We found this circuit in the 1983 Radio Electronics Special projects magazine. The components are common, and the circuit drives a relay. The power supply must be isolated.
This reader with TTL logic compatible output uses an LM139 comparator. The circuit was found in...
This circuit can be used with common transistors, from general purpose to medium power. The...
Although it is a common configuration today, these circuits were taken from an old publication. The...