Eliminating influence of external light on opto-electronic keyboard - determining whether keying surface receives outside light or reflection of emitted light is increased as surface is activated

摘要

The opto-electronic keyboard is provided with a transparent cover, divided into sev eral keying surfaces and each of these surfaces under the cover has a device emitting light pulses in the direction of the cover and detecting light coming from the cover. This device gives an electrical signal with a magnitude which depends on whether the keying surface receives outside light or the reflection of the emitted light increased as a keying surface is activated. The signal given by the detecting device is received inside one or more time intervals at three different points in time: the first signal is before the emission of the light pulse, the second signal during the light pulse, and the third signal after the end of the light pulse. The differences between the signals are found in order to determine which keying surface has been pressed by the finger. USE - For data processing and other systems.