This alarm with automatic shutoff was found in the April 1975 Radio Electronics magazine. The activation time is given by C1 and R3. The alarm uses series and parallel sensors.
Found in a 90’s American publication, this circuit has a voltage gain close to 1, as shown in the...
Using a pair of 741 op amps, this 90 s Radio Electronics circuit works with the previous one. The...
This circuit is from a 1966 Motorola Field Effect Transistors Manual. The circuit makes use of...