Found in a 90s Popular Electronics, this circuit checks if a remote-control transmitter is emitting signals. The sensor is a general-purpose type found in many electronic devices.
This VCO makes use of components from the 1980s. The circuit can be implemented with modern...
This circuit uses an LDR as a sensor to trigger an LED indicator at a preset lighting level. The...
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...