Proximity sensor with a light-emitting diode which simultaneously emits and detects light
US4564756A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jan 6, 1984 |
| Grant date | Jan 14, 1986 |
| Priority date | — |
| Expiry date | Jan 6, 2004 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03K17/968
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.