The sensor array served two purposes, as described in the problem assessment. First, it held all of the sensor circuitry and brought it into close proximity to the test units, and second, it isolated each test unit from all of the others.
In its final form, the sensor array was a 0.5 inch thick piece of plywood, with 9 holes drilled in a grid, through which the sensors were placed. Circuitry for the photosensors was mounted on top of the array, and connected to the photosensors placed through the holes. Underneath the array the shades, used to isolate the lights, were placed in grooves cut into the bottom. The shades took the form of a grid of thin walls, constructed from cardboard, 6.5 cm in height.
The sensor array was guided at its four corners by interacting with the frame through notches cut out of the corners. The frame had aluminium angle bracket mounted, and the sensor array had corresponding angle bracket. The sensor array slid up and down on these rails, which were lubricated by PTFE in order to reduce friction.
The sensor array was lifted by two stepper motors with attached gearboxes and a spool. Stepper motors were selected so that the vertical travel of the sensor array could be precisely controlled through the microcontroller. At each of the four corners of the sensor array, an eye hook was attached. A single piece of 10-pound test fishing connected to one eye hook, led up through another eye hook attached to the frame, through a hole in the spool, and continued symmetrically on the other side (see Figure \ref{fig:stepper_mechanism}). Through this mechanism the sensor array was lifted without twisting from four points. The high gear ratio of the gearboxes attached to the stepper motors (9:1) meant that the sensor array stayed in the raised position without any power being supplied to the stepper motors.