STM32 detection signal frequency

The goal is

The signal ：500kHz±50Hz Square wave signal , Duty cycle 50%, Low level ：0V, High level ：3.3V
testing ： The frequency of the signal , Sampling rate 100Hz, Record the frequency value

analysis

Signal period 2μm, High level 、 The low level lasts 1μm;
sampling frequency 100Hz, That is, every 10ms Record the primary frequency value , Counting range ：5000±50（4950~5050）;
Use STM32F103 Single chip microcomputer , External crystal oscillator 8MHz, Internal clock frequency doubling up to 72MHz：

• External interrupt ： One rising edge at a time / The falling edge enters an interrupt to record the number of pulses . Low frequency （＜10KHz） You can use , The disadvantage is frequent access interruptions , It takes a lot of time , Cannot be used to measure high frequency
• PWM The input mode ： Use it directly STM32 Hardware PWM Input mode to collect frequency
• Enter capture mode ： Rising edge trigger , Record the start time , Record the second time at the next rising edge , Two time differences are one cycle .<100KHz The effect is very good , However fast the speed is, repeated in and out interruptions will reduce the detection accuracy
• External clock counter ： Use two clocks , A clock is used for accurate and timely adoption , A clock is used for counting , Detect the number of pulses in a fixed time . For example, a clock is precisely timed 10ms, Another clock is used to record 10ms Number of internal pulses cnt, So frequency f=cnt/10ms. This method uses two separate timers , It can detect 2MHz The signal of .

Principle of frequency measurement

The idea of frequency measurement method is shown in the figure below , At a fixed time Tc1 Inside , Count the measured signal pulses to get N1. If the frequency of the standard signal is fc, Then the frequency of the measured signal fx = N1*fc

Reference resources ：1. use STM32 The timer measures the signal frequency —— Frequency measurement method and cycle measurement method
2. Use STM32 Several methods of measuring frequency and duty cycle
[1]: https://www.cnblogs.com/helesheng/p/14107012.html