Batteries on the Magic Trackpad last an amazingly long time. I would say about 6 months for my usage (on alkaline cells).
Nevertheless, eventually running out of batteries is always annoying so the other day I decided to power the Magic Trackpad using an USB cable.
This mod has already been documented on macrumors.com’s forum. My twist on it was to drill a hole in the stainless steel battery compartment cover instead of leaving wires exposed or drilling through the trackpad’s body.
Be warned that drilling stainless steel requires a lot of patience. You also need a drill that can rotate a slow speed and Cobalt drill bits. It is really important to take your time and not to drill for too long otherwise the heat will turn the stainless steel into super hard steel you will not be able to drill through.
In the case of that battery cover, being small it will get hot very quickly so I drilled for 30 seconds at a time, waiting a minute or two in between to allow for the piece to cool down.
It took me a whole afternoon to drill through the cover!
I used three 1N4001 diodes in series to step the voltage down a bit (from 5V to about 4.2V). You could use an extra two to bring the voltage closer to 3V, but the trackpad doesn’t seem to mind being powered by tensions over 3V (don’t try with more that 5V though) (I’m pretty sure Apple’s engineers used regulators to protect the trackpad’s internals).
In the process, I discovered that the positive end of the battery ersatz have to reproduce the shape of the + side of an AA battery. If the + end is flat it will not work. There is clever mechanism that doesn’t close the electrical circuit to prevent from damaging the trackpad if you insert the AA batteries in the wrong orientation.
A small piece of soft wood, cut down to the dimension of two AA batteries in series
A beer cap (for the negative pole)
The positive tip of an AA battery
A couple of 1N4001 diodes to step down the USB voltage
A few month back my friend Zaf replaced the top case of his macbook pro and had the kindness to give me his old one. The reason he changed it is the trackpad button wasn’t clicking anymore.
This was the perfect opportunity for me to try converting the top case into an external multi-touch trackpad!
Up to February 2005, Apple laptops’ keyboard and trackpad where still using ADB. Since the top case I had in my hand was coming from a Macbook pro, I presumed the is trackpad would be connected to the main board using an USB bus. The challenge was to guess the pin out of USB connection on the trackpad and, given the size of the connections on the board, manage to solder the 4 wires required for USB connections on the board.
Looking at the flex cable connecting the top case of the macbook pro to its motherboard, it didn’t took me long to guess the trackpad board was a controller for both the trackpad and the keyboard. Having a closer look I first got discouraged by the smallness of the flex connector and thought I would never be able to connect any wire to the board…
Back to the problem a few weeks later, I realised there were testing points on the board that are used on the production chains to make sure manufactured boards are functional. These test points would allow me to solder the wires of my USB cable!
On the right side are four pictures showing the pin-out for the USB connections on the board and how I soldered small wires to the test points and tested the board. As you can see I melted the some of the plastic connector whilst soldering. It is so tiny it’s really easy to do some real damage.
Once I got the trackpad working I cut the top-case in order to isolate the trackpad and have it nice and compact, standing next to my keyboard. The trackpad works a treat (apart from the button that doesn’t click but it was this way to start with) and it’s great to be able to use the two-finger scroll and tap functions!
The text step would be to make a nice housing for it because at the moment it’s impossible to have the trackpad sat still on the desk, not to mention the back of it isn’t protected, which isn’t very reassuring.