Building the Controller

MPXPLAY supports input from a keyboard, mouse, joystick, serial port, or parallel port. A keyboard offered the most options, though obviously using a full size keyboard in a car would be cumbersome. A more suited solution was required. Borrowing inspiration from another install by TomG involving the adaption of a stock Ford headunit to control a IR remote for his Nakamichi headunit which was hidden out of sight, I decided to use the stock Toyota headunit in the car as the controller. This also added an extra element of stealth to the install.

The initial phase was much easier than expected, as the donor keyboard itself undid via 9 clips:

This opened to reveal 3 layers of plastic film and a circuit board that sat under the caps-lock/scroll-lock/num-lock LEDs. In this shot the circuit board has been removed:

Under the top layer of rubber "springs" that activated the keys, the key switches themselves were simple tracks printed on the plastic that once depressed connected to the layer beneath in a matrix fashion:

Once opened out to show the two layers it is possible to trace where the various lines run. These coincide with various pins on the circuit board. From there it is possible to draw up a matrix of what pin connections coincide with which "key", in the photo below I'd already started marking some out in pen:

Once I had a list of keys I then set about stripping the stock head unit out to just a case and the fascia:

Then I set about wiring buttons on the head unit to the relevant pins on the keyboard controller circuit. To make life easier I only used one "row" of keys, though if I chose I could wire up more keys at a later date:

For good measure I also took the stock volume controller and wired RCAs to it so I could feed my output into it before it went to the EQs, to enable me to have an analogue volume control for ease of adjustment.