This circuit was found in a Signetics documentation from the 1980s. The integrated is a PLL and the SCR is a general purpose type The pitch frequency is given by R1 and C1 as formula next to the diagram.
This circuit was found in a Popular Electronics of June 1978. The circuit is interleaved between the...
To protect your home, vehicles or even objects, what we present is a sensitive alarm circuit that...
This circuit was obtained from an English magazine from 1979, but can be easily assembled...