LED with PWM
Question
I have learned to change the brightness of LED with PWM pins but what actually PWM pin is
doing? Decreasing voltage?
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Basudev
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Answers ( 2 )
1. Whenever you want analog Output with digital mean we use PWM (Pulse Width Modulation). And can be used to controlling the brightness of LED, speed control of DC motor, controlling a servo.
2. The Arduino digital pins either gives us 5V (when turned HIGH) or 0V (when turned LOW) and the output is a square wave signal. So if we want to dim a LED, we cannot get the voltage between 0 and 5V from the digital pin but we can change the ON and OFF time of the signal. If we will change the ON and OFF time fast enough then the brightness of the led will be changed.
3. You need to understand a turn duty cycle. Duty cycle is the percentage of time when the signal was high during the time of period. You can use the syntax analogWrite( ) function to use it. This function takes two arguments: the pin number and the duty cycle value. The duty cycle value should be between 0 (completely off) and 255 (fully on).
In the attached example, the LED connected to pin 9 will vary in brightness between off and half-brightness because we set the brightness variable to 128.
At 50% duty cycle and 1Hz frequency, the led will be high for half a second and will be low for the other half second. If we increase the frequency to 50Hz (50 times ON and OFF per second), then the led will be seen glowing at half brightness by the human eye:
analogWrite(0) means a signal of 0% duty cycle.
analogWrite(127) means a signal of 50% duty cycle.
analogWrite(255) means a signal of 100% duty cycle