Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the Sonalert type with included oscillator.
This circuit was found in a 90s American documentation. The circuit uses an LED that can be of a...
Damped sine oscillations can be produced when short pulses are applied to the input of this...
We found this circuit in the Philips integrated circuits manual of 1990. The circuit must be...