mini MIDI to CV converter with Gate and Trigger outputs

PHOBoS

I added a simple MIDI to CV converter to a MIDI keyboard. At the moment it only makes use of NoteOn and NoteOff messages but I might
add Pitch Bend later. The keyboard I used also has some knobs that send out CC messages so maybe I will do something with that too.
I tapped the midi signal of from the keyboard PCB but if you want to use it with a regular MIDI input you can add the circuit with the 6n137
optocoupler. I don't have the right rotary encoder (with a switch) yet so that'll be installed when it arrives. (could take a couple of weeks)

Here's some info, a schematic, the arduino sketch and some photos.

ixtern · Joined: Jun 25, 2018 Posts: 145 Location: Poland

Thanks! Nice simple solution and clear understandable software. Although I have Midi2CV from Erica Synths, I am thinking about my own to make.

PHOBoS · Posted: Mon Oct 14, 2019 2:33 pm Post subject:

here's version 1.1 with some small changes:
- replaced digitalWrite for Trigger and Gate outputs with direct PORT manipulation (faster).
- moved the encoder debounce from the adjust_dac_value() function to the read_enc() function.
- added inputs for (DIP)switches to set the octave range.

The switches are optional and if left out the default range (set with low_octave) is used.

mini MIDI to CV [V1.1].gif

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MINI_MIDI_TO_CV_V1_1.ino

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MINI_MIDI_TO_CV_V1_1.ino

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ixtern · Joined: Jun 25, 2018 Posts: 145 Location: Poland

Maybe it would be better to separate initial debug sequence with if statement and debug on/off variable (or debug define). Debug is very useful during development and test phases but not needed when code is mature so anyone can set temporary debug preference.

I prefer such approach in my sketches. With if - all debugs are ommited during execution, with define - debugs are not compiled making program smaller (if there are many and complex debugs).

PHOBoS · Posted: Tue Oct 15, 2019 10:00 am Post subject:

I am not sure what 'initial debug sequence' you are refering too.
Almost thought I accidentally uploaded a test version.

ixtern · Joined: Jun 25, 2018 Posts: 145 Location: Poland

PHOBoS · Posted: Wed Oct 16, 2019 6:09 am Post subject:

oh, that's a feature Laughing

I thought it might be usefull if you calibrated it and wanted to save the dac settings for some reason.
I used it myself to paste into the preset array after calibration, and it could be used to save different scales.
You can take it out of the code but I don't really see a downside to it being there.

Pastor McPurvis · Posted: Fri Nov 22, 2019 2:28 pm Post subject:

Hey PHOBoS,

Just wanted to say thanks! Built this the other week and it is working great.
Basically built it up on veroboard and have it behind a plywood panel (it is the middle panel in the pic below).

Thanks again!

PHOBoS_midicv.jpg

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PHOBoS · Posted: Fri Nov 22, 2019 3:34 pm Post subject:

awesome!

I like the panel designs, makes me curious what the one on the left is.

I am working on a version with an arpeggiator but haven't implemented the latch function yet. All controls are done through
midi CC so it wouldn't require any extra (or changes in) hardware, besides maybe an input for an external clock input.

Pastor McPurvis · Posted: Fri Nov 22, 2019 3:55 pm Post subject:

The one on the left is a simple passive multiple I use to split CV, and a power input because I set up my power supply as a bench top unit to use both for testing and power for the rack.

The additions sound great. I'll be sure to keep an eye out for them.

All the best!

bubzy · Posted: Sun Jul 12, 2020 1:16 am Post subject:

hi phobos!
wondering how difficult it would be to implement multiple channel outs?
obviously would require separate DACS for each out but could make sequencing from software more interesting Very Happy

PHOBoS · Posted: Sun Jul 12, 2020 7:19 pm Post subject:

hi bubzy

you mean multiple CV outs by using multiple midi channels ?

that would be possible and yeah you need more DACs. The nano only has 2 I2C outputs and I don't think you can even change it on the DAC.
You could use a DAC with multiple outputs though. Not exactly sure if tuning would work well as the voltage for every note is stored in the
internal eeprom and there's not much room in there, but that could also be added. Code wise it probably wouldn't be that hard to do.

blue hell · Posted: Mon Jul 13, 2020 4:59 am Post subject:

Usually you can have like 8 of the same device on one i2c channel with external address selection bits ... that would be a bit hard with a 6 pin device though .. time to have a look at the data sheet [1] ...

Ah, datasheet says the DAC has one external address line A0, so you can have two per i2c interface ...

And then it also says that that it has 8 possible addresses .. hmm .. how .. right .. that comes form the order code [2] ... you can order different combinations of A1 and A2 .. so that makes eight per i2c channel .. so then you could have 16 ananalog outputs Shocked

Hmm .. but you'll have to contact µChip about that, default for (A2, A1) seems to be (0, 0) ... so the other three combinations may be for big customers only ...

Four then I guess on two i2c channels.

[1] https://www.microchip.com/wwwproducts/en/en532229

[2] order codes are: MCP4725 xx T E /CH where xx can be A0, A1, A1 or A2 for address bits (A2,A1) being (0,0), (0,1), (1,0) or (1,1)), T for tape and reel. E for temperature range, /CH for package type.

blue hell · Posted: Mon Jul 13, 2020 5:02 am Post subject:

Hmm .. they seem a bit expensive too?

Edit, stumbled on a bad supplier I guess .. also seeing now that Mouser has A1, A2 and A3 versions as well as A0. Cool

PHOBoS · Posted: Mon Jul 13, 2020 5:40 am Post subject:

you can also use an I2C mux like the 8 channel TCA9548A which you can get on ebay for around 2,-

blue hell · Posted: Mon Jul 13, 2020 6:47 am Post subject:

gabbagabi · Posted: Mon Jul 13, 2020 10:41 am Post subject:

do you've used the arduino that is ava on tayda ?

https://www.taydaelectronics.com/nano-3-0-controller-compatible-with-arduino-nano-ch340-usb-driver.html

for those who care about insects (as i do alot) they have also this
https://www.taydaelectronics.com/arduino-pro-mini-atmega328p-16mhz-5v.html
a bug and a half cheaper, dunno if it has I2C?
i can imagine the pinout is not equal, so it would need code adaption if i would use the cheaper one?

it seems u have the dac in a red enclosure? is it a kind of smd2dip adapter?

anycase nice compact and extremly usefull circuit this is!

PHOBoS · Posted: Mon Jul 13, 2020 11:47 am Post subject:

Oh, I hadn't noticed Tayda sells arduinos too! Shocked

I'd have to look at the specs for the pro mini but I doubt it is very different. However, it doesn't have a USB port so programming it is a little bit less
convenient. Code will probably work mostly as it is, because the actual pin mapping is done by the IDE. For example in the code the encoder button
is connected to digital pin 4 which is actually pin 22 on the nano and a different pin on the pro mini but it doesn't have to be adjusted. Of course you
will have to connect the button to the correct pin. Maybe the I2C pins are different let me check,..

nope, looks like those are the same too, I guess it makes sense as both boards are based on an ATmega328P.

bubzy · Posted: Tue Jul 14, 2020 10:15 am Post subject:

welp, i built the single version on breadboard quickly and it works like a charm Smile

nice job.
will dig into your code and see if i can play about, maybe get a few mcp4922's running.
does the midi library support polyphony? Very Happy

PHOBoS · Posted: Tue Jul 14, 2020 10:33 am Post subject:

great to hear it works! Very Happy

Polyphony would work fine. All the midi library does is make it easier to process the midi signals.
Unless there is some sort of polyphonic midi command I am not aware of.

michelangelo_n · Joined: Sep 14, 2020 Posts: 1 Location: Italy

Hi, this is a nice project! which kind of encoder are you using? does a normal potentiometer do the job? I'm using a B100k pot and measuring the voltage out of the wiper for calibration. but I'm not sure I'm doing it right.

PHOBoS · Posted: Mon Sep 14, 2020 10:40 am Post subject:

no, a potentiometer doesn't work with this code. A rotary encoder doesn't work by changing resistance but by sending pulses that are
out of phase. you can find some more info about that here: https://howtomechatronics.com/tutorials/arduino/rotary-encoder-works-use-arduino/
The one needed for this project also has a built in momentary switch, though you could use an encoder without a switch and just
add a seperate one. For the rest it is just the most basic encoder that you can find pretty much anywhere.

wallybob · Joined: Sep 26, 2015 Posts: 7 Location: Iowa

PHOBoS, I was wondering what it would take to use this device with my USB MIDI keyboard? Could the Nano USB port be configured to either a programming port or a MIDI port?

PHOBoS · Posted: Tue Jan 12, 2021 3:43 pm Post subject:

not the nano but the arduino pro micro can do midi over USB, that would require some changes in the code of course.
Shouldn't even be that hard, it's just the midi reading section that needs to be replaced to get the midi note data from USB.
There is a USB MIDI library available to make things a lot easier.

also
welcome

Grumble · Posted: Wed Jan 13, 2021 7:16 am Post subject:

Some time ago I stumbled upon a project called HIDUINO (it is still there, just google) where a class-compliant USB-MIDI device from an Arduino UNO or Mega 2560 can be programmed so you need no drivers because it’s native to windows.
Just be sure to get an UNO with an ATMEGA8U2 or ATMEGA16U2.