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 circuit, when triggered, locks, and remains so until the source is switched off for a moment or...
With an op amp with FET, this 1977 circuit uses an LDR as a sensor and drives a relay. The relay...
This low power bass booster is from the 1977 National Semiconductor Audio Handbook. The circuit is...