GB2073422A

GB2073422A - Computer touch panel

Info

Publication number: GB2073422A
Application number: GB8006217A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-02-25
Filing date: 1980-02-25
Publication date: 1981-10-14

Abstract

A touch panel for use with a computer comprises a matrix of rows and columns of conductors insulated from each other at their cross-over points and arranged so that they can be bridged at their cross-over points by the finger of an operator. The two wires shown are connected via resistors R1, R3 to respective inputs of inverting and non-inverting amplifiers A1 A2 and also via resistors R2, R4 to floating supply FS3. When the wires are bridged at their cross-over points by the operator the current flow through the circuit R2, R1, finger, conductors and R3, R4 causes the outputs of the amplifiers to rise and activate the opto-couplers connected thereto. The touch panel may be in the form of a transparent screen which can be mounted over a cathode ray tube. <IMAGE>

Description

SPECIFICATION Computer touch panel This disclosure concerns the construction of a simple finger operated switch which is suitable for incorporating in a matrix of conductiong wires laid over the screen of a computer terminal.

Touch switch One of the many ways in which man can communicate with a computer is by means of a touch panel. The touch panel is a transparent screen mounted over the front of a computer cathode ray tube terminal. The cathode ray tube is observed through the transparent touch panel. Touching the screen with a finger generates a signal which is sent to the computer 'telling' it where the screen has been touched. In operation the computer is programmed to display a list of choices (a Menu) and the operator is required to touch his choice. He is actually touching the touch panel which overlays the computer cathode ray tube. The signal generated by the touch panel 'tells' the computer which choice has been made. The display can then change and the operator is given a further choice.Such 'interactive' dialogue with a computer is a very powerful method of communication as the operator needs no keyboard skills and can make no errors as he is led through the sequence to be followed by being given lists of choices to be made.

Touch panels have not been much used because of their cost. Methods used so far have been with capacitive or pressure operated switches. This disclosure concerns the construction of a cheap touch panel using a novel form of switch operated by finger conductivity to a minute electric current.

Construction of the touch switch See Fig. 1 Amplifier A1 is an inverting amplifier so connected that its input is shortcircuited through the resistance R2, typically 1 Megohm. The output of the amplifier is arranged to be low such that the opto-coupler, connected to its output is not activated. Amplifier A1 is supplied from a floating power supply S" typically of 5VDC. The input of the amplifier is connected to R1, typically 5 megohms.

The remote end of R, is at the moment floating. Amplifier A2 is a non-inverting amplifier so connected that its input is shortcircuited through the resistance R4, typically 1 megohm. The output of the amplifier is arranged to be low such that its output optocoupler is also not activated. Amplifier A2 is supplied from floating power supply S2, typically 5VDC. The input to amplifier A2 is connected to resistance R2, typically 5 megohms.

The remote end of R3 is floating.

The negative sides of the power supplies S, and S2 are held apart by a high voltage, typically 1 OOVDC generated by floating power supply S3.

In operation then, both the output optocou plers are non-activated. However, if the ends of the two resistances, R, and R2, are joined by touching them simultaneously with a fingertip, a small current driven by supply S3, will flow in the direction R2, R1, finger resistance, R2, R4 and back to S3. This current will cause both amplifiers to have an input. A1 will have a negative input and as it is an inverting amplifier, its output will rise and activate its optocoupler output. Amplifier A2 will have a positive input and, as it is a non-inverting amplifier, its output will also rise and activate its optocoupler output. Notice that as all the supplies are floating, there can only be current flow through the fingertip and none along the finger.

Note that the A1 circuit operates when current is drawn from it; the A2 circuit operates when current is supplied to it. It is possible to easily construct a matrix using an equal number of A1 circuits and A2 circuits. Fig. 2 shows the construction of a simple 2 x 2 matrix. A3 is the same type of amplifier as A1; A4 is the same type as A2. If a finger tip connects the input of A1 and A2, then both A1 and A2 have outputs (as described above). If a finger joins the inputs of A1 and A4, then A1 and A4 have outputs and the two other amplifiers have no output. The matrix has four crosspoints, A B C and D.The ouputs of the four amplifiers depend on which crosspoint is touched: Crosspoint A1 A2 A3 A4 A 1001 B 1 100 C 001 1 D 0 1 10 The number of lines on the matrix, which is the touch panel covering the computer VDU screen, can be increased almost indefinitely, but there is no point in spacing the lines closer than a finger width. An 8 x 8 matrix is convenient for most applications. The lines from each side are normally reduced to three by means of a 8 to 3 priority encoder before computer entry.

Construction of the touch panel This is shown in Fig. 3. It is a sheet of transparent plastic vacuum formed to conform to the shape of the VDU cathode ray tube. It is covered with the horizontal and vertical lines of the matrix. These lines are of fine wire glued to the panel or can be conductive' lines (metal based paint) silk screened on. Also possible is conductive foil. Notice that the horizontal wires are insulated from the vertical wires at the crosspoints by either the insulating coating on the wires (scraped clean on their top surfaces) or by a blob of insulating varnish for the two other methods.

As explained before, the touch panel is operated by bridging over one of the horizontal to one of the vertical wires by touching one of the crosspoints. Fig. 4 shows this in detail and show in particular how the DC current flows in the finger tip.

Safety considerations As all the power supplies are floating there can be no body currents up the finger. These supplies are normal transformer isolated and insulation resistance from primary to secondary gives the necessary high resistance. The circuit nevertheless has to drive the computer input, which is referenced to earth, so the outputs of the horizontal and vertical circuits is coupled into the computer via opto-couplers.

Claims

CLAIMS I claim that the above described method for the construction of a finger operated matrix switch is novel. In detail I claim:

1. The construction of a switch operated by the bridging of a gap between two metallic conductors with a finger tip: a high voltage provided from a floating power supply driving a small current through the finger tip and this current being detected by amplifiers.

2. The modification of the above to produce two types of current operated switches; one which is operated when a current flows from it and the other when a current flows into it. The combination of these two types of switch to give a very simple matrix switch.