teensy 4.0 eurorack shield

open source hardware and software for a teensy 4.0 eurorack shield

These circuit boards provide the peripherals necessary to interface a teensy 4.0 with stereo line audio and eurorack modular equipment.

• specifications
• open source software-stack
• support
• social media
• printed circuit boards
  • mainboard
  • breakout board
• panel design
• assembly technical drawings
• videos
• versions
• todo

specifications

• microcontrollers:
  • 600 Mhz ARM cortex m7 ( teensy 4.0 board )
  • SAMD21 32bit 48Mhz micro-controller (based on arduino mkr1000)
• audio: multi-channel audio codec ( 6-in / 8-out 24-bit sound card - CS42448 )
  • the audio codec circuit originally started as a discussion on quad audio channel outputs and a pcb design integrating teensy and cs42448 from Paul Stoffregen on pjrc forum
• analog control voltage ins/outs: -10V to 10V 16bit/sample, 8 x inputs and 4 x outputs ( ad7606, ad5754 )
• display: ST7735 128x128 16bit-color tft display
• breakouts:
  • microSD card socket,
  • USB host/device,
  • midi in/out,
  • knobs (4 x pots, 3 x RGB encoders w/switch)
• gpio: 4 x configurable 5v logic inputs/outputs. PCA9536
• panel: 24HP aluminium panel mounted for eurorack case
• programability:
  • write arduino compatible c/c++ firmware & program using arduino/teensyduino
  • arm gnu toolchain downloads
  • teensy audio library

MIT open source license

• MIT license unless otherwise specified on a per file basis.

Open source software stack

• All schematics and boards are created using Kicad
• All mechanical designs are created using FreeCAD
• Some images have been rendered using Blender 2.81

support

This project is a work-in-progress! The functionality has been tested and are working at a basic level.

There are some improvements I'd like to make later

• improve noise to signal ratio on pots on breakout board.
• add 4x jack sockets for analog output of knobs on breakout board.
• use 3.5mm jack sockets (as well as standard midi din connectors) for midi in and out.
• switch to active audio input and output circuitry, allow switchable 0dB / 12dB gain, for guitar signals.
• let me know if you're think there something else that can be improved, added, removed.

There is a journal of my progress, journal.md

What you can do if you like to see progress with this project?

• star this repository (means you need a github account - go for it!!)
• subscribe Nic N on youtube
• download kicad and freecad, clone this repo, make improvements, commit & send pull-requests, and raise issues...

social media

• facebook:
  • Moolet
• youtube:
  • Nic N

printed circuit boards

mainboard

• standard double layer printed circuit board
  • thinkness: 1.6mm
  • minimum trace: 6 mil
  • minimum clearance: 6 mil
  • dimension: 118mm*102mm
• socket to connect teensy 4.0 board
• cs42448 audio codec
• 3 x stereo 6.35mm TRS jack inputs
• 4 x stereo 6.35mm TRS jack outputs
• pin sockets to connect breakout board
• PCA9536 gpio

breakout board

• standard double layer printed circuit board
  • thinkness: 1.6mm
  • minimum trace: 6 mil
  • minimum clearance: 6 mil
  • dimension: 110mm*111mm
• 8 x 3.5mm jack socket for analog control voltage inputs
• 4 x 3.5mm jack socket for analog control voltage outputs
• 4 x 3.5mm jack socket for 5v GPIO (general purpose inputs or outputs)
• midi in/out DIN sockets
• usb device/host
  • USB-B: USB device mode
  • USB-A: USB host mode
• micro-SD card socket
• 4 x linear pots
• 3 x RGB rotary encoders with switches
• SAMD21 32bit 48Mhz micro-controller for pots and rotaries
  • Based on Arduino MKR Zero board (can be programmed through standard arduino ide)
• Communicates with mainboard via standard serial uart RX and TX lines.

panel design

assembly technical drawings

videos

• Teensy 4.0 eurorack shield design intro

• 0v to 10v control voltage input, output and display using teensy 4.0

• DIY assembly build - teensy 4.0 eurorack audio module

• assembling teensy eurorack shield

• assembly timelapse

• Eurorack digital audio modules powered by teensy micro-controller

• side-channel stereo audio separation with teensy 4.0

versions

v1.8.1 (current)

cleanup, minor improvements, and reduce number of distinct components

• breakout board:
  • changed C6 (1nF) from 1206 to 0805 to match C2 - reduces number of unique components by 1
• mainboard
  • cleanup of footprints to reduce number of distinct parts
  • removed pull-up resistor on AD_RESET signal
  • increased size of power traces to 350 mil

status:
  15/03/2020:
    * placed order with JLCPCB.com, total ￡63.33
      * 20 x mainboard @ v1.8.1 + top stencil (￡15.53 + ￡5.38 )
      * 20 x breakout @ v1.8.1 + top & bottom stencil (￡15.69 + ￡10.76)
      * shipping: ￡15.97

v1.8

status:
 * 25/02/2020: placed pcb order with jlcpcb
 * 28/02/2020: order dispatched
 * 02/03/2020: pcbs arrived, but parts are still waiting to be delivered. 
 * 08/03/2020: mainboard v1.7 + breakout board v1.8 - all features tested successfully.

• breakout board:
  • fixed: midi DIN connectors pin 4 and pin 5 switched
• mainboard remains same at version 1.7

v1.7b

status:
 * 26/01/2020: placed pcb order with jlcpcb 
 * 22/02/2020:
   * boards assembled, sanity checks pass, form factor is good - no known issues so far 
   * adc AD7606 tested briefly, looks better
   * usb-device type-b socket tested successfully, serial-over-usb and programming connection seem good
 * 23/02/2020:
   * issue with midi in/out circuits 
     * pin 4 and pin 5 on the midi din connectors appear to be switched on both rx and tx midi sockets
     * tx may need logic level shifter or buffer.   

• breakout board:
  • fixed: net 3v3 collides with net VIN
    • LDO footprint imported from eagle is causing DRC check to succeed even though the two traces collide

v1.7

status:
 * 10/01/2020: placed pcb and stencil order with jlcpcb 
   * total is ￡36.05
     * Shipping Charge: ￡13.05
     * Merchandise: ￡23.00 
       * 2 x aluminium stencils: £10.66
       * 2 x 5pcs x pcboard: £12.34
 * 12/01/2020: order dispatched
 * 24/01/2020: pcboards and stencils arrived.

v1.7 changes

• circuit corrections
  • adc: corrected AVSS net, should have been VSS
  • removed unused through-hole pads from underside of teensy board.
• physical
  • merged knobs-controller and top-breakout pc-boards into single board
  • tft display rotated 90 degrees
  • sd-connector socket rotated 90 degrees
  • replaced fine-pitch FPC/FFC connectors with standard 0.1' pin-headers and sockets, allowing boards to connect physically

v1.6:

• circuit corrections
  • corrected: knobs-controller: tx/rx nets were not connected to socket
  • enhancement: extra uart exposed
    • allows serial communications via the unused pins in the eurorack power-connector
    • 2 jumper-switches added to switch between master/slave - (rx/tx cross-over configuration)
    • connects to RX7, TX7 (pins 28, 29) on the under-side of the teensy 4.0 board
  • enhancement: adc: AD_RESET net connected to micro-controller
  • enhancement: introduced PCA9536 i2c GPIO integrated-circuit to free-up some pins on the micro-controller

todo

• General
  • cleanup / refactor footprints, replace footprints and symbols imported from eagle with kicad equivalents
• Breakout board for rotary encoders and pots
  • Order
  • Assemble
  • software
  • document
  • certify
• panel
  • measurements
  • design
• finalize circuits / boards
• testing
  • CS42448 audio codec
    • Audio input
    • Audio output
  • control voltage input
  • control voltage output
  • gpio (input & output)
  • usb host
  • usb device
  • midi in/out
  • st7735 display
  • sd card extension & adapter
• Document
  • order & build process
  • software process
• Firmware
  • Sliced audio loops
  • Midi looping

build

• testing automated build and packaging
• github.com/pwuertz/kicad_picknplace_assistant
• github.com/productize/kicad-automation-scripts