Crystal Radio with one wiper and two variable capacitors.

[@user-rk6uw8xp8d]

I did project in Jr high 1968 . Ordered kit through school from greymark, am radio transmitter. Got A on project.

[@kensmith5694]

You may find my video about a tuned loop antenna useful. It shows how performance varies with the coupling. In my case, the coupling is by means of a small capacitance. I use two wires twisted together for coupling.

[@TheD3cline]

I had one of those kits when I was a kid in the 90s. Bought it at a yard sale. Also built my xtal set with it, good fun.

[@qwertykeyboard5901]

@@TheD3cline The Sciencewiz one? I believe that one was released in the 90's.

[@TheD3cline]

@@qwertykeyboard5901 radio shack kits, with the lil springs. and the lil books too. "engineers mini notebooks"

[@spvillano]

Erm, they still make germanium transistors, they're just less common specialty devices now, as not a lot requires the lower band gap of germanium, compared to the higher band gap of silicon. The theory behind the device is simple enough. Although, it did take me a minute or two to duck seasickness to figure out the circuit... :P Great idea on the smoke detector piezo though, I'll be on the lookout for some. Stripped one out of a recently deceased smoke detector, along with its radiation source for another project (building a particle spectrometer from a CERN design), so why not? Can have the detector to plug into the computer (on the CERN project is the calibration data for the optical diodes used as a cheap particle detector) for the one, stick the other inside of a small cloud chamber for parties. Once I finish my can of oatmeal, I'll grab some wire and make a wiper AM radio, probably just build the diode with raw mineral, lead pot and cat whisker, then a twin with a standard germanium diode, as they cost under a dime anyway. There are lower band gap diodes one can use, but then you're going into the realm of indium or lead semiconductors with no realistic benefit. Oh, another fun detector is an old fashioned cat whisker spring to rusting razor blade. Should be entertaining at parties. Have a homemade particle mass spectrometer next to a homemade cloud chamber, next to some crystal radios from scraps and wedge in the computer to read the spectrometer on one small shelf. Sounds like I'll need another Pi...

[@qwertykeyboard5901]

@@spvillano Do keep in mind that many piezo speakers have limited frequency responses. This one came from a "talking" smoke detector. Ones from vintage ones _work_ but, well, _it sounds like it's playing through a smoke detector._

[@spvillano]

@@qwertykeyboard5901 actually, I'm kind of counting on that. I've rather severe tinnitus and midrange hearing loss, so the tinny sound if wide enough spectrum I'd actually be able to hear (I can still hear extremely high frequencies that most of my peers can't). Besides, mom taught me the glass bowl trick for piezo headphones. ;) And it's another toy to play with. The current transducer I have has a resonant tap, so likely it'll resonate electrically and mechanically a bit too much at its sounding frequency. Convincing something to do what it's not quite designed to do is more of an art. :D

[@stickplayer2]

Just like the one I built in electronics shop in about 1971

[@qwertykeyboard5901]

@@stickplayer2 They're fun!

[@ColaTai]

Yes the 'tism its a crazy thing

[@redhedkev1]

Only works with AM radio?

[@qwertykeyboard5901]

@@redhedkev1 I get some shortwave too!

[@graemezimmer604]

If appropriately re-tuned, will work on FM broadcast band as well. Do a search on "Slope Detection". Or for that matter, do a search on "FM crystal sets".