How do you measure the duty cycle of sinus with a arduino uno?

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Unkown21:
My school project is to measure the frequency output from a buzzer. The manufacture from this buzzer is PUI Audio inc with the type number AI-2604-TT-R. The minimal frequency output specification is 400Hz(+-100Hz) that is located in the datasheet from the buzzer.
Link datasheet: http://datasheet.octopart.com/AI-2604-TT-R-PUI-Audio-datasheet-17019779.pdf

Iam using a microphone to record the sound signals from the buzzer. I am using a pre amplifier circuit to amplify the out coming signal. This signal is the input for the ardruino(Analog input).

Kind Regards,
Dennis

A sinusoidal waveform has a 50% duty cycle.

To measure frequency or duty cycle of other waveforms, look for the zero crossings and measure the time.