Touchscreen Manufacturers plus EMC

Well that's my hols over with for another year :-( I can highly recommend Bulgaria by the way. However, back to work....

Does anyone have any experience of different manufacturers of resistive touchscreens? I'm almost at the time where I have to decide which make to go for and I have three main choices (others may be considered but only if they are obtainable by the people who will be sticking them to the LCDs they will be selling us):

3M - Already in use on the development system and have been good and reliable (not their capacitive screen though - shafted me good and proper ) but they are not cheap.

DMC - About half the price of 3M and appeared to allow more light through when I saw one demonstrated. Might have just been a brighter LCD though.

eTurboTouch- Roughly the same price as DMC but I haven't seen one in action.

Also does anyone have any experience with EMC on touchscreens. I imagine that, being conductive, they are good at blocking emissions from the hole cut in the box for the LCD but could prove sensitive to receiving noise. How much of a problem am I likely to face?

Reply to
Tom Lucas
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I've used both glass and polycarbonate touch panels ( I currently use a poly panel in a shipping product), but my supplier is a fairly small outfit in the south of England (I'll get the name once I'm back at work in the morning).

EMC - Use a fully differential driver and ADC system. I use an integrated solution with AC97 (because it was on the initial dev board and the software group bitched when I asked about changing it). If I had started the whole thing from scratch I am not sure I would have used it. Anyway: Wolfson WM9712

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This device is rather sensitive to the CCFL drive when it's in close proximity, (as most do one suspects) so shield it and get one with a nice big analog ground pad underneath. If you end up using it, let me know and I'll email you the details of what it took to get it really clean. If you're using another controller, you'll probably still end up with the same issues I did. Every product is different, of course, but a lot depends on the positional relationships of the internal signals and HV wires.

This device is in close proximity to the CCFL drive, LCD signalling, GSM/GPRS modem, Bluetooth unit, 802.11, barcode scanner-imager and an RFID reader and works just fine. [That's no different from a lot of products, of course; just mentioning it so you know the amount of interfering radiation I had to worry about ;) ]

The unit is used for signature input (amongst other things) and that works fine during GPRS sessions (the GPRS antenna is perhaps 3/4 inch behind the touch panel and the one side of the radiation pattern is aimed directly at the touch panel (but with the LCD in the way, thankfully). Ditto for BT, RFID and 802.11.

The panel itself doesn't really absorb too much of the energy passing through - a few dB at most - and that was actually an issue at EMC compliance testing. The best advice I can give is to make sure your LCD is solidly grounded to it's perimeter shield all the way around. That also means that the panel shouldn't be particularly susceptible to external interference; certainly mine isn't, but see the note about fully differential drive :)

Poly absorbs more light than glass based units, but it's far more rugged (and easier to get safety approval on). Depends on your application, of course, and panel size. It's also more expensive.

Hope that helps

PeteS

Reply to
PeteS

My controller is built into the Sharp MCU I use to drive the screen but it should be fairly well partitioned off from where the CCFL is. The inverter can be positioned away from most things as well.

We don't have any RF stuff so that's one less thing to worry about.

Noted about grounding the LCD shield. Our whole chassis is earthed so perhaps I improve the conductivity to the screws holding on the panel to help to ground it.

The application is in a boiler room so a little bit of ruggedness is required. However, it doesn't have to be bombproof and if they manage to break it then they can put their hand in their pocket for repairs. It's a touch screen not a jab screen ;-)

Thanks for your detailed reply.

Reply to
Tom Lucas

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