AccuTouch Product Guide - Elo TouchSystems

Touchscreen Simulation
The action of the touchscreen can be simulated with a variety of circuits, several
of which are described below. A dummy touchscreen can be useful in
troubleshooting when many systems are being maintained or when controller
linearity is suspected.
The simplest dummy touchscreen is the “paper clip test” described on
page A-64. Another simple dummy touchscreen is shown in Part I of Figure A.1
on page A-68. This circuit will produce the action of a constant touch in the
middle of a real touchscreen. The coordinates that the controller outputs will be
about 2000,2000 when using ELODEV uncalibrated and the TOUCHES
diagnostic utility. This circuit can also be modified by adding a switch between
the junction of the resistors and the input to pin 3, and can then emulate a touch
by closing the switch. Acceptable resistor values (R) are from 100-500 ohms,
1/4 watt or greater.
If a potentiometer is substituted for the two resistors in Part I of Figure A-1, the
dummy touchscreen in Part II results. It simulates a touchscreen with touches
moving from the upper left to the lower right as the pot is turned. Typical values
would be 0-20, 4092-4095 at one extreme and 4092-4095, 0-20 at the other
extreme. Potentiometer values (VR) from 100-1000 ohms are acceptable.
A dummy touchscreen which can produce a full range of coordinates (0-4095)
in each axis is shown in Part III. This circuit is good for looking at controller
problems, as the coordinates in each axis can be varied independently. A
joystick can be used for a dummy touchscreen of this type, as long as the pots
(VR) are of the appropriate range (100-1000 ohms). Diodes (D) may be
1N4148, 1N4000, etc. If the procedures above indicate a hardware problem,
subsequent troubleshooting depends on which controller is being used.
A-67