praxworld.com Electronics, music, electronic music! general geekery

29Sep/100

Building a Bliptronome, part 2

In the first posting, I walked through the steps I took to build a Bliptronome, up to the point of plugging it in and testing it using MaxMSP. The remaining steps now consist of:

  • Cutting a little slot in the case to expose the header pins.
  • Mounting and connecting the potentiometers.
  • Stuffing everything back into the enclosure and screwing it back together.
  • Re-sticking the little rubber feet.
  • Downloading some Monome apps and stuff.

Marking the Slot
My goal here is to mark the spot on the top shell where I will cut a slot so that the USB-BUB can plug in to the header pins. Since my circuit board seems to be angled up a bit, I first put a screw into the mounting hole nearest the pinout to get a more accurate idea of how it will fit with the top. I then set the top of the case on the bottom half, taking care not to offset the placement of anything.On my unit the header pins protrude exactly to where the edge of the case will be. You can see the spot where I used a marking pen to draw the shape of the slot.

Cutting the Slot
[WARNING: The next section features using an X-acto blade. These blades are very, very sharp. Please use caution when working with them!]

I busted out my X-acto #11 blade, thinking that it will be the best tool for the job. Well, the plastic on the case is mighty thick. I don't have a micrometer, but my eyeball tells me it's in the vicinity of 3/32". So I keep cautiously cutting along the outline of where I think the slot should go, trying to get deeper without slipping and scratching the edge. Well crap, at least I tried. It's difficult to get a good hold on the piece, and also avoid slicing into my own tender flesh. As I cut, I can see that the top line is a bit crooked, so the suggestion to finish with a flat file seems like a good call. Hopefully I have a file that'll fit because man, that is one sloppy looking slot.

Finishing the Slot, Painting
In fitting the top half to the bottom again, it's pretty clear I didn't make my slot deep enough. I was going to see if I could deepen it with a file, but I couldn't find a file! I could have sworn I had at least 3. I found some sandpaper and tried that, and ended up making some very noticeable scratches. So add spray painting the sides to my list. In the meantime I need to go out and get a file! A quick rummage through my bin of potentially useful miscellaneous items turned up a quite handsome set of small hobby files. Perfect! The slot is a bit deeper than I wanted but it's about as square as it's going to get. I'm gonna find some spray paint to hide those scratches and beautify the finish a bit. I sure wish I'd have looked in that box before using the damn sandpaper. Ah yes, and I also dabbed a bit of model glue on the edge of the play button to keep it from rattling around.

[Fsst! Fsst! I'm spray painting in my driveway at 11:45 p.m. Dry, dry, dry.]

The next morning...
The paint is dry and it looks good! I used a silver metallic, let it dry for about half an hour, then laid on some irridescent overcoat. I masked off the knob area so I could paint over the default markings since they're no longer applicable. The messed up slot looks a lot better, too. Overall a success! One minor tip, try not to fudge with the case too much like I did, you can see in the photo that the metal outer layer is offset a little, the result of my efforts to carve the slot.

Installing the Potentiometers
The potentiometers that came with the kit are pretty typical. They are nice and compact with three contacts, to be connected in series (the instructions detail this). Before installing them, I am going to mark where the flange points line up with the case, and then drill some teeny little holes in there with my electric drill. As mentioned in the instructions, a 1/8" bit looks the way to go here. First I set one of the pots into its spot, then use an X-acto knife to mark approximately where the flange will sit. If you plan to do any kind of case mods for projects (circuit bending, anyone?) this is a great technique to use. In this case, we can even avoid poking our flange holes through to the other side.

Drilling the Flange Holes
I use my drill to put the holes in. Some of them overlap the edges of the holes that are already there, but that doesn't matter. Plus the metal part acts as a shield for people like me who wait until they feel the bit hit the metal. It's like they saw me coming!! I used a 10mm socket to hand tighten the nuts down. As the instructions say, do not overtighten or you will squoosh the innards of the potentiometers.

Soldering the Pots
The pots are in, so as Buck Owens once said on Hee-Haw, it's time to start Strippin and Tinnin. At least I think that's what he said. I've got some 26awg hookup wire that should do just nicely, since those holes are pretty small. The pots are to be daisy chained, so I'll strip and tin each set of connections. I made my wire segments about two inches long. First I'll chain the GND solder pins (left-hand side), and then the 5V solder pins (right-hand side). The middle pins are a bit more complicated, so I want to double-check against their positions on the board as I make those connections. And here are the completed potentiometers, or ADC controllers as they should now be known.

Putting it Back Together
This part took me a couple of tries, as the black insert sheet got knocked out of position and subsequently de-clicked one of the middle buttons. A second attempt was 100% successful. monome_test reveals that all buttons and ADCs are fully functional. In the ArduinomeSerial settings, I have left the Cable Orientation set to "left". One more note, plug the unit in BEFORE turning on ArduinomeSerial, or else your device might not be recognized. Also there is a setting called Address Pattern Prefix that seems to be specific for each type of MaxMSP app you run. You need to set that field in ArduinomeSerial to match the app you choose.

Aaaand, here is the final finished product:

I ended up going with the Boss-style stompbox knobs because I really like the way they fit these pots.

And here are some excellent resources for the Bliptronome Kit, Monome, electronics and that.

Resources:

Now to spend some time with my new creation. I'd like to write a bit more about the software aspects of Bliptronomics, but first I'd like to play!

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