"Exhaust Fan" draws on previous experience in electronic products only when, during soldering, welding each component are used a multimeter to test whether Weld, check to make sure the whole circuit complete welding, no weld, turn the power on and debugging. Debug: The first part is composed of part of the 555 chip, we need to look at when Huang experiment, whether Green light! 555 chip depends on whether to issue a three-pin high and low frequency. The second part is the part count of 4017 chips, the need for debugging the test chip 14 feet high and low frequency, and then see whether the alternating light emitting diode.