The controller is a PIC 16F84 on a purpose designed pcb, fitted on the top of the chassis at the front. Larger than a typical PIC board, the pcb was designed to fit on the chassis while allowing interconnection via labelled screw connectors - these were to simplify reconfiguration, as the project was intended to be experimental from the outset. It also allows in-circuit programming, via the plug which can be seen on the near edge of the board in the picture and using the programmer described on the PICs page.
Laser printed labels, again, helped to keep things simple. Not including an on-board reset switch was an oversight - a reset switch is glued to the chassis next to the controller board and the components associated with it are soldered onto the expansion board.
The expansion board can be seen on the left of the photograph, behind the controller. Now somewhat tarnished, it was intended for whatever additional or experimental circuitry might be required as the project developed, using a top-soldering technique which I have used a lot and find very suitable for one-offs and temporary or experimental circuits. My expectation was that a number of sensor/interface circuits would eventually be assembled on this board.