Gameboy oscillator documentation

Hi! I am looking for some info on the Gameboy (triple) oscillator. I got an old Gameboy already and installed the background light.
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Ordered a cartridge with mgb from catskull electronics, but apparently it has not been shipped yet… I have the ltc1799 for pitch bending, but I am missing some things, like

  • what value for the potentiometer on the ltc1799 would be good?
  • for CV just add a vactrol or is there another trick with the ltc1799?
  • how to power the Gameboy with eurorack? It needs 6V, I only have 7805…
  • how to do the mounting on the panel?
  • did Sam document the midi injector(?) somewhere? I mean the arduino(boy) that has additional inputs for wave selection?
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From the LTC1799 datasheet: image
I guess that the Gameboy runs at 8MHz, so you would need a 12k resistor (or 6k8 in series with a 47k pot) with the DIV pin on GND.

You can do something like that:
image
But you would need a floating source, or at least some weird shenanigans… Start with a vactrol.

I think your Gameboy is ok with only 5V, you can try without fry it, at least.

Sam did some clever trick for the mounting, check his video.

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Thanks! I will try powering the gameboy with 5V today. Also I found this video when looking for the mounting options:

EDIT: The original stripboard had a mistake!! The 1k resistor should go to the lower left pin of the LTC1799 (pin 4)!!

(from this video)

That looks like a voltage mixer to me! I will go with that!

Edit: I found more info in the zine!

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Would you have to strip the stripboard under the ltc1799 like you would under the t072?

Always strip the stripboard between the two rows of legs of a dual-in-line IC, otherwise they will be electrically connected. You almost never want that.

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Screenshot from 2020-08-27 18-12-19

Looking at this from the datasheet, I am wondering a little if the stripboard has a bit too much voltage…

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Yes and no… Here only the current count, and the input will be protected by the resistor.
So this circuit is not perfect, but if it works, it works, I guess ?

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It is not yet working :wink: I only get oscillations (I measure the output with my scope) when I touch the lower left pin on the breakout board… That one that is not supposed to be connected to anything. So I am looking to understand the circuit :wink:

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Now it’s working! The layout had a small mistake, the 1k resistor needs to connect to pin4 (the lower left) of the LTC1799! Now I can play Kirby’s Dreamland in slow motion speed until the mGB cartridge arrives! :sunglasses:

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The mGB cartridge arrived and I built the Arduinoboy. But it is not yet working… as soon as I play any note on the midi keyboard the Gameboy crashes :-/ I already swapped the Gameboy connections (rx and clock) but then nothing happens at all… Ideas anyone? :slight_smile:

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It works now!!! Just resoldered, as always xD
Still crashes a lot, if I enable or disable the cpu freq Modulator… but it works!!
Now for the coding part! I need to find out how to send additional CC commands from the Arduinoboy sketch based on potentiometer turning…

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Did you find out how to write the code for the CC manipulator thing? Its an important thing I’m missing, I’ve only found really brief info in one of the game boy mega-machine updates, other than that I’m lost. Never really done anything this…“out there” before so I’m completely mythed by it all.

Any help or guidance would be insanely appreciated. :slight_smile:

Hey, yes I did, have a look at this commit:

I have 4 pots now next to the gameboy, 3 for changing the waveform for the 3 channels and 1 for changing the offset of the 3rd wave. you can easily check the CC codes for other parameters and make the knobs do other stuff :slight_smile: I also changed the code so the arduino is always in mGB mode. There are some issues though: the cc messages are only send when a knob is turned, so on reset the gameboy uses the default values until you turn a knob (this can be easily fixed, by calling the update function once in the init() part). And I also have the problem that I need to press B on the gameboy after I turn it on to reset it. Before that, there must not be any midi message to it, otherwise it completely crashes… I have no idea why that is and how to fix it. Maybe anyone has an idea?

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Could you run another script on the arduino to press b through relays or smth once it detects its on? Also thank you so much for this documentation, its gold

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Could i be a pain and ask to see how you’ve got all your knobs wired in and configured? I’m not massively great at code, ill have a look with my teacher or something and see if i can draw a wiring map from it but if you can provide any help in that field ill be infinitely great-full :slight_smile:

(edit)
So…i read the code through and sort of understand the code, does the CC injection happen on another arduino and then passed through to the arduinoboy? Im just not sure what im doing. I got all the parts to build the triple oscillator but idk if it would be much use for me without all the CC stuff so im stumped.

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Ive found the point with your addition with the potentiometers and it makes alot more sence now, could i ask which value your potentiometers are? I think by the looks if it this runs off all one arduino and i assume the knobs are in the same panel? that would be awsome for having everything neat and tidy. Apologies if i seem like im nagging, im just got into this hobby a few months ago, going from piano to synths so im extremely excited, the gameboy oscillator would be an awsome addition to my ever growing box

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All good! :slight_smile: I’m happy to help! The potentiometers are 10k, but you can also use 100k or whatever you have ready (10k is the “optimal” value for Arduino, but I guess it does not really matter so much). They are set up as voltage dividers, so the left leg goes to ground, the right leg to 5V (from the Arduino) and the center pin goes to the arduino analog input. The same of all four (you can of course add more). Yeah, the knobs are directly next to the gameboy, I posted a photo somewhere in this forum, I will see if I have it still on my phone…
For the rest of the wiring, its basically the circuit from this thread for the LTC1799 (pitch mod), with only one CV input, then the Arduinoboy wiring from the github. And I also power the gameboy from a 7805 and not batteries. In the gameboy I also did the “pro sound” mod, that means soldering the audio out before the volume pot, if I remember. And I also added a simple opamp amplifier after the audio output, because the gameboy output is very quiet compared to synth levels.
Does this help? I can also take it out and make some more photos so you get a better idea?

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Thats amazing, thank you so much, taking it out and having a look would be really really helpfull if it isnt too much hastle for you.

Thank you so much :slight_smile:

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image
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Not sure if that helps though… I will draw a little circuit when I got time xD

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welp - i know who im bugging when i wanna build one of these… lol

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