microcontroller for capacitive touch screen?

For capacitive screens then the controller needs to be very closely married to the touchscreen and you would do well to use a controller and screen from the same manufacturer. Also, I'm not aware of any MCU's that have a capacitive controller and I bleieve it is for that reason.

Are you sure you don't want a resistive screen - they are cheaper, simpler and many MCU's have built in controllers which are compatible with nearly all screens. For vandal-sensitive uses then they can be almost as tough as capacitive screens.

I've worked with both types and have settled on resistive screens after much heartache and many reliability problems with capacitive. It also means I can write my own driver for it and I'm not tied to someone else's controller protocol.

In article , Ajab writes

Sharp ARM parts... now NXP ARM part since they bought them.

ARM7 core with screen controller built in

Which ones might they be? The (ex-)Sharp parts that I'm aware of have ADC subsystems suitable for resistive touch screens but not capacitive ones.

That's correct, they are very good for resistive screens (up to 8 wire is supported) but to use a capacitive screen you need to use a UART to talk to a controller. If you were very clever with a bit of analogue circuitry you might be able to put together something to control a capacitive screen using the existing ADC but it would be pretty hard.

I haven't tried it, but here's one:

Currently, we use resistive 4 wire for GUI input and I've wondered if capacitive would work better (not so pressure sensitive). I haven't figured out what the capacitive sensor configuration would be for a graphical input (X/Y). Anybody know? Bob

Cypress is pushing the 8bit PSOC for this. The have an eval kit. I think TI has the same thing with the 430

Qprox chips provide a self-calibrating ready made solution with serial outputs. Parts are available to scan up to 8x8 matrix:

It looks as though you might need two layers of transparent conductor on your LCD.

Jan Coombs

I want to use capacitive screens because the resistive ones get easily damaged by sharp objects.(this is what i read).

If you want touchs screen that is hard to damage then look at SAW technology. You can mount these on glass that sits on top of LCD panels to help save the LCD as well.

Yes. But SAW are prone to liquids. I need a touch screen which is resistant to sharp scratches,liquids(may be hot). Also it should be unaffected by IR and mobile radiations in vicinity. Projected capacitive seem better.

so, did you like the Qprox parts? From the white paper cited above:

QMatrix devices are digital charge-transfer (QT) ICs designed to detect touch using a scanned, passive matrix of electrode sets to achieve a large number of touch keys driven by a single chip. . . .

QMatrix circuits offer tremendous signal-to-noise ratios, high levels of immunity to moisture films, extreme levels of temperature stability, superb low power characteristics, ease of wiring, and small IC package sizes for a given key count, For these reasons, QMatrix circuits are highly prized for automotive, kitchen appliance, and mobile applications.

Jan.

Snip..

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First time I've ever seen S/N ratio specified as "tremendous"

Nah - just reluctantly quoted it, because the OP seemed unable to follow posted link to Qproc's docs!

Yes, "tremendous" is hardly a technical term, but I believe that their patented process does significantly simplify the effective application of capacitive sensors.

Jan Coombs