Detect a tone

Using Arduino Audio
1

I'm trying to make a simple arduino based tone detector.....

the block diagram is as under

The input is through the speaker. when it detects a specific tone (a simple sinewave tone which sounds like Tuuuuuuuuuuuuuuuuu), it switches on the red led...

for testing purpose im generating this tone input sound via a arduino+voice codec+speaker
left_out is the left channel of audio output.
temp2 is a sine wave signal
counter ensures that the tone is produced for roughly 3 seconds duration

 //sine wave output

  if(counter<4000)
  {
  left_out = temp2; // put sinusoid out on left channel
  right_out =0; // put inverted version out on right chanel
  counter++;
}

at the receiver end.... i need to trigger an event (like led switch on) when this tone is heard.
I know in theory what to do....
detect the frequency of inputsignal. when frequency matches the frequency i want to detect, trigger an alarm/event.

I dont know how to write this in code !!!! :blush:

2

First question is what frequency do you need to detect?

Assuming its within range I think you need to google search "Arduino Fast Fourier Transform" if the signal is not clean (with other noises). If it is clean then there are several hardware/software options like using comparator, schmitt trigger to convert to digital or just reading analogue and finding peaks.

3

Another possibility: add a discrete bandpass (LC) to an Analog input and switch the LED above given threshold

4

I would use an LM567C tone decoder chip:-