The inductor is 15 turns of 30awg(I think) wire around a 1 inch in diameter paper cylinder, the capacitor is 33pf, using a germanium diode to demodulate and the speaker are just a normal crystal earpiece.

When salvaging 18650 cells from old electronics, measuring the voltage seems like an obvious first step, but I'm wondering how much that actually tells you about the battery's condition.

A cell might show a reasonable voltage but still have poor capacity, high internal resistance, or problems that aren't obvious from the outside.

For those who regularly reuse salvaged cells in DIY projects, what's your testing process before deciding whether a cell is worth keeping?

Do you use a dedicated capacity tester, measure internal resistance, or follow a different set of checks? Also, what warning signs make you reject a cell immediately rather than risk using it?

I'd be interested in recommendations for affordable testing equipment and a sensible safety checklist for hobbyists.

Hey everyone. I wanted physical media shortcuts on my desk without cluttering up my setup with extra macro pads or buttons.

So I wired an MPU6050 accelerometer to an ESP32-C3 Super Mini, mounted the whole thing to the underside of my wooden desk, and connected it over Bluetooth. When you tap the table, the IMU picks up the shockwave.

I initially struggled with false triggers from typing noise, so I trained a small neural network classifier using Edge Impulse running locally on the ESP32 to tell the difference between a deliberate tap and normal background vibrations.

Now, a single tap pauses music, a double tap skips tracks, and four taps switch the profile over to volume control. Completely invisible and wireless on top. Let me know what you think!

I printed my first Design.

STL files

Hey guys,

I need help from someone smart. I need to connect this device to check voltage of my battery but I have no idea how to connect it safely. I know I can probably just cut the big wires and connect these smaller ones and wrap it in electrical tape or maybe I'm just supposed to pierce the big wire with this needle😭 but I don't want no issues. I tried finding an adapter like shown on picture 2 but couldn't find anything. Maybe use some other adapter? Anything helps!

Hello,

a few years back I bought this hand ventilator, which worked great until a few months ago. The motor is still spinning, but no flow of air is feelable.

Only when shaking the ventilator hard once, one is maybe able to get it into a state where it is able to move air like when it was bought.

A video to the phenomia: https://youtube.com/shorts/Ioo9q0lbe3A

I don't know how to describe this phenomenon further. If it's not understandable, please tell me

I would prefer not to just throw it in the trash because everything else seems to be working great. What would you do to fix this problem?

I got a 3d printer, so my idea was maybe to print new fanblades.

What would you do and what do you think?

Hi all,

First time trying something like this and looking for some advice please. I soldered this radio kit together and it powers on, has static sound, the buttons work and I can change the frequency/volume. However, the radio does not pick up any stations.

Any advice for this noob would be welcome. I will try and add a picture of the rear of the PCB in the comments.

TIA

The best way I’ve found in order to make a crystodyne is to take a low quality fool’s gold crystal that works as a pretty good detector diode and find an area near the sweet spot that is kinda bad at being a detector diode and put a steel wire there. The way I tested my crystodyne is with a simple AF tunnel diode oscillator and the coil from a pencil sharpener motor that I put a rectangular iron core through, and for the capacitor I use a .1-.05 uF capacitor, in order to hear it I use a crystal earpiece from a crystal/transistor radio set, by lowering and raising the iron core in the coil I’m able to tell if the quiet hum I hear is actual an oscillator or just my brain making up noises(happens a lot when your hunched over a rock for 20minutes trying to make it sing). Now keep in mind my results are simply from experimenting with fool’s gold not zincite or galena and also keep in mind I’m not a scientist just a guy who messes with magic rocks, if you want to see what frequency my oscillator got well you can’t cuz I A. Don’t own an oscilloscope (I’ve been putting off buying one) B. Don’t have a frequency meter(I’ve been putting off buying one).
PS- please be nice to me about my punctuation , grammar very hard.

Well, there were an accident with this airduster and pu foam. Don't ask.... Does anybody know where can I get this Jarvis X3 25.12.E or a compatible electric motor?

I would like to know how I could learn to repair these radios. The ones below are Xhdata 220 (I bought them for my father but he broke both) and the ones above are Daewoo DRP 12 and Mx Onda MX RD911.

What tools would I need?

If I can't repair them, I'd also like to know what DIY projects they can be used for.

A lot of beginner projects seem to involve following a tutorial, connecting the components, and getting the expected result. That's useful, but actually figuring out why a circuit isn't working seems like a different skill.

What’s a good first or second project that teaches you to read a schematic, use a multimeter, and diagnose common mistakes without requiring expensive tools or dealing with mains voltage?

I'd love to hear which projects helped you understand the reasoning behind a circuit rather than just how to assemble it.

The battery on my old iPhone 5c swelled up and broke the phone completely. Instead of throwing the shell away, I want to remove all the internal components and install a simple digital clock display inside the casing.

The phone itself is fully broken and won't turn on anymore, so just downloading a clock app won't work.

​My issue is finding hardware thin enough to fit inside the phone body. I would prefer it to be battery-powered if possible, but wired is fine too.

​What components or thin displays should I look into to make this work?

Any advice on how to approach this project would be greatly appreciated.

This is inside of my Pod Go effects pedal. The tip of an adapter broke off and got stuck inside of the jack. I tried to get it out with tweezers but that didn’t work. I think it actually pushed it in deeper. I also tried to remove it by putting some super glue inside of the tip and set a screw inside of it to maybe pull it out after it dried. That didn’t work.

Would I be able to replace this part? Can I take this part off and disassemble it to get the piece out and then reassemble? Any ideas on how to get it out?

Got a vintage amp here(Pioneer SA750) , it's got 2 big 8200uF, 56V capacitors on the board. They are fully covered in black pvc film, both sides and top.

One is perfectly flat while the other seems to have an elastic bulge on top that I can push up and down.

Once I push the top down I can move the bulge around almost like an air bubble, if I push fully down it feels flat rather than slanted.

I've never had a problen with my amp(except for a mechanical failure of some springs, which is why I opened it in the first place.) It gets warm but never too hot, I can always put a hand on top without it being uncomfortable.

I'd really like to avoid getting to the back of the board since it's a real pain in the butt, and I don't have a multimeter with which I could check voltages at the moment.

Here's the footage link: https://imgur.com/a/xCcKebt

Is it possible that there has been uneven shrinkage of the sleeve and that's what caused the bulge?

The power supply isn't pictured, and is irrelevant. Anyone knowledgeable in tube circuits see any issues with this?

Hey everyone, Just wanted to share a quick experience and remind everyone to ALWAYS record a continuous video while unboxing your package, no matter how small or cheap the order is.I recently ordered some parts from Rytronics.in .

The invoice clearly lists:
2x Stepper Motor (28BYJ-48) + Driver Board
1x 4-Cell AA Battery Holder

I received the shipment today, but upon opening the box, only the battery holder,stepper motor was inside—both stepper motor drivers were completely missing. Because I opened the box in a hurry without recording a video, I only have photos of what was in my hand, which usually isn't considered strong proof by seller support policies. I have emailed their support, but since I don't have video proof, I know my chances of getting a replacement/refund might be slim.

Takeaway for the community:
1.Record a full unboxing video showing the shipping label, package condition, and the opening process in one single uncut clip
2.Don't assume smaller items or cheap orders won't have missing components
3.Inspect your packages immediately upon delivery if possible.Has anyone else faced missing item

issues with Rytronics or similar vendors, and were you able to get a resolution without an unboxing video?

Hello! I have a car charger mount I want to swap with a longer one, but the longer one doesn't have the charging head on it so I was thinking I could swap the heads since they're essentially the same looking mounts. I'm running into a problem trying to get the bolt out as it doesn't look like the bolt has a head on it?

Here are the links to the mounts:
https://a.co/d/070wIDqw
https://a.co/d/0grRTqlI

Just ordered parts to make this, I did not liked the dischargers from Amazon/AliExpress, so I designed one. The bridge is made of 1N4007, the voltage display shows 1/4 of the real voltage but as the goal is to reach zero volts, it's ok for me.

Hi everyone, I was wondering if I could get some advice. I’ve had an idea for my pumpkin carving contest this year (i promise this is relevant), and I want to create an electrical circuit, but I have no clue where to start.

I want to make a circuit where you press a button, and then LEDs and music goes off. I kind of understands the basics like I need a breadboard, mp3, speaker, etc, but i’m genuinely just clueless. To clarify, I work in healthcare and never studied this stuff 🤣 I do know how to code though.

What would be the best way to self learn this kind of thing? I’m more of a hands on learner but I don’t want to buy a bunch of things without knowing what i’m getting if that makes sense. And following on from that, where do you even buy all this stuff?!

(p.s I’ve been looking through this thread and wow you guys are creative and clever asf!)