I mentioned in the initial post of the iPad 3 LCD project log that I purchased an iPad 3 digitizer in addition to the LCD. I don’t want to call this article “Hacking” the iPad 3 Touch Panel, because I’m not sure how far I’ll get with it. But I want to at least make a page for this in case my findings may be useful for anyone attempting a similar project.
This is a digitizer for the 9.7″ iPad 3 display panel. It is, per Apple’s website, “capacitive multitouch”, although the particular type of capacitive is undocumented. It is likely to be projected capacitive or some derivative thereof. The connector at the center is a 2×37 pin, 0.3mm pitch FFC. The contacts are on only one side of the flex cable, so a connector such as Molex 503566-3700 should be compatible.
The cable does not appear to have any embedded electronics. It is connected to the digitizer for about three tenths of an inch at bottom left and right in the above photo (top left and bottom left in the assembled iPad), and is glued down and appears to be occasionally connected along the remainder of the length. Looking closely at the connection points, we can see how the contacts are structured:
The contact structure of the transparent section of the panel is typical of a mutual type projected capacitance design. Forty-one very fine wiggly lines travel unbroken from left to right across the iPad display, while thirty rectangular contacts along top and bottom (as seen above) frame four short wiggly horizontal line segments between each unbroken horizontal line. All horizontal lines terminate at a single contact on the right side of the iPad display and are individually connected at the left; all columns of line segments are bounded at both top and bottom by rectangular contacts (but are not in physical contact with them). I have tried to photograph the pattern with a microscope, but it is very difficult, so I have illustrated the basic idea below.
The effective resolution of this touch panel is then 41×30, but of course by interpolating between points a position can be calculated to much greater accuracy. It also explains the number of pins on the connectors – with 74 available contacts and 41 row + 1 row common + 30 column, only 2 pins are yet to be identified – although much work remains to map the functions to the pins.
Things are already looking quite good for getting this panel to do something. With a waveform generating MCU and a little math, this may well be workable.
That’s enough on that topic for today. See you next time.