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4Oct/102

Interfacing MaxMSP and Arduino

Building the Bliptronome got me thinking about microcontrollers in general, and how cool they are. I've been teaching myself to program using an Arduino Duemilanove, and it's a blast. Inevitably I began to wonder how to communicate with Arduino using MaxMSP. The Arduino and the Bliptronome are similar in many respects. Each can use what is known as a serial proxy to communicate with host software. The serial proxy is device-specific, and functions to translate serial messages to and from the USB port to which the devices are connected. The Bliptronome and its cousins Monome and Arduinome can all use a purpose-specific serial proxy that makes it easy to write MaxMSP code for 'nomes. But how do you set things up quickly and easily for a standalone Arduino? You could write your own serial proxy, but who has time for that? Arduino kindly offers one on their site, but it only works to move data between serial port and a network connection, not USB. This is great for Flash users. But what about MaxMSP users, particularly those who want to get straight to I/O with a minimum of fuss?

Thankfully you don't have to reinvent the wheel, as there are a couple of brilliant free solutions that work very well together: Maxuino and Firmata. Firmata is a generic protocol that provides the foundation for MaxMSP (and many others) to communicate directly with Arduino. Maxuino is a collection of Max patches that uses the Max serial object to implement Open Sound Control (OSC). Together, they provide the magic of communicating with your Arduino by using OSC.

Get Started
Get started by visiting Maxuino.org, and following the instructions. I won't duplicate any of that here, since it's fairly straightforward, although I will note that they have their own customized version of Firmata. Once you've got the files all nicely ensconced in your search path, and Firmata Standard is loaded on your Arduino, test it out to make sure it works (hit pin 13 with a digital out or something). Be sure that maxuino.help.maxpat is set to the correct port. If this is your first time, be warned that getting Max to talk to Arduino can be somewhat fiddly. If it doesn't work the first time, you can try hitting the reset button on the Arduino and then resetting to the correct port. If that doesn't work try unplugging and replugging the Arduino, and then resetting to the correct port.

Minimal Max Patch
I don't know about you, but after poking around in those patches I wanted to create my own patch for a fuller understanding of the bare minimum required to get things working. There is a lot going on in there! To be clear, so far all I want to do is send a signal to the Arduino to light up the default status LED on pin 13. Once that all-important task is done, I can be sure that communication is enabled, and attempt to send data back to Max. The first thing to address is setting the correct port number for the Arduino. I lifted the function straight out of maxuino.help.maxpat and plopped it into my patch:

The heart of this patch is the "devices" patcher, which looks like this:

Now I'm primed to add the rest of the Maxuino code, which consists of two parts: maxuino-gui.maxpat which handles OSC routing and UI interaction, and maxuino.maxpat (shown here as "maxuino a"), which contains JavaScript that interprets output from maxuino-gui.maxpat and sends it to the Arduino to be interpreted by Firmata. I also copied maxuino-gui.maxpat and maxuino a from maxuino.help.maxpat. Note that I first had to rename "maxuino-gui" to "maxuino-gui.maxpat" in maxuino.help.maxpat. I patched them together as shown here:

That's a good start, but I still need to flash that LED. The example patchers in maxuino.help.maxpat demonstrate how to set pin modes and use the various outputs. I took the code on the far right side and added it to my patch. I connected the output of the prepend object to the first input of maxuino-gui.maxpat. Now it looks like this:

Now I should be able to click "update", set to the correct patch (in this example it's COM4), set the pin number for pin 13, and click the toggle to turn my LED on, and then turn it off! Again if this doesn't work the first time try resetting your Arduino and setting the port again. The message box at the bottom shows what the OSC message looks like. This will only work on a digital pin, as we're sending a digital out message.

Get Some Input

Although flicking an LED on and off can be hours of fun, it's only half the fun we could be having. What if we were to interpret a signal sent from a digital pin on the Arduino? That would be so awesome. The part of maxuino.help.maxpat that shows how to handle input is the Analog-Digital-Inputs patcher. In order for it to work though, the pin of choice on the Arduino must first be set to mode 0 for digital input. This is demonstrated in the Pin-Modes patcher. I went ahead and copied both of those, pasted them into my patch, and connected them as shown here:

NOW we're really ready for some hot Arduino on Max action! Connect one lead of a button to digital pin 7, and the other to ground. Now open the Analog-Digital-Inputs patcher, and watch what happens when you press the button. More hours of fun!!! At least three hours and 27  minutes by my last estimate.

Watching Messages

The maxuino a subpatcher has a couple of gswitches that you can use to print out messages and see what they look like. Open the subpatcher, toggle the switches, and watch what happens when you press buttons in the maxuino-gui.maxpat interface. Set a digital pin to PWM and move the slider around. A handy way to monitor what's going on when you use the Maxuino patches. Of course you can also attach your own print objects wherever you like.

Analog Input

What's the most popular kind of input? Analog input! Well okay, I'm not sure if that's 100% true, but wouldn't it be fun to get a potentiometer wired up and watch it moving a slider around? I think so! First, wire up a potentiometer according to these instructions. Next, open the Pin-Modes subpatcher and set your analog pin of choice to mode 2 for Analog In (I selected pin 0). Finally, open the maxuino-gui subpatcher and turn on the pin of choice in the list of Analog pins. Now twist the pot, and you should see your slider moving around. For extra fun you can add a print object and watch the values come out. I connected mine to the output of the maxuino a subpatcher along with a gswitch.

Now What?

As promised, Maxuino and Firmata together enable you to completely program the functionality of your Arduino from within MaxMSP. At this point you can add any type of functionality you want, from something as simple as connecting the button to the LED, to reading input from a sensor and adjusting a parameter on a synthesizer, to detecting input and dynamically generating user interface elements to match. You could write a patch to control a dancing monkey with LEDs for eyes. And all you need to do is use OSC to make calls to Maxuino from within MaxMSP. Pretty sweet!!

Obviously the excellent Maxuino patches serve well for instructional purposes, and I found it really helpful to break them down and simplify them to have a closer look at how (most of) it works. When I write an actual Max patch, I foresee a somewhat different design pattern. First of all, my code is going to be directed at an Arduino-based device that is hard-wired for a specific purpose. I think it would be easy to come up with a subpatcher to initialize the Arduino with the correct configuration at startup (loadbang), so that all of the pins are set to the right values, activated, etc. I'm still not sure if enabling/disabling pins has any effect on the performance of the unit. Obviously UI design is a consideration, and the Maxuino patches are a wonderful starting point for that. I think my design would probably still include judiciously placed Print objects, since I like to see values when I'm programming (who doesn't).

There are other issues as well, such as whether it is possible to have multiple instances of a Maxuino patch running at the same time. I did run into some behavior while writing this posting that suggested you can only have one instance open at a time. I'm not sure which steps to take to bypass this seeming limitation. Another issue is "how would this work in Max for Live?" and you will find that there is a Maxuino.amxd patch included. I intentionally did my experimentation in Max proper to avoid having to deal with any Live-specific issues, although I did run the .amxd and it worked fine.

Source Code

Here is the source code for my humble little patch: maxuino-simplified. Copy it to your clipboard, and then use File/New From Clipboard to open it in Max. Note that none of this will work unless you have properly set up Maxuino on your system.

More Information
Read these interesting articles on the creators of Maxuino and Firmata:
An Interview with Chris Coleman
An Interview with Ali Momeni


Comments (2) Trackbacks (0)
  1. The maxuino-simplified path does not work, otherwise this is a great tutorial.
    n.


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