This circuit operates from 20 Hz to over 20 kHz and is easily tunable. We found it in a 70s documentation. The circuit can be implemented with modern operational amplifiers.
This circuit uses common diodes as sensors, triggering when the temperature rises by touch,...
Simple timers can be designed using inverters or any other gate that can be connected as inverter. Figure...
This circuit was found in the 1987 Radio Electronics magazine. The components used are integrated...