Hello, would you like to help me?
I want to try simple audio frequency meter project (https://www.arduino.cc/en/Tutorial/SimpleAudioFrequencyMeter)
But until now, I am not yet success to create it.
I am using samd21 compatible arduino zero from wemos, I has uploading the code to the arduino zero, but when I open serial monitor, there is not frequency detected as output.
What the cause of this error?
Please help me if you know some suggestion. 
The code is:
/*
Simple Frequency Meter for Arduino Zero
Demonstrates how to sample an input signal and get back its frequency
This example code is in the public domain
http://arduino.cc/en/Tutorial/SimpleAudioFrequencyMeter
created by Arturo Guadalupi <a.guadalupi@arduino.cc>
10 Nov 2015
*/
#include <AudioFrequencyMeter.h>
AudioFrequencyMeter meter;
void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
Serial.println("started");
meter.setBandwidth(70.00, 1500); // Ignore frequency out of this range
meter.begin(A0, 45000); // Intialize A0 at sample rate of 45kHz
}
void loop() {
// put your main code here, to run repeatedly:
float frequency = meter.getFrequency();
if (frequency > 0)
{
Serial.print(frequency);
Serial.println(" Hz");
}
}