This two-tone alarm siren was found in the January 1975 issue of Radio Electronics magazine. The power transistor can be changed and with it, Rx has values from 10 to 47-ohm.
The automatic modulated siren circuit shown in the figure really produces an interesting sound...
This circuit was found in the August 1973 issue of Radio Electronics magazine. The Darlington...
This circuit has three settings, central sound frequency, modulation speed and modulation depth. The...