GitHub - arduino-libraries/AudioFrequencyMeter: Allows the Arduino Zero and MKR1000 to sample a generic input audio signal and get the fundamental pitch
![FreqMeasure Library, for Measuring Frequencies in the 0.1 to 1000 Hz range, or RPM Tachometer Applications FreqMeasure Library, for Measuring Frequencies in the 0.1 to 1000 Hz range, or RPM Tachometer Applications](https://www.pjrc.com/teensy/td_libs_FreqMeasure_1.jpg)
FreqMeasure Library, for Measuring Frequencies in the 0.1 to 1000 Hz range, or RPM Tachometer Applications
![FreqMeasure Library, for Measuring Frequencies in the 0.1 to 1000 Hz range, or RPM Tachometer Applications FreqMeasure Library, for Measuring Frequencies in the 0.1 to 1000 Hz range, or RPM Tachometer Applications](https://www.pjrc.com/teensy/td_libs_FreqMeasure_sch.gif)