Photos (3)  New roll reader - pneumatic sensors
Roll perforations are detected by electro-pneumatic sensors (switches) that operate in the same way as the pneumatic valves in a player piano. The difference is the output signal is MIDI data.
Sensor construction. Photo shows partial assembly in which neoprene diaphragms are glued to a body of two pre-drilled and routed PVC sections that are sandwiched and glued together. A third layer sits on top of the assembly and the PCB holding the Hall effect switches forms the top layer.
Block of four sensors. Bipolar Hall effect devices sense the movement of a small section of flexible magnet attached to the aluminium risers, which sit on top of neoprene rubber diaphragms. Travel is less than 1 mm.
Adjusting the sensors. Dynamic tests are applied to each sensor involving various levels of suction and pulse repetition rate. The output from a Hall effect device is monitored with a digital oscilloscope and the position of the Hall effect device is adjusted to achieve the correct waveform. A pulsing pneumatic signal is applied using the motorised rig on the right.
New roll reader (2006-2011)
Suction pump. Photo shows the pump and regulator pneumatic only. The DC motor speed depends on the position of the regulator pneumatic relative to a Hall effect device. Any deviation from the set point (adjusted by the spring tension on top of the pneumatic) causes the motor speed to adapt accordingly. The suction level is adjustable between 2.5"  and 3.5" WG.
Sensor array and tubing. The 25 sensor units comprising 100 sensors, grouped into four lots, are mounted on a PVC baseplate and are connected to a manifold on the back of the spool box. Each group is covered by a clear plastic cover that seals against the baseplate, and suction is applied to the inside of each cover.