Patent GB-1249955-A (GB)
Title: Probing apparatus
IPC: H03M1/00
Filed: 1969-11-21
Abstract: 1,249,955. Analogue to digital conversion. INTERNATIONAL BUSINESS MACHINES CORP. 21 Nov., 1969 [27 Dec., 1968], No. 57013/69. Heading G4H. [Also in Division H4] Probing means associated with a display apparatus comprises two parallel conductive elongated elements such as 11, 12, Fig. 1, spaced apart to define an area 10, and an oscillation generator 18 connected to said elements, so that each radiates electromagnetic energy into the area. A probe 20 is movable within the area, and is tuned by a circuit 22 to the frequency of the oscillator. It gives an output signal whose strength is determined by the resultant at its location of the energies radiated by the elements 11, 12. Means are provided for deriving from said signal an indication of the position of the probe within the area relative to the two elements. As described, the elements 11, 12 are vertical, for determining the horizontal coordinate of the probe 20, and a second pair of elements 13, 14, which are horizontal, is also provided for determining the vertical coordinate of the probe 20. A separate generator 28 of different frequency from the generator 18 may be provided for the elements 13, 14, when the probe 20 must include means for responding to the two frequencies. However, both pairs of elements may be supplied at the same frequency on a time-sharing basis, when a single generator is sufficient. Each pair of elements is so energized that an, intermediate null line is formed. The probe is provided with a switch 26 arranged to render said probe effective only when it is pressed against the display in the area 10 at a point at which a determination is desired. The apparatus may be embodied in combination with devices such as cathode ray tubes, film strip projectors, and the like, which require threedimensional cabinets. In one such arrangement a metal cabinet (40), Fig. 2 (not shown) has a rectangular aperture (10<SP>1</SP>) in front which defines an effective display. Two loops of fine wire (41), (42) are effectively screened by the cabinet except for respective vertical and horizontal portions (11<SP>1</SP>, 12<SP>1</SP>) and (13<SP>1</SP>, 14<SP>1</SP>) running along opposite edges of the aperture (10<SP>1</SP>). An embodiment is shown in Fig. 3 which comprises loops (411, 42<SP>1</SP>) (as in Fig. 2) which are alternately energized by a 25 kHz generator 48 when AND gates 51, 52 are respectively enabled by a vertical-horizontal latch 54. Output from a probe 20<SP>1</SP> is applied to a differential band pass amplifier 106 which is followed by a rectifier and filter circuit 108, output voltage from which is compared in a comparator 104 with output voltage from a ramp generator 100. A Schmitt trigger type match detector 110 controls a probe cycle advancing circuit 112 operating the latch 54, which determines which of the gates 51, 52 is enabled. Input to the ramp voltage generator 100 from an AND gate 70 is coupled via respective AND gates 126, 128 to vertical and horizontal counters 82, 84. Numbers in said counters are read out in parallel in the form of digital binary coded levels on a bus leading to terminals 60-5 to 60-15 of an interfacing unit 60 to a computing system when, for example, a response command signal appears on terminal 61 thereof. In order to determine in which quadrant of the four formed by the two intersecting null lines the probe lies, one phase of the differential band pass amplifier 106 is connected via a saturating amplifier 116 to an AND gating circuit 78, 80. The output of the amplifier 116 is substantially zero if the probe is placed on one side of the horizontal null line, and substantially unitary if the probe is on the other side of the line. In this manner, an upper-lower sector latch 118 and a right-left sector latch 120 are sufficient to indicate in which quadrant the probe lies, and binary digit information to that effect from said latches is entered into the interfacing unit 60. The initial putting in readiness of the system is effected by a pulse from terminal 60-1 of the unit 60. If a repeat operation is necessary, simultaneous outputs from terminals 60-1, 60-3 of the unit 60 set a latch 92, which causes a lamp 90 to light.