High resolution light pen for use with graphic displays

Details High resolution light pen for use with graphic displays High resolution light pen for use with graphic displays

H - Electricity

01

J

375/38, 340/74,

H01J 5/16 (2006.01) G06F 3/033 (2006.01) G06K 7/10 (2006.01) H03K 5/24 (2006.01)

Patent

CA 1221480

ABSTRACT OF THE DISCLOSURE A high resolution light pen is disclosed for use with graphic displays. More particularly, a light pen is disclosed having a collimation tube slidably mounted within a housing. The collimation tube includes an axially extending channel having a non-reflective surface. A photodetector is fixably mounted within the housing aligned with the channel. A lens is mounted adjacent the front end of the channel and has a focal length equal to the spacing between the lens and an aligned pixel of the video screen. By this arrangement, all light rays emanating from an aligned pixel and passing through the lens are refracted axially along the channel and directed to the photodetector thereby maximizing the input thereto. The subject invention further includes a new and improved discrimination circuit for determining valid input signals from the light pen and producing an interrupt signal at a time substantially independent of the amplitude and slope of the input signals. In accordance with the subject invention, each input signal is compared with an upper threshold level to determine if a valid signal has been detected. In addition, each input pulse is compared to a lower threshold level for timing purposes. The result of the comparison with the lower threshold level is delayed and supplied to a gate means with the output of the first comparison. The gate functions to produce an output signal when the results of both comparisons received are simultaneously positive thereby indicating the validity of the input pulse at a time independent of the amplitude of the pulse whereby the effects of jitter are reduced.

420927

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