If you repeat this on-off pattern fast enough with an LED for example, the result is as if the signal is a steady voltage between 0 and 5v controlling the brightness of the LED. The amount by which the pulse width varies is. To get varying analog values, you change, or modulate, that pulse width. PWM is only available for the Pulse waveform, and the pulse width varies according to the modulating signal. The duration of "on time" is called the pulse width. Digital control is used to create a square wave, a signal switched between on and off. This on-off pattern can simulate voltages in between full on (5 Volts) and off (0 Volts) by changing the portion of the time the signal spends on versus the time that the signal spends off. Its a fancy way of allowing you to change the ratio in the amount of time a signal is on vs the time that it is off. Pulse Width Modulation, is a technique for getting analog results with digital means. To output analog voltages, the computer uses averaged voltages, flipping between 0 and 5 volts at an appropriate interval to simulate the desired output voltage. It can output only digital voltages, either 0 or 5 volts. PWM stands for pulse width modulation, and it’s important because your Arduino controller can’t actually output analog voltages.
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