Found in American documentation from the 1990s, this circuit generates a whistling sound when applied to an amplifier. The power supply must be symmetrical.
This setting appears elsewhere in this site from other sources or projects. Instead of the lamp...
This remote-control circuit was found in Radio Electronics magazine from June 1962. It drives a...
We found this circuit in the 1964 RCA transistors manual. The sensor may be a common LDR and the...