The Chameleon System

A Eurorack hardware module with digital flexibility.

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The Chameleon System consists of a hardware module, a Chameleon, that can be flashed with software files to decide its functionality. There are already files developed for the system, but it's also possible to write own programs that utilize the user interface and controls.
It is based around Teensy 3.5 MCUs and Audio Shields from PJRC.

There are two types of Chameleon:

This is a module equipped with a MCU as well as an audio shield. This module is for files that handles audio input or output, such as oscillators, filters etc. The available files are:

• PANTHER Digital Synthesizer Module.
• NAMAQUA Four Oscillator Module.
• TIGRIS Stereo Filter Level Shaper.

This is a module equipped with just a MCU. This modules is for files that handle data manipulation, LFOs, envelopes etc. The available files are:

• NAMIBIA Note Input/Output and Data Randomizer.
• JACKSON Function Gen

SPECIFICATIONS CHAMELEON.SONIC MODULES ARM Cortex-M4@180MHz, 2-channel audio I/O, 3xC11D I/O, 3xGate I/O, TFT 2.2"-screen, Four potentiometers, One rotary encoder.

SPECIFICATIONS CHAMELEON.SIGNAL MODULES ARM Cortex-M4@180MHz, 4xC11D I/O, 4xGate I/O, TFT 2.2"-screen, Four potentiometers, One rotary encoder.

POWER DISTRIBUTION Power is supplied to a Chameleon connected to power via its USB-port.

DATA COMMUNICATION The Chameleons communicate with each other using standard 3.5mm cables sending and receiving 11-bit data. I call this technique C11D or Controlled 11-bit Data as a digital equivalent to CV, Controlled Voltage. Values between 0 and 2048 are sent and received. A parameter with High and Low modulation shelf subtracts 1024 from the incoming value making it possible to modulate between 0 and 2048 or -1024 and 1024.

PERFORMANCE CONTROLLERS The four analog potentiometers on each module work as controllers for real-time control of key parameters.


  • 1 × PJRC Teensy 3.5 USB Development Board
  • 4 × Alpha 10K potentiometer Performance Controllers
  • 1 × 2.2" TFT Screen with SPI interface and ILI9341 driver.
  • 1 × PJRC Audio Adapter Teensy Audio board add-on for the Teensy 3.x line development boards.
  • 16 × 3.5mm audio jack Audio, Gate and Data I/O.

View all 11 components

  • PANTHER synthesizer

    Johan Bilén11/07/2018 at 16:02 0 comments


    Just finished the Panther synthesizer module. These are the specifications:
    3xDCO, Noise and Mixer.
    Semitone, Detune and Glide.
    State Variable Filter with resonance.
    Pitch LFO, pulsewidth LFO, filter LFO and amplitude LFO.
    Pitch envelope, filter envelope and amplitude envelope.

  • Chameleon4 - Modular Digital Synthesizer

    Johan Bilén10/30/2018 at 09:48 0 comments


    I'm putting together a complete synth consisting of four chameleon modules in one frame.
    As I have mentioned in a previous post this synthesizer will have the following specs:


    Software files used:
    Slot 1:  Namibia MIDI I/O
    Slot 2: Namaqua oscillator module
    Slot 3: Tigris filter module
    Slot 4: Jackson data modulator

    MIDI IO with channel select and MIDI clock out. Note, velocity, pitchbend and modulation wheel output.
    Arpeggiator with external or internal sync. Up, down, up/down or random pattern.
    Chaos Designer randomizer with external or internal sync. Range and speed adjustable via performance controllers. Note (0-112) or frequency (0-2047) output.
    DCO x 4 with individual stereo panning, mixer level and semitone tuning. Pulsewidth modulation and FM. Nine waveforms (Sin/Saw/Sqr/Ramp/Tri/Pulse/WhiteNoise/PinkNoise/FM). Manual mode where each oscillators frequency is adjusted via performance controllers. Legato between 0-635ms.
    DCF x 2 with link function, two individual mono filters or one stereo filter. State Variable Filter with Low, Band and Highpass filter. Resonance and manual frequency adjustable via performance controllers.
    DCA with external control and bypass function.
    ADSR x 2 with fast, medium and long mode.
    LFO x 2 with fast, medium and long mode. Four waveforms; triangle, sawtooth, square and S&H. Cycle end indicator via gate jack. Rate controlled via data input jack or performance controller. Amplitude controlled via data input jack or parameter value.
    56 point modulation matrix with 14 gate input jacks, 14 gate output jacks, 14 data input jacks and 14 data output jacks.
    Audio Interface with 4 audio input jacks and 4 audio output jacks. Daisy-chain function where the audio inputs are routed and mixed directly to the audio outputs.

  • Everything's working!

    Johan Bilén10/05/2018 at 09:26 0 comments


    Having tested all the modules I'm now ready to complete the project.

    MIDI module NAMIBIA is working!

    Data Out 1-3: MIDI-Vel-PB/MIDI Arpeggio/Chaos Notes/Chaos Freq.
    Data Out 4: Mod. Wheel/Perf. 1
    Arp Mode: Up/Down/Up-Down/Random
    Arp Speed: Manual/Gate In 1
    Chaos Trig: Manual/Gate In 1
    Pitchbend: 0-10

    Four oscillator module NAMAQUA is working!


    Data input 1: Note/Frequency/Performance/Performance+
    Waveform 1-4: Sinewave/Sawtooth/Ramp/Squarewave/Triangle/Pulsewave/White Noise/Pink Noise
    Audio Out 1-4: Left Ch./Left/Right Ch./Right Ch.
    Audio Level 1-4: 0-10
    Semitones 1-4: -24/+24
    Detune: 0-100hz
    Glide: 0-100

    Stereo filter and amplifier module TIGRIS is working!

    Type L: Lowpass/Bandpass/Highpass
    Frequency L: Data In 1/Performance/Performance+
    Type R: Lowpass/Bandpass/Highpass
    Frequency R: Data In 2/Data In 1/Performance/Performance+
    Amplifier In: Data In 3/Bypass

  • Yet another change of plan

    Johan Bilén09/12/2018 at 18:58 0 comments


    Analog potentiometers as devices for entering values are not suitable for this project since I cannot seem to get steady readings. The four potentiometers will therefore be used as PERFORMANCE CONTROLLERS controlling the "tweakable" parameters like filter frequency, oscillator frequency etc.

    The rotary encoder will take over the role as data entry device. One click to enter, change value, then one click to exit.

    So now I'll have to come up with a new UI.

    Also the five UARTS I mentioned in a previous post is not possible on the SIGNAL modules since UART 2 pins are used for the TFT. Bummer...

  • Change of plan

    Johan Bilén09/09/2018 at 18:48 0 comments

    Now three Core modules are assembled apart from the 3.5mm jacks. The Xtend module did not work, I had switched VCC and GND for the OLED and probably missed other things as well when designing the PCB.

    So I decided to skip the Maple Mini and use the PCBs I have for the Core modules. The audio I/O jack can easily be replaced by two more UART connections (TX/RX2 & TX/RX3). So the XTEND module be similar to the CORE modules except the audio I/O will the replaced by two more data I/O=5 UARTS!

    CORE is now SONIC.

    XTEND is now SIGNAL.

  • Plans for the first final setup

    Johan Bilén09/07/2018 at 11:23 0 comments


    The basic setup when everything is assembled and checked will consist of four modules:
    This will be a system with:
    MIDI IO with integrated Arpeggiator and Randomizer.
    4 x DCO
    2 x DCF
    1 x DCA
    3 x ADSR
    2 x LFO

  • First Core module assembled

    Johan Bilén09/06/2018 at 19:24 0 comments


    The first Core module is assembled with some spare parts lying around and is now tested, all gates I/O, all data I/O, encoder switch and rotation, all four potentiometers, the TFT-screen and power pins are working!

    I'm going to skip the LEDs because of space issues. I have to use straight 3.5mm cables instead of angled for the same reason.

    My decoupling cap (01uF) that I placed between signal and ground on the potentiometers did absolutely nothing to smooth the incoming signal so I'll have to implement a software solution.

    The next step is to wait for headers and 3.5mm jacks to arrive from China so that I can assemble and test the Xtend modules.

  • Third version of PCBs has arrived

    Johan Bilén09/04/2018 at 07:45 0 comments


    I received my PCBs from JLCPCB, top quality as always. I changed the size of the holes for the pots and the 3.5 jacks for this iteration and now they fit perfectly. As soon as my shipment of header pins and sockets arrive I will begin to assemble the boards.

View all 8 project logs

Enjoy this project?



Sophi Kravitz wrote 02/20/2019 at 17:49 point

Now we need to hear how it sounds :)

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