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teensy eurorack audio shield

updates

14 August 2021 : software and examples have moved to this repo newdigate/teensy-eurorack-software

sponsor
specifications
license
open source software-stack
build
source code
improvements
printed circuit boards
- mainboard
- breakout board
schematics
panel design
assembly technical drawings
youtube videos
versions
todo
continuous-integration
credits
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sponsor

patreon/teensy_eurorack
paypal.me: paypal.me/nicnewdigate

specifications

microcontrollers:
- 600 Mhz ARM cortex m7 ( teensy 4.1 board )
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 8 x outputs ( ad7606, 2x ad5754 )
display: ST7735 128x128 16bit-color tft display
breakouts:
- microSD card socket,
- USB host/device,
- midi in/out,
- knobs (4 x pots, 3 x encoders w/switch)
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

license

All artifacts are 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

build

order pcbs

Use these gerber files to order 3 pcboards
- the uSD-card extender should be about 0.6mm - 0.8mm thick
- if you're using solder paste, you'll need to order the stencils of the bottom-side of main- and breakout boards.
gerbers-breakout.zip
gerbers-mainboard.zip
gerbers-uSD_extender_male.zip

sourcing parts

Most parts are available from mouser.com - you can use the mouser BOMs below as a template to create an order.

mouser boms

parts not on mouser boms

panel:
- order from Front Panel Express: .fpd
  - for US: download Front Panel Express
  - for Europe: download Front Panel Designer
- CNC your own with FreeCad: panel.FCStd
mainboard:
- 2.54mm pitch pin headers and sockets
  - J28: Eurorack power header: either male or female (2 x 8), I use female as my eurorack power (tip top) has male connectors.
breakout:
- uSD card socket: pjs008u-3000-0 yamaichi
- display: ST7735 (1.44 inch TFT LCD ST7735 SPI display module 128*128 8pin 65K color)
  <img src='hardware/images/st7735.jpg' width='200px'/>
- 16 x thonkiconns: PJ398SM
- 4 x 9mm snap-in pots: alpha-9mm-pots - You want linear (B-series) not audio (A-series) B5K or B10K should be ideal.
- 3 x rotary encoders w/switches: Half axis (D-shaft) rotary encoder, handle/axis length: 20mm, EC11/EC12 digital potentiometer with switch - 5Pin

Update: USB-A-S-X-X-VT is no longer available. Amphenol Commercial Products GSB11111ALF looks like it may be a good replacement.

interactive html boms online

source code

Teensy Audio library drivers for ad5754, ad7606 via SPI
- teensy-audio-ad5754-ad7606
simple standard midi file reader
- midi-smf-reader
generic sequencer
- teensy-quencer
variable rate playback
- teensy-variable-playback
oscilliscope and x/y scope display components
- teensy-audio-libtftscope
cmake macros for compiling c++ for arm cortex
- teensy-cmake-macros
Audio level and CV level meters
- teensy-audio-display-components

improvements

At this point Im just focusing on finalising/polishing the current version, but there are some improvements I'd like to make at some point.

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 (its a bit out of date, sorry) - journal.md

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

#sponsor...
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...

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

breakout board

2 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
8 x 3.5mm jack socket for analog control voltage 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 rotary encoders with switches

schematics

panel design

assembly technical drawings

youtube videos

Nic N

versions

v2.1 (Saturday 3 April 2021)

Improvement: Mainboard: Tie LRCLK pin 20 to pin40 to sync DAC/ADC sampling w/ audio sampling
FIXED: breakout: add 1k pull-up resistor to MIDI rx pin
mainboard: silkscreen: add Kicad OpenSourceHardware logo
breakout: silkscreen: add Kicad OpenSourceHardware logo

v2.0.3 (Saturday 13/02/2021)

breakout: st7735 display changed vcc, reset, backlight from 5v to 3v3.

v2.0.2 (31/01/2021)

Mainboard: spaced out traces as there appeared to be some interference under certain circumstances.

v2.0.1 (27/01/2021)

Mainboard: add daisy chain TX/RX connector on back side to communicate between multiple boards
Breakout board: changed back to double layer board.

v2.0.0(b)

Breakout board: Corrected polarity of +-12V pin headers on breakout board (ouch!!!)
change ADC to use external 2.5v voltage reference, same as DAC voltage reference now

v2.0.0

SPI: separated ADC, DAC from display:
- st7735 display has its own dedicated SPI - (SPI0, stays the same)
- ADC / DAC are now sharing SPI1
integrated ADC and DAC into teensy audio library.
added one more ad5754 DAC for total of 8 control voltage analog output channels

v1.9.1b

mainboard: correction: reconnected LRCLK to codec.

v1.9.1

connected DAC_SCK output (pin 19) to pin 31
- allow cable select to be asserted on minor spi data cycle after every 24 or 48 spi clock cycles, using interrupt on pin 31.
  - hopefully this will allow DMA spi transfers to AD5754 and which will make integration with teensy audio library much easier

v1.9

updated to teesy 4.1 and improvements to make easier to build

updated from teensy 4.0 to teensy 4.1
schematic, footprint and pcb clean-up
- replaced footprints imported from eagle with native kicad footprints
removed atmel samd21 and gpio ICs
replaced gpio with AD5754 (extra 4 DAC channels)
replaced RGB encoders with regular encoders
replaced analog-GND-to-digital-GND footprint with a 0805 zero ohm resistor footprint. (DRC checks can pass now...)
(temporarily) removed serial TX/RX to unused eurorack power pins