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.
This 1.5 A source for FM transmitters was originally intended for the transmitter described in...
This useful power supply can provide voltages from 0 to 12 V with currents up to 2 A, set in...
November 2016 - NXP ARM Cortex microcontrollers for serial interfacing applications, NXP 32-bit...