This small transmitter appeared in the March 1989 issue of Radio Electronics magazine. The two-transistor circuit used an electret microphone and had a range of a few dozen meters.
This circuit is from Popular Electronics. The buzzer is of the Sonalert type with built-in...
This circuit makes use of an unusual Analog Devices component today. The circuit is from a 90's...
The AT21CS11 memory device offers an extended voltage range to accommodate lithium-ion battery...