This reader with TTL logic compatible output uses an LM139 comparator. The circuit was found in the 1994 National Semiconductor Linear Applications Handbook.
When the sensor receives light, the relay closes its contacts and remains so even after the light...
The indicated circuit is an intermittent one in which we use two 555 integrated ones, one as a low...
The indicator for this circuit is a 0 to 1 mA milliammeter. The operational is from the 70s, when...