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[Build Thread] Arduino based String Machine
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author [Build Thread] Arduino based String Machine
Hi everyone,

as announced wink here, I'm giving this little device published in these two blogs... h/

... a chance. I'm adding the LPF described in the second one, and will also include a MIDI-In jack so I can sequence it. Hopefully, since I have absolutely no programming skills whatsoever and must rely on the sourcecode as published in Jan Ostman's blog.

Anyway - the total (!) costs come up to about 40 Euros or slightly less, so there's not too much risk should I fail wink.

I got a good-as-new Garagekeys Mini for about 15 or 16 Euros off German Ebay, took off the upper part of the case, and built a wooden case very similar to the one in the second blog mentioned above - the keys need to be removed for dismantling it, and I re-installed the outer ones so I coud properly fit the top cover a bit later on:

Since I didn't like the gaps between the lowest and highest keys and the wooden case, I made the top cover cover them:

Some support construction for the top cover (the wooden parts on the sides turned out to be impractical so I removed them again):

Inbetween doing the woodwork, I designed, etched, drilled and populated the PCB for the little LPF (the plastic pot will be replaced with an Alpha pot, however):

The upper part of the now keyless-for-mounting keyboard sitting in the painted case:

The keys are back in place:

And finally, that's how the top cover is placed. The 'gap' will be covered by an aluminum plate (cut to size and drilled yesterday).

Dan Lavin
Nice job! Excellent documentation of the mechanical parts of the build! applause
Some update here as well grin.

The LPF and the output jack are mounted in the case:

The front panel - anodized sheet aluminum, and self-adhesive foil. It has to be assembled from two parts (the foil, that is) as the length exceeds ~ 30 cm/12 in.

I mounted the Arduino clone plus the opto coupler components on a small piece of perfboard to make handling easier. The keyboard connections are already made on this picture. I simply soldered them instead of using some connector:

At this point I'd like to point out that I encountered some problems in compiling the software: C&P from the PDF plus inserting the MIDI lines from Jan's site didn't work out. I was actually about to abandon the project since I have no programming skills nor knowledge whatsoever, making it impossible to fix any bugs. I was very lucky (and am so glad and thankful) someone on another forum helped me by fixing the file and providing it for me (thanks Lars and Jens!) grin.

Anyway, here's how the 3 "left" pots (the other two ones plus a bypass switch are connected to the LPF) are connected. I just attached a bit of cardboard to make handling easier again. The wipers of the pots go to the Arduino, the 'outer' connections go to 0 and + 5 V, respectively.

The little machine is mostly ready by now. I hope I'll have it finished by the end of the week.
Can the keyboard size be extended I wonder ?
Synesthesia wrote:
Can the keyboard size be extended I wonder ?

I doubt it (at least with the software as is) since the software is kinda fine-tuned to that specific keyboard. Maybe someone with programming skills can adapt other keyboards seriously, i just don't get it ?

However, hopefully the MIDI in allows for an extended range (sequencer, external keyboard).
I finished the build on Saturday smile.

I use a common 9V wall wart, from which I take the original 9V for the LP and (via a 7805) 5V for powering the Arduino clone:

Time for powering it up, connecting it to my little practise amp I always keep near my workbench, and to my utter amazement the thing actually works woah lol.

OK, that means mount the aluminum panel to the wooden cover part, put the pots and the switch in their positions, and place the upper panel on the boat:

Does it sound like a real Solina?
Nah, that'd be a bit too much to say. But considering the total costs of under € 40 (or $ 50) - which made it a no-brainer for me - it is definitely not bad, even without using the LPF (which I actually prefer at the moment). The three parameters regulated by the "original" pots do a nice and really effective job.

So, all in all: Not replacing an original 70s string machine, which easily costs 40 - 50 times as much. But still a nice gadget, and surely even more so when played through some big fat effect - I'll of course try it through the Oakley SRE330 once this one is finished grin.

Programming (or at least debugging) skills are certainly of advantage, as I pointed out before.

That's it from my side so far.
Cool. I approve!
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