This conventional relay light detector circuit uses a 741 as a voltage comparator. The sensitivity adjustment is made in R1. The supply voltage depends on the relay used.
This amplifier is from a May/April 1969 Popular Electronics. The components are from the period and...
This circuit may be used in IF steps of dual-conversion receivers, i.e., a type of receiver that uses...
This 555 IC circuit was found in the November 1994 issue of Radio Electronics magazine. The...