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welcome to the CHEAP, FAT and OPEN wiki

here we will collect all relevant links and information about the CHEAP, FAT and OPEN project. feel free to join in and edit!


uncertain how to edit? this wiki uses the same editor as wikipedia, here is a good (superfast) introduction:

what is CFO?

CHEAP, FAT and OPEN (CFO) is an open source synthesizer, mixed with a stylophone, a gameboy, a circuit bent toy, and then some software too

it is open source and designed to be OPEN and hackable, and therefore the project is inherently messy.

you can do a lot of things with CFO, but CFO has a lot of limitations as well. that's the beauty of it, go with the flow.

this is NOT a finished product. many (most) things are still under development, so expect bugs! errors! glitches! -- treat them as features ;) or dig the code and change them for the better.

the following is a kind of feature list. quite incomplete. feel free to add.

features CFO

  • monophonic sound via 12bit DAC
  • stylophone input (can be overridden by CV / analog input)
  • pitch bend / expression control via body switch (can be overridden by CV / analog input)
  • CFO is programmed in arduino programming language. cpu: atmega328.
  • midi in via (programming) FFT-USB cable is possible (although not implemented in code)
  • sync+data send+receive via infrared connection possible (limited support in code)
  • op amp with bass boost + distortion
  • 16x2 character LCD displays
  • 16 LEDs for step sequencer
  • rotary encoder + navigation buttons for general UI
  • custom tracker software is available for programming arpeggios / instruments. tracker software is programmed in processing.


errata (things to fix)

CFO MFRU 2010 revision ERRATA

CFO MFRU 2010 eagle/pcb revisions

  • create lbr with all parts revisions
  • review VOLUME potentiometer (layout + schema)
  • review MCP4921 part (schema)
  • review LM386 part (schema)
  • fix stylo input layer from top -> pad (schema + layout)
  • fix USB TTL RX/TX
  • review missing grounds here and there (schema)
  • review power lines names here and there (schema)

new addition to LCD:

  • pin 15 on LCD can go straight to VCC (5V), no weird little 4,7 ohm resistor is needed for LCD module

jacob adds

  • rotary encoder, button function could be accessible with 2 holes for connection to XXX
  • move reset button, so it can be reached easier when acryllic is on
  • noise on stylo is high (is the signal line to close to VCC?)
  • edit silkscreen + names so that explanatory txt is shown // component names
  • LCD display should be placed lower (lower female headers), for slimmer design, and so no extra spacers are needed for assembly
  • buttons are still a bit flakey -- could we accomodate their footprint better in eagle design? (holes in PCB?) something that would secure the right placement/rotation too?

nice to have // possible future features

put your ideas here :)


  • hold feature fro stylophone playing
  • ADSR envelope
  • expression control could determine gain
  • better gate sequencer select
  • substeps in sequencer, for possible groove / swing settings and polyrhythmic jams
  • store settings in EEPROM



the tracker part of this project is a programmed in processing, and is a way to program sequences which can be stored in the CFO program memory.

  • the tracker and how to use it should be documented

on this wiki / the internets

  • document synth interface (buttons, encoder etc.) -- how do you play it?
  • better build instructions


  • better video demo


CHEAP, FAT and OPEN is an open source platform for musical exploration, composition and performance.

The platform is CHEAP, and OPEN – welcoming you to experiment.

A combination of the old and new: the raw 8bit / chip tune approach combined with wireless connectivity, state of the art open source hardware, and expandability – gives us that FAT sound.

It is portable, allowing you to make music on the go.

The platform is a performance instrument, giving a full 1½ octave keyboard control in compact packaging, through a classic stylophone interface. It is also a sequencer, allowing you to program rhythms and melodies, and play them back in sync with other platforms and instruments.

This is NOT a finished product. It works as is, but inside the platform rests an atmega328 processor, which can be programmed in the Arduino environment. This means that the platform can be modified, expanded, and tweaked to meet your needs.

CHEAP, FAT and OPEN is designed for geeky musicians, the chip tune community, the makers, the circuit benders, the interaction designers and the musical programmers, and anyone else who wishes to experiment with sequenced / networked / low-level musical exploration.


This project was started by jacob sikker remin for his CIID thesis in 2009.

This project is based on knowledge and inspiration from many different communities. It is the hope, that by bridging these different creative communities, we can create something beautiful together.

image of the first edition of CFO. made in 4 copies for CIID thesis by jacob sikker remin

CFO in hand.png

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