Using a 4046 PLL, which is uncommon today, this circuit was found in the October 1994 issue of Electronics Now magazine. The circuit can be modified by changing the capacitor.
This simulation shows how to use an operational amplifier as a voltage comparator. The sample uses the...
This circuit automatically activates the relay when the phone is answered, closing the record...
This car alarm was found in an American '80s documentation. The circuit automatically activates...