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Kosmo Multitool

This repository contains schematics, PCB and source code for a synthesizer module in Kosmo format. This module consists of an Arduino Nano Every, CV and gate input and output options, MIDI, rotary encoder and an OLED display. It is meant as a development platform for DIY synthesizer enthusiasts.

Here is a full list of features:

4x CV input (0-10V)
4x CV output (0-10V)
4x gate/trigger in
4x gate/trigger out
1.3" OLED display
DIN serial MIDI in/through/out
Rotary encoder with switch
3 switches
2 LEDs

Kosmo Multitool Assembled

Modules

ADSR
Arpeggiator
MIDI to CV
Multiple
Quantizer

Building

Gerbers for the main PCB can be found here and for the front panel here.

Kosmo Multitool Panel Kosmo Multitool PCB

BOM

Reference	Quantity	Value	Comment
A1	1	Arduino Nano Every
C1 C2 C3 C4 C6 C7 C8	7	100n
C5 C9 C10	3	10uF
D17 D18	2	LED 5mm
D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D19	17	1N4148
FB1 FB2	2	Ferrite Bead
J1	1	MIDI_IN	Molex KK 2.54mm 2 pin
J10	1	CV_OUT	Molex KK 2.54mm 5 pin
J2	1	Display I2C	OLED display 1.3" 128x64 I2C SH1106
J3	1	GATE_IN	Molex KK 2.54mm 5 pin
J4	1	GATE_OUT	Molex KK 2.54mm 5 pin
J5	1	ADS1115 breakout	ADC, pin order: VCC GND SCL SDA ADDR ALERT A B C D
J6	1	MIDI_THRU	Molex KK 2.54mm 2 pin
J7	1	MIDI_OUT	Molex KK 2.54mm 2 pin
J8	1	MCP4728 breakout	DAC, pin order: VCC GND SCL SDA LDAC READY A B C D
J9	1	CV_IN	Molex KK 2.54mm 5 pin
POWER1	1	POWER	IDC 10 pin
R1 R2 R3 R4 R11 R12 R15 R16	8	1k*
R5 R8 R13 R14	4	22k
R9 R10 R17 R18	4	33k
R25 R26 R27 R29 R30 R31 R32 R33	8	220
R28 R34 R35 R36 R37	5	10k
R6 R7 R19 R20 R21 R22 R23 R24	8	1k
SW1 SW2 SW3	3	SW_Push	Tactile Push Button 6x6x15mm
SW4	1	Rotary_Encoder_Switch	Rotary encoder with switch, 20mm
U1	1	TL074
U2	1	74LS14
U3	1	6N137
U4	1	L7805
		Pin sockets, 2.54mm	Needed for the Arduino, OLED display, ADC and DAC
	16	Jack sockets 6.35mm
	3	DIN MIDI sockets

* match in pairs to get more accurate ADC readings

Installation and calibration

Clone the repository and open up the src/main folder in the Arduino IDE or whatever you use for compiling. You need to install the libraries mentioned below into you Arduino library folder. The ADC and the DAC need calibration to get proper results.

ADC calibration

Set CALIBRATE_CV_IN variable in main file to 1. Apply a fixed, known voltage to CV1 input, eg. 5.000V. On USB serial console (9600 baud) you get the actual reading from the ADC. Calculate the correction factor FIXED VOLTAGE / ACTUAL VOLTAGE, eg. 5.000 / 4.9884 = 1.0023. Enter the value in the CV_IN_CORRECTION array in the top lines of main.ino. Repeat this procedure for all CV inputs. In the end it should look something like this:

float CV_IN_CORRECTION[4] = {0.9995f, 0.9956f, 1.0013f, 1.0009f};

Notice the trailing f to tell the compiler that these are float values. Don't forget to set CALIBRATE_CV_IN back to 0.

DAC calibration

Make sure to calibrate the ADC first. Set CALIBRATE_CV_OUT variable in main file to 1. Plug in patch cables from all four CV inputs to the CV outputs. Calibration is done automatically and stored in a look-up table. Set CALIBRATE_CV_OUT back to 0. This step is only needed once, from now on calibration values are loaded from EEPROM on start up.

Development

Source code is in src/main. If you want to develop your own module just copy the files example_module.h and example_module.ino and rename all functions and variables that are globally available. Include your header file in the main.ino file and add your entry to the main menu. Take a look at the already existing modules on how it works in general. If you created a nice module please file a pull request and I would be happy to merge it.