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 Forum index » DIY Hardware and Software
Monotron Duo.
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sneakthief



Joined: Jul 24, 2006
Posts: 531
Location: Berlin

PostPosted: Thu Mar 27, 2014 10:05 am    Post subject: Reply with quote  Mark this post and the followings unread

First of all, nice work.

You're definitely going to need to implement some kind of auto-tune function because there doesn't seem to be either tempco's or oscillator-scaling trimmers, therefore the MCU is taking care of all that. Otherwise the tuning is going to drift all over the place. That's how they can make this thing so cheap.

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alfa66



Joined: Mar 03, 2014
Posts: 3
Location: Bay Area, California USA

PostPosted: Sun Apr 13, 2014 10:11 pm    Post subject: Completely Midi-fied Monotron Duo using Teensy 3.1 Reply with quote  Mark this post and the followings unread

I kept working on it since my last post, here it is - i get between 4 and 5 octaves:
https://www.youtube.com/watch?v=4ZYha-b2i_g&feature=youtu.be

In short:
Vrib controls 18 half tones, it requires linear voltages from 0.1V to 3.3V.
The Gate signal is generated by the TI processor of the Monotron Duo.
The voltage "knob pitch" goes from 1.4V to 5V: this was tricky to tune.
I used the DAC of the Teensy 3.1 to control Vrib, and another DAC to control the octave pitch.
To control resonance and frequency of the low pass filter, I used two digital potentiometers (AD8402).
The board that I designed has also an output for the Gate signal (which i ended up not using it, per the above explanation).
So the board will also work for the regular Monotron.

I also thought about swapping completely the TI processor and replace it with the Teensy 3.1, but that's tricky - more work on the SW side as it appears that the Monotron Duo has some auto-tuning function as somebody has already pointed out.
So if you are interested in Midi-fying your Monotron Duo with the existing controls and if you are willing to remove the main VCO tuning pot we now know how to do this....

This was a great project.
I have 4 boards left, let me know if anybody is interested.
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alfa66



Joined: Mar 03, 2014
Posts: 3
Location: Bay Area, California USA

PostPosted: Mon Apr 14, 2014 12:02 pm    Post subject: Using the MSP430 won't give you full MIDI pitch control Reply with quote  Mark this post and the followings unread

-> KalleWhoever outstanding work... I will look at the asm later.
Regarding adding MIDI to the MSP430, I need to point out that if you are able to accomplish that, you will only get control over the 18 half-tones of the ribbon - that's it.
And this is easily do-able by accessing the Vrib pad of the Monotron Duo.
I stopped seeing the value of reprogramming the MSP430 after realizing that we could only get about an octave worth of keys.
Please share if you see other reasons, the work you have done is remarkable.
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jlerhun



Joined: Aug 05, 2008
Posts: 2
Location: France

PostPosted: Thu Apr 24, 2014 8:17 am    Post subject: Re: Programm your Duo with Energia and the TI Launchpad
Subject description: New discovery
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KalleWhoever wrote:
My next step was to take a raw dump, hexout and disassemble everything via mspdebug.

That's great! I wanted to do exactly that as soon as i've seen the Monotron Duo schematic. Unfortunately, though i do have a Launchpad i don't have a Duo now, only a Monotron Delay.

KalleWhoever wrote:
Since there are 3 unused Pins on the MSP430 and a spare opamp on the PCB I see many possibilitys for extending the Synth.

You can look here to implement a MIDI input on MSP430 : http://naturetm.com/?p=111

alfa66 wrote:
I stopped seeing the value of reprogramming the MSP430 after realizing that we could only get about an octave worth of keys.

And why is that? Just because of the supply voltage of the MCU? Couldn't we then increase the gain of IC3b to increase the available range?

Did anybody try and hook an oscilloscope at the spare pins of the MSP430 (P1.5, P1.6 and P1.7) ? Or to feed some MIDI messages there (at adequate voltage) ? Maybe Korg already implemented a MIDI interface there, as they did in the Monotribe ?
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retroware



Joined: Apr 26, 2014
Posts: 1
Location: united states

PostPosted: Sat Apr 26, 2014 5:40 pm    Post subject: Re: Programm your Duo with Energia and the TI Launchpad
Subject description: New discovery
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First, thanks kallewhoever for all the hard work. But the rom dump looks like it might be incorrect. It is mostly zeroes and the disassembly doesn't look right. I've been interested in modding my duo as we'll and would be willing to spend some time figuring what software korg has implemented.
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damosuzuki



Joined: May 06, 2014
Posts: 1
Location: silver spring, md

PostPosted: Tue May 06, 2014 10:56 am    Post subject: CV for monotron duo
Subject description: sending CV via Arduino
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Hello all, Finally joined this forum after lurking for way too long... Evil or Very Mad

I just got a monotron duo recently and have been working to try to send CV to the synth via an Arduino to use it as a "poor man's sequencer". Thanks to all who posted previously, it was a big help in getting this to work.
The final solution for this was to send a 0-3VDC signal out to the Vrib connection on the PCB. I used the PWM out function on the Arduino through an R/C filter (100ohm R, 10mF electrolytic C) and it works great so far. Added a 10K pot to control the note duration and then for now just manually programming in the sequences.
Hope this helps someone looking to do the same thing as me. Can give more details if requested.
One question: what is the Vbias used for? What I'm hoping is that I can use this to "tune" the monotron and/or expand the range beyond 1 1/2 octaves. Anyone tried this yet?
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