DMX and Arduino

It’s got to be fast, that’s all that matters really.

#include <DmxSimple.h>

int incomingByte = 0; 
int ch = 0;
int alt = 0;

void setup() {

  Serial.begin(115200);
  DmxSimple.usePin(5);

}


void loop() {

        if (Serial.available() > 0) {
                incomingByte = Serial.read();
                
                if (alt > 0) {
                  DmxSimple.write(ch, incomingByte);
                  alt = 0;

                } else {
                  ch = incomingByte;
                  alt = 1;
                }
        }
}

Simplified Controller

Placing the components for the controller I’m building. Will trim the breadboard and drill some holes soon, but this is the general idea.

All encoders are pushbutton, rgb illuminated and detentless (except the 9th encoder on the right, which has clicks and will be used mainly to select options in menus).

The buttons are modifiers that will change what the encoders do for each channel.

I’ve already decoded the Mackie Control protocol, I built a Max for Live patch as a proof of concept and it is working very well within live. Once the hardware is working with the Arduino I’ll be coding this up as a perfect MCU clone.

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Let’s pitch in for Chelsea’s Birthday!


Chelsea Faith is one of the bay area’s best kept secrets in the Techno Scene.  Her all hardware approach to a genre that has been taken over completely by software and laptops is a breath of fresh air.  Often playing just for the love of the music and little to no financial compensation, Chelsea has given much of herself to those of us whose lives are enhanced by her talents.

I’ve been Chelsea’s friend since 2007 and am lucky to be a part of her band, Easystreet.

For her birthday this year (September 14th!) I thought it would be great to enlist the help of her friends to finance and build for her a custom x0xb0x analog synthesizer.

This is a perfect clone of the iconic Roland TB-303 synthesizer that is a staple of classic and modern techno.   A brand new, prebuilt x0xb0x costs $600, but the kit is only $370.  There are also some inexpensive mods that can be added very easily, and those of you familliar with my work will know that building and modding this kit should be a fairly simple task once I have all of the needed parts.

I thought it would be fun to do a kickstarter style campaign for this, but kickstarter said it wasn’t a good fit.  So instead I figured we could do this privately, and I can offer these rewards to anyone who wants to chip in.  If you would like to contribute, I can accept paypal (my address is insolace [at] yahoo [dot] com) or you can mail me a check (just email me at that same address and I’ll send you my snail mail contact).  I’ll be happy to post your name below under the appropriate reward level, or if you prefer not to be listed publicly that is fine too.

The minimum amount I need to do this is $395, which will cover the cost of the kit and shipping.  Any amount after that up to $550 will be used to fund the custom modifications, which at the $550 level would include making a transparent case with ColorSynth lighting installed (very similar to the custom shruthi synth that I made for Chelsea last year).  If for some reason we don’t reach the $395 level, I will refund everyone’s money and return any checks sent to me.  I will edit this post with updates as I get donations so everyone will know where we stand.

Rewards:
$5 – a digital download of an exclusive track from Chelsea’s band Easystreet, remixed featuring the x0xb0x

$10 – same as above, + a physical CD of Easystreet’s new album, “international supernatural”, signed by the band

$20 – same as above, + a signed 8″x10″ photo of the band posing with the x0xb0x and our mascott, a greyhound named Bowie.  Band and dog in full costume.

$50 – same as above, + a custom Easystreet themed ringtone, composed by Chelsea for you using the x0xb0x

$75 – same as above, + your name engraved on the bottom of the synthesizer

$100 – same as above, + your custom 80 character message engraved next to your name

$200 – same as above, + an invitation to join the band (in full costume) for a night of Karaoke at the Mint in San Francisco, where you get to present the completed customized x0xb0x to Chelsea.

Please email insolace [at] yahoo [dot] com if you’d like more info on how to help/contribute.

…baby step onto the elevator… baby step into the elevator… I’m *in* the elevator.

Like many of my projects, the controller I’m building is an ambitious endeavor.  It sounds simple on the outset, add 8 encoders and an LCD screen to an 8×8 RGB Monome and program the new controller to run a monome patch in one color and a Mackie Control style DAW controller in another, with the third color used for channel meters.   My current prototype for this is pictured in the banner of this website, it’s a 4×4 grid with an LCD on the side.

Functionally this prototype can print text to the LCD while reading and storing button/encoder states.  It can also light up the LEDs, although I have yet to perfect the timing of multiplexing the four rows so that the colors show up correctly and balanced, with minimal flicker.

That last part is actually no small matter, and I’m finding it hard to dedicate the real time needed to make timely progress.

With that goal of mind (the theme for my projects in 2011 is “of substance”) I am declaring an intermediary step.  Remove the RGB monome for now, and instead build a controller that is 9 push-encoders (8 + 1 master) with an LCD and a two shift buttons.  Everything I develop for this version of the controller will port over to the bigger one, and it gives me the added benefit of having another (less expensive) product to offer.  Also small controllers are awesome (hopefully this one wont be much wider than the short side of the arduino).

Last night I perfected reading the encoders via the shift in register, and applying the inc/dec commands to (0-127) ranged values displayed on the LCD, and for fun applied those values to some of the red LEDs still connected to the board.  The next step will be to make it pretend to be a Mackie Control, or perhaps build a custom map in Ableton Live.  I’m leaning towards the first option, even though it’s a bit more complex, as it will be a more universal option.

The only other question is do I use plain old pushbutton encoders, or do I go with these sexy little numbers?

A Tale of Two MIDIs

One of the considerations for the class I’m teaching at RobotSpeak is that most people using an Arduino as an USB MIDI controller will want to communicate over USB without having to also connect the controller via MIDI ports.  However I’m a purist, and I want my students to be able to use their controllers for any application, including as a hardware controller in a non-computer based setup.  To do this our serial communication will have to be at 31250 baud.  For the hardware side, a single 220 ohm resistor and a 5-pin din MIDI port are all that is needed to connect the Arduino to a MIDI device.  However on the software side, we will need to run a utility that listens to the Arduino USB serial port, and then sends that data to a virtual MIDI port (OSX supports this natively with the IAC bus in Audio/MIDI setup, PC users can use Maple or MIDI/OX) which can then be read from our DAW software.

This is easier said than done.  A quick check of the Arduino Playground shows several different solutions, however many are either no longer available, or only support MIDI note on/off and CC data.  This may work for my RobotSpeak class as it is just an introduction and basic controller class, but plans for my own controller will include emulation of commercially available controllers that use SysEx for channel names and Pitchwheel data for high resolution 14-bit values (like channel volume).  This is a problem that must be addressed in the future.

For my class I have chosen the application made by Spikenzie Labs.  For windows users, S2MIDI is an option, but the Spikenzie app is written in Java (technically made in Processing with the MIDIBus library) and they do offer versions for both operating systems.

With this choice I ran into two problems, the first being that the OSX version of the application would hang when selecting 31250 baud.  I can only assume this means that the Spikenzie hardware that this utility was written for runs at a faster baud rate, and that MIDI communication in the software world can actually go faster than what I thought was a hard limit in the spec.  (Otherwise they would have caught this, no?)  After some furious Google searching I found that someone had solved this.  Apparently this is a limitation in the RXTX Java Serial library, and by adding the fix from the IRQ5 blog I was able to get the Spikenzie converter to work.  Sort of.  This brings me to my second problem, turning the knobs on my controller I was getting erratic results and useless data.  The MIDI equivalent of a garbled message.

When I developed ColorSynths and coded the entire MIDI spec in Assembly (something I try to mention casually in conversations as often as possible), one of my first oversights was the implementation of running status.  Most MIDI data packets are three bytes: one status byte followed by two data bytes.  The MIDI specification requires us to store the most recent status byte, and if a two byte data packet is received without a status byte, we re-use the last one.  This frees up data to allow us to transmit more information, and while it may seem like a more advanced function of the MIDI spec, it can trip up even the most basic of applications if you aren’t aware of it.

As far as I can tell, the MIDIBUS library that Spikenzie’s application uses (and from the contact page I think it’s possible Spikenzie wrote the library) doesn’t support running status.  This of course wouldn’t be a problem if our Arduino code was directly addressing the serial port and only sending 3 byte data packets.  But I had originally written my code for the class using the Arduino MIDI library, which of course uses running status.  The Spikenzie application had no way of recognizing these two byte data packets that lacked a status byte.

I opened up the included source code to get a better understanding of what was going on.  I had assumed that an application like this would be a simple pass through of data from the serial port to the corresponding MIDI port, byte per byte.  Instead what I found was that the Spikenzie labs app is actually handling and interpereting the data, it’s analyzing each byte and waiting for a Note ON/Off or CC status byte followed by two data bytes, and only transmitting when it receives them in that format.  This wasn’t too tough of a fix, I wrote a routine that recognized the entire MIDI spec, including running status and SysEx, in a few hours (nbd).  But because the MIDIbus library doesn’t support the transmission of MIDI using the runningstatus format, the incoming serial data would overflow the outgoing MIDI data (since it was 33% slower).

My eventual solution was to remove the Arduino MIDI library from my source code and to instead manually create 3 byte only MIDI data packets by addressing the serial port directly in the Arduino code.   This solved all problems (that and replacing the RXTX serial library with the one that supports 31250 baud) and gave us working code, but it’s not optimal and our controller could be 33% faster.

Clearly two features need to be added to the MIDIBus library.  The first is support for transmission and reception of running status.  But the second is a way to handle raw data to and from the MIDI port.  I can see the benefits to having a library that creates the MIDI packets for you (that’s why I preferred the Arduino MIDI library to creating the bytes manually) but this application doesn’t need it.  A simple byte-to-byte pass through of the data would eliminate any errors in implementation of the MIDI standard, and avoid complications like Realtime System events (which are single byte and can occur in the midst of a 3 byte event) or SysEx timing.  SysEx is of particular concern to me, because some commercial controllers will send SysEx data and expect a timely response.  The last thing you’d want is to wait for your SysEx handler in the library to get back to you when your code is supposed to be responding.

I’ve written to Spikenzie Labs and hope they’ll update their app, there are no suitable OSX alternatives listed on the Arduino Playground and eventually the correct solution might be to write my own utility that is a simple pass through.  It’s a shame to have to reinvent the wheel though.

Arduino MIDI controller

Lots of progress on the new control surface I’m making. The 4×4 RGB buttongrid, encoders, and LCDs are all communicating with the Arduino. I’m using Shift registers and pwm led drivers so it’s easily expanded to the 8×8 size of the planned controller, could go even bigger.

Next up: lasering the faceplate, bezel, and plastic buttons. And of course, programming the libraries for the controller so anyone can program it.

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