The IR emitting diode (top right) consists of a photodiode in series with a 100Ohm resistor. This allows for a large current of 33mA to flow through the diode, which was under the max 40mA spec while producing a beefy IR emitting signal. The tape sensors (PhotoNPN) incorporate a simple trans-resistive stage to allow for a linear input current-to-voltage response from the Photo NPN. The reference voltage is set at 4.2 V, sufficiently low to forward bias the PhotoNPN while allowing for a large band (from 0V to 4.2V) of output voltages. The gain resistor, set at 2.2K allows for the optimum separation between the white, black and green tape that is necessary to sense for the game. Each output from the trans-resistive stage feeds directly into an AD port on the E128 and software controlled.

The Death Star - ME218B - Winter 2009