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 circuit is basically the same configuration as the previous one with a power stage with...
Found in a 1969 documentation, this circuit for the 20 MHz band does not use a transformer. The circuit is...
This circuit can provide a voltage of up to 900 V depending on the input voltage. The diodes must...