This temperature control was found in General Electric documentation from the 90's. The circuit uses a 10k ohm NTC sensor as a sensor. The triac must be in accordance with the controlled load.
This circuit is from a 1980s Motorola documentation. The circuit can be made with modern...
This well-known circuit triggers a relay when light striking the phototransistor is cut off. The...
This circuit generates a pulsed tone whose frequency depends on C2 and whose flashing depends on...