texts:
I have a beautiful old variac, with a sliding (rotating) center contact.
I would love to use this on a nice LED string inside a glass bulb on top of the device.
But also, use the variac as the dimmer, by rotating that glass bulb.
The contact points are bare metal, so mains is not an option.
I have a nice AC/AC transformer for 240V -> 24V AC, That would be nice, but I have to limit the current. This LED string gives a nice light-output at 250mA, which flows at about 3.1 volts (it's 100pcs parallel, no datasheet available. Used to be battery operated, 3x AA with a 10ohm resistor).
What would be a good way to drop the voltage, keeping the Variac in circuit?
I have been thinking of an capacitor after the coil, but I wouldn't know if the current-output would be constant at the frequency, or also depending on the variac-state?
Or would a decent resistor be the only option? (5.5 watt minimum, 20.9V at .250A)


texts:
Hi,

I'm just wondering about the current rating of the JST-XH and JST-VH connectors PER pin. For example, in the XH connector above, **

it says 3A current rating, is that split between all pins or does
that mean one pin can carry 3A?

**

So in essence, if I dedicate two pins to VCC, then I could achieve 6A?


texts: Does low power in the mains causes damage to household supplies?

texts:
I live in Cambodia and power outages here are not uncommon.

One of the things I have noticed today that devices like kettle or induction heater would switch off after working for 10-20 seconds. I am assuming this is due to low current (or maybe lack of potential) in the power line. Does low current damage equipment? If yes which household supplies should I switch off not to cause permanent damage (fridge, tv, PC, etc), or should I just keep switching kettle on and make some coffee?

Does low power in the mains cause damage to household supplies? If it does should I disconnect any of them?


texts: What is the main carrier in a semiconductor with n-type material being electrons and p-type materials being holes?

texts:
Not even gonna lie this is for a crossword. it is a 15 letter word. I have searched online, in my textbooks and I cannot figure out what it is. Closest I've found is Extrinsic Semiconductor but it's too big for the box.

Anyone know what it is or care to point me in the right direction?


texts:
I recently purchased a ATTEN APS3005D Regulated DC power supply from eBay and I'm having some odd and potentially alarming results that I'm trying to get my head around.

Note: I'm testing this with a reliable Fluke multimetre.

The device is plugged into 240v Australian mains supply - which it is rated for.

Test 1:
The device is switched off.
Fluke Multimeter is set on AC, leads are placed between the Ground (green) and both the positive and negative terminals on the APS3005D.
The result reads ~110VAC between Ground and Positive
The result reads ~110VAC between Ground and Negative

Test 2:
Turning the device on, the device appears to work correctly. The control circuitry is working, 7-seg display is working. The power supply is switching when the voltage is turned up.
Placing the multimeter onto DC mode and measuring between negative and positive, I get the correct readings that are also described by the 7-seg displays.

Test 3:
Device is on as per Test 2
Multimeter in DC mode between Earth and either positive or negative terminals, gives wrong floating readings. (Probably because theres actually 110VAC not DC).

Test 4:
Device is off
Ohmmeter measuring the output resistance between ground and either positive or negative terminals gives an infinite resistance reading.

It does not seem safe at all to have 110V between the Earth terminal and either positive or negative terminals. This could seriously hurt someone.
This doesn't seem right does it?

I was under the impression that the ground terminal was a reference ground between positive and negative yielding this sort of behaviour:
-15V ----- 0V ----- +15V
<----------30V--------->


texts:
I am trying to use RS232 to TTL convertor much like this: https://www.amazon.com/MAX3232-Female-Serial-Converter-Module/dp/B00BXX2OU2 I am not sure if the chip is authentic MAXIM or some knock off.

When I connect the convertor to the rs232 device (a home alarm), the led on the convertor flashes on a regular interval. When I connect the  (ttl) rx/tx leads from the convertor to my computer I see activity on the serial port, but it looks like gibberish. It does not follow the protocol of the system. If I attach the ground and +5 vcc to the ttl side, my led shines continuously, but I see NO activity on the serial port.

I have checked the RS232 converter via a loopback (crossing the tx/rx lines) and verify that I can see characters echoing back. I tested the connector by hooking it up to another one I had and verified that sending on one serial port results in the correct text arriving on the other. I can see that RS232 device (the alarm) is active and there is voltage on the TX pin when I put a voltmeter between TX and GND. The voltage is roughly the nominal 9V that is indicated in the manual.

I am not an electrical engineer, so I am out of ideas. What am I doing wrong? Do I need to solder in a resistor on the RS232 TX pin? Do I need a voltage divider?

Thank you!


texts:
I'm building a small project where I have 12v @ 8amps batteries and on some occasions, I would want to plug in an adapter so I can still use my motor board in the absence of not having a fully charged set of batteries. I want to isolate both power sources too.

What options do I have available? I'm currently looking at some power multiplexer chips (I might have the terminology wrong) but I cannot find any that will meet my requirements.


texts:
I want to make induction heater. So I want to make oscillator for this. I want to make oscillator with transistor, inductor, resistor, diode and capacitors but not IC, relay switch, op amps etc. Which oscillator should I make?

The required frequency of oscillator is from 15-50 kHz.


texts:
I have a NodeMCU and a website (free website domain provided by hpage.com) and I have to send and receive some data (suppose a 8-bit number) from the website to the NodeMCU via internet.

The NodeMCU is connected to internet through WiFi hotspot of an Android phone.

Can anyone provide an example code?

I have seen the system working on WiFi LAN, and I don't want to limit it to local network.

How can I address the NodeMCU from the website?
Does the NodeMCU need to be a server or just a client?

Thanks in advance for kind help. I can't use a WiFi router, I have to use a android phone hotspot in this case.


texts:
A three phase machine, instead of having six terminals, two for each slip ring, has only four terminals. Because the starting point of all the three coils have a common junction which is usually earthed and the other three coils are connected to three separate terminals on the machine.

What does the starting point mean here? And how do we have 4 terminals when we are having six slip rings. Terminal from each slip ring would make it 6 terminals.


texts: How much time to I have to switch outputs on a CD74HC4067 multiplexer?

texts:
Looking at this datasheet, how do I determine the amount of time I have to switch between one connection and another?

It seems that as I switch from one connection to another I will go through several intermediate states as my software sequentially toggles the select pins to high and low appropriately, in principle selecting several undesired connections.

This is obviously not a problem, but how do I verify this from the datasheet?  How slowly could my processor set the pins and still work?


texts:
Is it possible to glow the both LEDs simultaneously in an anti-parllel circuit?

I tried with H-Bridge but I am not able to do it simultaneously. Please help me to solve this problem


texts:
So I have written a simple Verilog module which works well in the ModelSim emulator. I would like to now program my Cyclone 10 Dev board to perform this simple task, but I need to set up the pin assignments on my qsf file.

That being said, I don't know where to find the correct pins and how I would assign them to the inputs and outputs of my module. The model I am using is a 10CL025YU256I7G


texts:
The schematic shows one row of my 16(row)x32(Col) LED matrix. Each row has 32 LEDs.
I'm Scanning rows @ 1/16th rate.I'm using a PIC micro controller. I use 3V LEDs. The problem is LEDs are dim.
How to overcome my problem? I'm about to draw my new PCB, so changes are welcome.


texts: Are there batteries with separated charging and discharging ports?

texts: Are there commercial energy storage systems with such characteristics? Or, any reference guide on how to design such a system? Really appreciated.


texts:
I'm considering designing/building a fairly basic electronic load (constant current, but possibly also constant power and resistance). However, after drawing up a few ideas for the basic operation, I got stuck.

My first idea was to go the digital route, using a MOSFET driven by a DAC as the power dissipator, and a sense resistor + current sense monitor/amplifier read by a microcontroller to adjust the current to the user-set level.

I started doubting it a bit, though, for two reasons:

I'm not sure if it's "fast" enough. The code would have to check the current in the sense resistor, and presumably use some sort of PID loop or such to drive the MOSFET gate. The monitor I had in mind (TIs INA226 I2C current shunt monitor) can be read at least 1000 times/second, probably 3000; the datasheet is a bit unclear[1]. My guess is that this will do?
I have no experience with this; would a PID controller be a good fit? More specifically I really have no clue how, better than basic trial and error, to figure out e.g. what the MOSFET Vgs should be to allow a certain current though at a certain voltage (Vds).

After that, I thought a bit about an analog+digital design: same load and sense resistor, but with an analog instrumentation amp to amplify the sense voltage up, and drive the MOSFET with an opamp with negative feedback. The noninverting input would then be set by the MCU + DAC, but the digital control would only set the current, not actively control it.

The main potential downside I see here is that if the current is low, so that the shunt monitor output should be very low (say 5 mV, for ~ 0.005/5 of the full scale value), the not-truly-rail-to-rail nature of the amplifier might cause issues.
For example, if the "low swing" is 35 mV above ground, it'd essentially "tell" the op amp that the current is 7 times higher than it is, wouldn't it?

This turned out longer than expected. Anyway, the main question is really:
Would the first solution, with digital control by sampling the current at perhaps 1-3 kHz and some sort of PID controller, be a good one?
I figure that if I get that running, I can add more advanced modes such as constant power and constant resistance fairly easily, as opposed to with the analog design.
And if not, is the analog idea any better, and will it work at the case I mentioned with near-ground output?

[1]: They mention as an example that with a 588 µs conversion time and 4 averages, data can be read roughly every 4.7 milliseconds. I'm not sure why that's not every (0.588 * 4) ms instead.


texts:
My laptop battery is assembled from 4 cells in series. And the voltage of them all is 16.5V, (on battery it writes 14.8V). Can one cell be faulty even then?

Is this a sign that battery is faulty, because if 14.8V DC is declared on packaging, does this mean one of the cells is bad?


texts: Why does electric arc in a switch prefer a curved path over a straight path?

texts:
Recently I found this video of a 500 kilovolts line being opened under load.

When the switch contacts are pulled apart an electric arc predictably starts. While the contacts are close to each other the arc runs along a straight path between the contacts. Then as contacts are pulled further apart the arc starts to bend and turn into a steep curve and its length becomes several times greater than the distance between the contacts. Then finally the arc just fades out.

That doesn't make sense to me. As I see it the arc should take the least resistance path and that's clearly a straight path, not a steep curve. Even more, if the arc takes a curved path why would it fade out suddenly instead of just taking a less curved path of less resistance and continue running?

Why does the arc behave this way - first prefers a curved path and then suddenly fades out?


texts:
I'm working on a PCB Design with SuperSpeed signal lines with an Texas Instruments USB 3.0 Controller. I´m new on PCB design and I don't know if I'm doing something wrong.

Can I cross the USB DM/DP lines?
Are the ssrx/sstx routed ok? I´m putting ground planes between SSRX+ and SSRX- (the same for TX lines) and matching the length. Do I have to put more ground planes between SSRX and SSTX lines?
Another question, Is there any problem with vias on pads?
Thank you so much!


texts: Working of control system of an elevator?

texts:
I am interested in studying/learning how control system of an elevator works.?How its specs/parameters are controlled or adjusted? Especially rise time and steady state error.?to provide comfortable experience for humans inside the elevator so they do not experience oscillations or high speed(abnormal rise time) and other issues

Elevators use only proportional controllers or pi controllers or pid controllers?

I couldn't find a satisfactory link after Google search so i thought to ask it on ee stack exchange


texts:
When someone says they "flashed" firmware to a device, I'm curious as to what this actually implies.

Is firmware just a native binary that is stored in memory and that can be interpreted by the device's CPU (like any other EXE on a computer)? Or is firmware just data that acts as input to an immutable program already hardcoded/wired onto the device?
If the latter example isn't firmware, what would you call it? For instance, let's say a device has some binary (someapp.exe) on it, and you cannot remove or modify this binary. The binary, when ran, takes input from a memory chip. You can "flash" data to this chip, and thus affect the input/configuration of someapp.exe that will take affect the next time it runs. If not firmware, what would this be called?


texts: Potentiometers, little piece sticks off?

texts:
I'm not electronics savvy and am a complete newbie. So I'm in the middle of a project and am trying to stick a potentiometer through an aluminum casing and I placed a 1/16" piece of rubber between the fairly thick aluminum (A Hammond 1560BB enclosure) and the base of the potentiometer.

However, there is a little piece that sticks off of the base of my potentiometers, and it's preventing them from going all the way through so they can be correctly attached. How do I solve this, do I break this piece off, or is there another solution?

This piece:


texts: Understanding interrupts and software button debounce

texts:
I'm quite new to AVR programming (avr-gcc).

To react on button-press, I am using a PCINT ISR with the internal pull-up resistor enabled like this:

ISR(PCINT0_vect) {
    if (bit_is_clear(PINB, PB0)) {
        _delay_ms(40);
        if (bit_is_clear(PINB, PB0)) {
            // do something
        }
    }
}

It works okay but I guess it is not particularly smart to spend 40 milliseconds in an ISR just to debounce a button.

I have read Ganssle's Debouncing Contacts Part 2 which is a bit too advanced for my current level of experience, and there is one statement that I am not sure about:

  The undebounced switch must connect to a programmed I/O pin, never to
  an interrupt.

So is my approach to connect the button to a PCINT already wrong? I haven't gotten around timers yet, but should I rather use some kind of timed interrupt to evaluate the button state every 1 ms or so instead of the button triggering an interrupt directly?

I can live with my debouncing not being very smart for now, but at least I want to get the basics of reacting on a button-press right.


texts: what is the magnitude of total voltage in the below circuit?

texts:
I was working on some RLC circuits and I found a question something like this.

In series RL circuit, \$V_R\$ = 4V and \$V_L\$ = 3V. what is the magnitude of total voltage ?

I just thought \$V_T\$ = 4V + 3V = 7V but the book says its 5V. Could anyone explain me am I right or wrong in thinking so. Is it 5V or 7V ? Please help me with these.


texts:
I am working on a box for a project and I get a significant voltage drop when I wire in an indicator light.

This is an AC project and the light is a "Lamp 240v, Watts 0.5 Model 1609W21E BA".

It is wired in series, with it going from the wall to a switch, from the switch to the indicator light, and then to a black box.

wall -> switch -> indicator -> black box.

When measuring the voltage coming into the indicator light I get 110v, when I measure the voltage going out I get 40v, a 70v drop.

Am I using the wrong kind of light? Or do I need to wire it in parallel (I was told it should be in series though).

Any help on determining why I get such a drop would be great.


texts: Power Jack part number for YAESU FT 23R battery pack?

texts:
I am planning to design a small USB powered charger for the battery pack used with the radio YAESU FT 23R. I have been searching for the correct name / part number of the power jack connector shown in the following picture:

The corresponding power socket can be seen in the following battery pack. According to some measurements the socket's inner and outer diameter are around 2.54 mm and 3.85 mm respectively.

Does anyone have any idea where to find this power jack?


texts: Function generator changes output amplitude when connected to resonant inductive coupling circuit

texts:
I have the following circuit on a breadboard connected to a RiGOL DG1022 function generator as the input voltage source (V1). (R1 is supposed to model the resistance of the function generator and is not part of the circuit itself).

The function generator is set to output a sine wave of 1 MHz and an amplitude of 5 Vpp. As can be seen from the picture, it is set for high impedance mode.

The two coupled inductors inductors are realized using two soda bottles with 20 windings of copper wire each. When I bring the soda bottles together, and measure the voltage of V1 using RIGOL DS2072 oscilloscope, I get the following measurement:
. The Vpp shown in the oscilloscope is 4.36 (which is legit since the function generator is trying to output Vpp of 5 volts).

When I increase the distance between the soda bottles, the measured voltage ACROSS THE FUNCTION GENERATOR drops to 2.72 Vpp. As in the following picture:

I would like to know how come the function generator voltage drops when I increase the distance. I know that changing the distance changes the impedance of the coils, but how does it affect the voltage of the wave-generator? Is it because of its output impedance of the function generator (even though it is set to the High Z mode)? I tried changing the output impedance of the function generator but it still showed the same effect.


texts: What is the most energy efficient way to lower voltage? I want to lower 9V to 5V. But if I use resistance doesn't it consume energy?


texts: Specification of TL07X op-amp, and its hold circuit

texts:
I'm using a "TL07xx low-noise FET-input operational amplifier."
I would like to get an amplification of 100 ~ 300 by configuring the feedback loop; a feedback capacitor or resistor for a charge or voltage amplifier.
I don't know if this is closed-loop or open-loop. If this is closed-loop, I can not get a gain above 20dB according to Figure 6-9 in the specification sheet.
Is this correct?
Thanks for comments below! I understood.
I have another question. I would like to perform peak hold with TL07x and a diode. But, a hold delays due to some reasons. C is sufficiently small, slew rate of TL071 is 13 V/usec, which is still OK, specification of a diode: forward voltage, etc, is not good??
Duration for holding pulse : t = V/I * C
now, V = 100 mV, I is supply current of ~ 1.4 mA??, C = 0.01 uF
t = 0.6 usec
I guess Pulse width is sufficiently wide compared to charge time. Output short-circuit current (Sourcing) according to Figure 6-12: ~24 mA. This is not sufficient?? It looks that NE5534 (output short-circuit current: 38mA Max ~60mA) follows the peak in LTSpice level...
I pasted pictures showing my situation below. Blue is input, and green is the hold signal.
A diode I am using is a 1N4946.
Should I use another one, such as a 1SS270A or 1N4148?

I put simulation w/ TL071 (upper) or NE5534 (lower) where Green -> input pulse, Blue -> peak hold, and Red -> drive (output) current. C is set to be 0.1 uF and D is 1N4148.


texts: How to compare time-of-day numbers stored in Binary Coded Decimal in PIC

texts:
I am using a PIC18f which has an internal real-time clock. The the day, month and year values are stored in BCD format. The data sheet says these values are stored in BCD format in Registers.

I want to compare time. E.g. if (time==10.20) // 10 hours twenty minutes

Do I need to do some conversions to other data type like int/char while dealing with BCD in Registers?


texts: What would cause a voltage rail to be held low without measuring a short circuit?

texts:
I have a circuit that provides power (1.8VD) to an FPGA and some ADCs. I have seen in the past where damage (ESD, EOS, etc) occurs to one of the ADCs. This causes a short from 1.8VD to GND internal to the ADC, which can be measured. The FPGA and PROM device are connected to this 1.8VD supply. Therefore, when 1.8VD is shorted to GND, the FPGA doesn't startup correctly.

I have seen a few of these boards when powered on, do not measure 1.8V but measure around 0.1V. However, when I measure the resistance from 1.8VD to GND, it appears nominal and no short is measured.

Is it possible that the ADC isn't fully shorted internally but still can hold this voltage rail down? Any thoughts, comments or insight would be helpful. I also suspect it is possible that they ADC is shorted internally to some other signal or plane other than GND.


texts: Secondary voltage with parallel, mismatched transformers

texts: The thought came into my head, what if you had 2 transformers say they're both line level primaries and the secondaries are 6V @ 1A and 12V @ 1A. If you connect the secondaries in parallel, what is your resulting voltage and rating? I'd guess 9V, but I have no idea on the rating.


texts: Buck converter MOSFET (IRF4905) heating up

texts:
I tried to build a buck converter without any ICs, just transistors, a diode and passive components. Its purpose is to convert 12V to 5V at 2 Amps. It works, but the switching MOSFET (IRF4905) heats up very quickly and I can't figure out exactly what the issue is.

The idea was to build a sort of hysteretic buck converter. R3 and the trimmer R4  form a voltage divider, when the voltage across R4 is high enough (about 0.7V), Q5 opens and closes Q4, which closes the MOSFET. If the voltage on the output is too low, the MOSFET is open.

It regulates the voltage, but it heats up very quickly at 2A. I measured the switching frequency to be about 42kHz. I suspect that the MOSFET is not opening and closing fast enough, or not opening and closing completely. I can't verify that because I don't have an oscilloscope.

List of things I tried:

Decreasing/increasing frequency by changing C2.
Increasing inductance L1 to ~280uH.
Adding a 1k resistor from the MOSFET gate to +12V.
Adding 100nF and 4.7uF capacitors between Vcc and GND near the totem pole.

Does anyone know what could cause the MOSFET to heat up? Any suggestions would be appreciated.


texts:
I had got a question in job interview " Draw a circuit of common emitter amplifier using Non Bipolar Transistor."

As the question said Non Bipolar, so I assumed that it might be related to UJT. But I haven't found any common emitter amplifier related to UJT. It would be helpful if anyone could provide me the answer.


texts:
I am trying to estimate photocurrent from a photodiode in a general sense. When I read literature on the subject, I see something along the lines of:

Text and equation from Here

I assume they are referring to spectral flux  from what they describe as "energy spectrum of incident light" due to similar units.

Photodiodes typically report a responsivity graph and LEDs report relative spectral emissions. How would I calculate spectral flux (if that is the correct unit)?

The spectral emission and responsivity do not include distance from the emitter to detector, but if I move my LED closer to a photodiode then I expect to see a larger photocurrent, but I have not been able to find an example showing this. Any help would be appreciated.


texts:
So I have the schematic below and I am to insert diodes into the circuit to increase the efficiency of the circuit (can only insert diodes, not change the wiring). 'Target' is where I want the power delivered. I am to increase the efficiency of the circuit

when element 'b' is open circuited,
when element 'd' is shorted and
when element 'b' is open circuited AND when element 'd' is shorted.

However after doing circuit analysis on it I have found the the element labelled 'd' never adds power to the system.

It seems wherever I add diodes to the system I am simply blocking off one source (no current flows through the source) 'Target' does seem to receive more power when I put in a diode along the wire where element 'd' is however I feel like I am doing something wrong as it would appear that element d is completely useless and may as well just be removed from the system.

Can someone let me know if my thinking is correct or if I am missing something?

simulate this circuit – Schematic created using CircuitLab


texts: When people say recirculating currents in the context of a power system, do they mean Eddy currents? I'm just confused about the terminology and I couldn't find anything online to clarify this.


texts: When measuring input current to a primary winding of a transformer with an inline true RMS multimeter, can no-load current be measured, then full load current be measured, and then simply subtract no-load current from full load current to leave the apparent current being used for load and any losses?


texts: Fried Beaglebone Black. Would like confirmation to why

texts:
So I build open source grow room automation software but admittedly am a super noob when it comes to the electrical end of things.  Last night I attempted to run a dht22(temp and humidity) sensor an I wanted to solder it and use real wire rather than tacking together a bunch of jumper wires. I soldered everything up and on the beaglebone end, I just soldered the male end of jumper wires to my wire so they were able to easily plug in still.  On the sensor, I should have done the same but I decided to get tricky and try to solder my wire directly onto the sensor.  I desoldered the little jumpers that came on the sensor and soldered the wires directly on.

When I first booted the BBB all was fine but the system was not reading the sensor.  I took out a voltmeter and started to poke around.  I put my voltmeter on the continuity test.  When I touched the ground and hot I got a beep and I believe this is normal.  The part that I think may be the problem was it also beeped when I touched the ground to the data wire.  It seems like as soon as I touched them I got a beep and then the entire BBB went down for the count and is not able to come back up.  When I plug it in the power light flashes on for a micro second and then it goes dead.

Can anyone confirm what I did wrong and why?  I would really like to learn as much as possible from this experience.

Thank you!


texts: How would I make a circuit that takes a voltage (V) as input and outputs min(V, Vref)?

texts:
Simple question, how do I turn the following block diagram to a real world working circuit?

I know I could use the following:

1) A comparator, but that will give me only either +Vcc or -Vcc.

2) I could use a rail-to-rail comparator and set V- at 0 Volts and the maximum allowed voltage at V+.

3) I could use a Zener diode... But I've zero experience with using them...

simulate this circuit – Schematic created using CircuitLab


texts:
I have a 5KV DC output from a Cockcroft-Walton multiplier. The current is around few microamps as per the simulation.  To prevent discharge, the 200Mohm resistor holds the voltage of the Cockcroft-Walton multiplier stable.  The 200Mohm resistor is rated for 22KV for the voltage tolerance.
The current sense resistor is rated for 600V.
Is it safe to connect the current sense resistor like this?

The voltage across the resistor comes around 0.300V approximstely (calculated using Ohm's law.)
Is there a way to isolate the measuring setup from the high voltage?
They all share the same ground, and there is a seperate circuit that discharges the capacitors of the multiplier safely within itself without the current flowing to the common ground.
The ADC can measure differential voltages.


texts:
I have a contemplated DC electricity system that has a battery room at a distance from the use. The battery room would be about 150 feet away from where the power is used (for lighting, computer systems, etc). The total wattage of the system will be around 5000 watts or on that order.

I am concerned about the power loss over the 150 foot distance. There would seem to be two basic approaches: using a very thick braided transfer cable, or to step up the voltage from 48 volts to 220V or something like that, transfer it, then step it down again when it gets to the point of use.

What should be my considerations in designing this part of the system?


texts:
I wanted to use a sensor which should indicate low fluid level with a LED.
I don’t want to have a non working LED in that circuit and want it to be automatically checked everytime the circuit powers up for the first time.
Is there a self test circuit, like the lights in the dashboard of your car, which can check if the LED is still good and goes of after a few seconds?


texts: Help needed optimising simple current limiting circuit

texts:
I have been experimenting with simulating current limiting circuits. I am trying to limit current to ~500mA given a fixed 4.8V source. I have started using a circuit like the one found on this wikipedia page ...

I have made a simulation of this circuit using CircuitLab. I show the results below. The circuit on the left uses a simple series resistor to do the current limiting while the circuit on the right is based on the Wikipedia circuit. I have tweaked the values of R_bias and R_load to common resistor values that prevent more than 480 mA being drawn from the source when the load is 0 Ohms. I also set hFE of the transistors to 65 to match some multimeter measurements I made of some power transistors that I have to hand. The values adjacent to the ammeters are the simulated values.

If I now make a 10-Ohm load, it becomes clear why a current limiting circuit is superior to a series resistor. The current limiting circuit drops its effective resistance, allowing more current through than when using a series resistor . .

However, the current limiting circuit is still providing some series resistance in this case. An ideal current limiter would have no resistance at all until the load attempts to draw more current than the limit. Is there a way to tune R_bias and R_load to better achieve this, and/or are there circuit tweaks that can help better achieve this?


texts: Advice on connecting a Li-Po battery to SMD terminal?

texts: I would like to connect a Li-Po battery pack with female PH connector such as the one shown below to a PCB which will use SMD devices. I have also provided the circuit diagram below and highlighted the section with the battery connection below. I didn't have much luck finding a SMD male PH connector on lcsc.com where I will be ordering components from. Obviously any connector can be used as I can just remove the PH connector and attach another one. I would like to know what sort of connectors are generally used to connect Li-Po batteries to SMD PCBs. What would be the most convenient connection part for this application?


texts: I was wondering why do we so often want out transistor to work in saturation mode? Ie. For a MOS Current Steering Circuit we want our transistors to operate in the saturation region....


texts:
I am very new to making circuits and have tried to make an EHX LPB1 circuit:

When powered and plugged in, the 9v battery overheats and all I can hear in my amplifier is static noises and no output. ive tested connections and everything seems connected the potentiometer ranges a little with the multimeter when powered. My work is quite messy, also I couldn't buy any 830k resistors so i put 8 100k's and 3 10k's in series:

Please could you suggest anything I could do to the current circuit to repair it or do in future when I make another attempt. If you'd rather contact me using another media I have an email: squifflangdown@gmail.com

Thanks for any help. Also not sure if we're allowed to just post our attempts and ask for help but im not sure where else I can ask for help


texts:
This is part of a two-head EVSE. The two solid-state relays are used to drive contactors that supply high current power to the vehicles. I used to use a MOC3040 based triac circuit for this job, but decided to try SSRs to simplify things. First, the important part of the schematic:

(yes, that's not the right symbol for an MOV. The layout is optimal and I was too lazy to make a new symbol).

And because the layout may be significant, here's the board:

The symptom is that if relay A is on, relay B will fail to turn off until relay A is turned off. Not at the same instant, mind you - there is about a 1/4 second delay between the two turning off.

Now, the first thing I thought of was that despite the datasheet implying that I didn't have to worry about coil collapse that that must be the issue. So I added a snubber across each coil (EDIT: that's where I went wrong) consisting of a 39Ω 1/2W resistor in series with a pair of 0.005 µF 1kV caps in parallel (I wanted 0.01 µF, but it wasn't available from the local store on a Saturday). To my great surprise, that didn't change anything (EDIT: because snubbers go across the switch, not the load).

I am quite confident that the input side isn't the issue. the RELAY_A/B lines are outputs from an ATMega328PB running at 5v. I have every confidence that the firmware is not the explanation for the issue (it has a long history of correctly operating the old triac based circuit).

Very little makes sense to me about this problem. The only thing I can think of is that mere physical proximity of the two SSRs to each other on the board may be causing this, but I can't conceive of a mechanism for why this might be.

The wires going off the board to the contactors are 22 gauge stranded and are twisted together as far as possible before they have to separate to go to the coil terminals.


texts:
I need to drive and dim 4 parallel LED strings.

Each color (see below) dims separately. Another constraint is minimising the number of wires running from the light to the driver.

Here are my options as I see them.

Option A is the baseline, each string is driven separately. It's not physically reasonable in my case as the LEDs and the driver are on different PCBs and that would create a lot of wires.

Option B is how I do it currently. Each color is connected to a separate CC driver (LDD-300H). Although it works fine now and the brigthness seems pretty even, I know there are concerns around current imbalance between strings. I could probably connect the positive ends also?

Option C is to use a multi-channel CC LED driver like LP8860. Presumably I could connect the positive ends, which would leave me with 5 (1 positive, 4 negative) wires going from the light to the driver.

The space on the light PCB is pretty limited, so putting anything other than resistors on it would be difficult.

Am I missing any options? Am I wrong in my assumptions?


texts: So for an opamp with a Vin of let's say 1Vpp that is amplified to 10Vpp so the gain is 10. Will Vout ever exceed 5V peak value?


texts: Is there a popular small signal PFET equivalent to NFETs 2N7000 or BS170?

texts:
Some days ago I was considering using a small signal P-Channel MOSFET in a design of mine, but could not find a suitable part.

The specs I was looking for were something like the following:

\$I_D = -500mA\$ (continuous drain current)
\$V_{GS} = -5V\$ (gate-source voltage, for \$5V\$ logic level)
\$V_{DS} = -12V\$ (drain-source voltage)

I was expecting to find a popular P-Channel counterpart of N-Channel 2N7000 or BS170 in a TO-92 package, that may be in everybody's bins, just like BJT NPN/PNP pairs BC547/557 and BC337/327, but could not find it. I could just find vendor specific P-Channels in SMD packages.

Is there a popular counterpart for 2N7000 or BS170? If not, why not?


texts:
I have just bought a door bell from the State however, I am staying in Singapore, where the voltage is 240 in oppose to 110. The vendor told me to simply get a 16-24VAC transformer with 40VA. After installation, the system worked only half a day and it stopped working and there seems to be a burning smell from the transformer. Did the vendor give me the right set of information?

Do I need a step down from 240v to 110v then use another transformer to transform it to the required 40VA?

Please advise as I am stuck and need to install the system asap.

My transformer has the following set of data:
Input: AC220V 50 Mhz
Output: AC24V 2A


texts: In a brushed DC motor, why do the brushes have springs?

texts:
In trying to understand brushed DC motors, this post has been very helpful but I still have some fundamental questions about the brush mechanism. For instance, what is the purpose of the spring?

(source)

And since a brush looks mostly like a spring, how did the name "brush" even come about?


texts: Thermocouples - Understanding signal vs. power grounds

texts:
I have a simple circuit that reads a temperature and toggles a valve. The thermocouple functions when the dotted ground wire is unplugged, but fails otherwise.

Minor edit: The 3.3V going into the AD595 is actually 5V.

I'm not looking for workarounds. As a quick fix, I replaced the MOSFET with an optocoupler. It works fine, but I'm trying to learn from this experience.

My understanding:

The 24VDC source is a switching regulator, and has a ~50mV wiggle. The thermocouple is a µV-level sensor before amplification, so the regulator easily drowns out the signal.
Power and signal grounds are usually built separately, and then joined at one point near the voltage sources. This minimizes high-fluctuating power current traveling through signal currents.

What I've tried:

Placing the dotted wire between the negative power and a separate MC ground pin.
Adding a large cap to the 24VDC power to reduce (assumed) 50Hz switching noise.

So, my question is how do you handle sharing a reference voltage between signal and power?


texts:
in the following datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/OP07.pdf

Which is a OP07 a high precision ultralow voltage offset OpAmp, it says in the datasheet.

  The accuracy and stability of the OP07, even at high gain, combined
  with the freedom from external nulling have made the OP07 an industry
  standard for instrumentation applications

what is external nulling?


texts: What is the maximum frequency range of a Clapp or Vackar oscillators?

texts:
At the end of Russell McMahon's answer to this question (High-stability oscillators (non-crystal)) there is this reference:

"Shows that Gouriet-Clapp, Seiler, and Vackar oscillators have equivalent frequency stability given equal resonator Q. They differ only in how much the amplitude of oscillation changes when they are tuned. The three circuits are useful over frequency ranges of 1.2, 1.8, and 2.5 to one, respectively." (J. K. Clapp, "Frequency Stable LC Oscillators," Proc. IRE, Aug 1954.)

Does this mean that if I design a Gouriet-Clapp oscillator to have a frequency of 100MHz, I can change the tuning capacitor to give me a frequency range of 100 to 120MHz?

Background: I want to take advantage of the dielectric properties of soil and use it as a tuning capacitor in a variable frequency oscillator running at >80MHz (I need frequencies >80MHz in order to minimise the effect of minerals in the soil). The only catch is that the dielectric constant of the soil will vary between 4 and 80 depending upon how wet the soil is, which means that the value of the soil capacitor will vary from 10pF (calculated) to 400pF.


texts: Best solution for compact wiring on stripboard

texts:
When transferring a circuit from breadboard to stripboard, I often struggle to manage the wiring; often it starts looking like an overgrown garden; the components inevitably start disappearing under the wires. Not to mention the wires disappearing under each other, making mistakes near impossible to trace. But I want to keep the board as small as possible.

What kind of wires should be (or could be, or are most often) used for low voltage, low current circuits?

Up til now I've used the same wire as with the breadboard, (single strand) as I find it easy to work with since it retains its shape and I can route it round components. However, it's quite thick so doesn't lend itself to compact boards.  See pic below:

I searched on Google and decided that this looked like the neatest (or at least most manageable) stripboard circuit out of the results:

What kind of wiring is that? I can't find any cable like it for sale. (At least not single core, but I don't fancy spending hours taking the outer sheath off ethernet cables or the like.) (I assume they're multi-strand.) The closest I can find is 30awg hook-up wire, but the outer diameter of that doesn't seem much less than what I use for breadboards.

Advice would be great. Thanks


texts: I want to connect an LPC to the CAN bus in my car, and I found that LPC2129 have the CAN protocol implemented on the chip. Searching the Internet, I saw that most of microcontrollers are connected to the bus via MCP2515 and MCP2551. Because this LPC already has a CAN controller I don't need MCP2515. But do I still need MCP2551 or similar transceiver chip?


texts: Is self inductance and leakage inductance the same thing?

texts: I want to intuitively understand what they are and if they are the same thing.


texts:
I am designing a SEPIC power supply using the LT3758. I have simulated the circuit in LTSpice and all the waveforms are as expected except the L1 current.
Here I see massive overshoots when the MOSFET switches on (eg normal current is about 3A pk-pk and overshoot goes up to over 20A). The spike is extremely narrow (< 1nS).

I am new to LTSpice, so might be missing something obvious.

Is this spike real or a simulator aboration? What could be causing it and what can I do about it?

Input +28V, Output +40V 1A.

[Edit] I have posted a follow on question here LTSpice SEPIC design low freq ringing


texts: Why is the voltage gain \$=\frac{V_{out}}{V_{in}}=\frac{\Delta V_L}{\Delta V_B}=-\frac{R_L}{R_E}\$

texts:
I learn some knowledge of  common emitter from this website: https://www.electronics-tutorials.ws/amplifier/amp_2.html

But i am confused about this formula : voltage gain  \$=\frac{V_{out}}{V_{in}}=\frac{\Delta V_L}{\Delta V_B}=-\frac{R_L}{R_E}\$,here is the schematic of common emitter below

First,if we know the output and the input wave,we can easily understand why is \$\frac{V_{out}}{V_{in}}=-\frac{R_L}{R_E}\$,not \$\frac{V_{out}}{V_{in}}=+\frac{R_L}{R_E}\$,but if we don't know common emitter acts like an inverter amplifier,how can we know \$\frac{V_{out}}{V_{in}}=-\frac{R_L}{R_E} ?\$,because the opposite voltage means the opposite current direction,but i can't understand why \$I_C\$ and \$I_E\$ are opposite,is it because the \$I_C\$ flows "into" bjt and  \$I_E\$ flows "out of" bjt,so they are opposite?

Next is why is \$=\frac{V_{out}}{V_{in}}=\frac{\Delta V_L}{\Delta V_B}=\frac{\Delta V_L}{\Delta V_{RE}}\$,not \$\frac{\Delta V_L}{\Delta V_B}=\frac{\Delta V_L}{\Delta V_{R2}}\$,i think the reason of it is because \$I_B\$ is a input current of bjt,and \$V_{RE}=I_E\times R_E=(I_B+I_C)\times R_E\$ ,and  \$V_{R2}\$ has no relation with \$ I_B\$ ,so we can't say \$\frac{V_{out}}{V_{in}}=\frac{\Delta V_L}{\Delta V_B}=\frac{\Delta V_L}{\Delta V_{R2}}\$,however,i don't know the reason i think is correct or wrong,if wrong,can anyone tell me the reason of it??


texts: How is this servo amplifier made work in SPICE?

texts:
At page 13 of this Analog Devices document there is a circuit which consists of a servo amplifier and a bridge. The operation principle is explained in the document. Here is the the schematics given:

I wanted to simulate this circuit in LTspice with following same circuit:

According to document node A is the output. But this doesn't work at all. So basically:

How come the suggested circuit function at all? Initially there is no voltage at node A.

If it can be modified and work in LTspice, now my challenge will be simulation. Since this circuit tries to make Rf constant with respect to cooling effect, how could this be simulated to see the transient analysis to mimic its operation?

Edit: The second part needs to be a separate question


texts: Driving piezoelectric crystals, low to high or matched impedance?

texts:
When designing an interface between a fixed frequency RF generator and a piezoelectric crystal, should the aim be to match the load impedance to the source impedance (for maximum power transfer). Or should there be a low to high impedance (maximum voltage transfer).

It seems intuitive to me that a matched impedance should be required, as ultimately I am aiming for maximum acoustic power. However when researching the subject, I only seem to read about electrical energy mentioned in terms of voltage, not power. Which leads me to think that I should be aiming for a low to High impedance.

What should I be aiming for, maximum power transfer to the transducer or maximum voltage transfer to the transducer?


texts: Using LEDs in series with optocoupler for biosensor

texts:
Long time lurker, first time asker. I've been working through a biosensor schematic from a BME class to build an EKG (I'm a physician, aware of risks of these devices etc) (typical voltages being detected in the range of <100mV). After passing through a series of amplifiers and filters, it connects to an Arduino via a optocoupler for electrical safety.

In the original schematic I'm working with, there are 3 generic red LEDs in series  with a 220 Ohm resistor with the input side of the optocoupler (CNY17-3) producing about 10mA of bias current through the optocoupler. With this set up, the output waves look crisp with good amplitude. I tried to ditch the LEDs and just up the resistor value to maintain 10mA (in this case, supply voltage of 9V battery w/ resistors with values between 600-1k ohms), but the output waveforms I'm getting have much lower amplitudes compared to with LEDs.

CNY has a CTR of 100% at 10mA, forward voltage of 1.2 at that current as well (max is 60mA).https://docs.broadcom.com/docs/AV02-0772EN datasheet

Any thoughts on if this is a special effect of LEDs (if so, any way to use a different component to replicate this) or whether I'm choosing inappropriate resistor values?

Thanks!


texts:
So I'm currently writing VHDL code for a 7-segment display that will display (0-F) once each second. I have almost everything done, the only thing I'm stuck on is the controller.

I need to have 4 buttons, the first starts the counter, the second stops it, the third increments it by one, and the last one resets it back to 0 (I already have the last one done, I just need the first three)

Here is my overall code (Note that Problem 2 component is my counter):

entity SSD is
port (
   seg : out std_logic_vector (6 downto 0);
   an3 : out std_logic;
   btn1, btn2, btn3, btn4 : in std_logic;
   clk : in std_logic);
    end SSD;

    architecture Behavioral of SSD is

    component hex7seg is
    port (
        x : in std_logic_vector (3 downto 0);
        a_to_g : out std_logic_vector (6 downto 0));
    end component;

    component Problem2 is
    port (
        clr : in std_logic;
        ce : in std_logic;
        clk : in std_logic;
        b : out std_logic_vector (3 downto 0);
        tc : out std_logic);
    end component;

component clkdiv is
port (
    rst : in std_logic;
    clk : in std_logic;
    clkout : out std_logic);
end component;

component controller is
port (
    start : in std_logic;
    stop : in std_logic;
    inc : in std_logic;
    rst : in std_logic;
    clk : in std_logic;
    run : out std_logic);
end component;

signal b : std_logic_vector(3 downto 0);
signal run : std_logic;
signal clk_1sec : std_logic;
signal tc : std_logic;

begin

U1: hex7seg port map (x => b, a_to_g => seg);

U2: Problem2 port map (clr=>btn4, ce=>run, clk=>clk_1sec, b=>b, tc=>tc);

U3: controller port map (start => btn1, stop => btn2, inc => btn3, rst => btn4, clk => clk_1sec, run => run);

U4: clkdiv port map (rst => btn4, clk => clk, clkout => clk_1sec);

an3 <= '0';

end Behavioral;

Here is what I have so far for the controller code:

entity controller is
    Port ( start : in  STD_LOGIC;
           stop : in  STD_LOGIC;
           inc : in  STD_LOGIC;
           rst : in  STD_LOGIC;
           clk : in  STD_LOGIC;
           run : out  STD_LOGIC);
end controller;

architecture Behavioral of controller is

begin
    run <= '1';

end Behavioral;

I'm not really sure where to go from there to get the other 3 buttons working, any help or direction would be greatly appreciated.


texts: Voltage drop across PMOS (power mux circuit with two load switches)

texts:
I'm trying to build a power multiplexer (with two load switches made with pmos transistors). When 3V3 not present, it will use 1V8. I built this circuit but it drops the voltage to 2.6V (when 3V3 is present) and 1.12V (when only 1V8 is present).

I have tried NMOS and PMOS transistors but when I connect load to Source of transistor they drop the voltage.
How can I make this work properly? I want no voltage drop. I'm not sure this is the best way to make a power mux. If you have other suggestions please write.


texts:
I have a LED string with four different lights. The lights are in order red, green, yellow and blue and this pattern is repeated. It has a controller with a button to cycle through fading/blinking modes. All red and yellow lights form a group and all green and blue lights form a group. The lights in a group are always on at the same time and equally bright.

First (left) and second LED:

Wiring:

Two wires are going from the controller to the first LED.
Every LED is connected with two wires to the previous LED and with two wires to the next LED.
There is a wire from the first LED that skips the other lights (I thought all other lights, but I didn't check them all, still have to check) and goes into the last LED, so three wires are going into the last LED.

I expected there to be three wires from the controller to the first LED, one for each of the groups and one common wire that is either + or -. How can two groups of lights be controlled independently with only two wires?

Based on the current answers I drew this diagram, but I'm not sure if it's right. I still have to count the LEDs to see if it is possible with the 31V output specified on the adapter.


texts: Why is it called as a "1 bit" binary full adder?

texts: Where does the naming of this circuit come from?


texts:
[UPDATE The problem is fixed and the results are in my answer below]

I have designed a board with, among other things, six max31865 on it. From those six I use five of them. The device reads out the temperature of five domes and if the temperature is to low or to high it sends an alarm sms via a gsm module.

Here some knogledge about the device:

I use five 2-wire NI1000 RTD elements (like PT1000 just not as accurate)
The probes are connected via 2-wire connection and each of them have their own max31865
Every probe is connected via extension cable of minimum 20 meters
The Domes where the sensors are in can have up to 90% air humidity
the farthest probe is 100 meters away from the device
Every 5 seconds I read out a different probes. 4 seconds before I initiate the conversion VBias is turned on. After the conversion I shut down VBias.

Now to the problem:

Four of the sensors I can read out without a problem. But if I connect probe 5 which is the farthest away from the device among the other four probes the max31865 from probe 5 spits out a over/undervoltage fault (fault D2). But if i connect only probe 5, the max31865 gives back valid temperature data. The conversion also works if I connect a probe next to probe 5, which is directly connected to the board (without extension cable).
The fault means that the voltage on any input pin of the max31865 is >VDD or

I changed the timing of "VBias ON -> Conversion, VBias off -> VBias ON" and I tried to let VBias always on but it didn't work.

How can it be that this over/undervoltage fault only occurs constant when sensor 5 is connected? (without probe 5 the error sometimes occurs with another probe but not that much) Is it possible that the extension cable of the sensor is inducing so much noise that it can cause any protected pin to have a negative voltage or have a voltage greater than vdd?

Thanks in advance!

The schematic of the sensor:


texts: Can the intelligence message of an FM signal be cross-modulated onto another FM signal due to nonlinearities?

texts:
Can the intelligence message of an FM signal be cross-modulated onto another FM signal due to non-linearities?
Where I work we have several  FM two way, repeater radio sites.  Over the years I've heard complaints of reception of a message on the wrong channel.  Sometimes intermodulation or cross-modulation has been cited as the cause.  Reading the liturature however I can't find this phenomenon discussed.  I'm Using Leon Couch, Digital and Analog Communications Systems by the way.
Studying non-linearities; intermodulation and cross modulation, I see that the 3rd order output is:
\$V_{out} = K_{0} + K_{1}(V_{in})+ K_{2}(V_{in})^2 + K_{3}(V_{in})^3\$
If you put signals into the system where
\$V_{in} = (A_{1})sin(ω_1t) + (A_{2})sin(ω_2t)\$
Then part of the third order outputs are:
\$3K_{3}(A_{1})^2(A_{2})sin(ω_1t)^2 sin(ω_2t)  =  \frac{3}{2}K_{3}(A_{1})^2(A_{2})\{ sin(ω_2t) - \frac{1}{2} [ sin(2ω_1 + ω_2)t + sin(2ω_1 - ω_2)t ]\}\$
and another
Generally it's explained that term \$sin(2ω_1 - ω_2)t \$ accounts for intermod distortin thatis diffucult to filter because it is close to the desired signal.  Also they show that if ther is any amplitude variation on signal 1, that it can amplitude modulate signal 2, because,  \$\frac{3}{2}K_{3}(A_{1})^2(A_{2})sin(ω_2t) \$.
But I never see a discussion of an FM signal being cross-modulated onto another FM signal.  It seems to me that if signal 2 is an FM signal as:   \$sin((ω_2 \pm \Deltaω) t  ) \$. then the cross modulating term:
\$sin(2ω_1t - ω_2t)\$
=  \$sin((2ω_1t - (ω_2 \pm \Deltaω)t))\$
= \$sin((2ω_1 - (ω_2 \pm \Deltaω))t)\$
= \$sin((2ω_1 - ω_2 \mp \Deltaω)t)\$
= \$sin((2ω_1 - ω_2)t \mp \Deltaω t)\$
Which looks to me like the modulating signal would be impressed on the intermoduation product \$sin((2ω_1 - ω_2)t\$
Of course my reasoning might be totally incorrect.
Like I said, I've never been able to find a mathematical or physics treatment of the phenomenon, but I've heard people argu that it happens, and others argue that in the FM domain cross modulation will only cause noise, not the imparting of an intelligent signal on another signal like in AM.


texts: What is the name of this connector component?

texts:
First of all, I recognise how hopelessly difficult it will be for other users to find this question based on a StackExchange search. Such is the nature of image-based questions.

In any event, I'm looking to identify this connector, in order that I can buy another one. For reference, in this application at least, it's part of a 3.6V battery charging mechanism.


texts: need help making a c program that reads flow meter

texts:
For the past week, i've just started my first ever project to make a C program for a PIC16F877A under MikroC, where I would get pulses in from the flow meter and calculate the flow rate, then output it to the lcd.

However, when i connected it to PORTD of the PIC16f877A RD0, it gave random values everytime that go up and down on the lcd. What's wrong?

Water flow meter datasheet and program:

void main() {
     volatile unsigned int value;
     char str [20];
     double calc;
     lcd_init();        //initiallise lcd
     ADC_Init();         // and to read in values
     TRISD.f0=1;        //setting the signal input
     PORTD.F0=0;
     while (1)
     {
      if (PORTD.F0= 1)   //if water flows through the meter
      {
       value = ADC_read(PORTD.F0);  //read from RD0 and assign to value read
       delay_ms(100);                 //delay so i could see value on screen
       calc = (value * 60 / 7.5);     //calculation to show flow per minute

       byteToStr(calc,str);
       lcd_out (1,1, str);      //output to screen
       value++;
      }

     }

}


texts:
I'm trying to make a ATmega328 run on a breadboard.

I am stuck on deciding if I need a reset switch.

Do I need one? Can I just unplug and plug in the battery instead? If I do need one, how would I go about doing this?


texts: Connection of ESD return path the System GND

texts:
In my current design I have one RJ45, one RS232 and two RS485 ports. I have TVS diodes CDSOT23-SM712 for serial channels and ESD7104MUTAG for Ethernet port. Now I have connected the ESD GND of the TVS to a separate GND island (referred to as CHGND) and then AC coupled that to System GND via 1nF (2kV) in parallel with 10MΩ (both 1206 package). My idea is to not directly couple noise from ESD return to system ground. This is also suggested in Microchip App note AN2054.

My system is powered by 12V DC power supply coming from a mains Flyback or external 12V DC power supply. I don't have a Chassis GND or Earth. The enclosure is ABS.

Now my review engineer is against that, pointing out that once a ESD strike comes in, it lifts the CHGND high (or low) until the bleeding resistor discharges that. This makes the line we are trying to protect experience the high voltage relative to GND. (I simulated this for 8kV HBM pulse and the voltage rise was about 770V) Also not working for repetitive strikes.

What do you guys think? Is it better to directly connect ESD return to system GND or AC couple?

Thanks in advance.

simulate this circuit – Schematic created using CircuitLab


texts: Can't get 74LS00 and similar integrated circuits to work

texts:
I bought a pack of 5 ICs from radioshack. (74LS00, 74LS02, 74LS04, 74LS08, and  74LS32 to be specific). And I can't see to wire them correctly. I've wired pin 7 to ground, pin 14 to 5V(from an Arduino Uno), and nothing comes out of any outputs. What even worse is if I disconnect ground the led does come on. And by using the Arduino to measure voltage, all of the outputs are on. I've wired this perfectly and even checked with this site to make sure: https://www.facstaff.bucknell.edu/mastascu/eLessonsHTML/Labs/Logic/LabLogic1A.html
I've also checked to make sure that pin 7 is indeed ground and pin 14 is indeed high with the Arduino. I just can't figure out why none of it is working. What's even worse is all of the ICs are exhibiting the same behavior. And I've tried two different breadboards, with the same result. Any help?


texts: What is return current of crystal oscillator?

texts:
I belive that every signal on the PCB has its return current. One layout hint for crystal oscillator is that "The ground connection for the load capacitors should be short and avoid the return currents from USB, RS232, LIN, PWM......and power lines" and I just wonder what the   return current of crystal oscillator is. an image of crystal oscillator is shown below:

I have to two ways to draw the return current:

the first one:

the second one:

I just wonder which one is right or neither of them is right. can anybody give me some suggestions?


texts: Does low frequency PWM create reactive power in a transformer?

texts:
I got a 350VA transformer (230V~/24V~) which is directly connected to a heating unit at it's 24 V ends. The 230V end of the transformer are connected to 230 V~ mains over a solid state relay (SSR).

The scenario is that a controller triggers the SSR to switch through, the heating unit heats up to the target temperature and then a controller with a temperature sensor sends a 5 Hz pulse width modulation (PWM) signal to the SSR to keep the heating unit at a constant temperature.

The heating unit has a impedance of 1.0 Ω, the transformer 0.3 Ω (idle). The PWM frequency is as low as 5Hz and the solid state relay has a response time of 10ms (using zero-crossing, still 20 times faster than the PWM). I measured the actual voltage on the transformer with a RMS multimeter and measured 20 V (idle)

From what I understand the expected current would be

I = U / R = 20 V / (1.0 + 0.3 Ω) = 15.4 A

and the power user would be

P = U * I = 15.4 A * 20 V = 308 VA

That all worked well for a while, with a perfectly costant temperature on the heating unit, until the transformer started smoking and eventually failed.

Is there any reactive power generated in the transformer due to the PWM that actually causes a much larger current that the expected 15.4 A? What could I do to avoid this? Does it help if I put the SSR between the heating unit and the transformer instead of between mains and the transformer?

I need the PWM control since constant temperature is crucial in my application, the choice for AC power in combination with a SSR is simply because AC transformers are cheaper than DC power supplys in that range (15+ A).

Thank you for any advice!


texts: High Current voltage regulator. using 7805

texts:
I a have a battery that supplies a a voltage range of 11.1 - 12.4V depending on how charged it is.

I would like to regulate this down to 5v. The issue is I would need to draw up to 6 amps through it.
The voltage regulator i have access to is the 7805.

Looking at the datasheet I found the circuit using a transistor to carry most of the current.
I have a BD180 transistor which can carry up to 3 amps, but i would need 2 of these in parallel somehow, as 3 amps isn't enough.

I am not that well versed in electronics and dont really know how u would go about doing this, any help is appreciated


texts:
I have purchased an ESP-32 BLE module. I have programmed it to turn on to broadcast a Bluetooth text to my phone and then enter the deep sleep mode. Then continue this loop.
When the Bluetooth text code it been to run the current it pulls is around 150mA. Then the module enters the deep sleep mode for 15 seconds at which time the module now pulls only 10mA.
I want to know if I ran it of lithium battery like the 18650 with a capacity of 2600mAH, how long will the battery last?
Please note I know how to calculate the lifespan of the battery it is just the current pulled by the device divided by the capacity of the battery. But how is it done when the current is not constant but changes between 'two current states' i.e. 150mA for 2secs then 10mA for 15secs and then loops again?


texts: Memory allocation of constants and statics in structure?

texts:
I am working on IIR Filter implementation where I am initializing filter coefficients and memory (form-2 w) memory as follows.

typedef struct
{
const _iq b_coeff[NUM_OF_COEFF];
const _iq a_coeff[NUM_OF_COEFF];
_iq w[NUM_OF_COEFF];
}IIR_FILTER;

Since, there are constants and static variables in structure. Usually compiler allocates Constants in FLASH (.cinit) and static in RAM (.ebss). [I am using CCS Compiler with TMS320F28033 if that helps ]

So, My question is how will the compiler allocate this since its a structure.


texts: Trace-width calculation of a relay output for a 6A device

texts:
I have almost designed a PCB and I am willing to finalize soon.
A part of it has a relay and the contacts are directly connected to a card-edge connector.
The current will be contacted is about 5A and maximum 6A momentarily during start of a device. And that device can stay contacted for about 20 hours a day.
If I calculate Trace-width from here
The result can be seen below. It recommends 8mm trace-width. Is that really so?
And secondly, I like to protect the circuit by using a chip-fuse. What rate would you recommend?
A sample chip-fuse:


texts: Solving BJT transistor voltages and currents

texts:
I have been given this problem as Homework and I can't seem to figure this out. It seems that the only thing I have is emitter current Ie. However, it is known that BJT is in saturation mode, so I can't think of a way to find Vb, Ve, Vc, Ic, Ib. Assuming Vce = 0.1V for saturation and Vbe = 0.7V

Edited couple values that I previously entered incorrectly.


texts: Why is 100 volts or less generally "low voltage" and "safe"?

texts:
In the United States in many state jurisdictions, wiring that operates either exactly at or below 100 volts is not required to be installed by a licensed electrician, and no site plan, building permit, or followup inspection is required for electrical work involving these voltages.

I am trying to determine where this concept first originated, because I've tried looking through various editions of the National Fire Protection Association (NFPA) National Electric Code (NEC) going back about 1980, and I don't see a specific designation of "circuits above 100 volts" and a separate one for below.

,

There are many electrical standards that seem to be based on this..

about 90 volt AC ringing voltage of landline telephones
25 volt / 70 volt constant voltage speaker wiring systems (70.7v RMS * 1.41 = 99.6v .. so it's just barely "low voltage", no license needed to install in some jurisdictions)
48 volts DC for phone battery backup in central offices and remote terminals
up to 48 volts DC for phantom power in balanced audio microphone systems
up to 48 volts DC for Power Over Ethernet (though there has been a recent change to the NEC regarding network POE in excess of 60 watts per device)
up to 48 volts for signalling on computer communications cables.

,

It is also directly written into the statutory law of some states. For example, Wisconsin statutes 101.80 to 101.862:

https://docs.legis.wisconsin.gov/statutes/statutes/101/IV/86/1

101.80 Electrical Wiring and Electricians
(paraphrasing the weirdly written language) 101.862(4)(d) for equipment or systems that operate at 100 volts or less:

Anyone may engage in the business of installing, repairing, or maintaining this electrical wiring. They are not required to be licensed as an electrical contractor with the WI DSPS (Dept of Safety and Professional Services).
Anyone may engage in installing, repairing, or maintaining these systems. No licensing as an electrician or enrollment as a registered electrician with the WI DSPS is required.
A master electrician is not required to be at all times responsible for the person working on these systems.

,

In a search for historical references to 100 volts, I found this:

https://americanradiohistory.com/Archive-Electrical-Experimenter/EE-1915-08.pdf

The Electrical Experimenter, August 1915, Page 134: How Electricity Kills - [...] The average man can take a direct current of 100 volts and scarcely notice it. 200 to 400 volts will give rise to muscular cramp, while respiration is suddenly stopped at 550 volts. [...]

,

Is there a specific definitive point in history where this division of "0 - 100 volts is safe, but 101+ volts is unsafe" started?


texts: The equivalen reactance of an inductor and a capacitor

texts:
In my text book, I came across a problem where I needed to determine the equivalent reactance of a capacitor and an inductor (its ohmic resistance is negligible). To solve my problem I started to determine the equivalent reactance of both of them and to neglect the ohmic resistance of the inductor, and I thought of doing this:

  Z = √Xl²−Xc². (Where: Z is the impedance, Xl is the inductive reactance and Xc is the capacitive reactance.)

But in the problem statement, Xc is 3Xl.
So, putting them in the above equation is like:

  Z =√Xl²-9Xl²
      =√-8Xl²

Which has no sense because of the negative sign.
So my question is: What would be the equivalent reactance of an inductive and capacitive reactance? Is my approach correct but missing something, or it is wrong?


texts:
I am reading data from an IR sensor array (8 sensors) and converting the ADC result to binary via a set threshold.
If n is the current result, for example: (N.B: n-1 is the previous result)
n-1 = 0b00111000
n   = 0b01110011

I want to perform some logic operations in my Arduino code such that the result would yield 0b01110000 since the first group of 1's in 'n' 'anded' with 'n-1' yields a non-zero value, hence this is not discarded. Whereas the second gorup of 1's (consisting of two bits) 'anded' with 'n-1' yields a zero value, this is discarded. Another example:
n-1 = 0b00111000
n   = 0b10001110

Would result in 0b00001110 since the first group of 1's (consisting of 1 bit in this example) 'anded' with n-1 yields zero, hence this is discarded. Whereas the second group of 1's (consisting of 3 bits) 'anded' with n-1 yields a non-zero result. Hence, this group would not be discarded.I can't figure out what bitwise operations I should use and how to separate the current result in separate groups of 1's to achieve this result.


texts: Why can 2 xbee units not discover each other?

texts:
I have followed the steps outlined here and everything appeared to work 100%.  However, when I open up X-CTU and click "Digi Device Discovery" the two xbee units cannot find each other.

My suspicion is because the coordinator node is on channel and the router has an operating channel "12" whereas the coordinator node has an operating channel "11".

But I am not able to change either of them via the X-CTU GUI.

How can I change the channel or diagnose this problem?

I have read online somewhere it is possible the two xbee units have different version of firmware.  If this is the problem, how can I determine which version of firmware is installed on the two units?

The coordinator unit has version 20A7 and the router node has 22A7.

Is it possible this is the problem?

UPDATE:

coordinator profile:

XB24-ZB_20A7.mxi
80
0
251
20A7
0
[A]ID=100
[A]SC=FFFF
[A]SD=3
[A]ZS=0
[A]NJ=FF
[A]DH=13A200
[A]DL=408B81EE
[A]NI=COORDINATOR1
[A]NH=1E
[A]BH=0
[A]AR=FF
[A]DD=30000
[A]NT=3C
[A]NO=0
[A]CR=3
[A]SE=E8
[A]DE=E8
[A]CI=11
[A]PL=4
[A]PM=1
[A]EE=0
[A]EO=0
[A]BD=3
[A]NB=0
[A]SB=0
[A]RO=3
[A]D7=1
[A]D6=0
[A]CT=64
[A]GT=3E8
[A]CC=2B
[A]SP=20
[A]SN=1
[A]D0=1
[A]D1=0
[A]D2=0
[A]D3=0
[A]D4=0
[A]D5=1
[A]P0=1
[A]P1=0
[A]P2=0
[A]PR=1FFF
[A]LT=0
[A]RP=28
[A]DO=1
[A]IR=0
[A]IC=0
[A]V+=0

router profile

XB24-ZB_22A7.mxi
80
0
251
22A7
0
[A]ID=100
[A]SC=FFFF
[A]SD=3
[A]ZS=0
[A]NJ=FF
[A]NW=0
[A]JV=0
[A]JN=0
[A]DH=13A200
[A]DL=408B820C
[A]NI=ROUTER1
[A]NH=1E
[A]BH=0
[A]AR=FF
[A]DD=30000
[A]NT=3C
[A]NO=0
[A]CR=3
[A]SE=E8
[A]DE=E8
[A]CI=11
[A]PL=4
[A]PM=1
[A]EE=0
[A]EO=0
[A]BD=3
[A]NB=0
[A]SB=0
[A]RO=3
[A]D7=1
[A]D6=0
[A]CT=64
[A]GT=3E8
[A]CC=2B
[A]SM=0
[A]SN=1
[A]SO=0
[A]SP=20
[A]ST=1388
[A]PO=0
[A]D0=1
[A]D1=0
[A]D2=0
[A]D3=0
[A]D4=0
[A]D5=1
[A]P0=1
[A]P1=0
[A]P2=0
[A]PR=1FFF
[A]LT=0
[A]RP=28
[A]DO=1
[A]IR=0
[A]IC=0
[A]V+=0


texts: Do Broadcom's Ethernet chipsets need special software to operate?

texts:
I want to implement an Ethernet switch using Broadcom's chips. Are singing an NDA and getting the datasheets enough to work with the chips? I have heard that the chips must be programmed by a special OS and software that are not available easily, even by Broadcom!

Could anyone who has worked with Broadcom's Ethernet switching chips explain them and their setting up procedure? What steps are needed to make them work? Is it hard to work with them?


texts:
Why is the max frequency of AVR MCUs a function of VCC? Maybe they have  constant current sources that starve as the power demands go up?

Is this relationship unique to the AVR line, or is this typical?

Edit: I am not looking for a quantitative figure or equation. I realize the function exists, and have the datasheets. I'm asking why it exists.


texts:
I had a hard time getting a right title for this question since I'm a software guy trying to get the basics of my hardware down. Since all computers basically start with logic gates and go from there I encountered the phenomenon called a flip flop.

Schematics are like so:

Now I can read this diagram and conclude things based on the outcomes of each nor-gate. What I have a hard time wrapping my head around is the following. Say S=1 and R=0. Any NOR operations with any of the two inputs at 1 (or a high current I presume) ends with a 0 (low) output. In this case I can quietly forget that the second INPUT of the S-gate is the result of an operation that requires the OUTPUT of the same S-gate. There is a 1, I can pretend it doesn't matter where the other input comes from.

This makes Q a 1 since the output of the S-gate is 0 and the R-input is 0 as well. The problem starts when S-input is 0 and R-input is 0. This means "maintain state" or keep outputting a 1 at Q and a 0 at /Q (Not Q). In this case what wins? I simply can't understand how R can be based on output-S while S is based on output-R. At first I thought maybe R is always "first" and the lack of an output-S just means a 0-signal, but I don't know if this is really how it works and if S being 0 by default works in all cases.

Can anyone explain me the concepts that make this work in layman terms?


texts: Powering sub-sytems on a robot with a single battery

texts:
I am making a robot for a project, and have a quick question about the power system for my robot. I have to power an AVR MCU (5V), 6 servos (also 5V), 4 dc motors (12V), and a camera (9V). I really want to use just one battery for the whole robot. I was thinking of using 4 voltage regulators (i.e.LM780*s) to provide the correct voltage for each sub-system from a LiPo battery (each in parallel with the battery). Will this work the way I need it to?

If so, what kind of things do I need to consider. For example, will the servos create a lot of noise on the MCU's power line, or would they be completely separate despite being connected to the same battery?

Essentially, I would like to know what the ideal and/or widely used method of powering various components with a single power source is.


texts: DRV8871 (DC-Motor Driver) extremely reduced output voltage

texts:
I am working on a PCB which contains a PCA9685 PWM Driver and four DRV8871 motor drivers. The basic idea of the board is the PCA is controlled by a micro via I2C which then creates a PWM signal sent to the DRVs which then drive a bunch of BDC motors. I actually have already made one of these boards to drive 3 motors and it works a treat however after adapting it to 4 motors I am running into a strange issue.
The I2C signal going into the PCA is clean and the PCA is able to generate the desired PWM signals. This PWM signal is fed into the DRV however the DRV output is a tiny signal (nowhere near the 12V that is being provided to it).
Here is the schematic and the board layout:

I have run a number of tests to try and determine the issue:

I bypassed the motor drivers and sent the PWM signal from the PCA directly to a DRV8871 motor driver breakout board (made by adafruit) however the breakout board showed the exact same signal on the DRV output as was seen on my board.

I bypassed the PCA by using a breakout board (also adafruit) however this also showed no change to the signal coming from the DRV

I soldered a 47uF cap directly to pin 5 (power) on one of the DRVs to see if it was a power delivery issue but that had no effect

Now for the signals from the board. All these tests are done with only the PCB (no external breakout boards) however the tests mentioned previously had identical results. In this capture you can see Chanel 1 (Yellow) is on the output pin of one of the DRVs and has a amplitude of 300mV (varying from -20mV to -300mV). Channel 2 (Blue) is the PWM output from the PCA which is as expected, 50% duty cycle at 3.3V. Channel 3 and 4 are the SCL and SDA lines respectively and are sending data to the PCA accurately.

Any help with this would be much appreciated. It has me very confused since an identical design (albeit with one less motor driver) works exactly as expected. Incase it is of any help here is a picture of the board in question (bodge wired up as I've been trying to diagnose it). And also a picture of the working 3 motor version (I removed the PCA on this one to test if the chip was broken on the 4 motor board).


texts: Which device will allow me to simply capture 24v?

texts:
I'm new to electronics, struggling to work out whether this is simple and I'm missing something or whether it's a lot more complicated that what I anticipated.

I have something (some device) that is currently outputting a 24v pulse. Via USB (so that I can listen on a serial connection in code), I want to receive that 24v signal on my PC.

So, device outputting 24v outputs it through wires to a device (the device I need) which then (via USB) tells my PC it's received a signal which I can poll from code.

What I've Tried

Not sure if it's something like this that I need?

https://www.ebay.co.uk/itm/8-CH-24V-Computer-PC-Intelligent-USB-Control-Switch-Drive-free-Relay-Switch-/232737498890

or in fact something simpler, like this....

https://www.amazon.co.uk/TOPINCN-Intelligent-Protection-Converter-Regulator/dp/B07MZ67FZR/ref=asc_df_B07MZ67FZR/?tag=googshopuk-21&linkCode=df0&hvadid=294684076205&hvpos=&hvnetw=g&hvrand=2434218583429612698&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9046540&hvtargid=pla-664205036318&psc=1


texts: Fet is named field effect transistor,why?

texts: FET is named Field Effect Transistor while field effect is also producing in bjt. What are the factors/reasons that FET is called field effect while bjt is not? I have read textbook but it didn't explain it.


texts: Get distance covered by a wheel using a gyroscope placed on it

texts:
I have to calculate the distance covered by a wheelchiar using data gathered from a gyroscope that was placed on one of the driving wheels.
I know the total length of the corridor we used for the measurement was 8.4 meters, but I would like to know the distance that the wheelchair covered when the velocity was constant (or almost constant).
The radius of the wheel is 0.17m and the distance between the gyroscope and the centre of the wheel was 0.08m.
The Gyroscope gives me the velocity in deg/s and this is how the plot looks.

The sampling frequency of the gyroscope is 75Hz and this is the code I wrote in Matlab to unwrap the angle:

Gyr_Z1(isnan(Gyr_Z1)) = 0 % substitute Nan with 0

splrate = 1/75;

values = zeros(length(Gyr_Z1),1); %create empty vector

for (i=2 : length(Gyr_Z1))

  values(i) = values(i-1) + Gyr_Z1 (i)*splrate;

end

And this is the bit of code I am using to get the distance covered by the wheel:

for (i=1 : length(Gyr_Z1))

    values(i) = 2*pi*.17*values(i)/360;

end

But when I plot the results this is what I get

So as you can see from the picture the path of the plot looks correct as wheelchair appears to travel at a steady velocity as the Gyroscope graph indicates, but the values are clearly wrong. The length of the corridor was approximately 8.4 meters.
I know I am making a mistake somewhere (and is likely something quite trivial), but I can't see where. Is anybody able to tell me what I am doing wrong?
Thanks!


texts:
I got a Smart Card reader out of a laptop. There's not much going on on the board, just the card receptacle on one side, with the contact springs, and two ICs on the back side:

A Cypress CY7C63001 A-SC USB micro controller, which is the bigger of the two, and finding datasheets for that is no problem.

Now the chip that interfaces the Smart Card chip, is a Texas Instruments 36A2DKK (2nd line: HC02), no datecode. It's a 14 pin SOIC-150 package.

I can't really show you a picture, I don't have any camera or macro lenses, that would make a decent photo of the markings.

I checked the usual places for datasheets, and manufacturers websites, but I can't find a single thing about it. The datecode on the micro controller is 0406, 4th week of 2006 would make sense.


texts: Calculate distance between two vehicles without using GPS

texts:
I am trying to understand if there is any way to measure the distance between two vehicles, possibly moving, without the aid of GPS.  I want to measure a distance of more than 50 meters but less than 100, with an accuracy of at least 5 meters.

The purpose of this type of measurement would be so that vehicles could understand the proximity of each other if out of sight of each other in dense forest/bushland

I would like to read this measurement from both vehicles.

If anyone could give me a push in the right direction, or suggest a way of achieving this, I would greatly appreciate it.


texts:
I need a cheap, somewhat accurate (~0.5%) voltage reference for some DACs. At first I was going to use a LDO voltage regulator (a TC1223 specifically) for this, it seems to fit the bill looking at the datasheet. Then I saw there is a separate category of ICs called voltage references rather than voltage regulators. But from what I can tell the voltage references with the same initial accuracy as the regulator I mentioned above, costs more, and also requires one or more external resistors (at least the shunt diode reference types).

So I was wondering what the difference between regulators and references are, and whether or not I can make do with a regulator for my needs or if I should get a reference, regardless of the higher price for seemingly similar specs. Thanks.


texts: Replacement part for a buzzer to eliminate beeping

texts:
We recently bought an aroma diffuser. Itʼs operated from a 24V DC wall adapter, but for most of the electronics itʼs dropped to 5V (24V is only needed for the actual diffuser part). It works like charm, except every time you press a button it beeps. Itʼs quite annoying and pretty useless, too, so i decided to remove the buzzer instead of reducing the volume. The buzzer is a small piezo one, but it doesnʼt have any identification numbers on it.
The question is, is it safe to just remove it, or should i add a resistor/capacitor (or just a wire, but i doubt that would be a good idea) in place?


texts: How to produce a register bank comprising four such registers in Logisim, sharing common data lines D0 ... D7 and outputs ?

texts:
I made a D-Latch circuit that looks like this:

and I converted it into a subcircuit and made an 8 bit register like this:

But how do I make a register bank using four such registers? Any help is appreciated thanks.


texts: Voltage divider or zener clamp when coupling a comparator output signal to a DAQ?

texts:
As shown in above figures above, a comparator is outputting 16V pulse signal when it is ON.

For some reason I want to lower this voltage around 8V pulse.
In Config 1, it is coupled to a voltage divider. In Config 2, it is coupled to a zener clamp.
This final 8V pulses will then be coupled to a DAQ which will count the pulses.
The reason of stepping down the voltage is that the DAQ has 10V input limit.
The DAQ has input impedance 100Gohm.

I can use both Config 1 and 2. But is there an advantage of one configuration to another?
Which one would you use and is more convenient?


texts: 74LS245 octal bus transceiver doesn't transmit bus

texts:
I'm doing a bit of testing with the SN74LS245 IC which is an octal bus transceiver. According to what I understand in the datasheet and the given truth table, pulling the DIR (pin 0) high (5V) and the OE (pin 19) low (0V) should result in the A side channels to be passed to the B side channels. (Ax to Bx)

I have a breadboard wired up in this configuration:

However, instead of measuring a 5V potential at B2 when 5V is present at A2, no voltage is passed through the other side. I've tried fiddling around with the direction pin but receive the same results in either direction.

Am I missing something in the datasheet or is it a possibility I have come across a bad chip?


texts: Do I need buffers prior to a comparator?

texts:
I have the following circuit which generates digital noise...

The reason for the 2 diodes has to do with stochastic uniformity of the noise output and I don't really want address this aspect.  The comparator is like a LM311 with a <500ns propogation delay. Some other supporting bits have been ommited for clarity. The noise coming off the Zeners is around 1Vp-p when measured 10,000 times.

I intend to have a 8 sets of this circuit so I am interested in reducing the component count and not having a huge circuit board. I have bread boarded this, and it seems to work.  I have measured the noise signal running at up to 8MHz bandwidth.  In reality, I would be expecting to read the noise signal at around 2Mhz.

My question is, should I have (op-amp) buffers on the inputs to the comparator given the presence of the 200K resistors?  What would best practice recommend?


texts: I know that commutator is used in dc motors to convert dc to ac and vice-versa. But I don't understand why we need to convert the dc into ac in armature conductors of a dc motor?


texts:
I'm designing a battery controlled circuit using a 555 timer to control a mosfet to provide power to a load. The problem I'm trying to solve is to reduce the current draw while the circuit is not being used to the minimum possible.

I found this question: Low power delayed off circuit which is close to what I am wanting to do. However, in my case, the 555 timer is the load.

The function of the circuit is that the user presses a button and power is supplied to a high current load for a set period of time of 2 minutes. Once the 2 minutes expires, power from the battery is removed from the timing circuit as well as the high current load. As the circuit is powered from a single lithium battery, the timing circuit may also need a regulator to provide high enough voltage for the timing circuit. The power to the regulator should be cut as well when the circuit isn't in use. This seems like a common problem, so maybe I'm over thinking it or just not using the correct search terms to find my solution.

At first glance, it seems like it should be straightforward - use a mosfet on the power supply between the supply and the timing circuit. While the timing circuit output is active, keep the input mosfet on to keep the timing circuit powered up. When the timing circuit becomes inactive, power is removed from the mosfet powering the timing circuit and thus the timing circuit cuts power to itself. The implementation is eluding me, however.


texts:
I have this 13 pin FFC cable inside my Canon Typestar 5 thermal typewriter. It connects the LCD display to the main board. I'd like to pull the display outside the machine and for that I need an extension (not long).

Do extensions exist for such cable? If so where do I find one?

PS: There is a number of posts on extending FFC cables but they are all quite technical. I just need to find an extension.


texts: I'm replacing the capacitors in a very old tape recorder (1957) and I'm ok with the electrolytics but there are 4 with values 0.001 (x2), 0.002 and 0.005 uF i.e. 1, 2 and 5 nF. Two are marked as 250v and two as 750v. Can anyone suggest what to replace them with please?


texts: 12v 4.8Ah DC regulated to BOTH 5v with 1.9A and 5v 5A

texts:
I am in the process of designing a circuit. I am unsure how to design a regulator to power the system.

I don't know of a way to be able to achieve what is shown in the diagram above. Looking online I have found similar problems with 12v to high current voltage regulators. I don't know how to design a circuit for this specific set up nor which regulator to use.

It will use a PCA9685 to drive 16 servos via I2C on a raspberry pi. The total amperage for all of the servos is from 3760mA to 4460mA.

I could separate the systems power supplies into two batteries but this would be better, if possible. If I do need to use different power supplies could I have recommendations for the specs and which regulator to use?

Does anyone know what regulator specifically could meet these requirements and how the circuit would be configured?

EDIT: Thinking about it, maybe the current needed for the PCA9685 will not be as much as originally thought if due to I2C the servos aren't underload at the same time. Am I thinking correctly here? This would decrease the current needed dramatically.


texts: Linear regulator doesn't keep the right voltage when connected to ESP8266

texts:
I am trying to use a MCP1700-3302E LDO to regulate voltage from single-cell LiPo battery to my ESP8266 (Wemos D1 package). I intend to use the LiPo down to 3.5V, and since ESP8266 requires 3.3V, that leaves 0.2V headroom. MCP1700 has a dropout voltage right under that requirement (178mV @ 250mA).

For testing, I hooked it all up on a breadboard, powering from my PSU to monitor voltage and current. This is the exact schematic of how it is all hooked up:

As you can see, I added two 1uF (105) ceramic capacitors to the input and output of the regulator, just like the datasheet suggests. Also, I use two 470uF capacitors (because I don't have larger one at the moment) to handle the current spike during ESP8266 booting. ESP8266 might spike up to 435mA, but the MCP1700 has a current limiter of 250mA, so without these capacitors ESP won't boot. After it boots, it runs a simple onboard LED blink sketch.

Now, the problem is that after booting, the voltage on ESP8266 3V3 pin drops to 3.1V. PSU provides 3.5V, I double checked - no drop there. And ESP8266 consumes around 70mA with this sketch, which is way below the 250mA limit of MCP1700. According to the datasheet, dropout voltage at 70mA draw should be around 45mV, but in reality is more like 400mV (3.5V before LDO, 3.1V after LDO).

I know ESP8266 can function with slightly lower voltage, but I need stable 3.3V supply for it because I'll be making some analog measurements, and ESP needs a stable reference voltage for that.

I cannot figure out why this is happening. I am using proper, self-made jumper cables, not the cheap stuff from China. And I am measuring voltage directly on the MCP1700 legs (like shown in the schematic), so the breadboard shouldn't be at fault either.

I tried replacing all the components, including the regulator and the ESP8266 (I have plenty of both), but all of them show the same results. If I increase supply voltage on my PSU to 3.7, then I get correct 3.3V after LDO, but the whole point of this setup is to use a voltage as low as 3.5V, and according to datasheet, this regulator should be able to provide that easily with such small current.

What am I missing here?


texts: I want to understand the Math behind the Solar Power Panel Wattage requirement in order to charge 10 mobile phones (use 0.8A each) at the same time. No battery is required. Solar panel output is 12V DC.


texts: How to power an Atmega328P and Pi from 12V?

texts:
I have a bare-bones Arduino (basically an Atmega328P) and a Raspberry Pi 2. I have them communicating with each other over I2C and a 5v/3.3v logic level converter.

Right now I power the Pi (micro-usb) and Atmega (5v from FTDI) separately. I have a 12V 6A DC PSU (5.5mm barrel jack) that I would like to use to power both the Pi and the Atmega (and my LED strip lighting).

What's a good way to go about doing this? I have a few LM7805 chips on hand if I could use those, but I'm open to ordering new stuff if I have to.

Do I convert to 5v from 12v and then use that to power both Pi via GPIO and Atmega or is there current draw issues with doing that?


texts: how to make an easy dc/dc transformer to run a lenovo laptop on 20 volt from a 12 volt battery

texts:
I was thinking of making my own dc/dc converter for my laptop.
The original Lenovo charger can give 20 V at 4.5 A. I
I have a few questions:
right now I wanna build a 12 volt to 20 volt converter.
I have been looking at boost and buck converters but I don't know what toroid to use or how many windings or what electrolytic capacitor to use.
I have a lot of electrolytes form disposable cameras, maybe I could use them.
I also found this on ebay. would it work? https://www.ebay.com/itm/150W-DC-DC-Boost-Step-Up-Converter-12V-32V-to-15V-35V-24V-6A-Laptop-Power-Supply/262983318200?hash=item3d3b06fab8:g:fg4AAOSwIaFZFtCT

I have been looking at Powering laptop from 12V sources without inverter

the cuicuit in this post looks to complicated for me.

I rather wanna build my own using arduino or a 555 timer instead of buying a new , to learn , thanks. Hope it wasent to long


texts: speed control PWM, DC motor, L298n with LPCxpresso 1549

texts:
this is my first post and I'm just asking a little bit about motor control in a team project, where I'm member of.

This is a bit of a "not so serious" project so probably the solar panel system consumes much more energy than it generates but anyways... Our parts budget for the project was not very extensive and we just had whatever was  available at the school for parts.

So, we are using 1x DC motor to control the rotation of a solar panel tracker system. It was given to us by our teacher so we don't know much about it. We did test that it works at full speed in both directions, but as the supply voltage became too low, it didn't work so good. (less than 3v wasnt very good)

The system works like this basically

there is a solar panel plate on which the actual solar panel attaches on a hinge, and the other end of the solar panel has a hinge and a part into which the "top-end" of screw attaches, and solar panel is able to tilt, by using a screw, which is turned by the stepper ("bottom-end" of screw is attached at the stepper"). The stepper is mounted on a hinge at the solar panel plate
also that solar panel plate has wheels at the bottom,
then there is a second "baseplate" and the solar panel plate rests on that baseplate.
baseplate has the dc motor which turns the solar panel plate, the rotation part

Then we have that L298n chip.

The tilting axis is controlled with a separate stepper motor

I think we are connecting 12v into the power of the DC motor, but this results in too fast of a speed for the motor.

I think that after consulting an arduino tutorial (and the chip L298 datasheet), it was recommended to use PWM into the enableB pin, to control speed.

We are using SCtimer functionality from the lpcxpresso to pulse the PWM

questions

it appears that on this website, it was recommended to PWM into the in3 and in4 pins L298n PWM frequency . Is it better solution to PWM into the in3 and in4 pins, as opposed to the enableB pin? We require good speed control in our project, and the motor speed should be able to be fairly slow, and we would want to have the ability to rapidly stop also...
Overall, I would say that we require of the motor: slow speed, ability to stop quickly, ability for direction changes.
I would say that of course one channel PWM into the enableB pin is the simplest PWM in the software to configure. But, I suppose that we could also make a two channel PWM, while leaving the enableB pin = TRUE. Then, we could control the directions, by changing the dutycycles of in3, and in4, by switching around the dutycycles like (0%,25%) and vice-versa. I suppose we could also have the stop motor at (0%,0%)

Is there any way to know a good PWM frequency for a DC motor, if you don't know much about that motor directly in terms of specs and datasheet, and make&model? I think that we succeeded in some early tests with 1khz PWM freq, but some of our classmates had used that same DC motor with about 400hz PWM freq?


texts:
I'm trying to determine the input current required to operate the following SN65HVD233 CAN transceiver at 1Mbaud: http://www.ti.com/lit/ds/symlink/sn65hvd233.pdf

The first spec I see listed is receiver output current:

I don't understand why this ranges from -10 to 10mA. The receiver outputs to the CAN controller's Rx pin so why would it be sinking current?

The next spec I see is output current for the driver:

Again, I'm not sure why the driver would be sinking current.

Schematic provided on datasheet of driver and receiver:

Later in the datasheet, the supply current for the driver and receiver is provided:

(both driver and receiver are identical, with 6mA of current draw in dominant and recessive state)

These are specified at "No load" - can I use these figures for power calculations when the device is actually attached to a bus?

Also, do the high level and low level output currents for driver and receiver factor into the current draw of the transceiver?


texts:
I came across this clipper circuit:

I was analyzing this circuit. I could not very clearly understand what is the purpose of resistance, R here.

I understand that if we do not include this resistor, it would mean that we are actually assigning a fixed voltage to Vo.

What I do not understand is how its presence is solving 'some' issues. How is the voltage at Vo being affected by this resistance?


texts:
I'm reading some texts (single supply circuits collection) about circuits and I encounter the symbol ||.

What is the meaning of it?

For an example in a circuit about an op-amp circuit that provides gain i see in the "inverting" description:

Gain = -R2/R1

R3 = R1||R2

(I can't insert a schematic, circuit editor never starts)


texts: Amplifying a high frequency signal of 30 Mhz or above using OpAmps

texts:
I am testing a 34 Mhz amplifier in an inverting configuration with a gain of 20.

The cutt-off freqeuncy of amplification stops almost at 15 Mhz , which is very low. I want it to continue up to 27 Mhz to 30 Mhz. (It doesn't stop , but the amplification ratio becomes very low).

I searched a lot for op-amps with a high cutt off freqeuncy an d I found many , but when I look at the data sheet for Freqeuncy VS Outut Voltage the freqeuncy stops before 10Mhz. The gain VS freqeuncy graph looks fine and shows that it can amplify untill 30 Mhz and more.

Here is a picture of the nearest one I found ,at 26db (20 volts) the freqeuncy I think  approches 30 or 40 Mhz , is that correct?

Links : The first the voltage isn't amplified properly at 30 Mhz and stops amplifying before 10 Mhz almost , second link similar problem , but gain seems to be OK.

First link
Second link