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 an old American magazine for radio amateurs. The circuit is based on a...
The LDO series (Low Dropout) TPS80 from Texas Instruments (www.ti.com) can provide output voltages...
This circuit is from Motorola's 1990 Linear Databook. We can implement it with other operational...