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Instructions and code for using a Raspberry Pi as an IR remote control
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README.md

Raspberry Pi IR Remote Control

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Goals:

  1. Using a Raspberry Pi and an IR LED, send IR codes to control audio/video equipment.
  2. Control the Raspberry Pi via voice commands through Google Home.

There are a number of projects like this around the internet. The hardest part for me – and for others, it seems – was the IR driver/lib configuration, so this project documents what worked for me given my combination of hardware and software.

Send IR codes with IR LED

My setup:

  • Raspberry Pi 3 Model B
  • Raspbian Stretch Lite, release date 2017-09-07

Step 0: Set up the hardware

There are many ways to set up your LED driver circuit. I used a basic transistor circuit like the one depicted at http://www.raspberry-pi-geek.com/Archive/2015/10/Raspberry-Pi-IR-remote.

Make note of the GPIO pin connected to the base of the transistor, as that's the pin we need to control to drive the LED. In my case that's pin 23 (you'll see this number in the configuration instructions below).

TIP: Your eyes can't see infrared light, but your phone's camera can. Useful for debugging your circuit.

Step 1: Install LIRC

sudo apt-get install lirc

NOTE: I'm using stretch (Debian 9), so this installs LIRC 0.9.4c. 0.9.4 is quite different from 0.9.0, which is what you'll get if you're running jessie (Debian 8). If you have 0.9.0 Step 3 will be different1.

Step 2: Enable lirc-rpi or gpio-ir kernel module

NOTE: Whether you enable lirc-rpi or gpio-ir depends on the kernel version you're using (check with uname -a). On 4.14 you'll use lirc-rpi and on 4.19 you'll use gpio-ir. Instructions for both cases are given below. See the Appendix if you'd like to read more about this.

We're going to do this via the device tree by editing /boot/config.txt.

sudo vim /boot/config.txt

You'll see these lines in config.txt:

# Uncomment this to enable the lirc-rpi module
#dtoverlay=lirc-rpi

If you're on kernel version 4.14, uncomment the dtoverlay line and change it to look like this:

dtoverlay=lirc-rpi,gpio_in_pin=22,gpio_out_pin=23

If you're on kernel version 4.19, add these lines (you can leave any lines containing lirc-rpi commented out, or you can remove them):

dtoverlay=gpio-ir,gpio_pin=22
dtoverlay=gpio-ir-tx,gpio_pin=23

See how gpio_out_pin / gpio-ir-tx's gpio_pin is set to 23? If you're not using pin 23 change that. You can ignore gpio_in_pin / gpio-ir's gpio_pin. It's used for an IR receiver. TODO(mtraver) document that if I ever actually use the receiver for anything.

Optional: To enable more verbose logging (which you'll find in dmesg), add debug=1 like this (as long as you're on 4.14; adding debug=1 didn't seem to change the behavior of gpio-ir on 4.19):

# Uncomment this to enable the lirc-rpi module
dtoverlay=lirc-rpi,gpio_in_pin=22,gpio_out_pin=23,debug=1

DO NOT edit /etc/modules. Other tutorials may mention putting something similar to what we added to config.txt into /etc/modules. This is unnecessary.

DO NOT add a file in /etc/modprobe.d. Other tutorials may mention putting something similar to what we added to config.txt into a file like /etc/modprobe.d/ir-remote.conf or /etc/modprobe.d/lirc.conf. This is unnecessary.

Step 3: Configure LIRC

The default LIRC configuration does not enable transmitting. From the LIRC configuration guide:

From 0.9.4+ LIRC is distributed with a default configuration based on the devinput driver. This should work out of the box with the following limitations:

  • There must be exactly one capture device supported by the kernel
  • The remote(s) used must be supported by the kernel.
  • There is no need to do IR blasting (i. e., to send IR data).

Let's fix that.

sudo vim /etc/lirc/lirc_options.conf

Change driver to default and device to /dev/lirc0. Here's the diff between the default config and my config:

$ diff -u3 /etc/lirc/lirc_options.conf.dist /etc/lirc/lirc_options.conf
--- /etc/lirc/lirc_options.conf.dist  2017-04-05 20:23:20.000000000 -0700
+++ /etc/lirc/lirc_options.conf 2017-10-14 14:58:18.584886645 -0700
@@ -8,8 +8,8 @@

 [lircd]
 nodaemon        = False
-driver          = devinput
-device          = auto
+driver          = default
+device          = /dev/lirc0
 output          = /var/run/lirc/lircd
 pidfile         = /var/run/lirc/lircd.pid
 plugindir       = /usr/lib/arm-linux-gnueabihf/lirc/plugins

DO NOT edit or add hardware.conf. Other tutorials may mention making changes to /etc/lirc/hardware.conf. LIRC 0.9.4 does not use hardware.conf2.

Step 4: Add remote control config files

We need to tell LIRC which codes to transmit to talk to the equipment we wish to control. LIRC maintains a repo of config files for many remote controls: https://sourceforge.net/projects/lirc-remotes/

Find the one for your remote control and place it in /etc/lirc/lircd.conf.d. As long as it has a .conf extension it'll be picked up.

If there isn't an existing config for your remote, you're in for an adventure... I happen to be controlling a Cambridge Audio CXA60 amp with my Raspberry Pi and there was no config file for it so I made one. It's checked into this repo.

Here's what my config directory looks like:

$ ll /etc/lirc/lircd.conf.d
total 52
drwxr-xr-x 2 root root  4096 Oct 14 11:49 .
drwxr-xr-x 3 root root  4096 Oct 14 14:58 ..
-rw-r--r-- 1 root root  2679 Oct 14 11:49 cxa_cxc_cxn.lircd.conf
-rw-r--r-- 1 root root 33704 Apr  5  2017 devinput.lircd.conf
-rw-r--r-- 1 root root   615 Apr  5  2017 README.conf.d

Step 5: Reboot

sudo reboot

Below are some sanity checks for modules and services and stuff after you reboot.

On kernel version 4.14 using lirc-rpi:

$ dmesg | grep lirc
[    3.276240] lirc_dev: IR Remote Control driver registered, major 243
[    3.285866] lirc_rpi: module is from the staging directory, the quality is unknown, you have been warned.
[    4.340562] lirc_rpi: auto-detected active low receiver on GPIO pin 22
[    4.340882] lirc_rpi lirc_rpi: lirc_dev: driver lirc_rpi registered at minor = 0
[    4.340888] lirc_rpi: driver registered!
[   11.929858] input: lircd-uinput as /devices/virtual/input/input0

$ lsmod | grep lirc
lirc_rpi                9032  3
lirc_dev               10583  1 lirc_rpi
rc_core                24377  1 lirc_dev

$ ll /dev/lirc0
crw-rw---- 1 root video 243, 0 Oct 14 17:08 /dev/lirc0

$ ps aux | grep lirc
root       343  0.0  0.1   4208  1084 ?        Ss   17:08   0:00 /usr/bin/irexec /etc/lirc/irexec.lircrc
root       381  0.0  0.1   4280  1140 ?        Ss   17:08   0:00 /usr/sbin/lircmd --nodaemon
root       516  0.4  0.4   7316  3980 ?        Ss   17:09   0:00 /usr/sbin/lircd --nodaemon
root       517  0.0  0.1   4284  1164 ?        Ss   17:09   0:00 /usr/sbin/lircd-uinput
pi         574  0.0  0.0   4372   552 pts/0    S+   17:09   0:00 grep --color=auto lirc

On kernel version 4.19 using gpio-ir:

$ dmesg | grep "lirc\|gpio-ir"
[    3.459164] rc rc0: GPIO IR Bit Banging Transmitter as /devices/platform/gpio-ir-transmitter@17/rc/rc0
[    3.459396] rc rc0: lirc_dev: driver gpio-ir-tx registered at minor = 0, no receiver, raw IR transmitter
[    3.522934] rc rc1: lirc_dev: driver gpio_ir_recv registered at minor = 1, raw IR receiver, no transmitter
[   14.468862] input: lircd-uinput as /devices/virtual/input/input1

$ lsmod | grep gpio_ir
gpio_ir_tx             16384  0
gpio_ir_recv           16384  0

$ ll /dev/lirc0
crw-rw---- 1 root video 252, 0 May 26 17:10 /dev/lirc0

$ ps aux | grep lirc
root       364  0.0  0.1   4268  1088 ?        Ss   17:11   0:00 /usr/sbin/lircmd --nodaemon
root       369  0.0  0.1   4196  1072 ?        Ss   17:11   0:00 /usr/bin/irexec /etc/lirc/irexec.lircrc
root       555  0.1  0.3   7296  3428 ?        Ss   17:11   0:00 /usr/sbin/lircd --nodaemon
root       556  0.0  0.1   4272  1172 ?        Ss   17:11   0:00 /usr/sbin/lircd-uinput
pi         893  0.0  0.0   4368   544 pts/0    S+   17:13   0:00 grep --color=auto lirc

Step 6: Test

irsend SEND_ONCE cambridge_cxa KEY_POWER_ON

Replace cambridge_cxa with the contents of the name field from your remote control config file, and KEY_POWER_ON with some code from the codes section.

At the very least this should execute without errors. If you enabled debugging in the device tree (see Step 2) you can get some insight into what happened by executing dmesg | grep lirc. Use your phone camera to watch the LED light up.

Control via voice commands

NOTE: I built this before Google launched smart home Actions. At the time there were only conversation-based Actions, which don't fit this use case. A smart home Action is a better solution than what I describe below.

I wanted to issue IR codes by voice, so I did the following:

  • Wrote a web server that runs on the Raspberry Pi. It exposes one endpoint for each IR code (e.g. /volup to turn up the volume), and POSTing to the endpoint will call the irsend command line utility to issue the code. See below for more info on deploying the web server.
  • Exposed the web server to the internet using ngrok. The docs are great so I leave this step as an exercise for the reader.
  • Use IFTTT webhooks to set up rules such that when I say something like "Ok Google, it's music time" to my Google Home, IFTTT fires off a request to the ngrok endpoint that points to the Raspberry Pi, instructing it to issue the IR code that turns on the sound system.

Build the server

The server is written in Go. The main package is cmd/server/main.go. This repo includes a Makefile that builds it for your host architecture as well as ARMv6 (e.g. Raspberry Pi Zero W) and ARMv7 (e.g. Raspberry Pi 3 B3). It will produce binaries in the out directory.

Security!

NOTE: Again, I built this before Google launched smart home Actions. Using smart home Actions is the most secure and elegant way to do this.

Security is good. The knobs available to us aren't great [insert rant here about the current state of IoT security] but we'll do what we can to lock it down.

  • ngrok (config options here)
    • ngrok can do HTTP basic auth. Use it. Of course the password is in the clear in your IFTTT rule but it's better than nothing.
    • Set bind_tls: true in your config to expose only an HTTPS endpoint.
    • Set inspect: false in your config to disable request inspection.
  • Web server
    • The web server has a basic token check built in. In the JSON payload POSTed by IFTTT, include a token key. If its value doesn't match the token defined on the Raspberry Pi it will stop and return a 403.

That's all that's possible as far as I can tell. IFTTT webhooks don't allow for any kind of secure token authentication.

Running the server

The web server is a statically linked binary. We'll use systemd to start it up and keep it running.

  1. Place the server binary built for your required architecture in /home/pi.

  2. This repo contains a systemd service definition at config/systemd/irremote.service. Copy it into the /lib/systemd/system directory on the Raspberry Pi.

  3. To enable and start the service, run

    sudo systemctl enable irremote.service
    sudo systemctl start irremote.service
    

Running ngrok

There is also a systemd service definition for ngrok in config/systemd. Follow the same steps as above to install and enable it.

The service definition assumes that the ngrok binary is at /usr/local/bin/ngrok. Change the service definition (both ConditionPathExists and ExecStart) if you'd like ngrok to live somewhere else.

Appendix

Warning: Cannot access device: /dev/lirc0 on kernel 4.19

NOTE: This is just a record of my debugging process from when I upgraded to 4.19 and LIRC stopped working. All actions required for 4.19 are already included above.

On 2019-05-25 I upgraded my pi and it ended up on Linux 4.19.42-v7+ #1219 SMP Tue May 14 21:20:58 BST 2019 armv7l.

LIRC no longer worked! Checking the logs I found this:

$ grep lirc /var/log/syslog
...
May 25 15:27:01 irremote-pi lircd-0.9.4c[793]: Warning: Cannot access device: /dev/lirc0
...

Thankfully I had checked the kernel version before upgrading. It was Linux 4.14.52-v7+ #1123 SMP Wed Jun 27 17:35:49 BST 2018 armv7l.

As a first step I tried rolling back to that version using rpi-update. I found the commit in github.com/Hexxeh/rpi-firmware that upgraded to 4.14.52 and passed that commit hash to rpi-update to roll back:

sudo rpi-update 963a31330613a38e160dc98b708c662dd32631d5

After rebooting, the kernel was indeed rolled back and LIRC worked again.

Alright, now time to find the breaking commit!

First I jumped straight to the last 4.14: kernel: Bump to 4.14.98 (a08ece3d48c3c40bf1b501772af9933249c11c5b, committed 2019-02-12). This put me on Linux 4.14.98-v7+ #1200 SMP Tue Feb 12 20:27:48 GMT 2019 armv7l GNU/Linux and LIRC worked. Woohoo!

The next update goes all the way to 4.19.23. I upgraded to 1c60d16af8cc43214495f18549228dde83e99265 and ended up on Linux 4.19.23-v7+ #1202 SMP Mon Feb 18 15:55:19 GMT 2019 armv7l GNU/Linux. LIRC did not work; the warning about /dev/lirc0 was back.

gpio-ir on 4.19

I was all set to call it a day and leave my pi on 4.14, but then I found this: https://www.raspberrypi.org/forums/viewtopic.php?t=235256.

The TL;DR is that 4.19 does not include lirc_dev so one must use gpio-ir. It's simply a change to the dtoverlay in /boot/config.txt and it works as before. For sending IR codes that's all that's required.

For recording there's more to do but I'll leave it as an exercise for the reader to follow the instructions in the aforementioned raspberrypi.org forum post. For me sending IR codes worked both with and without the patched LIRC; I don't record IR codes in this project so I stuck with the stock, unpatched LIRC.

Footnotes

[1] Other projects around the internet tend to be built using 0.9.0, leading to some frustration while configuring, even though configuring 0.9.4 is a nicer experience. I hope this project can help others in the same boat!

[2] Alec Leamas, LIRC maintainer, states here that "0.9.4 does not use hardware.conf."

[3] "How can this be!? The Raspberry Pi 3 B uses the BCM2837, a 64-bit ARMv8 SoC!" you exclaim. "That is correct," I reply, "but Raspbian is 32-bit only so the chip runs in 32-bit mode. It therefore cannot execute ARMv8 binaries."

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