127 represents ~50% duty cycle, and so on. Thus, the value of 255 corresponds to duty cycle of 100%. Thus, the duty cycle can vary from 0 to 255. Now, note that an 8-bit number is used to represent the duty cycle. Thus, the LED will keep getting brighter, till the max duty cycle (100) is reached. We will connect an LED to a PWM pin, and keep increasing the duty cycle on that pin, thereby increasing the voltage on that pin. We will consider the LED brightening followed by dimming example. The frequency of the square wave is 490 Hz (about 2 ms time period) on all pins except 5 and 6, on which it is 980 Hz (about 1s time period). For other boards, please refer to the datasheet of the board.Īs can be seen from the above picture, only pins 3,5,6,9,10 and 11 can support PWM. On the Uno board, the pins are specifically marked with a ~ symbol. After all, we are essentially outputting analog voltage, instead of reading it. With this application in mind, it shouldn’t be a surprise that the function used to perform PWM in Arduino is called analogWrite(). So, if your HIGH level is at 5V and LOW level is at 0V, and you need 3.5V output, if you generate a square wave which stays at the HIGH state for 70% of the cycle, or, in technical terms, has a duty cycle of 70%, and if its time period is very less (in milliseconds), then the node receiving this square wave will experience a voltage of 3.5V. PWM can also be used in general for generating voltages between HIGH and LOW. The RPM of the motor can be controlled by the PWM output. An important application is running motors. In very simple terms, we can output a square wave from certain pins of the Arduino board, and we can control the fraction of time for which the wave will be at the HIGH state (known as the duty cycle).

Arduino pwm program