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24 Oct 2013

Controlling Linux with a Remote Control

I listen to Pandora all the time at home, and I often want to control it without using the keyboard or mouse. So, a few years ago I bought a USB infrared receiver for $14. Of course, since I use Linux, the hidden cost was hours and hours of time figuring out how to set it up. I never wrote anything down back then, but since I had to relearn it all last weekend to make a few changes, now is a good time to document it.

This article is written for Ubuntu 13.04, so some things might be different for other operating systems. It also assumes you want to use an infrared remote; you could also use a bluetooth remote or some cellphone app, but I don’t know anything about those.

Summary

  1. Buy a “USB Media Center IR receiver” (plus a remote if you don’t have one.)
  2. If you have an MCE remote, disable the keyboard emulation in X.
  3. Run irrecord and follow the instructions to generate a remote definition file.
  4. Set up /etc/lirc/ to use the new remote definition file.
  5. Restart LIRC and test with irw.
  6. Either (a) configure /etc/lirc/lircrc, or (b) configure ~/.lircrc and set up irexec to start at session startup.

Hardware

Buying the IR reciever

First, you need an IR receiver. The safest bet is to buy a “USB Media Center IR receiver,” aka an “MCE receiver.” I got the following one for $14, including shipping:

My IR Receiver

Note that IrDA ports found in older laptops won’t work for this purpose.

Choosing a remote

Second, you need an IR remote. You could use an existing remote if you know it won’t cause a conflict—say, you no longer use the TV it goes with, or the TV and the computer are in different rooms. Or, you could buy a new remote just for the computer. But the most likely option is that you have an existing remote that has a “universal” feature. In that case, all you need to do is configure the universal feature to use some non-existent device. For example, if your TV remote can control a DVD player, and you don’t have DVD player, configure the remote to control any DVD player listed in the remote’s manual. It doesn’t matter which one—LIRC can (probably) handle any.

Configuring X (if you have an MCE remote)

If you have a Windows Media Center (MCE) remote (as opposed to, say, a TV or DVD remote), or if you have set up your universal remote to send MCE codes, then X will automatically interpret some buttons as keyboard keys. If this is all you want, then you’re done!

Unfortunately, most people will want more than this, in which case the built-in keyboard emulation will just get in the way. So, you need to disable it. If you forget to do so, X will send the keyboard keys in addition to whatever you configure LIRC to do, and it will appear that you’re getting double key presses.

First, you need to determine the product name for your IR receiver. To do this, make sure your IR receiver is plugged in and look through /proc/bus/input/devices to find the name of your device. Here’s the output on my computer:

$ grep '^N:' /proc/bus/input/devices
N: Name="Power Button"
N: Name="Power Button"
N: Name="Microsoft Comfort Curve Keyboard 2000"
N: Name="Microsoft Comfort Curve Keyboard 2000"
N: Name="Logitech Unifying Device. Wireless PID:101b"
N: Name="Media Center Ed. eHome Infrared Remote Transceiver (1934:5168)"
N: Name="MCE IR Keyboard/Mouse (mceusb)"

Find the one that sounds like “Media Center … Remote Transceiver.” Then, create the file /usr/share/X11/xorg.conf.d/10-mce-keyboard-disable.conf with the following contents, replacing the value of MatchProduct with whatever name you found above. (In the old days, we would have added this to /etc/X11/xorg.conf, but now evidently we create these xorg.conf.d files.)

# Disable the MCE remote from acting like a keyboard.  (We use lirc instead.)
Section "InputClass"
    Identifier   "MCE USB Keyboard mimic blacklist"
    Driver       "mceusb"
    MatchProduct "Media Center Ed. eHome Infrared Remote Transceiver (1934:5168)"
    Option       "Ignore" "on"
EndSection

Setting up LIRC

LIRC is the program that interprets IR signals. To install it, run:

$ sudo apt-get install lirc lirc-x

LIRC works in two steps: the lircd program that translates remote signals to generic “buttons,” and then client programs—notably irexec—translate buttons to actions.

So, three are things you need to do: 1. Create a remote definition file, unless one already exists. 2. Tell lircd to use the proper definition file. 3. Configure irexec.

If you’re using a non-MCE receiver, you may also have to spend some time configuring LIRC to use your receiver, but thankfully MCE receivers work out of the box.

Training LIRC

Unless there already happens to be a file in /usr/share/lirc/remotes/ that works with your remote, you are going to have to train LIRC to understand all the buttons on your remote. (If there is one already, skip to the next section.)

Make sure that lircd is not already running, and then use the irrecord program to create what I am calling a remote definition file. Obviously, replace WHATEVER_YOU_WANT with, well, whatever you want to call your remote.

$ sudo service lirc stop
$ sudo irrecord --device=/dev/lirc0 /etc/lirc/lircd.WHATEVER_YOU_WANT.conf

Follow the on-screen instructions, and when it when it asks you to “Please enter the name for the next button,” open up a new terminal window and run

$ irrecord --list | less

to find an appropriate name for the button you want to learn. I recommend only programming four or five buttons for now, and then moving on to the next section. I ended up having to delete my config and start over several times, so it’s not worth investing too much time now.

Once you have tested your config with irw in the next section and are confident it is working, you can run the same irrecord command again to add more buttons. As long as you point it to the same config file, you won’t have to go through the training step again.

Configuring lircd and testing with irw

Now we have to tell lircd to use the new definition file. We do this in two places:

First, in /etc/lirc/lircd.conf, include your remote definition file. This will be the only command in the file.

include "/etc/lirc/lircd.WHATEVER_YOU_WANT.conf"

Second, in /etc/lirc/hardware.conf, set REMOTE_LIRCD_CONF to the remote definition file. (I don’t think this does anything, but it doesn’t hurt.)

REMOTE_LIRCD_CONF="/etc/lirc/lircd.WHATEVER_YOU_WANT.conf"

Now, start lircd and test it with irw. Press a few of the buttons you have trained in the previous section and make sure they show up in irw. For example:

$ sudo service lirc start
$ irw
000000037ff07bed 00 KEY_CHANNELUP mce_custom
000000037ff07bec 00 KEY_CHANNELDOWN mce_custom

If you get one line per press (plus repeated lines if you hold down the button), it works! Feel free to go back to the previous section and configure more buttons.

Configuring irexec via lircrc

The last step is to configure irexec, which is the thing that actually does something useful when you press a button. You have two choices here:

A. Create /etc/lirc/lircrc and have irexec run as root. This has the advantage of starting and stopping irexec automatically whenever you start/stop lircd.

B. Create ~/.lircrc and have irexec runs as your user. If you do this, you need to configure your desktop environment to automatically start irexec at the beginning of each session. You will also need to restart irexec every time lircd restarts.

Create one of the two files listed above. The documentation is pretty good, but here is my config file for reference:

begin
    button = KEY_VOLUMEUP
    prog = irexec
    config = /usr/bin/pactl -- set-sink-volume 0 +2%  # vol+
    repeat = 1
end

begin
    button = KEY_VOLUMEDOWN
    prog = irexec
    config = /usr/bin/pactl -- set-sink-volume 0 -2%  # vol-
    repeat = 1
end

begin
    button = KEY_PLAY
    prog = irexec
    config = /home/mark/local/bin/pithos-control play
end

begin
    button = KEY_PAUSE
    prog = irexec
    config = /home/mark/local/bin/pithos-control pause
end

begin
    button = KEY_STOP
    prog = irexec
    config = /home/mark/local/bin/pithos-control pause
end

begin
    button = KEY_FASTFORWARD
    prog = irexec
    config = /home/mark/local/bin/pithos-control skip
end

begin
    button = KEY_SLEEP
    prog = irexec
    config = /usr/bin/xset dpms force off  # blank monitor
end

The file is pretty self-explanatory. Each button is something I defined in my remote definition file. The pactl program works with PulseAudio, which is the default audio system on Ubuntu. The pithos-control program is described in the next section. And the xset line turns off my monitor, which I often want to do if I’m listening to music.

When you’re done, remember to either sudo service lirc restart if you are using /etc/lirc/lircrc or irexec -d if you are using ~/.lircrc. Otherwise, nothing will happen when you press a button.

Aside: My Pithos control script

I always use Pithos to play Pandora. Not only is it way lighter than the bloated web-based one, it is also controllable via D-Bus. Sending D-Bus commands manually is a bit ugly, so I made a little wrapped called pithos-control. The main advantage is that it adds discrete play and pause commands, which Pithos lacks.

Appendix: (Not) Using ir-keytable

When I was trying to set up my remote, I found plenty of suggestions on the Internet to use something called ir-keytable instead of, or in conjunction with, LIRC. I did use it for a while, but in the end I found that using straight LIRC was way better.

The main problem was that ir-keytable (by itself) creates virtual keyboard presses for each button press. If you want to control, say, the volume, you would configure the “Vol-“ button to send the XF86AudioLowerVolume key. This sounds fine, but the issue is that, at least in XFCE, the media keys cause the foreground window to lose focus each time they are pressed. So, if I were typing something and my wife hit the volume button, a few of my keystrokes would be lost, which was really irritating. It was even worse when I was playing a game.

I put up with the above for a long time, but the final straw was when I tried to get the xset dpms force off command to work. It was impossible with ir-keytable because the virtual keyboard button that I had to map the command to would immediately wake the monitor up. This ended up being a blessing in disguise, since it made me realize that I could ditch ir-keytable for LIRC.

I also found that ir-keytable was less reliable than LIRC. I have no hard evidence of this and I am not inclined to set it up again, but that was my impression.


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