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.
This circuit uses an operational amplifier to simulate an inductor. The circuit is from old...
This voltage level-triggered circuit was found in a 1969 Ferranti English documentation. Modern...
Found in a 90s General Electric documentation, this circuit has a drain current of just 1.5 uA....