Sega Mega DRIVE SYNTH

DIY STUFF
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I did some testing with the algorithm switch. I was able to get it working with digitalRead() hooked up directly to the arduino, on a fresh sketch, with the center connected to +5V and the outside pins connected via 1K resistors and LEDs to GND. Controller.cpp does set INPUT_PULLUP on digital Mux pins though, and looks like the code monitors for a state change on the button, not necessarily a high or low. In that case, it seems like the only way to connect it is to have the center pin connected to GND and the other switch pins floating? I tried that too, but it doesn’t seem to be working. It does send a value of 119 for the algorithm CC when I first turn it on, but nothing else when I turn the knob.

@Caustic thanks for all that info! So I guess if I have the 16 channel ones with 4 address lines, I can technically use 16 multiplexers?

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Well, it means you can have 16 addresses. Whether or not it ends up working well with that many is another matter, but i dont see why you wouldnt at least try. :slight_smile:

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So the number of multiplexers you can feasibly use depends on the sampling rate of the analog → digital converter of the arduino? And maybe if I used said Beaglebone I could use more? :smiley:

On a lighter note, I think mine is finally looking pretty enough to share a picture of!

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Words cannot express the level of jealousy that i have for this sanic case.

And yeah, its the sampling rate limit. So its not like it shouldn’t work, you just might experience less smoothness depending on how many you use, and how fast you make the changes.

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After messing with this in its relatively complete form for a bit, here are some thoughts / findings / helpful things:

Some helpful YM2612 info:

https://www.smspower.org/maxim/Documents/YM2612#regb4

https://2xaa.github.io/genmdm-editor/

-MIDI channel switcher knob needs to be wired up with +5V on the center pole and the resistors / LEDs to GND. When the pins are not selected, the resistors act as pull downs, so that stuff actually needs to be hooked up for it to work (I didn’t realize this at first.) I wired this up with 1-6 and ALL, which required me to use digital pin 13. I have heard of issues using this pin, but I think they are all related to using it with INPUT_PULLUP, which we don’t have to use here. Seems to work fine.

-Algorithm switch and any other buttons / switches should be hooked up to GND and have the pin to the mux or arduino floating. I ended up having a bad multiplexer which caused the confusion in my previous post.

-I found that passing the MIDI notes from the poly arduino through the RX of the CC arduino actually doesn’t work too well. Even if I have something playing a fast arp directly into the CC arduino, it will start dropping notes if I also adjust the knobs while it’s playing. In that case, I guess the “correct” approach would be to somehow merge the output of the 2 arduinos before sending it to the OUT jack. Is that what the original THRU circuit does? I wasn’t sure where that schematic came from and didn’t really understand it.

-I did switches for LFO enable and Amplitude Mod enable. If you want to implement switches, you can add a new boolean property on the Button object and some logic to make the CC return to zero when the switch is opened (don’t want to do this for load/save instrument and algorithm CC’s, as LMNC found out.)

-SSG-EG (might want to rename this on the schematics) - there are some pictures in the RYM2612 manual / genMDM editor of the various modes, but they don’t really seem to match up, or it’s not really clear in which order the modes are applied, which register / CC values match up to which waveforms, etc.

-I want to experiment with CH3 special and DAC mode. It looks like DAC mode has a means of receiving “direct data” on CC79. Has anyone messed with this? Does that mean you can “stream” 8 bit samples into the DAC over MIDI?

EDIT: also, does the behavior of velocity with this synthcart seem weird to anyone else? It seems to be very quiet for the normal range of key pressures, and then go off a cliff with loudness. I’ve just been sending all the notes as velocity 127 because otherwise it seems very unpredictable. It doesn’t really seem possible to get a smooth increase in intensity (at least with the default instrument?)

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Hello bro can i find you on facebook to ask you something i try to build sega mega synth but need litle help. Best regard . Aleksandar

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I’m having trouble with Unison mode. In midi-ox, I’ll get all six notes playing, then I’ll release all the keys on my keyboard, and only one note releases. Then I’ll mash the keys and all the notes will release, but the next key I play, only one note turns on in midi-ox.

somehow merge the output of the 2 arduinos

Leapfrogging from Juha’s splitter arduino to the CC arduino is meant to be the merging of the signals, or rather—as I understand it—the sequential processing of MIDI signals. Simply merging two MIDI signals electronically would give you, as I understand it, a big long stream of 1s where there should be 0s mixed in for normally comprehensible MIDI data.

The fact that you’re dropping notes while adjusting knobs suggests we may be hitting up against hardware limitations. It may be that we’re simply using the wrong kind of processors. Does anyone have an extra MEGAfm to reverse engineer?

I’m steadily working my way to a working prototype utilizing all the knobs, so I may soon share your pain.

DAC

I remember reading somewhere in the GenMDM manual that receiving samples has yet to be implemented. Perhaps in the next version…

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Has anyone successfully built one of these? This has to be one of my all time favorite projects!

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Not yet, very work in progress

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Has anyone a contact info for catskull electronics?

It’s about the genMDM.

After being sold out for an eternity, i read that some are being assembled, than they were available. For what i feel was about a week or so. And now they’re sold out again. Couldn’t grab one in time, cause at the right moment, i didn’t have the money. I really wanted to make that MD Synth, but now i have like no hope that it will be available again.

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GenMDM is available again!

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