Noise-insensitive optoencoding techniques with compensation for device variations

摘要

A method of detecting quadrature signals in a computer input device allows a microprocessor in the input device to perform comparator functions, thus eliminating the need for external comparator circuitry. At least one light-emitting element in the input device emits light pulses, and these light pulses are selectively received by a light- detecting element. A notched encoder wheel separates the light-emitting element from the light-detecting element, allowing various amounts of light to be received by the light-detecting element depending on whether a notch separates the two elements. The microprocessor loads a sample of the output from the light-detecting element: a first sample taken at a selected time value and a second sample taken at twice the selected time value. The second sample is used for quadrature calculations used in determining cursor movement on a video display device. The first sample is retrieved by the microprocessor and determined if it is a digital "1" signal. If it is, then the selected time value is decremented by one sampling period.