Disc Alignment

Encoder pulses from the motor signify that the disc has rotated by a certain amount, but without a reference point, embedded software doesn't know the absolute position of the disc. The encoder provides three channels of output: the A and B channels are quadrature signals that yield the rated count-per-turn resolution of the encoder, and the I channel pulses as the motor turns through one complete revolution. The I channel can be used to determine absolute position of the disc.

Disc alignment can be performed in one of two ways; the first is to physically rotate and lock the disc so that a door is centered over the drop target as the I channel goes high. The second method is to measure the angle from the drop target to the center of the nearest door when the I channel is high. The measured angle is then coded into embedded software as an offset.

A quick and easy method to rotate the motor to the location of an I channel sensor is to connect the channel output to a speaker and manually rotate the disc until a 'click' is heard. Rotating about this point should produce multiple ticks. If the Luminary Micro is used, this can be done by connecting the I channel to the PWM1 pin on the Luminary (which duals as a speaker output). The disc position should read zero at this point.