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I'm developing a project that I would like to use the Ipad capacitive touchscreen(digitizer) with mTouch controller PIC16F707 but by now I have no clue about the specifications of Ipad touch screen. I would like to use it because the OEM Ipad screen is not too expensive.

I know that mTouch controller can handle up to 32 sensor channels. I got the details of the controller on this website http://www.microchip.com/pagehandler/en-us/technology/mtouchscreens/products.html They even offer a development kit.

Anybody know how would I get a clue ? I did find on internet but found almost nothing. I found this interesting topic here also Capacitive Touchscreen for DIY usage?

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Felipe
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  • I think the new chip [MTCH6301](http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en559101) from Microchip is what you're after. It also has associated development kit. –  Feb 02 '13 at 20:42

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No. The touch-panel controllers that you'll have access to are designed for building capacitive button panels like those that might be found above your laptop keyboard or on the side of your TV, not for building high-resolution touchscreens. Quoting the datasheet:

16.0 CAPACITIVE SENSING MODULE

In a typical application, the capacitive sensing module is attached to a pad on a Printed Circuit Board (PCB), which is electrically isolated from the end user. When the end user places their finger over the PCB pad, a capacitive load is added, causing a frequency shift in the capacitive sensing module.

For an example application, check out Sparkfun's MPR121 keypad, which uses an IC that performs a similar function as the capacitive module in your PIC.

You can build a rudimentary X-Y touch panel with 16 horizontal pixels and 16 vertical pixels (or 20 and 12, or whatever) by laying out your PCB like this:

enter image description here

As shown by the blue line, every other horizontal row is connected by a trace on the back side of the PCB.

Real touchscreens are constructed in a similar fashion, but have hundreds or thousands of these rows and as many channels. The rows and columns are laid in transparent metal layers of indium-tin oxide on glass layers. If you have to ask, it's probably not in your budget. If you really want a capacitive touchscreen, you'll be better off reverse-engineering the output of the OEM module with the capacitive sensing already built in. Note that your PIC16 doesn't have the horsepower required to decode this information; you'll need a big ARM processor or an FPGA for that.

Kevin Vermeer
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  • Hi Kevin.. thank you for your explanation. I would like to use an ARM processor. But the question is.. do you think this reverse-enginnering on ipad screen would be complicated ? I'm software develeloper and I don't have deep experience on this field. You know if this is possible would be very cool to use it with ARM boards. It's cheap also. I already have one OMAP 4 dual core board.. what I would need more ? – Felipe Mar 09 '12 at 22:16
  • @FelipeOliveira - Yes, it would be complicated. You'd need to hook up an oscilloscope or logic analyzer to a working iPad screen, and monitor the signals being sent from the screen to the controller, including the initialization codes. Then, you'd need to correlate those signals to actual inputs. Finally, you'd need to develop a driver for your board which would work with these signals. It will be most helpful if your OMAP4 has an onboard peripheral which can be used to decode the input. The OMAP4 ought to be sufficient, a PIC16 will not be. – Kevin Vermeer Mar 09 '12 at 22:36
  • Ho okay.. do you know any OMAP4 board that come with this kind of decoder peripheral ? I think it would be great and usefull because if it works we can build ARM tablets with this OEM high quality screens at low cost. What you think ? – Felipe Mar 09 '12 at 23:03
  • @FelipeOliveira - The manufacturers are already building tablets with these screens; there's nothing guaranteeing the low cost. Also, don't know what the peripheral needs to be, you'll know that after you reverse engineer the protocol. – Kevin Vermeer Mar 09 '12 at 23:05
  • Yes they are, but imagine if the people could build it by theirselfs. I know ARM boards with price starting at $150 dollars. The OEM replacement LCD screen of Ipad is $70 and the touch screen $55. – Felipe Mar 10 '12 at 00:04
  • Costs are cheaper at extremely high volumes. A home-made tablet with OEM replacement parts would always cost more than the original tablet, even after the manufacturer's profit. You seem to be leaving off some expensive parts, notably including the battery, Flash memory, mechanical enclosure, and assembly costs. – Kevin Vermeer Mar 10 '12 at 00:08
  • Yeah, you right.. I was a little high-minded. I forgot all other costs thinking about the screen. But I hope soon we will can choose all pieces of the laptop and tablet like we choose on PC. Thank you anyway :) – Felipe Mar 10 '12 at 00:19