This circuit applies to an old dial phone by detecting light pulses in the dial. The circuit is from an old 80's Electronic Design.
This circuit, from the 1990 Motorola Dataar Databook, can use any LM139 series comparator. The circuit...
We find this circuit in a 1980s documentation for amateur radio. The circuit shows how to switch...
With this circuit found in a 1965 Electronic Design, it is possible to read a peak voltage of up to...