We found this circuit in the 1983 Radio Electronics Special projects magazine. The components are common, and the circuit drives a relay. The power supply must be isolated.
This simple timer or timer activates a low current bell or a buzzer according to the supply...
The integrated circuits used in this 1999 project are not very common today. However, they can be...
In the figure we have the way to obtain an adjustable constant current source of 2 mA. The...