IR Proximity Detector Schematic
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The schematic for the IR Proximity Detector is shown below.
The bottom half of the schematic show the power extraction and sensor interface
circuits. The top half shows the LED driver circuit. This is
a dual relaxation oscilator, with the first half gating the second half.
The switch is actually a three position switch, that puts two resistors
in parallel for the medium and long range settings. None of the component
tolerances are critical. If you are not looking for small packaging,
this circuit is not difficult to build.