Found in an old Popular Electronics this circuit is still current. The SCR can be of the 106 series and the relay according to the voltage used in the supply. The voltage can be 12 V.
This circuit that emits siren sound can be used in a fire alarm. We found it in an old American...
This circuit generates sinusoidal signals from 15 Hz to 15 kHz. The circuit is from Electronics Now...
In the figure a circuit that is the basic application of NE567 for the detection of a tone applied to...