We found this circuit in the October 1996 Electronics Now magazine. The circuit uses LDRs as sensors and drives relays. The relays must have voltages according to the power supply.
This general-purpose transistor amplifier stage was found in the November 1993 issue of...
This circuit of an old medical publication makes use of an integrated circuit of the time,...
We found this circuit in an 80's documentation. The circuit has a gain of 30 dB and uses a varicap...