Coil Winding Counter with Arduino

This works a lot better than the reed switch / cheap calculator setup I had before. Not sure what the maximum coil winding speed is with this unit using a 16 MHz Arduino Uno Rev. 3. Seems to be at least 40 turns per second. Optointerrupter is available out of inkjet printers. there is a shaft that the ink slides on. At the end of that shaft (opposite end from where the ink maintenance section is) there is a postion sensor made of an round piece of plastic and an optointerrupter. You may find other interrupters, too.