Directly use the door to shape, and then input the pin of the single chip microcomputer. This method can only detect low-frequency signals. For the standard 5 1, only a few hundred K signals can be detected at most, so it is difficult to get on M.

The best way is to amplify the signal first, then carry out zero-crossing comparison and shaping, turn the signal into a standard square wave, then use one or two counters to reduce the frequency, and then input it into the single chip microcomputer. This method can measure the frequency of 10MHz signal.