Electronics notes/Touch screen notes

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Types

http://en.wikipedia.org/wiki/Touchscreen#Technologies

Resistive

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Most simpler touch screens are resistive. For a while this was all we really had, for a while this was the cheaper option (probably largely though economy of scale).

They need more force than the later capacitive type, and may require a stylus to be useful.

Can have pretty decent resolution, but may not.

Each axis, when touched, will give a particular resistance in a range (usually interfaced with an ADC), so can report only a single touch. Touching on multiple places (or e.g. resting a palm while drawing) will typically mis-report.

There's 4-wire, 5-wire, 7-wire, 8-wire and more.

These relate to different accuracies, and some to variants that won't lose as much accuracy over timeTemplate:Verfiy

Capacitive

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Capacitive sensing in general can sense various materials nearby - you could say it measures the ease of accepting charge - which is called capacitance.

Touchscreens will effectively filter out touches, apparently doing so both by amount of capacitance, and area.

They can sense not only a change in capacitance, and reject small changes, short changes (that might be EMI).

As such a touchscreen functionally can be seen as a bunch of individual capacitive sensors side by side, they can also reject things that are too large, or too local.

In other words, it's looking for things that look most like a finger-like disturbance.

Which is why other things that work on a capacitive screen, from styluses to sausagees in latex gloves, have a relatively broad tip. The size is at least as important as the (change in) capacitance.

Capacitive tricks went from being there in only a few devices (e.g. nineties trackpads) to increasingly common (in MP3 players, and phone touchscreens) in the late noughties, to uniquitous in smartphones and tablets since.

Has a few subtypes -- see also capacitive sensing.

One of them can be multi-touch, and multi-touch tablets and phones are very usually capacitive.

Capactive touchscreens can be built in a more robust way than resistive (sensors are under the top glass, not part of the top layer as in resistive).

Capacitive touch can also be faster and more responsive than resistive. Some of the simpler/cheaper designs are less accurate than resistive, though; some handwriting recognition devices actually stuck with resisitive.