We found this multiple thermostat circuit in July 1980 Radio Electronics magazine. It uses opto-triacs for power control and operates on a 117 VAC mains.
For an operation with extremely low consumption, generating an audio tone, we can use the circuit of...
Using a 741 operational this circuit was found in the August 1993 Electronics Now magazine. The...
This circuit measures the RF power of oscillators and small transmitters in the range of 0.05 to...