Found on an 80's Radio Electronics, this circuit is designed to pass the 300 to 34,000 Hz voice range using standard operational amplifiers.
The sensor for this alarm is an LDR and it consists of an oscillator that goes into action when...
This circuit is from an 80's component manual. However, the circuit may be of a modern equivalent...
This 300 Hz to 3.4 kHz filter was found in the May 1989 Radio Electronics magazine. The circuit...