LSI/CSI LS7366R quadrature counter IC in DIP package This is a popular chip for reading quadrature encoders (such as those used on servo motors and other position tracking applications) Has can be used for non-quadrature counting as well, useful in many applications. One example is step/direction input from a CNC controller. Configure this chip for non-quadrature count mode via SPI and it can handle this by itself, providing your microcontroller with a simple and accurate pulse count. SPI interface allows connection to your microcontroller using only a few wires and retrieve up to a 32-bit count. Much more accurate than relying on the uC to catch every transition. Ardu - ino code and schematics/diagrams are readily available online Datasheet available from LSI/CSI: http://www.lsicsi.com/pdfs/Data_Sheets/LS7366R.pdf