PIC microcontroller PWM PWM principle-EEWORLD

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1. What is PWM

What is PWM? Professionally speaking, it is pulse width modulation. In layman's terms, it is the continuous output of high and low levels. For example, the microcontroller outputs a high level for 40ms, then a low level for 60ms, and then continuously and periodically outputs high and low levels alternately. This is a typical PWM wave. The high level output time of 40ms is the legendary pulse width, and 40ms+60ms＝100ms is the PWM cycle. Assuming that we set the cycle to 100ms, we can increase or decrease the high level time according to our needs. For example, the high level output time is increased to 80ms, then the low level time becomes 20ms. It is also possible to reduce the high level output time to 20ms, then the low level time becomes 80ms. This is pulse width modulation, and what is adjusted is the high level time. The proportion of time occupied by the high level (pulse width) in the cycle is called the duty cycle. Expressed in mathematical formulas, the high level time/cycle time = duty cycle.

2. PWM implementation method

How do we make the microcontroller output PWM waves? There are two ways: one is to use I/O output directly, and the other is to use the module.

2.1 Using I/O port to output PWM

If your microcontroller does not have a PWM output function module, you can write a program to output PWM waves yourself. Because PWM is not just high and low levels. An I/O plus a timer is easy to do for any microcontroller.

2.2 Using the module to output PWM

PIC microcontrollers have a PWM output module. Using the module to output PWM is actually simpler, more convenient and more accurate than using I/O to output PWM.

3. The role of PWM

What can PWM be used for? The more typical application of PWM is LED dimming and motor speed control. How does PWM dim and control? It is easy to understand. Take LED dimming as an example. If the LED is powered on all the time, the LED is the brightest. If the LED is not powered off, the LED is not bright. If the LED is powered on and off repeatedly in a very short period of time, the LED will appear bright, but at a low brightness.

If the LED is bright when the microcontroller outputs high level, then the longer the high level output time in the PWM wave, the brighter the LED will be, and vice versa.

Reference address：PIC microcontroller PWM PWM principle

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