Found in a 1967 Electronics World, this oscillator changes its tone when objects move in their environment. The output is made on a low impedance phone.
This 3-component circuit uses an analog indicator. We found it in an old publication....
Pulses in sequence can be generated from a clock input using the circuit shown bellow. Outputs A,...
This circuit simulates a low-level siren and can be supplied with voltages from 5 to 15 V....