Long Wave IR Theremin Theory & Operation 555 contest part 2

The detector mounts are ready to roll but the it is getting more than a bit cold outside, so here goes the theory of operation and block diagram section.

A simplified view of the long wave IR detector is shown in figure 1. The background radiation is ever present, and the detector is mounted in an isothermal block. As a result, the TO-5 can of the detector also serves to emit background radiation at the same color temperature as the ambient environment.

Long Wave IR Human Hand Proximity


As such, when a human hand enters the viewing area of the IR detector assembly, the radiated energy from the hand results in an increased output voltage. Figure 2 shown below, shows what happens as the human hand is moved back and forth. Namely the output varies as the hand transcends more of less of the detectors viewing area.

IR Proximity Output as a Function of Distance

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