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 circuit allows the use of headphones and microphones with diverse characteristics in audio...
Here we show how to add a reset key to the monostable using two NAND gates (CB127E). When the key...
This configuration using a CMOS IC produces a 1 MHz signal. The circuit can be used as clock in...