Using the LM3909 this circuit was found in the January 1992 issue of Radio Electronics magazine. Resistor R1 should be chosen according to the table given next to the diagram.
November 2016 - Already available from Mouser Electronics on Texas Instruments' new DS280BR820...
This circuit is from the 80's component manual itself, but can be applied to more modern...
We found this circuit in the June 1992 issue of Radio Electronics magazine. The sensor is a common...