RaspAC

An internet-enabled air conditioner remote running on the Raspberry Pi.

How does it work?

On the software side, an Apache web server running on the Pi serves a Flask app. This app makes calls to LIRC, the Linux Infrared Remote Control library, to replay previously recorded IR codes. The Pi is connected to a couple high- brightness IR diodes which transmit the codes to the air conditioner.

You can play with a mockup of the app here. It will accept the username Guest and password Guest.

How to put it together?

Hardware

I used the setup described by Alex Bain, but I added a temperature and humidity sensor with the data pin connected to pin 4. See this tutorial for a circuit schematic.

Software

The software part of this project consists of three pieces: the website that lets you communicate with the Raspberry Pi, the temperature sensor code, and the LIRC, which controls the IR diodes connected to the Pi. The installation instructions below assume you're starting from a clean Raspbian installation.

Installing and configuring LIRC

Follow the instructions here for installing and configuring LIRC. Note, though, that you will probably be unable to record the IR codes for your AC using the irrecord command line tool provided with LIRC. The structure of IR codes used by ACs is different from that used by TVs, for which irrecord was designed to work with. Rather than telling the AC what button was pressed (e.g., "Increase target temperature by 2 degrees", or "Switch unit on"), the code contains a complete description of the new state (e.g., "The fan strength is 3, the temperature target is 76, the operating mode is cooling, ..."). This structure is not compatible with irrecord.

Fortunately, LIRC provides another command line tool, mode2, which will directly record any sequence of IR pulses and spaces. You can use it to save the pulse trains produced by pressing buttons on the remote, and manually stitch together a LIRC configuration file, lirc.conf. Note that it's in general not enough to record the effect of pressing each button, since the signal encodes the full state of the AC. You will probably want to record the code associated with each temperature, or even every temperature/mode combination if your AC supports both heating and cooling modes. The lirc.conf file I created for my LG AC is provided as an example.

For more information on recording IR codes for ACs using LIRC, see here.

Setting up the temperature sensor

I used C code for the DHT provided by Adafruit. After compiling Adafruit_DHT.c using the Makefile, change its ownership so that it can be ran without sudo:

sudo chown root:root Adafruit_DHT
sudo chmod +s Adafruit_DHT

Copy the compiled executable to the folder containing tsensor.py. Edit the parameters in tconfig.py, then run tsensor.py in the background. The temperature and humidity sensor will be periodically queried, and the results will be recorded in a database.

You will probably want to restart tsensor.py every time the Pi is turned on. I found it most convenient to have a cron job spin it up on every reboot.

Setting up the web app

Step by step instructions are forthcoming!

For general information on deploying Flask apps on an Apache webserver, see the tutorial.

Helpful references

The idea of using the Raspberry Pi as an internet-enabled IR remote is not new, though most people use them to control TVs rather than ACs. I found Alex Bain's description of his Open Source Universal Remote particularly helpful. Recording the IR codes is discussed by Peter Li in his AC control project.

Licensing

The parts of this software that I have written are covered by the MIT license. This excludes the following files:

• leaves.css
• app.yaml, appengine_config.py, requirements.txt and vendor.py, which I borrowed from the Google App Engine Flask template. These are covered by the Apache license.
• Adafruit_DHT.c (BSD license).