Proximity sensor with a light-emitting diode which simultaneousl

Details Proximity sensor with a light-emitting diode which simultaneousl Proximity sensor with a light-emitting diode which simultaneousl

1984-01-06

1986-01-14

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

250206, 250214R, 250221, 250561, G01D 534

Patent

active

045647569

ABSTRACT:
An optical proximity detector of very small size and high resolution is provided by using a light emitting diode (LED) to illuminate a small detection region adjacent to the LED and by using the same LED simultaneously to sense light reflected from an object which enters the detection region. A circuit is provided which continuously forward biases a light emitting diode at a substantially constant bias current, thereby continuously illuminating a small region adjacent to the diode. When an object enters the illuminated region and reflects light back to the LED, it has been found that the impedance of the LED changes by a small amount. This small change in LED impedance and consequently the presence of a light reflecting object in the illuminated region is sensed by the circuit.

REFERENCES:
patent: 4286171 (1981-08-01), Hara et al.
patent: 4417140 (1983-11-01), Adolfsson et al.

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