:
I need to find the DC value or the average value of the distorted waveform. First the waveform is given to op-amp voltage follower circuit to prevent it from loading and then to a RC low pass filter, but getting an error of around 10% (Comparing it with the DSO output).
Can someone suggest me a good circuit model for the same or any IC for this special purpose?
Edit: We don't need to find the RMS value here, for that case there is an IC AD736 for this special purpose. What we need is to calculate average value or DC value. Like the waveforms shown below:


texts: Why is electron flow taught in some contexts?

texts:
The standard as I learned it is that the flow of current is from positive voltage to negative voltage. The direction of current flow is opposite the direction of electron flow. This is what I learned in school, the assumption made by almost every engineer I've worked with, and the standard in every simulator I've ever seen.

I've encountered two exceptions. One is this textbook, which a colleague has on his shelf from his associates degree training. The other is a pair of former navy personnel I've worked with, both of whom were taught electron flow in the navy and had to unlearn it when they left.

I understand that both are valid mathematical models of the same phenomenon. What I don't understand is why anyone would purposefully and knowingly train people in a fashion contrary to a near-universal standard. (It took a lot of work to make that textbook!) Is the standard as I understand it not as standard as I think it is? Is there some analytical advantage to the electron flow model that I'm not seeing, perhaps in realms of EE I don't visit often?

Why is anyone, anywhere, ever taught that current flows from negative voltage to positive voltage?


texts: What is the purpose of this 5 V protection circuit?

texts:
I'm working in the OEM company and I want to know what the purpose of the below circuit is.

Whether +VCC5V0 or -VCC5V0, Q8 is off so I don't know the purpose of this circuit. It should be a protection circuit, I think.

Can anyone explain this curcuit?