When I want to start work on a new synth, follow these steps:

• set the number of IO pins on each card via the dip switch x4.
• change the potentiometers and buttons on each card to what is needed.
• edit the Audio System Design Tool and import the new code into TeensyAudioDesignTool.h.
• update the Teensy synth setup in the setup function.
• modify the midi control functions.
• look at the new muxData array to modify the “updateControls()“ function.

I do not have to worry about the mux circuits or the mux program.  The busses and control circuitry on each card allow the mux code to automatically read just the inputs that are connected.  By looking at the array muxData[]  I can use the collected signals from the inputs to help me control new synths and synth code.

I am really pleased with how the system works.  So far it is doing exactly what I had hoped for.  As I build new projects, I will update this page to show what I have created.

If you spot any mistakes or issues, please point them out.  I am self taught in Arduino and Teensy so have probably made errors in the way I coded the project.  Or if you can think of improvements, please let me know.  I have a few ideas of how I would like to develop the system in the future but for now I plan to use it to mess around with Teensy Synth designs.

Future Plans

Just a quick list of possible improvements

• Make the address bus 4 line to allow the system to control up to 16 cards.
• Add the option to make the mux circuits outputs as well as the current inputs.  This would allow me to control lots of LEDs and other outputs.
• Make a PCB of the mux card circuitry.  I would like to make something that looks a bit like a Eurorack.  Each card would have a front panel with whatever inputs/outputs are needed.  The cards would plug into a bus connected to the teensy.

Resources

The following resources were a huge help.

A good place to start when you get a Teensy. Getting started tutorials and lots of information.

It is also where you can buy a Teensy and the audio adapter.

PJRC, “Teensy USB Development Board”

https://www.pjrc.com/teensy/

Within the PJRC website the Teensy audio section in Libraries is also useful.

PJRC, “Teensy Audio Library”

https://www.pjrc.com/teensy/td_libs_Audio.html

I followed this set of tutorials when I first started to use the Teensy to design synths.  The videos and resources are awesome.

Nuts and Volts, “TEENSY-Synth PART 1 – 11”

https://www.notesandvolts.com/2018/05/teensy-synth-part-1.html

 I used the following datasheets to help me design the address decoder circuitry.

Texas Instruments, “High speed CMOS logic analog multiplexers/demultiplexers,” 74HC4051 datasheet, https://www.ti.com/lit/ds/symlink/cd4051b.pdf

 Texas Instruments, “SNx4HC245 Octal Bus Transceivers With 3-State Outputs” 74HC245 datasheet, https://www.ti.com/lit/ds/symlink/cd4051b.pdf