Switching circuit for a contact display panel

Details Switching circuit for a contact display panel Switching circuit for a contact display panel

1990-10-30

1992-09-08

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

2502221, G01V 904

Patent

active

051460815

ABSTRACT:
The invention relates to a contact display panel circuitry in which the phototransistors are on two adjacent sides of the contact display panel and the diodes emitting infrared radiation to the phototransistors are on the opposite sides, and in which, under the control of shift registers, each phototransistor in turn is coupled to a common line, the logic circuit of the device being capable of computing the location of a possible contact point on the basis of changes in the signal in the common line. According to the invention the use of controllable switches and numerous resistors and capacitors is avoided by coupling in series with the phototransistor a diode in such a manner that the collector of the phototransistor is coupled to the transfer register and the emitter is coupled via the said diode to the common line.

REFERENCES:
patent: 3764813 (1973-10-01), Clement et al.
patent: 4703316 (1987-10-01), Sherbeck
patent: 4719339 (1988-01-01), Mizuno
patent: 4893120 (1990-01-01), Doering et al.

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