GB1302986A - - Google Patents

Abstract

1302986 Determining co-ordinates digitally INFONET NV 19 April 1971 [27 Feb 1970] 22464/71 Heading G4H The digitized co-ordinate position of a stylus on, say, a graph, borne on a grid of cross-wires is determined as a number of cross-wires plus the distance from a cross-wire to the point of stylus tact, so providing positional accuracy when the stylus is between two wires. The x and y coordinates are determined separately in turn. The co-ordinate wires 1-10 ... each receive from register 16, driven by clock-pulse generator 14 and divider 15, five pulses, the first pulse of each series being 90 degrees behind the first pulse of the series to the preceding conductor. A stylus P capacitively receives the sum of two such pulse trains when positioned between two wires. The signal from the stylus after amplification (20) stops by its leading edge the gate 17 from feeding clock pulses to counter 18 whose total then expresses the coarse position of the stylus, which is the lower numbered of the two wires between which the stylus is found. The regi - ster goes on to pulse the remaining cross-wires of the co-ordinate to complete its cycle. Meanwhile the relative amplitudes of a pair of peaks in the stylus signal, indicating the distance of the stylus from the lower numbered cross-wire, is digitized, 28 (Fig. 7, not shown), and added to the coarse measurement in the display 19. The other co-ordinate is now determined in a similar way. Any number of pulses in the stylus signal other than five is detected by a unit 22 to erase the display.