This circuit was found in an American documentation from the 70s. The operational amplifier is from that time. Modern equivalents can be used.
This circuit, from Texas Instruments documentation, fires a relay when light strikes the...
This circuit was found in documentation from the 1980s. The circuit can be implemented with other...
This circuit is from an 1977 American publication. The coil consists of 30 + 70 turns of 28 AWG...