A motley collection of ideas
Dear Children, I thought I would show you a circuit that is not only for fun, but can also be useful at home for your parents and siblings. Surely it has happened before that someone forgot to close the refrigerator door, or didn’t shut it properly. This device gives a warning in such cases. Most … Read more
This is a simple sound generator that can be controlled by light or by your fingertip. If you illuminate the photoresistor with a lamp or cover it with your hand, the pitch of the sound changes. You can try it out in Tinkercad: https://www.tinkercad.com/things/aEJgBAQp91s-fingertip-organ Instead of the photoresistor, you can place two bare wires that … Read more
Manufacturers strongly advise against attempting to “recharge” disposable alkaline batteries. They claim the cells may leak corrosive electrolyte or the gas buildup during charging could cause explosions. Yet, these batteries can in fact be regenerated, which significantly reduces environmental impact and saves money. The regeneration of alkaline batteries is an old topic; even in the … Read more
In 1983, Rádiótechnika magazine published an article about a clock built around the TMS1122 IC. I redesigned the circuit and the PCB somewhat, then built it. It served continuously for 27 years, essentially without being turned off. Due to lack of space, I recently scrapped it, though it was still in working condition. The Clock … Read more
Spotters, SWL (shortwave listening) enthusiasts, and amateur radio operators all enjoy listening to aircraft communications — and nowadays, even drone pilots find it useful to monitor air traffic. A good handheld airband transceiver easily costs well over a hundred thousand forints, whereas the device described here is dirt cheap by comparison. Of course, it’s not … Read more
Sometimes I find myself wondering which of my portable digital voltmeters I can actually trust. The old 4½-digit M4650? The Fulke? Or the younger METEX? (Okay, I have one from Lidl too, but that’s not even a question.) Generally, they all show pretty similar values, and I rarely need better than 1–2% accuracy—but it still … Read more
I needed a compact power supply capable of providing roughly 5–20 V DC and 12–16 V AC. Because an AC output was required, I chose a conventional transformer—similar to those used in alarm control units and intercom systems. This project was inspired by the Chordless Lab Power Supply on Thingiverse. DC Section The DC side is quite simple: a … Read more
This gadget is actually a continuation of the glimm lamp project. No, I don’t keep horses or deer cattle, so I don’t have a light bulb. However, I do run into electric shepherds while walking through the woods, and it makes me wonder whether or not there is a jelly in it. This thing, which is barely bigger than a pocket knife, is designed to find out.
I built this inductance meter adapter a long time ago for use with a digital multimeter capable of frequency measurement. The basic idea came from an article published in Funkchau issue 1/1981. I slightly modified the original circuit and designed a new PCB. Of course, I no longer use this device for measuring coils today, … Read more
The magic plasma ball is a well-known decoration that used to be popular at parties and nightclubs. A simple structure on the surface, but the spectacular light effect is based on a very complex phenomenon. It can also be used to perform some interesting experiments to surprise your friends.