We found this circuit very simple in an old documentation. The relay is high voltage sensitive, but the circuit can be adapted to work with lower voltages than indicated. The audible alarm is a buzzer oscillator.
The TL431 integrated circuit consists of a programmable shunt regulator with an internal...
With this circuit, from a 1991 publication, it is possible to regulate the output of a symmetric source...
The frequency of this oscillator depends on the inductor and capacitors in parallel with it. In...