[Magic Mouse Teardown (5)] A Further Look at Touch Sensor
The H-shaped electrodes are longitudinally connected via wiring on the sensing side. And 10 wires are bound up near the connector electrodes and led to the back side of the flexible printed circuit board (FPC) by penetration wiring.
The E-shaped electrodes are horizontally connected by forming penetration wiring on the back side of the FPC. And 15 wires are bound up after longitudinally passing through the back of the FPC and led to the connector electrodes.
So, the number of signal wires is 10 in the longitudinal direction and 15 in the horizontal direction. And the number of connector electrodes is 28, three of which are used for earthing wires in the center and both sides.
On the back of the FPC, an electrode that looks like an equal mark is formed on the back of each electrode element and connected to an earthing wire.
"I do not know why Apple chose this shape or what kind of effect it has, but this electrode is used for reducing noise," an engineer said. "I think Apple aimed to enhance the sensitivity by improving the signal-to-noise ratio."
There are more improvements that seem to be made for reducing noise. For example, in the wiring to the connector electrode, an earthing wire is used for each of the 10 longitudinal signal wires.
"I think this is for reducing noise, but I do not know why this is done only for longitudinal signal wires," an engineer said.
Also, there is a lattice of earthing wires near the connector electrodes, and some of the wires connecting electrode elements have branch wires that do not connect to anything. And we could not know why Apple designed the Magic Mouse as such.
"There are many small twists that I found very interesting," an engineer said.