Blog
MC2 Build
28/8/2015
So the other day I was at rehearsal and the MC1 that built started to have some issues with the External control knobs (along the top). They were jumping all over the place and making it annoying to use. I did get around to pulling all the circuitry around those pots off and doing it properly later. But it occurred to me that I'm using gear that I have no backup for. There is no 2nd controller to swap out if this one dies at a gig.
And because I'd rather custom build one out of parts I [mostly] have lying around that means building the MC2.
For starters the MC1 uses a tiny micro-controller with no USB or network or any modern connectivity at all. I have an old XP computer JUST to reflash the damn thing (needs a REAL parallel port). For any new system I wanted an easy way to do software development and ethernet/USB connectivity. And because I had a Raspberry Pi already I settled on that as a platform to run everything. I already had a little touchscreen to go with it and some RGB led rings with encoders that I built for a different project that I never got around to. So with all those parts just lying around I got to making some bits to glue it all together. Here's a family photo:


1) The Raspberry Pi. This is the "old" B rev 2 version... which has the slower processor.
2) The touchscreen. This interfaces with the SDL api using the Linux framebuffer. Touch events show up as mouse clicks. It's all quite straight forward to be honest. The only gotcha is you HAVE to set the video mode back to text if you crash... otherwise you're stuck in video mode without a working console.
3) LED rings + encoders: These I built for someone else but was too slack to finish that project. They basically are an extension of the Mayhew LED ring except that I'm running Red/Green/Blue LEDs instead of just one colour. It also is designed to fit in a 1U rack box, so they are nice and compact. I'll have 3 pairs of these across the top of the box, giving me 6 independent continuous controllers. Just like the old MC1 box, but importantly I'll be able to update their "position" using software when the preset changes.
4) Neopixel chain: Each foot switch on the controller will have an associated LED. I settled on the Neopixels because they wouldn't require a lot of support circuitry and there is now a software library to make them work on the Raspberry Pi. Which I've used successfully on a bread board.
5) MIDI in and out ports. This is a direct implementation of the circuit used in the MC1. All I really have to do is connect it up to the Raspberry Pi's UART pins and then program the right frequency. *fingers crossed*
6) This is a bunch of extra GPIO (general purpose input/output) for connecting the foot switches and encoders up to. It runs on the I2C bus from the Pi so it's easy to chain lots of things and address them in software. (I love software solutions).
7) Some analog inputs for the expression pedals. I'll be able to have up to 4 connected at once.
8) This is the break out board for the expression pedals. It connects to (7) via a 4 wire bus and basically sets up the right voltages for the 3 pins on the socket. It allows me to detect when the pedal is connected and disconnected by limiting the valid ranges of input voltage when the pedal is connected to less than 0-3.3v...
That's an overview of the hardware side. But what about the software? Well I already have a lot of cross platform C++ code that will come in handy. Firstly I have written a library called LGI that allows the same code to run on Windows, Mac and Linux without much changes. So why not extend that to SDL on the Raspberry Pi? So that's what I did this month. Which gives me access to a whole bunch of little controls like, edit boxes, check boxes, labels, buttons, table layout controls, graphical design tools etc. Stuff I've already written.
But I still needed to work out the general look and feel of the user interface. Check it out:


Basically I'm drafting up the flow of buttons and the layout of the controls to get a feel for what I need to write in the software. I have this control that does layout for me, kinda like a HTML table in that it works out the spacing of everything based on the size of the content. And I can style all the controls with CSS which will make for a nice consistent look over the product.
I expect though it'll be some months before I get this all working. Only a few parts of this are tested and none of it has been integrated into a working system. I'll try and post updates when I can.


Tags: mc2

Comments:

Muzza
03/09/2015 11:11pm


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