OpenMoko workshop at ETel

Ian Stirling openmoko at
Tue Feb 27 19:14:28 CET 2007

adrian cockcroft wrote:
> Rough notes, taken as Sean talked.

> Multitouch - capacitive allows multi-touch, resistive doesn't. Lots of
> prior art, so this isn't going to be a patentable thing

This isn't completely accurate.

Resistive touchscreens have two resistive components.
One is a film over the glass part of the touchscreen (in some cases also 
the top layer of the LCD.
The other part is a coated plastic layer that is pressed onto the glass 

The simple resistive touchscreen has two connections per layer, along 
each side (across on one layer, up and down on the other).

These are generally driven by first connecting one axis wires to a 
voltage, and ground, causing a voltage gradient linearly across or down 
the screen, and then measuring the point at which the touch is on the 
axes by measuring this voltage using the other axis.

Then repeating on the other axis.

This gives you per axis - the 'average' (a non-simple average function) 
position of the whole touch area.

If however, in addition to, or instead of doing this, you measure the 
absolute resistance between X1, X2, Y1, Y2, you can get a 'bounding box' 
  of the touch area. (again, it's not quite the bounding box, as it also 
depends on touch pressure).

Now, there are more complex things that can be done.
If you split the X and Y axes electrically into several X and Y strips, 
then you essentially have (for up to two touches) lots of little 
independant touchscreens.

For three or more touches, it depends on if they are on the same 
column/row, to see if you can disambiguate them.

More information about the community mailing list