How to build a MIDI controller with the Arduino, Firmata and Pure Data

Time to start contributing some knowledge back to the wonderful world that is the internet; today, a step by step nice and easy tutorial on getting started to building your own MIDI controllers with the arduino.

When researching for my ableton controller project, I didn’t find much out there about using firmata on an arduino to send data to software. The standard approach just seemed to be create the code in the arduino language, upload it to your board and hack one of those MIDI to USB cables as a bodge job way of getting the MIDI out of the arduino.

So why firmata and pure data? Well the whole idea of firmata is that you flash it to your arduino, and it throws out serial about whats going on with the arduino inputs and outputs, then you decide how the software treats the readings coming in and going out.

Theory out the way, lets build some controllers. You’ll need a few things…


  • An arduino and something to wire into it (for this i’ll be using a pot)
  • A USB cable for your arduino



Install Pure Data and create a folder to store all your patches somewhere. Unzip Firmata and add the files ‘arduino.pd’, ‘arduino-test.pd’ and ‘arduino-help.pd’ to your new Pure Data folder. The ‘arduino.pd’ file is the object that we use in PD for opening up communication with your arduino and routing it to PD. Done? Awesome, your software is almost set up.


Install the latest version of arduino and open it up. Connect your arduino with the USB cable to your laptop (i’m using a macbook for this by the way). In the example patches, open up “Standard Firmata”, select your board (im using an arduino mega), and your serial port (look for tty.usbserial for use with a USB cable). Then compile and hit the upload button and your arduino is now ready to use firmata and communicate with Pure Data!


Potentiometers are cool, and theres a great arduino tutorial of how to wire one up here:

Basically, all you need to know is that there are three pins; your two outer pins govern voltage flow across the pot, meaning one has to be 5V and the other has to be ground. It doesn’t matter which, but your 5v pin is going to be where your pot reads maximum, so convention dictates this should be the right hand pin. The center pin needs to be connected to an analog in on the arduino and will read the value of the pot as it sweeps from ground (0v) to 5v.

All wired up? Plug it into your laptop and open Pure Data, we’re ready to get things talking.


Open the example “arduino-test.pd” Pure Data patch you copied over earlier. It should look like this one…

The test patch has everything we need to open a connection and enable pins. Firstly, lets delete a bunch of stuff and make our window a bit bigger. Hit Command + E to enter edit mode in Pure Data.

Ok a quick explaination; the key component here is the ‘arduino’ object. This is being drawn from the file you copied in earlier, and is what communicated with your arduino. Here we can do everything to control the arduino from opening a connection, to receiving data.
The large grid allows us to set the mode of each pin on the arduino. Remember pins 0 and 1 are reserved for Rx and Tx. I’m using analog pin 4 for this demo, so I’ve set my pin mode for pin 4 to ‘analog’.

Now we can plug our arduino in and get a reading from the potentiometer.


With your arduino plugged in, hit command and E to bring us out of edit mode. In our patch, click on ‘Devices’ above the arduino object and open up the pure data terminal. (That other thing that loads with PD that has all the scary code in)

The “Devices” message connected to the arduino object pings your computer to find what devices are connected and on what serial ports. Since we’re using a USB cable to connect our arduino, we’re looking for something with ‘usbserial’ in it, in this case; port 2.

Select the relevent port in the green box at the top (remember the first box is ‘0’, second is ‘1’ and so forth) and hit ‘Open’ to establish a connection. Check the terminal to see if the connection was sucessful.

Now lets check we’re getting something in. Create a number box (Command + 3) and connect it to the relevent pin on the ‘Route analog’ box at the bottom. In this case, pin 4.

One more thing; if you’re not getting any readings in, you’ll need to click on ‘pd old analog/digital controls’ and enable your pins here too. What I tend to do in my patches is just not include the large grid but make my own ‘old pd’ controls custom to what i’m enabling/disabling to save space.

Here’s what the ‘old analog/digital controls’ subpatch looks like (pin 4 enabled)…

Come out of edit mode and check that you’ve got readings. If so congratulations! If not, troubleshoot, start with making sure your usb connection is opened, make sure all the correct pins are enabled (remember you’re counting from 0 not 1 on most of these buttons in PD, it’s just the way computers work).


So we’ve got a reading and chances are it’s to 3 decimal places between 0 to 1. No problem, create a new object (Command + 1) and type “autoscale 0 127”. This allows us to scale the input to a min and max value, in this case 0 to 127 of MIDI. Next, lets get things looking nice, create a new object and type “knob”. Connect this AFTER the autoscale object. (the knob is default set to read inputs from 0 to 127. Then create another number to display the scaled MIDI data coming out, and finally a new object and type “ctlout 1”.

It should look something like this…

The second box should be outputing values from 0 – 127 now, and the knob giving a visual representation of your potentiometer.

Now lets patch it into ableton…


Firstly, you’ll need to set up your macs IAC driver if you’ve not done this. Basically you’ll need to go into Audio/MIDI preferences and enable your IAC driver. Then create a new input and output. One for input to DAW and one for output from DAW. Google around for a tutorial on this, its really simple, a 30 second job.

After you’ve set up your IAC driver, go back to PD and go to preferences > MIDI Settings, and connect your IAC driver.

Open ableton and go to its MIDI preferences. Create a device listing for your IAC driver and enable its ins and outs into ableton like so…

And thats it! Create an instrument and try to assign something! I’ve got it controlling the brightness of a bass sound here.

Shout out for Facu who requested this tutorial. Hopefully it’ll help some of you looking to get into this stuff and start building things but with no idea where to start.

Feel free to post this around and send me your comments and links to things you build with it 🙂

8 responses to “How to build a MIDI controller with the Arduino, Firmata and Pure Data

  1. enrique rodriguez

    Hi, I am very interested in learning more about this arduino to make a midi controller for ableton. I have done this example and successfully got it to work. I am stucked when i want to add another knob to assign different maps in ableton. The knobs just get confused and i am not able to map different functions. How can this be done if i want to add more knobs and buttons to the controller? Best regards and happy new year!

  2. thanks man, clearly explained i probably would have never came across PD if it wasn’t for you and even if i did it probably would have taken me much more time to figure out the basics.excellent tutorial and awsome midi controller btw.

  3. Henrique Vassalo

    This explanation is just what everyone needs, you’re the man, keep up the good work.

  4. hello spencerdixon,
    you save my life with your tutorial, It’s been a month since I try to establish a connection between my arduino and ableton, thanks a lot, however the explanation pictures are missing….
    I have a problem…. I have an Arduino Mega with 16 analog ins and i would like to add more analogins in my pure data sketch, I tried but I can not find, could you help me plz, I must make my project in two weeks …. thank you again and sorry for my english

  5. Hi, first of all, great tutorial! I’ve been looking for info on this topic for a while. I know this was a post from last year but I was wondering where I can find information on how to use more than one pot. Thanks.

  6. Probably the best tutorial on the subject. Big thanks! Got it working in 2 hours – and I’m a TOTAL amateur. I’ll definitely try to go for more pots now.

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