The code is designed to work with any encoder having a quadrature output. That means there are two signals, each producing a square wave signal as the shaft turns, but the A and B signals are a quarter-cycle out of phase with each other.
We're using US Digital's E4P encoders.
http://www.usdigital.com/products/e4p/index.shtml
I believe we bought them from Newark Electronics, but I'm not the one who purchased them, and I'm not certain.