I have central air-conditioning in my apartment, and it’s controlled by a remote, employing IR signals to send commands to the A/C control unit.

As any decent geek would, I’d like to be able to control my A/C using other means (e.g., a smartphone).

In a previous post, I covered thoroughly the details of using an Arduino to send IR signals to the A/C instead of the remote – but if I’m far away, how can I know if the command was received and executed by the A/C successfully?

Well, given that the A/C control unit beeps when it receives and executes a command, I thought I might take advantage of that – and virtually “listen for beeps” after sending A/C commands to verify successful execution!

The short version: A laptop running Ubuntu Linux is located in hearing distance from the A/C. Just before sending a signal from the Arduino, the laptop starts listening on the microphone (using the PyAlsaAudio library). It calculates Fourier transforms over the recorded audio sample, and measures the power around the beep central frequency (4100Hz), looking for power-peaks that correlate to a beep.

For the longer, detailed, version – do read on!

Also, check out the code that implements this on GitHub.

(nitpicks-alert: while I am aware that “power” and “energy” are different things, I am using the terms loosely and interchangeably throughout the post. please forgive me.)