Abstract: A double-fiber bidirectional interference fringe counter based on Arduino singlechip is presented. The device can achieve the bidirectional counting of fringes according to the gushing and the sinking of interference fringes. In the experiment of measuring the thermal expansion coefficient of metal by the interferometry，this counter is used to count the fringes. It has low cost，convenient operation，high counting accuracy，strong anti-interference ability，short reaction time and so on.

Key words: Arduino singlechip, interference fringe counter, double fiber, bidirectional counting, coefficient of thermal expansion