Unorthodox warning alarm circuit presented here is infact a single chip based general purpose sounder, which produces a pulsed alert tone when its input receives a valid trigger signal. The circuit can be easily interfaced with a number of electronic gadgets and sensors and it requires only 12V dc supply input for proper working. A positive level input at trigger point (J1) activates the warning alarm unit.
At the heart of the circuit is a popular quad – two input NOR gate IC CD4001, here wired as two independent gated astable multivibrators. Initially, in standby mode, T1 is off and the tone generators are inactive. When T1 is enabled by a proper +ve level trigger signal, pin 1 of CD4001 is pulled low through switching diode D1 first astable block enters in active mode and then activates the second astable block, which is configured as an acoustic alarm. A large piezo-ceramic element (acoustic transducer) at the output of (pin 11) CD4001 will give superb results.