This circuit was found in 1980s American documentation. The transducer is a piezoelectric capsule and the power supply voltage can be between 3 and 18 V.
The integrated circuits used in this 1989 project are uncommon today, including the IF coil that...
This circuit was found in a 1968 documentation. It makes use of both NO and NC reed-switches and small...
This delay circuit for a sound system was found in the December 1990 Radio Electronics magazine as part...