The mechanics, that is mostly solenoids, will be controlled by the main logic computer through a microcontroller and driver electronic.
This microcontroller (MC) will also "poll" several switches and other sensors in the game.
The old board design (PB-B03) used an 80C535N microcontroller, clocked at its maximum speed of 12 MHz.
I am currently changing my design plans to use an Atmel AVR microcontroller, which will control a CAN bus to which several types of I/O modules can be connected. This solves several problems I had with the matrix design before, at the cost of more money. As this is a single hand-made hobby machine, I accept this.
Further details on that bus are yet to be defined.
To power the coils, I plan to use two coupled transistors like BC238 driving a 2N3055.
Vcc will be +5V. There will be an opto coupler between the microcontroller board and the power driver circuitry to add an extra level of protection. The PB-B03 must not be fried.
The four or five bumpers I want to use in the game, though, will not be directly controlled by the I/O board, but directly connected to the appropriate ball sensors to make them fire, thus taking load off the main computer. The I/O board will only have the option to turn these bumpers off if the game requires this, and get notice of the bumper sensors firing through the switch matrix for scorekeeping.