Linux Infrared Control Part 2: Send IR

tl;dr

Would you like to use a remote control to control your computer? How about using your computer to send remote control signals to your TV or Stereo instead of using the remote?

This is the second in a series of posts where I will describe how to use a Raspberry Pi, Raspbian and Linux Infrared Remote Control (Lirc) to receive and send infrared remote control signals. This post will be focused on sending output and depends on Linux Infrared Control Part 1: Receive IR.

Background

Linux Infrared Remote Control (Lirc) has been around for many years and is an example of a ‘traditional’ unix application: it can do many things and is tricky to setup. With a Raspberry Pi and a few cheap electrical parts it is possible to create a custom remote control or have your computer respond to your existing remote.

The presence of the general purpose input output (GPIO) pins on the Raspberry pi allows the control of external circuits from a linux computer. These instructions will use Linux Infrared Remote Control (Lirc), a well established and tested collection of applications, to receive input and send output.

Configure Rasbpian and Lirc

Edit `/boot/config.txt` to add gpio pin 15 (output), this is in addition to the existing configuration for pin 14 (input) from part 1. The complete edit should look like:

sudo vi /boot/config.txt
#dtoverlay=lirc-rpi
# ADDED
dtoverlay=lirc-rpi
dtparam=gpio_in_pin=14
dtparam=gpio_out_pin=15

Reboot to make the changes live:

sudo reboot

Sender Hardware

Note

Shutdown the Raspberry Pi whenever connections are made to the GPIO pins.

In addition to the breadboard and Male to Female jumper wires from part one (you will need 3 more wires for this circuit), you will also need:

IR transmitter LTV-4208 infrared emitter – 940NM
https://www.creatroninc.com/product/ltv-4208-infrared-emitter-940nm/
https://www.sparkfun.com/products/241
https://www.adafruit.com/product/387

220 ohm Resistor (Red, Red, Brown, Gold stripes)
https://www.creatroninc.com/product/14w-assorted-resistor-kit/
https://www.sparkfun.com/products/10969
https://www.adafruit.com/product/2780

BC547 transistor
https://www.creatroninc.com/product/bc547-npn-bjt-50v-01a
https://www.sparkfun.com/products/8928

Data sheet for BC547 transistor
https://www.sparkfun.com/datasheets/Components/BC546.pdf

Note

If you get a different transistor, check the data sheet for the transistor to make sure it is wired correctly, otherwise you can fry your components and let out the magic smoke.

Our control input flows into the base, the output is tied to the collector and the emitter is kept at a fixed voltage.

Setup the circuit on the breadboard. There are three leads to the BC547 transistor, with the flat side facing up, and should be connected as follows:

+-------------------+ 
|                   +---------------------o Emitter, IR LED
|                   |						
|                   |   
|     Flat Side     + --------------------o Base, 220 ohm Resistor
|                   |
|                   | 
|                   +---------------------o Collector, Pin 14 (GND)
+-------------------+

The complete circuit diagram looks like:

     Pin 2 A o----------------------------+
     (+5V)                                |   (longer lead towards pin 2)
                                         _|_
                                         \ /  --> LTE-4208
                                         ---  --> IR LED
                                          |
                                BC547     |
                   ___                +---+  [Emitter]
    Pin 10 B o----|___|---------------|
    (GPIO15)     220 ohm       [Base] +->-+  [Collector]
                                          |
                                          |
    Pin 14 C o----------------------------+                                    
    (GND)
IR LED long leg is anode (+), towards pin 2 A
IR LED short leg is cathode (-), towards BC547 transistor
              Pin 1 Pin2
           +3V3 [ ] [A] +5V
 SDA1 / GPIO  2 [ ] [ ] +5V
 SCL1 / GPIO  3 [ ] [ ] GND
        GPIO  4 [ ] [ ] GPIO 14 / TXD0
            GND [ ] [B] GPIO 15 / RXD0
        GPIO 17 [ ] [ ] GPIO 18
        GPIO 27 [ ] [C] GND
        GPIO 22 [ ] [ ] GPIO 23
           +3V3 [ ] [ ] GPIO 24
 MOSI / GPIO 10 [ ] [ ] GND
 MISO / GPIO  9 [ ] [ ] GPIO 25
 SCLK / GPIO 11 [ ] [ ] GPIO  8 / CE0#
            GND [ ] [ ] GPIO  7 / CE1#
             Pin 25 Pin 26

Original ASCII art from:
http://aron.ws/projects/lirc_rpi/
http://weyprecht.de/2015/11/30/raspberry-pi-ascii-art/

The wiring should look like:

Configuration For Remote Buttons

The example configuration file `example.lircd.conf` created in part 1 will be used to test the sender hardware. Copy the config file to `/etc/lirc/lircd.conf.d/`:

sudo cp ~/example.lircd.conf /etc/lirc/lircd.conf.d/

The configuration should look something like this:

sudo vi /etc/lirc/lircd.conf.d/example.lircd.conf
#
# this config file was automatically generated
# using lirc-0.8.4a(default) on Wed Jul 29 02:33:44 2009
#
# contributed by
#
# brand:                       Example
# model no. of remote control:
# devices being controlled by this remote: 
#

begin remote

  name  example
  bits           16
  flags SPACE_ENC
  eps            30
  aeps          100

  header       4501  4446
  one           569  1663
  zero          569   545
  ptrail        561
  pre_data_bits   16
  pre_data       0xE0E0
  gap          46925
  toggle_bit_mask 0x0

      begin codes
          KEY_POWER                0x40BF                    #  Was: Power
      end codes

end remote

Restart `lircd.service` to load the configuration:

sudo systemctl stop lircd.service
sudo systemctl start lircd.service

Test Transmitter Hardware

This test will use a the example remote configuration by sending the only configured button, the `KEY_POWER` button. Move the circuit near the device that the remote from step 1 controlled and see if the device is powered on and off.

Alternately, most camera phones can observe IR light and can be used to view the IR led flashing.

Type the following:

irsend SEND_ONCE example KEY_POWER

If the result is nothing on the command line and device powers on or off, success!

If the result is:

irsend: command failed: SEND_ONCE example KEY_POWER
irsend: transmission failed

Check the status to see if there are any error messages:

sudo systemctl status lircd.service
● lirc.service - LSB: Starts LIRC daemon.
   Loaded: loaded (/etc/init.d/lirc)
   Active: active (running) since Sun 2017-02-05 02:59:55 UTC; 4min 50s ago
  Process: 924 ExecStop=/etc/init.d/lirc stop (code=exited, status=0/SUCCESS)
  Process: 967 ExecStart=/etc/init.d/lirc start (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/lirc.service
           └─976 /usr/sbin/lircd --driver=default --device=/dev/lirc0 --uinput

Feb 05 03:01:50 raspberrypi lircd-0.9.0-pre1[976]: accepted new client on /var/run/lirc/lircd
Feb 05 03:01:50 raspberrypi lircd-0.9.0-pre1[976]: removed client
Feb 05 03:01:53 raspberrypi lircd-0.9.0-pre1[976]: accepted new client on /var/run/lirc/lircd
Feb 05 03:01:53 raspberrypi lircd-0.9.0-pre1[976]: removed client
Feb 05 03:02:01 raspberrypi lircd-0.9.0-pre1[976]: accepted new client on /var/run/lirc/lircd
Feb 05 03:02:01 raspberrypi lircd-0.9.0-pre1[976]: removed client
Feb 05 03:04:23 raspberrypi lircd-0.9.0-pre1[976]: accepted new client on /var/run/lirc/lircd
Feb 05 03:04:23 raspberrypi lircd-0.9.0-pre1[976]: removed client
Feb 05 03:04:39 raspberrypi lircd-0.9.0-pre1[976]: accepted new client on /var/run/lirc/lircd
Feb 05 03:04:40 raspberrypi lircd-0.9.0-pre1[976]: removed client

Summary

If you want back and capture more or all of the buttons for the remote, you can completely control the device from the Raspberry Pi.

In the next post, we will show finalized hardware design options, where the prototyped breadboard circuits are soldered together for more permanent solutions.

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