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.

I printed my first Design.

STL files

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

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!

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.

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?

Hello guys!

I’ve been searching for the past 2 weeks for a free STL file or open-source project to build an off-road rover / RC car, but I'm struggling to find a chassis that fits my specific hardware layout.

Here are the components I plan to use:

• Microcontroller: ESP32
• Motor Driver: BTS7960 (High power)
• Motors: 4x JGA25-370 (12V, 100 RPM gear motors with encoders)

Does anyone know of an existing open-source design, 3D printable chassis, or a similar project that accommodates these components (especially the BTS7960 and 370-size motors)? Any links or advice would be greatly appreciated!

Thanks in advance!

Hello, I salvaged an E-Ink screen from a 2015 Kobo e-reader, but I don't know how to use it for my DIY projects. Here is the part number I found for the screen : ED060KG1.

Do you know which controller or other component to use?

Thanks in advance for your help.

First of all I wanted to say thank you knowing there's a dedicated community where I can ask this question.

I have 4 Solar Flood Lights that I bought and placed at the back and front of our house. It is a type of flood light that when its solar panel no longer detects sunlight it will automatically turn on. Its brightness is at 100% then after a few minutes it will automatically lowered to I think 70% or 50%. Because of that, its battery can only last for 3-4 hrs, what I do to prevent it from draining its battery is I manually lower its brightness to 10%, that gives me a 6-7hrs of light.

I realized, what if some of this flood lights only turn on when someone walked in, I can save most of its power. Like for example, if I have 2 lights back and front of our house, one of each is motion sensor so the other can stay on at its lower brightness while the other will only turn on when it detects motion.

I thought of just buying a flood light with a dedicated motion sensor, but its a waste of money if I already have one to modify.

I have a little background when it comes to electrical and electronics, but not confident enough to do it without asking questions from people with great experience.

So my questions, does anyone had already modify one with a motion sensor? Or is it possible to do it? All I can see on YouTube is people removing the motion sensor to keep their lights turned on.

(Picture indicated is the example of flood light that I have)

Thank you everyone!

All them seem to look the same I don't know what to do the first one I thought it's because I tried soldering but all this in the picture are fresh charging modules so it should have work so I'm at a lost could someone help me fix this?

I don't know why it's not working as I don't know what im doing wrong when setting this up could someone pls explain or help fix my problem

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?

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

Hi I’m trying to replicate the design for this breakout box. Could anyone help me identify what the plug contents are on the left and the red components on the right. I would greatly appreciate it

Thank you!