I thought I kept the message I wanted to respond to, but I didn't.
Anyhow, I wrote an article in qst way back in July of 1985 called the
squawker. It uses a 555 chip a couple resisters and a photo cell and
almost anything for a speaker. We actually used an old cassette recorder
mlicrophone for the housing and the cartridge as the speaker. I can put
up the circuit if anyone wants it. Will run on 5 volts, not sure how high
the 555 will go, but I ran mine on a 9v battery. If you put in a closed
circuit phone jack as I did, it can become a continuity tester.
Pitch changes with brightness.
73
Butch
WA0VJR
Node 3148
Wallace, ks.