Furby 2012 motor quadrature encoder

The Furby 2012 has a single DC motor that drives everything that moves.  The motor can be run continuously either forward or backwards.  There is a physical contact switch to determine the "home" position- when you wake a "normal" furby, it will do a wake up routine no matter what (with the familiar "Di Aylo Aat Too" good morning sound. This wake up routine finds and sets the home position. (can be adjusted using the set screw on the rear- it has red glue on it). The direction and exact amount of movement is monitored by the motor encoder- an optical rotary quadrature encoder.  You can see the encoder board in the photo below.

 

A crude control can be obtained from simply using the home switch and PWM for speed control using a motor controller like the one shown below from Pololu (it happens to be a dual motor controller).

The encoder board, front and back, are shown below.

Not pictured is the rotary wheel that passed between the emitter (LED) and collector (photo) diodes.  A complete circuit diagram is shown below (note the blue wire is ground, red wire is Vcc (5v), white and black wires are the two channels of the quadrature encoder:

 

The chip used is a TI CD54HC14 (data sheet)- essentially a bunch of Schmitt triggers.