Home | Concept | Body & instrument | Optical tonearm | Turntable platter | PIC code | Review
Mounted upon the turntable platter are disks prepared with black, white and grayscale patterns. A second tonearm taken from another turntable is placed above the optical platter, but with the stylus removed and an Infra-Red receiver (taken from a mouse) mounted internally instead, along with a pair of IR LEDs at each side. These are integrated into a simple circuit to convert the optical reflectivity of the section of the platter under this tonearm into an analog voltage, which is in turn converted by the PIC to a digital 8-bit signal routed to the computer by USB.
The optical tonearm angle (and thus the 'track' on the disk being read) is determined by a servo motor being controlled by the PIC, under USB control from the computer using the ForceFeedback gamepad protocol. The servo receives pulse signals at a period of around 33ms (close to the minimum rate for the servo motor), whose pulse-width varies between 1.0 and 2.0ms to specify the desired degree of rotation of the motor.
Example disk patterns:
