This optical theremin was found in a 90s Hands-On Electronics. The basic frequency is given by C1 and the output is made in a speaker through a small output transformer.
The output current of this circuit reaches 12 mA. The zener diode determines the output voltage. The...
Found in Maxim's documentation from the 90's, this circuit uses an integrated from the time...
Found in a 1980s documentation, this circuit makes use of components from that time. Modern...