We found this circuit in the April 1978 issue of Radio Electronics magazine. The power supply must be symmetrical, and the maximum recommended frequency is around 10MHz.
This circuit uses two relays that switch when the voltage exceeds the value given by zener D2. The...
This circuit is from the 80's integrated circuit manual itself. The component is not as common today...
This circuit was found in a French publication called Generation Electronique, It can be assembled...