Arduino Library implementation of the Goertzel algorithm, originally written by jacobrosenthal. Adapted fixes for running on an SAMD Arduino Metro M0
void loop()
{
goertzel.sample(sensorPin); //Will take n samples
float magnitude = goertzel.detect(); //check them for target_freq
if(magnitude>THRESHOLD) //if you're getting false hits or no hits adjust this
digitalWrite(led, HIGH); //if found, enable led
else
digitalWrite(led, LOW); //if not found, or lost, disable led
Serial.println(magnitude);
}