This circuit was obtained in an Electronics Now from the 90s. The circuit uses operational amplifiers from the time and the indicator is of the Sonalert type with internal oscillator.
This circuit generates frequencies determined by R3 and C1. We found it in the Radio Electronics magazine...
Found in a 90s Elektor, this circuit makes use of general-purpose transistors, except T4 that can...
This circuit is based on a component from the time, the MSM0322 integrated circuit. It modifies the...