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 is of great use today, when solar energy is becoming increasingly important. The...
This circuit was found in a Popular Electronics from the 90's. It triggers an audible warning at...
This circuit detects when a powered circuit suffers a malfunction, lighting an LED. The supply...