Controlling WeDo 2.0 motor from Linux

LEGO Education released the WeDO 2.0 some months ago and I bought a kit. I returned to LEGO thanks to WeDO 1.0 and since I’m already using BLE with the SBrick, using the WeDo 2.0 seemed natural.

But LEGO Education made the Android app very restrictive and only a few Android devices are allowed to install it – I have two different BLE enabled Android phones and none complies with LEGO Education definitions. Although LEGO Education promised a SDK for the new WeDO 2.0, there’s still nothing available and since I don’t own a Windows computer or an Apple device, my WeDO 2.0 kit was rusting on the shelf, waiting for better days.

Then yesterday I found a Microsoft guy’ with some bluetooth code samples with references for the WeDO 2.0 – how ironic!

So it took me only a few hours to achieve what I think is a world premiere: a linux system controlling a LEGO WeDO 2.0 motor. And what better linux system than a LEGO Mindstorms EV3?

Next post will I’ll give more details.

How to remote control a LEGO DUPLO Train

Some weeks ago, a fellow from my LEGO User Group reached me for some Infrared electronics insights. He was trying to remote control his LEGO DUPLO Train with an infrared remote.

I never played with IR before but got curious. I love the idea of remote controlling something. But not manually, it has to be programmatically so one can use it for automation or robotic purposes. So after some weeks I found the LIRC definitions for LEGO Power Functions IR and used it to remote control LEGO from my laptop via the audio output.

Then it was the anniversary of one the kids and he asked granny for a major upgrade of their DUPLO train track:

LEGO® DUPLO® Deluxe Train Set

So I thought it would be great if they could control the train back and forth… and ordered a used DUPLO Train Locomotive Base (5135c01) from BrickLink.

Opening it was difficult but I managed to do it without breaking anything, thanks to these two previous brave pioneers:

(their locomotives are from a different set but the idea is the same)

The locomotive has a pair of free wheels at front and another pair drived by a motor and some gears at back where there is also a piezo buzzer, a printed circuit board and a pair of wires comming from the batteries holder. There are also two rubber buttons that press some small metal rings against the surface of the PCB to act as switches – the smaller one, hidden in a small hole, makes the sound of fuel being pumped into the tank when the fuel hose is inserted, the bigger one controls starts/stops the train but also indirectly controls the sound of the locomotive (when in movement) and the sound of the breaks (when stopping).

The PCB has 6 wires soldered at points labeled J1 to J6:

  • J1 and J3 – buzzer
  • J2 and J4 – batteries
  • J5 and J6 – motor

As the batteries holder is for just 3 AA batteries, the board works with 4.5V. Not much but enough for a LEGO Power Functions IR receiver or a Vengit SBrick.

We could just dessolder the wires at J2/J4 (power) and J5/J6 (motor), get a LEGO Power Functions cable, cut it in half and solder the tips from one half to J2/J4 and the tips from the other half to J5/J6. But that will make the buzzer useless.

As the buzzer is controlled by an IC on the PCB, I choose to keep the power lines going to the PCB (J2/J4) and deriving from there to the Power Functions cable (but still dessoldering J5/J6). This way, when the batteries are inserted, both the remote and the PCB are ON so the two buttons maintain their functionality. This gives us as an unexpected possibility: we can also use the PF cable to power the train instead of using 3 AA batteries – with special caution because LEGO PF batteries or LEGO 9V batteries give more than 4.5V so some reduction has to be done, like adding some 1N4001 diodes or a voltage regulator… but a USB 5.0V battery pack will be perfect.

Since I didn’t want to drill or cut the plastic, I managed to pass the PF cables through the start/stop button hole (before soldering it) but later found out that it was to tight for the rubber button – so no more «tchoo-tchoo!» nor breaks (some may consider this a feature, not a bug).

Some more photos are available at this Brickshelf folder.

The final result is a LEGO DUPLO train that:

  • can be remotely controlled by Infrared or Bluetooth, manually or programatically
  • can move forward AND backward
  • can use LEGO batteries (PF or 9V) with a special cable or a USB battery pack

Raspberry Pi + SBrick

Finally got time to return to the Pi.

Yes, the Raspberry Pi can talk to the SBrick. It’s only necessary to install Bluez 5.

But as the standard Raspbian is based on Debian Wheezy, if you install bluez from the repositories

sudo apt-get install bluez

you will get Bluez 4 (today, 1 December 2014, it’s version 4.99). I can make a Low Energy Scan (lescan) and find the SBrick but my gatttool commands fail with

Host is down (112)

So we need Bluez 5. There are at least two ways:

  • get Bluez 5 source code and compile as in RPi Bluetooth LE
  • update Raspbian to Debian Jessiea as it already includes Bluez 5

I’m lazy, I don’t like to compile anything. I’m also afraid that any update might brake compatibility and forces me to recompile again. And my laptop (Unbuntu) and my EV3 (ev3dev) are already running a version of Jessie so let’s update.

Warning: Raspbian update from Wheezy to Jessie takes almost a day – so compiling Bluez might appeal to those in a hurry.

We need enough free space on the SD card. I used a 4 GB card and my first try failed miserable after a long night. So the second time I removed some things to assure an happy end.

First I transfered the most recent image available (2014-09-09) to the 4 GB card and edited networking to get wi-fi (I only use SSH with the Raspberry, like I do with the LEGO Mindstorms EV3).

After first boot with the fresh card run rasp-config to expand the file system with all free space available.

sudo rasp-config

after next boot remove some heavy things and clean:

sudo apt-get remove x11-common midori lxde
rm /opt/vc/src/hello_pi/hello_video/test.h264
rm -rf python_games
sudo apt-get clean
df -h

there are now 2.0 GB available on the 4.0 GB card. That’s enough, let’s change the source of our packages:

sudo nano /etc/apt/sources.list

replace ‘wheezy’ with ‘jessie’ and save.

sudo apt-get update
sudo apt-get upgrade
sudo reboot
By now we have near 1.8G available.

sudo dist-upgrade
sudo reboot

Now we are already using a Debian Jessie version of Raspbian.

sudo apt-get install bluez

As of 1 December 2014, Debian Jessie for Raspberry Pi uses bluez 5.23-1. Now remove all garbage and check space again:

apt-get autoremove

df -h

807 MB avaliable, not bad.

My bluetooth BT 4.0 USB dongle is recognized (it already was) but is not active by default so before using it

sudo hciconfig hci0 up

now gatttool commands work with the SBrick, and so all my scripts from Ubuntu and EV3.







LEGO WeDO – Temperature Sensor

As the WeDo USB Hub uses some kind of ADC (Analog to Digital Converter) to read the tilt sensor values, we can use this ADC for our own analog sensors.

So let’s start with  a Temperature Sensor.

The most simple/easy temperature sensor is just a NTC thermistor: every regular resistor has some minor variations when the operating temperature changes and a thermistor is just a resistor designed to have a significant and well-known variation. A NTC (negative temperature coefficient) thermistor has a decrease in it’s value proportional to the temperature increase.

We can buy a cheap (less than €1) 10 kΩ NTC thermistor and use it as a temperature sensor knowing that at 25°C (average ambient temperature) it has a 10 kΩ value – we also need to know its temperature coefficient from the manufacturer datasheet or from our own calibration tests. Just solder two wires and provide some insulation and we’re done:

Or we can just use an old LEGO Mindstorms (RCX) Temperature Sensor 🙂

To use this sensor we can make our own cable with just one 3.9 kΩ resistor between C1 and 0 to makes the WeDo think we have a tilt sensor connected to it. Then we connect our sensor between C2 and 0 or between C2 and 9V.

Our we can piggyback a real tilt sensor with a modded cable and just connect our sensor to it:

In this scenario we must assure that the tilt sensor always stays flat so it doesn’t get in our way when we’re reading the temperature sensor and since the tilt sensor already has a 10 kΩ resistor between C2 and 0 I prefer to connect the sensor between C2 an 9V.

Early first readings, room temperature compared to the readings from a SensorTag :

RAW Temp (°C)
159 20
158 20
165 36.5
157 19.8
157 19.5
157 19.6
156 18.8
157 19
156 18.9

LEGO WeDO with EV3 – kernel support

Last night the ev3dev people released a Linux driver for WeDo. For now it is just for ev3dev so it works only in Mindstorms EV3 but hopefully it will get to other distributions and it will allow anyone with a Raspberry Pi or an Ubuntu laptop (like me) to use WeDo without python WeDo or WeDoMore libraries – just a shell is enough!

We need a ev3dev with kernel 3.16.1-7 or above:

root@ev3dev:~# uname -a
Linux ev3dev 3.16.1-7-ev3dev #2 PREEMPT Tue Nov 25 11:24:38 CST 2014 armv5tejl GNU/Linux

If your kernel is older, just

apt-get update
apt-get dist-upgrade

After reboot, creat a udev rule for WeDo – it will prevent the kernel to bind it to the usbhid driver, binding it instead to legowedo driver:

nano /etc/udev/rules.d/80-wedo.rules

SUBSYSTEM=="usb", ATTRS{idVendor}=="0694", ATTRS{idProduct}=="0003" ACTION=="add", \
    RUN+="/bin/sh -c 'echo $kernel > /sys/bus/usb/drivers/usbhid/unbind;           \
                      echo $kernel > /sys/bus/usb/drivers/legowedo/bind'"

Now just reboot or refresh the udev rules by

udevadm control --reload-rules

If you plug the LEGO WeDo USB Hub and check dmesg it wil show

[ 1222.200538] usb 1-1.2: new low-speed USB device number 5 using ohci
[ 1222.370828] hid-generic 0003:0694:0003.0002: hidraw0: USB HID v1.10 Device [LEGO USB Hub V1.00] on usb-ohci.0-1.2/input0
[ 1222.691293] wedo hub0: Bound 'hub0' to 'usb1-1.2:1.0'

We now have a new device ‘hub0’:

root@ev3dev:~# ls /sys/bus/wedo/devices/ -la
lrwxrwxrwx 1 root root 0 Nov 25 06:21 hub0 -> ../../../devices/platform/ohci.0/usb1/1-1/1-1.2/1-1.2:1.0/hub0

with the following properties:

root@ev3dev:~# ls /sys/bus/wedo/devices/hub0
clear_error  error  high_power  port0  port1  power  reset  shut_down  subsystem  uevent  voltage

So we may check if the USB port gives enough current for a motor:

root@ev3dev:~# cat /sys/bus/wedo/devices/hub0/high_power 

or check for the USB power quality (in mV):

root@ev3dev:~# cat /sys/bus/wedo/devices/hub0/voltage 

Now if we plug a LEGO Power Functions motor to one of the ports it will immediately be recognized by the kernel:

[ 1736.348469] dc-motor motor0: Bound to device 'port0'

and the motor is seen by the kernel as dc-motor like if we were using an NXT/EV3 to Power Functions or RCX adapter:

root@ev3dev:~# ls /sys/class/dc-motor -la
lrwxrwxrwx  1 root root 0 Nov 25 06:30 motor0 -> ../../devices/platform/ohci.0/usb1/1-1/1-1.2/1-1.2:1.0/hub0/port0/dc-motor/motor0
root@ev3dev:~# ls /sys/class/dc-motor/motor0
command   device      duty_cycle_sp  polarity   power         ramp_up_ms  uevent
commands  duty_cycle  name           port_name  ramp_down_ms  subsystem

So we can make it spin with 35% duty cycle:

echo 35 > /sys/class/dc-motor/motor0/duty_cycle_sp

And it’s the same for WeDo sensors – as I just have a tilt sensor, lets plug it:

root@ev3dev:~# ls /sys/class/msensor/ -la
lrwxrwxrwx  1 root root 0 Nov 25 06:40 sensor0 -> ../../devices/platform/ohci.0/usb1/1-1/1-1.2/1-1.2:1.0/hub0/port1/msensor/sensor0
root@ev3dev:~# ls /sys/class/msensor/sensor0
address   bin_data_format  commands  dp    modes  num_values  power      uevent  value0  value2  value4  value6
bin_data  command          device    mode  name   port_name   subsystem  units   value1  value3  value5  value7

The tilt sensor driver has 3 operation modes:

root@ev3dev:~# cat /sys/class/msensor/sensor0/modes

by default it operates in TILT mode:

root@ev3dev:~# cat /sys/class/msensor/sensor0/mode

This is the expected operation mode with LEGO WeDo software: it returns 0 when flat and 1 to 4 when tilted.

TILT-AXIS mode returns 3 values: -1 or +1 when tilted, one value for each axle, the third value being 1 whenever it’s not flat.

And RAW mode returns the original analogic value read at the C2 pin. Almost useless for a tilt sensor but VERY usefull if we want to make our own sensors (more of it in my next post):

root@ev3dev:~# echo RAW > /sys/class/msensor/sensor0/mode
root@ev3dev:~# cat /sys/class/msensor/sensor0/value0


The LEGO WeDO tilt sensor

I’ve made some reverse-engineering of the WeDO tilt sensor:

R1 = 3k9
R2 = 10k
R3 = 6k8
R4 = 1k2

The circuit is based on Philo photos of the WeDO internals, I just completed it with my own findings.

The value of R1 is critical – this resistor is connected between C1 and Ground (0V) and it is used to identify the tilt sensor – if possible use a 1% tolerance resistor.

The other 3 resistors are not so demanding because the driver of the tilt sensor accepts a range of values for each of the 4 possible states.

So we can make our own pseudo tilt sensors modifying a Power Functions cable. Since I had enough Mindstorms RCX touch sensors, why not use 4 to create a basic gamepad with 4 direction keys?

The RCX touch sensor has an internal resistor, near 600Ω when full pressed so we have to reduce R3 and R4 to near 6k2 and 0k6.

Here is a quick demo with an EV3 and 2 WeDo USB hubs. Each hub has a Power Functions L-motor in port A and one of the hubs has the 4-key gamepad. I didn’t have the right resistors so I had to use some combinations of serial and parallel, pretty ugly but it works.

How do I use two WeDo USB hubs? Since they are both seen as the same kind of device and they don’t seem to have an individual ID, I scan for all hubs (expect to find just 2) and test for the presence of a tilt sensor.

I don’t have more hubs to test but it seems that there is no limiti to the number of WeDo hubs we can use (the software from LEGO allows only 3), we just need some kind of initialization procedure (like at the beginning of our program we ask the user to connect a tilt sensor on hub #1, then hub #2 and so on until all hubs are identified – or make a motor spin a bit and ask for confirmation).

#!/usr/bin/env python

from wedo import *
from time import sleep


#check if there are two hubs

  # initialize both hubs

  #find which hub has a tilt sensor

  if (wedohub1.tilt<>None):

  # use the tilt sensor as a gamepad
  # 1 = LEFT
  # 2 = BACK
  # 3 = RIGHT
  # 4 = FRONT






  print "Number of WeDo USB hubs found was not 2"

LEGO WeDO with Linux

After almost 2 years of procrastination I finally offered myself a LEGO WeDO USB Hub:

I just love the WeDO idea: with just a small and somewhat simple interface (the USB Hub) anyone can use a PC (nowadays a ubiquitous appliance) to control a motor or read a sensor. Great for educational uses, specially with STEM (Science, Technology, Engineering and Mathematics).

Sadly the LEGO WeDO family got much less attention than his older and bigger related, LEGO Mindstorms (at least in my country, Portugal). Although a bit less expensive than an NXT or an EV3, it’s not cheap so the EV3 seems a better investment (more pieces, more diversity, more power).

Early this year I used a Raspberry Pi with a Piface Digital board as a clumsy but much more powerful DIY alternative to the WeDO. This was in fact the trigger to start using LEGO again, event registering myself in a LUG.

This week someone opened an issue with ev3dev asking for “Any chance of adding Lego WeDo hub + motor and sensors?“. Right after I suggested wedo (a python library for WeDO) Ralph Hempel announced he was working in linux kernel support for WeDO (not just for ev3dev, could be used with other systems… like my laptop). Wow!

So I got a pair of WeDO USB hubs and a tilt sensor. And while waiting for Ralph’s work, I’m using WeDo with a variant of the wedo library: WeDoMore.

This is what you need to get WeDoMore working with Linux (both Ubuntu 14.10 and ev3dev tested, no need to use sudo in ev3dev because I’m already root): first download it and extract it, then:

sudo apt-get install python-pip
sudo pip install pyusb
cd WeDoMore-master
sudo ./ install

With Ubuntu it was necessary to remove Ubuntu’s version of pyusb, much older than pypi version:

sudo apt-get remove pyusb

Now connect the WeDO USB Hub and check with ‘dmesg’ and ‘lsusb’.

On Ubuntu:

413.597110] usb 2-1.3: new low-speed USB device number 10 using ehci-pci
[  413.695628] usb 2-1.3: New USB device found, idVendor=0694, idProduct=0003
[  413.695639] usb 2-1.3: New USB device strings: Mfr=0, Product=2, SerialNumber=0
[  413.695644] usb 2-1.3: Product: LEGO USB Hub V1.00
[  413.700722] hid-generic 0003:0694:0003.0009: hiddev0,hidraw3: USB HID v1.10 Device [LEGO USB Hub V1.00] on usb-0000:00:1d.0-1.3/input0
Bus 002 Device 013: ID 0694:0003 Lego Group

On ev3dev:

[ 1263.539342] usb 1-1.2: new low-speed USB device number 4 using ohci
[ 1263.698363] hid-generic 0003:0694:0003.0001: device has no listeners, quitting
Bus 001 Device 004: ID 0694:0003 Lego Group

So Ubuntu has a better knowledge of the WeDO USB Hub than ev3dev, don’t know why.

Now let’s test it from the python shell:

~$ python
Python 2.7.8 (default, Oct 20 2014, 15:05:19)
[GCC 4.9.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from wedo import WeDo
>>> wd = WeDo()
>>> wd.motor_a=100

If you have a motor connected to port A, it shell spin (note that as WeDO gets it power from USB the motor will get only 5V instead of ~9V as with Power Functions batteries… so it will spin slower).

To stop the motor and leave the shell:

>>> wd.motor_a=0
>>> exit()

As I also have a tilt sensor I made this simple control script:

#!/usr/bin/env python

from wedo import WeDo
from time import sleep

wd = WeDo()
print("Tilt me!")

IR remote control – speed and position

iConor’s second LIRC configuration file,Combo_PWM.conf, allows us to use LIRC command ‘irsend’ to control the speed of a LEGO Power Functions Motor or the position of a LEGO Power Functions Servo Motor much like the 8879 IR Speed Remote Control.

This shell script sends a sequence of 7 increasingly values then returns to zero and repeat it in the opposite direction:

irsend SEND_ONCE LEGO_Combo_PWM 400B ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 401A ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 4029 ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 4038 ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 404F ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 405E ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 406D ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 407C ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 4083 ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 40F4 ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 40E5 ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 40D6 ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 40C7 ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 40B0 ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 40A1 ; sleep  1.2
irsend SEND_ONCE LEGO_Combo_PWM 4092 ; sleep  1.2

There is a total of 256 key codes in the configuration file (16 different values for the red plug x 16 different values for the blue plug). I used just the first subset of 16 so the first byte (for the blue plug) is always ’40’ but it doesn’t matter because I connected both Servo and M-motor to the red plug .

The sequence of key codes is not exactly the same as in the configuration file – I reordered the last 7 key codes.

The ‘sleep 1.2’  makes the script wait 1.2 seconds between each command. It is more or less the time the IR keeps the command active (bigger values would make the Servo return to center and the M-motor stop).

Infrared Remote Control

I discover this week that it is possible to use the headphone jack to send IR signals. The intructions are for a iPhone but one can use almost any audio source… even the computer audio card! And it is already suported in LIRC (Linux Infrared Remote Control), their page even includes a simple circuit!

LIRC – audio IR transmitter

Then I also found this lego-lirc repo in GitHub from a guy nicknamed iConor. It has the source code to generate LIRC configuration files for the LEGO Power Functions Infrared protocol… and also two configurations files:

The first file works like the 8885 – PF IR Remote Control and contains the usual FORWARD / BACKWARD / HOLD / BREAK codes; the second file works like the 8879 – PF IR Speed Remote Control and contains the codes to control the speed (duty cycle) of the motors.

So… why not give it a try?

I searched for more info about ‘lego-lirc’ but found nothing so I opened an issue asking iConor permission to publish those two files (and he promptly agreed, thank you iConor!).

My laptop has Ubuntu 14.10 x64. I installed LIRC and the required Portaudio library for using the audio card:

$ sudo apt-get install lirc libportaudio0

When LIRC is being installed it asks for an IR Receiver and an IR Transmitter, I chose ‘none’ twice.

Then I copied iConor configuration files to LIRC folder:

sudo cp Combo_Direct.conf /etc/lirc/lircd.conf
sudo cp Combo_PWM.conf  /etc/lirc/lircd.conf

and edited /etc/lirc/hardware.conf to create a LEGO_Combo_Direct transmitter associated to the audio card output:

#Chosen IR Transmitter

My audio card accepts sampling at 96 kHz but others may require lower values like 48 kHz.

I also edited /etc/lirc/lircd.conf to include both iConor configuration files

include "/etc/lirc/Combo_Direct.conf"
include "/etc/lirc/Combo_PWM.conf"

but I’m not sure if it is really needed since hardware.conf already has the right path.

I am also not sure if it is really needed or not but somewhere between my several tries I had to create a folder for lirc where it writes 2 files (one I think is a lock, the other contains just the process id)

~$ sudo mkdir /var/run/lirc/

Now let us start the lirc daemon:

~$ sudo service lirc start

and check if it is working:

~$ pgrep lirc

and what kind of transmitter does it understands:

~$ irsend LIST "" ""
irsend: LEGO_Combo_Direct
irsend: LEGO_Combo_PWM

and also  what codes are available:

$ irsend LIST LEGO_Combo_Direct ""
irsend: 000000000000010e FLOAT_FLOAT
irsend: 000000000000011f FLOAT_FORWARD
irsend: 000000000000012c FLOAT_BACKWARD
irsend: 000000000000013d FLOAT_BRAKE
irsend: 000000000000014a FORWARD_FLOAT
irsend: 000000000000015b FORWARD_FORWARD
irsend: 0000000000000168 FORWARD_BACKWARD
irsend: 0000000000000179 FORWARD_BRAKE
irsend: 0000000000000186 BACKWARD_FLOAT
irsend: 0000000000000197 BACKWARD_FORWARD
irsend: 00000000000001a4 BACKWARD_BACKWARD
irsend: 00000000000001b5 BACKWARD_BRAKE
irsend: 00000000000001c2 BRAKE_FLOAT
irsend: 00000000000001d3 BRAKE_FORWARD
irsend: 00000000000001e0 BRAKE_BACKWARD
irsend: 00000000000001f1 BRAKE_BRAKE

OK, we’re ready! Now suppose we want to make both motors spin forward:


Yeah! The motor(s) spin for about 1 second.

So if we want shorter runs we can send a BREAK or a FLOAT after a short time, say 0.1 second:

~$ irsend SEND_ONCE LEGO_Combo_Direct FORWARD_FORWARD; sleep 0.1; irsend SEND_ONCE LEGO_Combo_Direct FLOAT_FLOAT

I faced some strange behaviours (delays, lags) until I better read the LIRC audio page and saw this warning:

“It takes some time to set up (50 ms or so) so when no clients are connected to lircd the first transmission will have some higher latency.

A workaround for this is to keep irw running with a bash script like this:

 while [ true ]; do
 irw || true
 sleep 1


So i created a ‘’ file, gave it execution permissions and executed in the background:

~$ chmod +x
~$ ./ &

And it makes a REALLY BIG difference.

For anyone who might get interested in this, I suggest first trying with just a headphone or 2 common LEDs (I used a pair of red). If there is a click or a blink then use 2 IR LEDs. Mine are L-934F3C – IR Emitter 3mm 940nm (€0.25 each) and no resistor at all but if you want to play safe use a small resistor like 8Ω.

You also need a cable (just cut the cable of a old headphone set) and a soldering iron. I also used heat shrinking tube but any kind of insulation material is OK.

The required materials:

And the completed cable:

Now about the LEDs…

These LEDs are from Kingbright, their specs say

1.2V Typ @ 20mA, 940 nm, 50° angle, 10 mW/sr Typ @20 mA

I also tried a pair of TSAL6100 950nm High Power Infrared Led from Vishay:

1.35V Typ@ 100 mA, 10° angle, 170 mW/sr @100 mA

but I got more or less the same results and as their emission angle is much smaller I needed to point more carefully to the PF RC receiver. so I kept the first pair. The audio output is intended for headphone so it isn’t much powerfull and might not give enough current to notice a difference – or i just made a mistake.

My first tests achieved a respectable 3 meter range. Not bad for something so simple and costing less than €1 – now everyone can programmaticaly control their LEGO models. Kudos for LIRC people for being so open-minded and for iConor for creating this configuration files.

Next I’m going to try the same with a LEGO Mindstorms EV3 and also a Raspberry Pi.