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.
The sensor for this alarm is an LDR and it consists of an oscillator that goes into action when...
This circuit was found in American documentation from the 90's. The transformer is of the high...
The circuit shown is a white noise generator using a zener diode as a source of noise. The...