Found in a 1924 Gernsback publication this circuit uses 4 batteries for power and loop antenna. Listening is over a high-impedance type earphone or loudspeaker common at the time.
Using an optocoupler this circuit turns on the light in a bedroom for a set amount of time when...
This basic voltage comparator circuit has a reference voltage given by a zener diode. The input...
Found in a Hands On Electronics of the 80s, this circuit makes use of a gas sensor of the time....