Kosmo Teensy Module

As I mentioned in the introduction, I am planning to build a Kosmo format module around the Teensy 4.1. My interest is to combine the power and affordability of digital synths with analogue synths.

For now, there are some draft schematics. Maybe anyone would like to have a look :slight_smile:

The module has a rather generic interface with

  • 8 CV inputs
  • 8 control knobs
  • A TFT screen (with card reader)
  • A rotary encoder with push button for menus
  • Stereo audio out
  • Stereo audio in
  • DIN MIDI input
  • USB for programming and MIDI input on the front
  • Possibly a USB host interface
  • I may add some more push buttons or switches later on

This allows, for example, multi-operator FM synthesis or up to 8 harmonics additive synthesis etc., where each operator can be CV controlled in one parameter. I imagine also emulations of Braids/Plaits etc. are possible.

Besides the hardware part, I plan to implement some software interface for the whole thing. Like this, anyone can easily start playing around with the module.

My choice of components was driven by making it cheap :slight_smile: : Everything is available on Tayda, except for the Teensy, the Teensy Audio board, the display and the rotary encoder. The project is totally untested and I only have the schematics. I will order the components from Tayda and then hopefully test this out soonish, hoping that nothing will blow up :smiley:


This looks impressive. Have you considered reducing the size and cost by omitting the sound board? At 12bit most analog functions will sound pretty much the same.

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The complexity lies mostly in connecting the digital fairytale world to the wonky analogue world :wink:

I thought about dropping the audio board, but for now I have it lying around. Once I have tested the inputs and everything works, I will see if I can simplify the design and use directly some analogue pins of the Teensy. But this will still require a stage for attenuation, anti-alias filtering etc.

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The teensy can be configured as an audio interface itself. Hell you can even do audio over USB.


I would omit the Arduino for the display and knobs and use some port expander and/or an I2C display. The Teensy is quite powerful it can handle it all and you don’t need to worry about communication between both controllers. Nice project, keep us updated!


Just to add to this, I had recently worked on a diy midi controller with the teensy so if you need any help for your own project I can try and assist.


You have both good points. That should simplify the design quite a bit! I will try out to run the thing without the audio board and connect the display directly for now. I don’t have an I2C display and cable length might be of concern for the SPI display that I have. And there will certainly be question coming up!

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Great! I too have a Teensy 4.x and the audio board but haven’t done anything with it yet. So I’m looking forward to your progress.

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A small update to the project: I have removed the Arduino and directly use an OLED display via I2C. The KiCad schematics are available in a git repository and there is also the pdf.


So how complex is the code to run this?

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Teensy coding is graphical like pure data using their interface which writes a block of code for you. See notes and volts teensy synth for excellent example. Then is arduino ide for the hardware.


Ahhh, its like the old ArduBlock Graphical Programming Aid. Cool!

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Yes. Just drag an oscillator block to the screen and link to a stereo out block then execute and you get a pop-up of code for the ide.

Woops, extra things to do, ordered from Amazon last night. Delivery Today Sunday!!

I expect it will join a lot of other ideas in the projects to be started pile.

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Indeed, programming the Teensy is super easy! You essentially use the Arduino environment with some adjusted libraries. Also, you have a plethora of options for libraries for displays etc.

My intent is to develop also a small library that will allow intuitive access to the hardware UI (CV inputs, display etc.). Like that, we can focus on developing instruments :slight_smile:


Any update on this project? I’m looking to build a Teensy digital/analog hybrid synth as well.

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Wife has been asking for a Teensy module. I’d love to be able to tick this one off the list without… you know… having to do the work :stuck_out_tongue:

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Sorry, the I did not have a lot of time to work on this project recently because the power supply had an issue and other family projects needed some attention.

That being said, I can report that I have tested the ADC input filter and protection. I found some issues that I fixed. Also, I have hacked hard sync into the Teensy Audio library to understand the library better and because I wanted to integrate that into the synth that I’m building for our daughter. I feel well-prepared to go down the DSP road now :wink:

There is one thing that I would like to know: Is there a general interest in making this a PCB right away, or rather for strip board? I’m a bit divided about this. Also some feature suggestions are welcome, if they are not too complicated :slight_smile:

I’m happy to report some progress on this project! I found the time to test almost everything in isolation. In the process, I found some issues that I fixed and I also completely redesigned the input stage for the ADC (attenuation/anti-aliasing filter/protection). This part was quite tricky to get right, while keeping the number of op-amps low! :smiley:

I would be grateful, if someone finds the time to have a look at the schematics and check for glaring mistakes. I also decided that I will go with PCB because the module is quite complex. Oh, and there are some SMD parts in there, but those should be easy to solder because the legs have a lot of space. And in case of the buck converter, there is an option to replace it with an external 5V supply (e.g., with an inefficient linear regulator :wink:)

In any case, I will next design the front panel and PCBs. Hopefully, I can order some for testing soon! But I will need some time to learn that.


it would probably easier and about as cheap to just use an LM4040 for the voltage ref no?