Another VCDO by @HAGIWO !!! (he never stops 
)
it’s the same schematic that his FM VCO and Additive VCO, only the code change.
CHORD VCO , 5 voice , 8 waveform , 8 chord , and 16 type inversion.
It is based on mozzi library.
Code and schematic
Somebody local was selling a Music Things cord organ module - I was seriously considering picking it up and converting it to KOSMO format - but I just spent a lot of money on headphones.
Hagiwo is an absolute beast.
I think we really need a Hagiwo PCB, these look like they’d fit nicely into a little 5cm module in Kosmo format.
Since we need a 5v supply for the Arduino, would anybody object to using a 16 pin power header rather than the “normal” Euro 10 pin header and a voltage reference chip?
You don’t need 5 V for the Arduino. You can power it off +12 V.
Since the 5v rail on most busboards is just a single 7805, I’d advice against running multiple Arduino modules off it. It’s best to use the onboard regulator as AO mentioned. Or, if you want to run a bunch of LEDs etc, better add a dedicated 7805 or the likes. The onboard regulator is tiny and will run hot quickly. I personally add a regulator if the expected 5V current draw is above 100mA. Though it will theoretically do 200mA
Right, a bare bones ATMega328 powered with 5 V will draw in the ballpark of 20 mA by itself. An FC Power can supply only about 100 mA on the 5 V rail (vs. 500 mA on ±12 V).
If I were doing it I’d send +12 V to the Nano VCC pin and use a TL071 powered with ±12 V for the op amp. No need then for +5 V, except for the Schottkys on the inputs and outputs which can connect to the Nano 5V pin. @HAGIWO apparently is interested in building a synth that’ll run on a single +5 V supply (presumably one with a much higher current rating) but Kosmo builders don’t have that constraint.
I just have to say that @HAGIWO’s efforts also using the same schematics as well is just an amazing thing. Brilliant.
Maybe it’s not very important, but i’ve just see that 's not exactly the same schem, one cap value change.
In the Additive VCO in D9 there’s a 22nf cap to GND and in the Chord VCO it’s a 10nf.
Also I will add 2 caps of 10uf on the power + & - 12V (I will use a TL071) like in others modules, but is that also need a 100nf from the Vin pin to GND, as with opamps ?
thx
I’d put 100nF from the Arduino’s 5V pin to GND. They can freeze up with sudden drops on the 5V line (below 4.5V or so). The Vin pin is only the input to the regulator, so less important.
The nano has a bunch of caps on the 5V rail (both near the regulator and near the atmega) so not convinced you need external ones. They won’t hurt, though, so no need to remove them if you’ve already added them 
Agreed, in 99% of cases you won’t need them. I currently have something on the breadboard with a whole load of LEDs, and here I actually need one. Without, the Nano freezes if I turn on all LEDs at once. In the current circuit: won’t matter.
Gerber data of CHORD VCO has been uploaded!
It works flawlessly!
Please if I use a TL071 does the rest of the circuit remain the same ? no diode connected to -12 instead of GND ? or something else ? thx 
You need to power the TL071 with ±12 V to keep the signal away from the supply rails, but the signal path is still 0−5 V so everything else should stay the same (clamping diodes to +5 V and GND, control pots to +5 V, etc).
Maybe add 2 x 100nf on the TL071 and 2 x 10uf on the power rail ?
In @kenji’s version with the +5 V powered op amp I’d add a 100 nF to pin 8 of the op amp. I’d say a 10 µF on the +12 V rail probably wouldn’t hurt, though it might be superfluous.
thank you
(more ch…)
