So value of 65535 gives FULL BRIGHTNESS of LED AND FULL SPEED of DC Fan (100% Duty Cycle). With a 72MHz clock rate, a PWM output can have maximum period of about one millisecond. It has 16-bit PWM resolution (2 16), that is counters and variables can be as large as 65535. There are 7 timers and each PWM output is provided by a channel connected to 4 timers. STM32F103C8 has 15 PWM pins and 10 ADC pins. Duty Cycle =Turn ON time/ (Turn ON time + Turn OFF time) If the signal is always ON it is in 100% duty cycle and if it is always off it is 0% duty cycle. The percentage of time in which the PWM signal remains HIGH (on time) is called as duty cycle. But the PWM doesn’t provide pure analog output, PWM looks like analog signal made by short pulses, which is provided by duty cycle. We know that motor and led works on analog signal. PWM is a way to control the analog devices using digital value like controlling motor’s speed, brightness of a led etc. For that we use certain methods like PWM, Digital to Analog (DAC) converters etc. After processing those ADC values, again the output needs to be converted into analog form to drive the analog devices. Sensors outputs are of analog signals and these analog signals are converted into digital using ADC, because microcontrollers only understand digital. Analog signals have voltages like (3V, 1V.etc) and digital signals have (1’ and 0’s). 
We know that there are two types of signal: Analog and Digital.
In this tutorial, we will learn about PWM (Pulse Width Modulation) in STM32 and how can we control brightness of LED or speed of DC fan using PWM technique. In previous article we have seen about ADC conversion using STM32.
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