This circuit for the VHF band of analog TV was found in Motorola documentation from the 70s. The integrated circuit used is uncommon today.
The sensors in this circuit that triggers when the temperature goes out of a certain range are...
Old phones with dials can be used in a simple home intercom system, as this circuit from Popular...
This 10 kHz filter is based on a 741 operational amplifier. The circuit is from Electronics Now...