US Digital (Vancouver, WA) offers the QSB (Quadrature to USB) encoder interface adapter that interfaces standard quadrature encoder signals into a PC USB port for encoder verification. Single-ended or differential versions are available. Another version supports single-ended encoder input, digital I/O, and step/direction motion control output. Each device comes with demonstration software and source code. The devices read quadrature, PWM, and analog encoder signals, and offer field-programmable firmware.