This reader with TTL logic compatible output uses an LM139 comparator. The circuit was found in the 1994 National Semiconductor Linear Applications Handbook.
This circuit was found in the September 1984 issue of Radio Electronics magazine. The circuit is...
In the original version of this 1987 circuit, the loads are lamps, but it can be adapted to drive a...
This circuit is a version of the previous one, but with full wave control. The diodes must be...