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.
This power supply with several transistors can supply a current of several amps and a voltage of...
Found in a 1967 EEE, this circuit oscillates at 20 MHz according to the values of the given...
We found this circuit in a 1974 technical documentation. The circuit can be made with BC549...