Found in a 90s Popular Electronics, this circuit triggers a load from the audio signal applied to its input. The controlled load depends on the MOSFET.
Found in a 1980s publication, this circuit uses an operational amplifier from that time. The...
This circuit was published in an Italian magazine Radio Elettronica in February 1976. The...
This constant current circuit was found in the October 1993 Electronics Now magazine. The current can...