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.