Ultimarc Opti-PAC Optical Interface Board with USB Cable

The Opti-PAC (Optical Interface for Pc to Arcade Controls) is an interface for easily connecting optical-type arcade control devices including trackballs and spinners to a PC for use with emulators such as MAME. 

Features:
One USB cable handles up to two trackballs and 4 spinners/rotary joysticks.
No external power needed.
The active control (trackball or rotary) is automatically selected.
Supports buffered controls (Happ, Ultimarc U-Trak) or unbuffered (Suzo, Wico, Ultimarc 2 1/4), high or low polarity.
Configurable via software utility for active high/active low.
Full-Speed USB Interface. 16 Bit data.
Will work alongside PS/2 or USB mouse if required.

Optical Controls Technical Info:
A one-axis optical control such as a spinner has one LED which shines across a spoked wheel onto two sensors. 
The two sensor outputs are compared with each other to generate movement direction. 

Therefore the interface requires two parts: 
A voltage supply for the LED.
Inputs for the two sensors. 
The OPTI-PAC has voltage outputs for the LED and the 2 inputs for the two sensors. It takes all voltage needed from the USB port.

A dual-axis device such as a trackball has all the above multiplied by two. Two LEDs, two pairs of sensors. So the board has two independent circuits for the X and Y directions. These two circuits can either be used on the same dual-axis device or separate single-axis spinners.