so for context this exercise is driving me crazy even tho its simple i just didnt understnad the correction and tbf i dont even know if this is the right sub to ask for help but im out of options.

so i need to count i2 with thevenin, i found Rth no problem and now i found a problem in Eth, first i changed the 3 resistances uptop using triangle to star method and the circuit is much cleaner.

for Eth i think the correction is i just use the maille in like middle to right(maille is french word idk whats the english equivalent maybe circuit?) and the current going through R4 and R1 is just big I coming from the current generator on the left, what i didnt understand is, shouldnt the current be the difference between I and i1 since theyre opposite sides? AI's really dont help much in my experience in circuits cuz they cant draw them and its tiring af, but when i asked in google it said that when theres a voltage generator and a current one then the current one dictates, well, the current so i just use I? and on the right there isnt any current ofc cuz R2 is debranched for Thevenin.

is that how its done?

Hi everyone,

While replacing the battery in my Samsung Galaxy S21 Plus, I accidentally ripped off a small component from the motherboard.

Could anyone help me identify what this component is and, if possible, tell me its specifications or part number?

I would also like to know what soldering iron temperature I should use to solder a replacement component back onto the board.

A few questions:

• Does anyone know what this component does?
• Can the phone still function properly without it, or is it essential?
• If it needs to be replaced, what component should I buy, and what temperature should I use for soldering?

Any advice, identification tips, or repair guidance would be greatly appreciated.

Thanks in advance!

The battery is fine and fully charged at 4.2 V (red wires: L+ and B-). The LED is at the top (B+ and the blue wire). At the bottom, there is a switch with four modes: the first press turns the LED on at full brightness, the second switches to half brightness, the third activates blinking mode, and the fourth turns the LED off.

To the right of the switch, there are blue and green LEDs that indicate charging status, a full battery, or when the lamp is in use.

It's not visible in the picture, but there is some blue stuff underneath the IC, possibly copper oxidation or some kind of glue. Anyway, the lamp doesn't respond when I press the switch, so I believe the IC was damaged by the rain.

It's a cheap battery powered lamp, but I have some tools and would like to try replacing the IC. The problem is that there are no markings on it, and since I'm not an electronics expert, I can't identify it.

Does anyone recognize this IC?

I would like to build a converter in LTspice for illustration purposes, and then build it as a real circuit. I have a 48 V DC supply, and the current is unknown at the moment. The aim is to produce output voltages of 24 V, 12 V and 5 V. I have made a circuit in LTspice, but I get fA and fV on the secondary side. I believe the issue is the switch, so I would like pointers on why my circuit isn’t working and how I can fix it.

https://we.tl/t-KFQi58WquG25fKwr

I recently bought this Keyboard, made exclusively for the videogame Rockband 3. This is the Xbox 360 version.

Every key works normally, except for the up arrow of the D-pad (the top left key in the first picture).

I tried disassembling it and cleaning the contact with alcohol, but nothing changed. The circuit looks intact to me, I don't know why this key still's not working.

Is there something else I can try?

hey guys. have you ever used MOVGT for transient suppressors?

Do they perform the same as the classic configuration of MOV + GDT, are they trustable?

Hola, estoy haciendo un regulador de voltaje porque quiero hacer que 4 paneles solares que en total dan 20W carguen 8 pilas de cada uno 3.7V, me estoy guiando por un video de un señor que encontre en Youtube, y lo estoy probando con mi protoboard, pero no me quiere funcionar y ya queme dos diodos LED's por fabricar artesanalmente una bateria que si funcione con el relé, que es de 5 pines, y ya revise con mi multimetro si en verdad esta dando voltaje pero se queda en 0 el resultado y me dice que tengo los polos mal, pero revise y no veo nada, de verdad que me harían un gran favor si me solucionan esto. Aqui adjunto las fotos del diagrama esquematico y mi circuito del protoboard, muchas gracias.

Ptt: Tambien adjunto mi intento nefasto de una bateria con las tres pilas en serie, ya que el relé funciona a 12V y tuve que ingeniarmelas.

Hi everyone! I need some help designing a three-stage amplifier using BJT transistors, with a total voltage gain of 5000.

I'm not really sure how to approach the circuit or where to start with the calculations. I need to understand how to choose the right components and their values to achieve the required gain without driving the transistors into cutoff or saturation, or causing significant distortion in the output signal.

The circuit needs to meet the following requirements:

Consist of three BJT amplifier stages.

Achieve a total voltage gain of 5000.

Calculate the DC biasing of each transistor, including voltages and currents.

Verify that all transistors operate in the active region.

Calculate the voltage gain of each stage and the overall gain.

Take into account the loading effect between stages.

Determine the maximum input signal amplitude that allows the amplifier to operate without significant distortion, and calculate the output amplitude.

Include all necessary resistors, coupling and bypass capacitors, the power supply, and other components.

Simulate the circuit and compare the results with the theoretical calculations.

The part I'm struggling with the most is figuring out how to distribute the gain across the three stages, which configurations to use, and how to calculate the component values from scratch.

If anyone could help me with an example circuit, the initial calculations, or a step-by-step explanation of how to achieve a voltage gain of 5000, I'd really appreciate it!

Thanks in advance!

I am designing a PCB for a small microcopter drone right now and we want a 3.3V supply for our logic voltage.
Problem is that we use an 1S Batterie (Lava 2 580 mAh) which can drop below 3.3 V in terms of the discharging diagram. That's why we cannot use a simple LDO to regulate voltage as it can drop off our logic supply.
My question ist how you would solve this problem. My idea is to use either a buck-boost converter or a boost converter followed by an LDO. Benefit by the buck-boost would be an overall better efficiency but maybe a voltage ripple that could cause further problems, which would not be a problem with a following LDO to smooth. Also the question would be if the buck boost has problems when battery gives us 3.3 V to witch between boost and buck mode.

Thanks a lot for your ideas!

I already replaced the fuse on this amp but when I pulled out the amp everything looked okay. The only thing is maybe this big 400V capacitor is bulging a little.

The LM13700 should be configured as a variable-gain amplifier such that the control voltage (VC) varies from −3 V to +4 V, corresponding to a gain range of 1.333 to 20.

In other words:

- At (VC=-3V), the LM13700 should provide a gain of approximately 1.333.

- At (VC=+4V), the LM13700 should provide a gain of approximately 20.

- The gain should vary continuously between these two limits as (VC) changes.

Please delete if this isn’t allowed but I’m learning how to do this for the first time on my own. I got a small radio kit from Amazon to learn about circuitry and soldering. I followed the video but it was all in Cantonese and I couldn’t follow it other than visually. I checked the guide and video for each step and thought it went smoothly. But when I put the AA batteries in they seemed too huge for the battery box, the lights didn’t turn on for display or the LED, and then there was a weird chemical smell and smoke and the battery box felt hot.
If you don’t mind helping me learn does anyone know why this happened and what I can do next time to learn? Or a good resource to learn from

Edit: Thank you all so much for the helpful advice! I was scared of being massacred being new to this but everyone has given helpful advice I will follow and I appreciate it

Hey all, I would like to ask for some help and advice about a sync delay circuit. To my knowledge its used to control the Horizontal position of a video source being fed into a crt Tv. I'm being recommended a 74HC123. Is this a complex circuit, what would it look like?

These "SCART RGBS Adjustment Converter Picture Adjuster" exist but there is no documentation on them.

I would like to see schematic or a circuit for one or something similar.

Any help is appreciated thankyou.

I can't for the life of me figure out why my microprocessor isn't producing an output.

I know that the pass and load_acc are not being triggered as well as the data_bus is never triggering as having any voltage on it. I have gone through and verified that every single embedded circuit works properly. I just can't seem to get a good output on the final one.

Any help is appreciated. Attached photos so yall can know where I'm at with it

Small battery powered ESP32-C3-WROOM-02 board that sleeps most of the time and wakes on a Hall sensor, an accelerometer interrupt, or a DS3231 alarm, then logs a timestamp to I2C EEPROM. 1S LiPo (550 mAh) with DW01A + dual FET protection, charged from USB-C by a TP4056, with a P-FET + Schottky load sharing path feeding an AP2112K 3.3 V LDO. Native USB on IO18/IO19.

Rev 1 never showed up over USB (nothing in the device list, even holding BOOT). Reviewers here already helped me find real bugs in it: CE tied to ground, charge LED wired wrong, Hall sensor pins swapped, wrong FET pinout, missing bypass caps. Rev 2 (attached, 2 images: power, then MCU and sensors) is my attempt to fix all of those. I have not built it yet and only have one board, so I want it right before I order.

Main question: will this enumerate over USB on first power up? If not, what is wrong?

I would also love a hard look at:

- USB-C section: 5.1k on CC1/CC2, 22R series on D+/D-, D+/D- wiring to IO19/IO18, shield to GND

- TP4056 + DW01A + AO3400A x2, and the load sharing circuit (Q3 AO3401A, D2 SS14, R16 pulldown)

- ESP32-C3 strapping (IO2, IO8, IO9), EN reset RC, BOOT button, deep sleep wake pins (IO3, IO4, IO5)

- I2C pull-ups, DS3231 N.C. pins grounded, ADXL343 pin connections

- Anything else that looks wrong, even small stuff. I would rather hear it now than after I order.

Thanks! I will reply to every comment and post what changes.

Hi everyone,
I’m working on the hardware design of an ATEX / IECEx intrinsically safe circuit intended for Zone 0, and I’m currently confused about how to properly determine the voltage, current, capacitance, and inductance limits for the circuit.
I understand that for an intrinsically safe design, it’s not enough to simply limit the supply current. The stored energy in capacitors and inductors, fault conditions, component tolerances, and the associated apparatus parameters also need to be considered.
My main questions are:
● How do I determine the maximum allowable voltage and current for a Zone 0 Ex ia circuit?
● How should I calculate the permitted capacitance and inductance?
● How are Ci and Li of components taken into account?
● How do I determine whether a resistor/current-limiting network is sufficient to prevent ignition under fault conditions?
● How are Uo, Io, Po, Co and Lo determined for an intrinsically safe output?
● What happens when components such as capacitors, inductors, transformers, TVS diodes, etc. are connected to the circuit?
● What standards/calculation methods should I follow for an actual ATEX/IECEx product?
I’m particularly interested in understanding the engineering calculation and design methodology, rather than just using a certified barrier/module.
If anyone has experience designing Ex ia / Zone 0 electronics, I would really appreciate some guidance, examples, recommended standards, or references that explain the process from the circuit level.
Thanks in advance!

Small battery-powered sensor logger. It sleeps most of the time, wakes when a magnet moves away (Hall switch) or on motion (accelerometer), timestamps each event with an RTC and stores it in EEPROM. It charges a 1S LiPo over USB-C and shows status on an I2C OLED.

Rev 1 didn't show up over USB. I found and fixed these for Rev 2:

• TP4056 CE was tied to GND, so the charger was disabled
• The CHRG LED was wired to GND, so it could never light (CHRG is open drain)
• Added load sharing so the charger doesn't mix up load current with charge current
• Hall sensor pins 2 and 3 were swapped
• Protection FETs were a 3-pin symbol on a 6-pin dual FET, now two AO3400A
• Added the EN RC, strapping pull-ups, the DW01A VCC filter, and USB series resistors
• Wired the accelerometer INT1 and RTC alarm to deep sleep wake pins

What I'd like checked:

1. Is the load sharing circuit (Q3, D2, R16) right with the DW01A protection in the path?
2. Anything wrong in the battery protection section?
3. Anything else that would stop it enumerating over USB or waking from deep sleep?

Parts: ESP32-C3-WROOM-02, TP4056, DW01A, AP2112K-3.3, DS3231SN, 24LC256, ADXL343, DRV5032FA. Thanks for looking!

I’m a beginner, so maybe I’m missing something simple.

I have a DVR/audio source connected to an LM386 amplifier. If I power both from the same adapter, I get a lot of noise from the speaker.

But if I use a separate adapter for the amplifier, the noise almost disappears.

The confusing part is that I still connect the ground/negative of both together.

So what exactly is changing here? If the grounds are connected anyway, why does using a separate power supply make the noise go away?

I’ve also seen another thing. Sometimes, if I connect the amplifier negative/ground to 230 V earth, the noise becomes much lower. In some cases, even connecting the negative side of the big filter capacitor to earth seems to help.

Why does touching or connecting the ground to earth sometimes make the noise disappear?

How can I tell if this is power-supply noise, a ground loop, or noise being picked up by the circuit?

I’m mainly trying to understand what is actually happening, not just find a quick fix.

I’m a beginner trying to understand something.

Suppose I generate a low-frequency square wave (below 1 kHz) using a 555 timer or a microcontroller, and use a MOSFET to switch/chop a power supply.

Now I want to take a small amount of DC power from that same switched output, but I don’t want to change the original square-wave signal.

What would be the simplest way to do this?

Would a diode + capacitor work, or would the capacitor load the MOSFET too much and change the square wave?

If more power is needed, would a small transformer or some other method be better?

Just looking for a simple practical explanation.

Edit - I have a project that is now in the final stage, and I just need to power a small LED. I only need a little power, but pulling an additional cable is not practical at this stage and would add extra cost.

The only available option is the existing 24 V DC power-over-data line. There are also some microcontrollers communicating over this line, so I’m wondering if there’s a simple way to extract a small amount of power from it without disturbing the communication.

Beforehand trying to make a safer simulations with 555 or microcontroller before connected in live

Marking .506

Probably a mosfet but I dont know which one

Estou TENTANDO fazer o acionamento do componente através do ESP32 - PIN 25, e conforme algumas informações que estou lendo... o MOSFET IRLZ44N seria o ponto que de certa forma controla isso.

Montei esse projeto algumas vezes e algumas variações... mas sem sucesso!

Sucesso só quando gero uns curtos 😄😄

Avaliem pf, onde estou errando!
IMAGEM-> https://ibb.co/k2YtDz05

Hi everyone,

I have an out-of-warranty Siglent SDM3045X that is stuck on the boot/splash screen. The repair quote is higher than a new unit, so I’m trying to diagnose it myself.

Symptoms / observations after opening the cover:

• Constantly flashing orange/yellow LED (location not specified in the service manual).
• On the daughterboard: green LED that flashes twice, pauses, then repeats the two flashes indefinitely.
• Front-panel USB host port outputs only ~0.6–0.7 mV (essentially dead).
• J14 (main-board power connector, pins 1–2) measures 11.6 V. The service manual calls for +8.6 V ±2 V, so this is outside the upper limit.
• The unit otherwise powers up enough to show the Siglent boot screen and the internal LEDs above.

I have already checked the obvious (fuse, power cord, etc.). Has anyone else seen this combination of LED behaviour + elevated J14 voltage + dead front USB while stuck at the boot screen? Any ideas whether this points more to a power-supply/regulator failure versus the usual firmware corruption that the USB recovery normally fixes?

Any photos of the LED locations, voltage measurements from a working unit, or repair experiences would be greatly appreciated.

Thanks!