Found in a European magazine from the 90s, this circuit emits beeps that are several seconds apart to indicate that a device is on. The transducer is a ceramic or crystal capsule.
This Philips circuit of the 70's makes use of components of the time. The DZD40 is an uncommon...
This circuit with two operating modes was found in the September 1989 issue of Radio Electronics...
This circuit is from an old documentation making use of a 3,579,645 MHz analog color television...