This circuit of a 1964 Electronic Design uses a photodiode from the time. Modern equivalent can be used. The standby current is 1.2 mA.
This circuit can be powered by 2 or 3 small batteries. The resistor can have values between 220...
These circuits from a May 1994 Electronics Now take advantage of the noise from the junctions of...
This network can be used in a sound project to control the tone. The circuit is from an...