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Microsoft Touch Cover Mini Teardown

19 October 2014

In preparation for creating my own Thinkpad keyboard cover for my Surface Pro 2, I decided to take apart a Touch Cover to get a better look at how they worked. I bought a non-working Touch Cover off eBay for $10 and went at it.

Intact Cover

I used a knife to rip open the skin of the cover. Looks like it’s made of some sort of tough plastic cloth; it took some work to rip through it all.

Ripped Open Seam

Front of the cover exposed!

Ripped Open Cover

A first look at the capacitive touchpad.

Touchpad

Individual keys were glued to the fabric of the cover to make sure they connected well.

Connector

The Touch Cover uses force sensitive resistors to detect keypresses. Here, the top membrane layer is removed. As pressure is applied to the pads, they short the squiggly traces underneath, changing the resistance of the line.

Membrane

Looks like the space bar is split into two pads.

Split Spacebar

A look at the arrow keys.

Arrow Keys

Now, for the second layer. This contains all the circuitry, and is backed by some sort of laminate board on the other side.

Bare Board

Bare Board Top ViewCover

A better look at the touchpad.

Bare Board Touchpad

There are several test points on the board. Some JTAG test points for programming/debugging the main MCU, as well as some I2C test points for the accelerometer. I was able to confirm with a multimeter that the two left-most connectors on the cover are +5V and Ground, but unfortunately, the two I2C pins and interrupt pin weren’t broken out onto any test points. It should be fairly easy to determine by poking around the signals on a working cover, though.

Test Points

Capacitive Key Closeup

There is also a metal insert on the bottom left of the board.

Mysterious Magnet

It’s magnetic! Maybe it’s for detecting the open/closed positions?

Magnetic Closeup

Laminate backing on the other side of the board.

Board Back

All the goodies are glued up in the bottom.

Board Back Closeup

The skin is mostly just held in place by the force of the connector, with the exception of a few anchors.

Skin Attachment

Removed Skin

Backside of the connector.

Removed Connector

I cut out the capacitive sensing layer. You can see that it’s a big matrix of sensors all feeding into the main board.

Removed Capacitive Layer

Capacitive Layer Closeup

With some force, I managed to pry the PCB free. Unfortunately, it was glued in pretty tightly, and the board suffered some casualties.

I was able to identify a few of the big ICs inside.

First up is the Atmel maXTouch mXT112E. This is a capacitive touchscreen controller that’s likely used for the touch pad.

The markings on this chip were:

ATMEL MXT112E MASH1R0 2U29S0B

The main MCU is a Freescale MK10DN512Z. This is one of Freescale’s Kinetis MCUs based on ARM Cortex-M4 cores.

The markings on this chip were:

MK10DN512Z AB10 4N30D UYDM1233A

There was a third IC marked:

2233 C3H GKXCQ

I am not quite sure what it is, but I suspect it may be a Texas Instruments MSP430 G2233, which comes in QFN packages.

Removed PCB

Removed PCB Different Angle

Removed PCB Different Angle 2

I removed the connector and FPC. Should be useful to use in my own cover.

Removed Connector