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.
The circuit shown in the figure can be used as an indicator of presence and high voltage in a...
This circuit uses the 2N626, the first commercial Darlington transistor. We found it in Radio...
This circuit can generate signals from 80 to 800 Hz with an amplitude of 0.3 V. We find it in a...