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Multipoint Light Probe for Raster Scan Displays Disclosure Number: IPCOM000076580D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 54K

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Featherston, JR: AUTHOR [+2]


This arrangement affords discrimination in the horizontal direction of cathode-ray tube (CRT) raster scanning.

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Multipoint Light Probe for Raster Scan Displays

This arrangement affords discrimination in the horizontal direction of cathode-ray tube (CRT) raster scanning.

Consider a viewer response method using a pattern of response points n the screen 10 of a raster-scan CCR display. The viewer points a c conventional light probe 12 at a point on the screen and the timing of the probe output, referenced to the scan time frame, is used to determine the point selected. A basic limitation exists in present methods of this kind as a result of the slow decay of the CRT phosphor. The rise and fall times of available phototransistors present no limitation.

Consider a CRT screen 10 raster scanned and divided into a matrix of sectors, as shown. The screen 10 is divided into eight divisions vertically and four divisions horizontally.

As area "N" is touched the output of light probe 12, amplified in a circuit 14, applies a pulse at terminals 16 of about 0.4 milliseconds duration. If area J were touched instead, a similar pulse would be produced except about 2.0 milliseconds earlier as measured from the known instant of vertical scan commencement. The time discrimination of sweep, phosphor, and light probe is quite able to discriminate between 8 or possibly 16 positions in the vertical dimension.

By contrast, if it is desired to discriminate between areas N and 0 the time difference is only 50 u sec divided by 4 = 12-1/2 mu sec. This is seen in the light probe output as a time shift in the rise of light probe output. However, this is difficult to use because the phosphor decay is of the order of a millisecond, thus the output of the probe 12 (which follows the actual light output quite closely) has dropped only slightly from the previous line compared to the pulse from the new line.

This limitation is avoided in the present arrangement which provides a repetitive showing of a series of fields, each of which contain only a subset of the columns being used.

For example, a field is shown in which the sectors A-E-I-M-Q-U-Y only are illuminated. This is followed by the next field in which sectors B-F-J-N-R-V-Z are illuminated. The third field displays...