Patent ID: 9553579
Date: 2017-01-24
CPC Classifications: G01V,G06F,H03K

Claim:
1. An optical keypad, comprising: at least one transparent panel having a plurality of apertures surrounded by closed areas, which optical keypad comprises a plurality of light transmitting diodes (LEDs) emitting modulated light and at least one photo detector diode placed in a relation to the apertures that enables light from the LEDs to be transmitted through the transparent panel and reflected by scattering from a tool or fingertip producing a keystroke in relation to one of the apertures in the transparent panel, back through the transparent panel to the at least one photo detector diode for demodulation, a: modulation frequency of the emitted light from the transmitting LEDs ( b: the sequence in which the transmitting LEDs ( c: the time interval between lighting of the individual transmitting LEDs ( where at least one of the parameters is varied randomly, and where detection of the reflected light is able to be performed by a synchronous detection of current flowing through the at least one photo detector diode (