A simple way to check wether an input signal stands within a two voltage threshold levels. This is a teaching example and would be considered according DC or AC applications. I suggest to try it using a LM339 comparator, (note that here an OPAMP option is defined instead), which provides for a single supply feeding. In that case please remember that its outputs are open collector configured, thus a suitable resistance value should be used for the output circuitry. See the Datasheet for further details. The provided schematic herein enclosed would explain the limit comparator concept and users will modify accordingly. Threshold have to be set with a resitor network where precision must be considered for the intended use. Example : an HW key is wanted to unlock an electric circuit. Any comment is welcome.
