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.
The gain of this circuit at 1 kHz [and 40 dB falling rapidly when the frequency deviates from this...
This circuit has the effects indicated in the table next to the diagram. We found it in the Radio...
This ultra-low frequency receiver circuit was published in the August 1973 issue of Radio...