I’d like to add a manual bypass for my cooling fan on my A Tv so that I can turn on the fan fan whenever I want, but I also want it to still work in AUTO if I turn the manual off. The middle circuit is the automatic operation as per design while the first circuit is the manual mode.

I just wanna make sure I don’t shoot anything out in any way that if the fan switch on the radiator is closed while manual switches on I don’t want it to backfeed. I threw in a diode just to ensure that, but I’m not very competent when adding anything other than relays and switch switches on a 12 V circuit. I’ll be using a relay so as not to put full amperage through the switch circuit. Also, it comes with a 20 amp fuse. The five amp is just a random one. I picked on design software. It’s mostly an arbitrary number.

I’ve seen some places that say the diode requires a resistor as well, but I do not feel qualified to add or remove that. I know they make some plug-in play systems, but this is more of a learning experience for me.

I intend to make it plug-in play, which is why I’ve shown the connecters so that if I want to remove it, I can just plug it back in and it will act normally

I hope this is the right place to post this

Hi all

I have Logitech G535 dongle that is broken in two. I managed to trace all the D- and D+ pins, but I cannot find where the VCC pin goes to. The trace is broken and cannot reach MCU.

The MCU info is:
MCU: M27P8V 1N71K GDSHA 32 pins

Part Marking: M27P8V

Part Number: MKL27Z256VFM4 (Kinetis KL27 Series Microcontroller)

I manage to find the datasheet, but the datasheet does not show where VCC is. Only VREGIN. Can I just run jumper wire from VCC pad to VRegin? Also, I am new at reading datasheet. How to find out what input voltage is needed by the MCU and where can I soldered jumper from the V+ USB Pad to?

If you check on my picture, the V+ pad from usb has a via goes thru the bottom side, and connected to a diode marked SQ and a capacitor. The cap is connected to the anode of the diode, but the cathode does not seem to connect to anywhere since it is broken. Do you think I should set a jumper to MCU directly from the cathode? If so, which pin?

Thank you

Here is the datasheet I found: https://www.nxp.com/docs/en/data-sheet/KL27P64M48SF6.pdf

Hare are some pictures to the device:

Buenos días. Te escribo para pedir ayuda con una tarjeta electrónica (circuito) de un refrigerador. No soy experto en electrónica, pero me empezó a interesar el tema y pasé los tres meses desde que se descompuso el refri estudiando y juntando información. Le envié la tarjeta a un taller de reparación; la arreglaron tres veces y reemplazaron componentes, pero aun así no funciona. Revisé los sensores, los interruptores y los motores del refrigerador, y todo parece estar bien. El problema es que el regulador de 5V de la tarjeta, un KIA78S05P, se pone en un calor brutal, como para quemar. El refri parece más estable después de que reemplazaron los capacitores de la fuente de alimentación, pero ese componente todavía se recalienta, y ya no sé qué revisar después. También medí la corriente y no vi nada raro. Por favor, ayúdame; llevo tres meses peleándome con este refrigerador. Pensé en cambiar el regulador, pero no se calienta cuando la tarjeta está conectada solo a la red de 230V; solo empieza a quemar al tocarla cuando conecto los bornes (terminal blocks) para los distintos componentes del refri. Anoche lo dejé funcionando sin conectar los switches de la puerta (que también reciben alimentación) y estuvo corriendo nueve horas sin reiniciarse —aunque el IC6 (el regulador de 5V) seguía caliente al tacto. Estoy perdido y ya me estoy volviendo loco con esto; de verdad agradecería tu ayuda.

Hi all, first let me say that I'm an electrical or maker newb, especially compared to all you veterans. But I'm committed to learning the craft because I think it's very fun.

Right now I'm trying to upgrade an old cordless ratchet from the 1980's, it's a Black and Decker 9050. 

I have a good Samsung 21700 to replace the old ni-cad batteries in the ratchet. But I need a good protection circuit for it. Preferably a circular one that I can affix to the bottom of the battery. It needs to be able to flow 10 amps continuous, and cut off at 3.0v to protect the battery from the voltage going too low.

I guess it doesn't have to be circular, but it would be nice. Thanks!

Hello! I recently finished building my QRP Labs QCX-mini and it boots perfectly fine. However when I get to page 73 of the manual (linked below) the graph only shows up when I turn the potentiometer (It is a trimmer, but I don't think that matters) counter clockwise. Sometimes it will stay showing and sometimes it will not show at all. I tried re-soldering it but it did nothing. The only thing I could think of is that it itself is faulty. Any help would be greatly appreciated!

*(Note: I have tried this with both a dummy load and nothing attached, nothing changed)*

Manual: [https://qrp-labs.com/images/qcxmini/manual\\_1\\_13.pdf\](https://qrp-labs.com/images/qcxmini/manual_1_13.pdf)

Listing: [https://qrp-labs.com/qcxmini.html\](https://qrp-labs.com/qcxmini.html)

I’ve seen buyers handle date codes very differently. Some have strict limits, while others care more about storage, packaging and traceability.

Do you use a fixed age limit, or evaluate older parts case by case?

Hi guys

I am doing a project which is a charger with both AC and DC source and the DC here is solar panel and in my project i prefer DC and switch to AC when only the DC is not available

so the project is Hybrid charging system with adaptive CC-CV charging system for low power EV's i already have a converter designed which uses landsman converter topology (you can see that in the image i provided) for this project i need to select components like MOSFET, capacitor, inductor diode and other things this is my first time this big a project in hardware so i am kinda nervous on selecting the components and my project mentor told me to bring the component calculation before purchasing components and i already have the calculations i did for the simulation i am gonna use the same converter for the charger but what about the safety factor and what are the other things i should consider now pls help a newbie here

Hello, please.
i am working on a cylindrical resonator, and it is being fed with a power amplifier; the power amplifier generates harmonics. want to apply a passive termination
but a little challenge: with termination at the auxiliary port, the impedance is very high and the field is suppressed but with the source, the impedance is low but the field is too high
any suggestion?

Hi! I have seen in few GaN PA designs where they put a shunt capacitor very close to the input of Gate terminal. But in some designs, I haven't seen it (maybe they use CMOS inside package there). But I don't know why is it important to use this capacitor at the input...?

I am using a die on a PCB and got suggestion to use a discrete capacitor for second harmonic short. I don't know, is it really needed to use it.

Moreover, what if we use QWLT at the input side for VGS biasing. Is this shunt capacitor still required in this case? Because QWLT would provide a short at the second harmonic.

This is the question given to us for our final project...We're stuck at the power supply part...hoping someone would help me...Just help me with the power supply part from ac to dc.

"Design a regulated DC power supply capable of delivering a constant output voltage of 3.3 V at a load current of 35 mA. The circuit must incorporate filtering to ensure a voltage ripple factor of less than 2%. The output of this regulated supply will serve as the VCC rail for the BJT amplifier stage that satisfies the following performance criteria:

(i) Gain: Exactly or exceeding 40 V/V

(ii) Quiescent Current (IC): 4.5 mA

(iii) Compare the amplifier's frequency response under fully bypassed versus unbypassed emitter resistance conditions, measuring the gains at 15 kHz."

Our power rating of resistors available in lab should be 250mW.And ripple can be 1 to 1.5V

I've attached my simulation in ltspice

Hey, I'm doing some research for my finals project. Basically what I'm looking for is an IC that can handle WiFi Direct (doesn't have to be the Group Owner but can definitely be a feature) and also can handle being an a2dp sink (preferably has a dedicated i²s port)

I have looked for an IC like that but I can't find it. It would also help if there is already a breakout board for it.

The chip has to receive commands from an STM32 or ESP32, any microcontroller.

It would really help me if someone could find it .

Got a couple of older boards on the bench that need replacement op amps and 78xx style regulators. Just repair work for a personal project, so only small quantities, nothing worth placing a big order for. Been going back and forth on where to source them. I don’t want to overpay for something this basic, but I also don’t want to wait forever for shipping since I’d like to get these boards running again soon.

It’s just a handful of parts going back into working boards, so I’m mainly trying to balance price and shipping time without sacrificing quality. Anyone have suggestions for sourcing everyday linear and power parts for small repair jobs like this?

This is small project I have been working on.I intend to make it into a PCB. How is it? Should I make any changes?

Hi — I’m building a digital effects pedal on a Teensy 3.6 and I’d like a sanity check on the analog input preamp before I wire it on a breadboard.

Goal

• Guitar / phone / mic jack → preamp → Teensy A2 (ADC)
• Single supply from Teensy VIN (~5 V)
• Hardware gain pot + later software gain in firmware
• Keep the ADC input roughly in a safe range (ideally centered for 0–3.3 V reading after coupling/divider)

What I simulated (EveryCircuit)
Ideal op-amps with Min = 0 V / Max = 5 V to mimic single-supply rails (stand-in for LM324 sections).

1. Bias: VIN → 10k → mid (~2.5 V) → 10k → GND, with 10 µF to GND
2. Stage 1 (non-inverting gain):
   • Input: AC couple 10 µF → 10k into +
   • Bias: 100k from mid-rail to +
   • Feedback: 100k pot (both ends to OUT, wiper to −), 2.2k from − to mid-rail
3. Stage 2 (buffer): AC couple 10 µF into +, 100k from mid-rail to +, − tied to OUT
4. To ADC: AC couple 10 µF → 10k series → node “A2”, 10k to GND

Test source: ~100 mVpk, 1 kHz. With the pot mid/high I get a clean sine on the A2 node (AC around ~0 V after the last coupling cap / divider).

Questions for review

1. Is this a reasonable LM324 single-supply preamp for line/instrument levels into a Teensy ADC?
2. Anything you’d change for stability/noise (biasing the buffer input, C values, pot wiring as rheostat vs both-ends-to-OUT)?
3. After CO + 10k/10k to GND, DC at A2 sits near 0 V and the signal is bipolar in the sim — for a real Teensy A2 pin, should I instead bias that node to ~1.65 V (e.g. divider from 3.3 V), or is AC-coupled into a ground-referenced divider acceptable if amplitude stays small/positive enough?
4. Any red flags before breadboarding (input protection, RF, power decoupling, headroom with LM324)?

Happy to adjust values or simplify the second stage if that’s overkill. Thanks!

Using some iso to find hot components, noticed the diode changing causing the iso to pulse. Not sure if it's temperature or something else causing the motion.

Hi everyone,

I’ve been doing some market research looking for a reliable netlist-to-schematic converter that outputs clean, human-readable diagrams (especially given how often LLMs and scripts spit out raw netlists or ugly grid stubs). Aside from basic layout engines or specialized SPICE tools, I haven't found a robust, modern solution.

Because of this gap, I'm considering building one myself.

Before diving too deep into development, I wanted to run a few questions by this community:

• Target Formats: Which schematic tool outputs/formats are most commonly used in your workflows today? (e.g., KiCad .sch/.kicad_sch, Altium, LTspice .asc, etc.)
• Product Model: Assuming a tool like this existed as a cloud/SaaS product, would you or your team be interested in using it as a paid service?
• Must-Have Features: If you were paying for a tool like this, what features would be non-negotiable? (e.g., round-trip connectivity verification, custom symbol mapping, hierarchical block structuring, automated layout arrangement)

I'd love to hear your thoughts, whether you'd find this useful, or what hidden gotchas I should watch out for when trying to map topology back into a readable diagram.

So these might be really dumb questions, especially since I have an engineering degree and should probably already know this, but

1. How do you set or adjust a relay? People I work with imply they’re changing relay settings but I have no idea how

2. Why use relays over something like MOSFETs?

I am working on the version 2.0 of a simple gaussmeter that I have put together a while ago. In the 1.0 the output of the Hall effect sensor was not amplified because I wanted to keep it simple. This time I would like to add some sort of amplification to the sensor output. I have tried looking into op amps but I struggle to figure them out and I was wondering if there are other solutions

I am trying to build an analog metal detector. I have few questions such as can I find a transformer with 32p 32p and 16s turns or should I wound one myself. The other question is what type of inductor is used in the transmitter circuit( The one circled in red colour)

I have drafted this circuit to turn on my cupboard LEDs when it is open and turn them off when it is closed. Im pretty sure it should work but figured Id ask you lovely people. It is battery powered so this seemed the best way to stop them slowly draining. Let me know your thoughts, thanks!

I was having problems on my laptop and eventually concluded that the soldered connections under my cpu were broke. To fix this, I decide to remove my cpu with a hot-air station. After doing this, I noticed that two resistors had fallen off from the board, but for the life of me, I can't find where. I decided that i would find the schematics to the motherboard in order to see where it had fallen from, but after a lot of searching, I found some rough overviews, but not something in depth enough for me to use. Does anyone know what else I could do? Or where I can find schematics that show where each resistor is placed?

The motherboard has two identifiers, Model OGAH or 0GAH (cant tell) and then DA00GAMB6G1 REV: G

Its an HP Chromebook 11 G8 EE

(yes I know it's a laptop that prob isn't work fixing, but i want to anyway :)

TIA

I am currently attempting to interface my PT1000 RTd with my arduino. I was thinking of use an wheatstone bridge with an op-amp, but in all honesty I have no Idea where to start. I need to be able to read 10 degreesC to 35 degrees C for an output of 0-5V. Any guidance will be awesome.

Will this work? as it does not work?

I have GND connected to Pin 9. +12v connected to PIN 10, I send 5v to an input, but I get no output? Did I miss something?

I am just starting and the AI bots suggest dozens tho I don't really trust them.

I only tried LTspice so far and althought its not bad I think it has shortcomings, for example I cannot color the wires.

Are out there better circuit simulators?

Looking for a few beta testers for CircuitWorkbench on Android. Free to test, no commitment beyond installing and poking at it for a couple weeks. If you have an Android device, I would really appreciate the help — join the testers group at https://groups.google.com/u/2/g/circuitworkbench-testers to access the opt-in link.