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A pulse width modulated signal or (PWM) is a method of relaying an analog result through a digitally readable signal. This is achieved by generating a square wave of alternating high/ON (typically 3.3 or 5 V) and low/OFF (0 V) signals. This essentially simulates an average voltage between the high and low value corresponding to the value of the effective analog signal. The portion of a wavelength (λ) that is spent at an ON or high state is the pulse width and the percentage of "active time" per wavelength is the duty-cycle. For example; a signal that is in the high state only 1/4 of the time is said to have a duty-cycle of 25% which for a 5 V high value would result in an average voltage of 1.25 V. The frequency (f) of the incoming signal is the inverse of the period (T) which is equivalent to wavelength for a time varying signal.
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