#samd21 — Public Fediverse posts

XIAO ESP32-C3 MIDI Synthesizer – Part 6

Expanding on my previous posts, I thought it might be interesting to see how I might be able to add some additional IO to the MIDI Synth. This is an exploration of some options there.

• Part 1 – Getting started and getting code running.
• Part 2 – Swapping the ESP32-C3 for a SAMD21 to get USB MIDI.
• Part 3 – Taking a deeper look at the SAM2695 itself.
• Part 4 – A USB MIDI Synth Module using the SAMD21 again as a USB MIDI Host.
• Part 5 – A Serial MIDI Synth Module using the original ESP32-C3.
• Part 6 – Pairs the Synth with a XIAO Expansion board to add display and potentiometers.

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

These are the key tutorials for the main concepts used in this project:

• Getting Started with the XIAO MIDI Synthesizer
• XIAO SAMD21, Arduino and MIDI
• XIAO SAMD21, Arduino and MIDI – Part 6

If you are new to microcontrollers, see the Getting Started pages.

The Synth Grove Connector

One option to immediately explore for me was the Grove connector on the Synth – highlighted by the blue rectangle in the photo below. I’m thinking at this stage of the XIAO Expander Module (more here) and how that might give some options for easily hooking up to the Synth.

There one obvious issue with this, and one not so obvious issue.

First, of course, there is no access to this connector through the case. My initial thought was to simply remove the PCB from the case and use it as a stand-alone board. On initial inspection it seemed that there were two screws holding it down. Not so, a more thorough inspection (after remove the two screws and still not being able to remove it), revealed a third screw underneath the “light pipe” for the LEDs.

Unfortunately that light pipe is pretty well wedged into the case making removal particularly tricky. But without removing the light pipe, it isn’t possible to get to the screw at all.

I did wonder about making a hole in the 3D printed case. A better option might be to get hold of the published 3D print files and add a hole and make my own (they are available via the product page).

But both options would probably end up changing the original case somehow – even if printing my own, I still need to get the original PCB out somehow and that brings me back to the light pipe issue.

The second issue isn’t quite so obvious. In that photo we can see that the pins for the Grove connector are labelled as follows (top to bottom):

• NC
• TX
• 5V
• GND

The UART on the XIAO expander board, which I’d like to use, is labelled:

• RX7
• TX6
• 3V3
• GND

Checking in with the Synth schematic, the connector is wired as follows:

SYS_MIDI connects to the MIDI_IN pin of the SAM2695, so actually connecting “TX to TX” in this instance should be ok.

5V might be an issue though, as it really does look like (to me) that it really means 5V – it is the input to the TPL740F33 that generates the 3V3 power signal, as well as feeding the amplifier directly. The datasheet of the TPL740F33 does seem to imply that if receiving 3V3 it can still generate 3V3 so it might be ok? The amplifier obviously won’t be as powerful though running off 3V3.

Anyway, for now, instead I’ve just opted to use the GPIO again, wired into the expansion sockets with the XIAO removed.

At the XIAO expander end, I’ve used the additional pins rather than the Grove connector, as they support a 5V output.

The downsides to this approach:

• I’m not using the Grove connectors, which would have been really neat.
• I have no access to the four buttons on the XIAO MIDI Synth.

But I do now have access to two I2C Grove connectors, a GPIO Grove, and the RX part of the UART Grove too as well as the on-board display.

If a XIAO SAMD21 is used, then the previous code for USB to the Synth can be used directly – see XIAO ESP32-C3 MIDI Synthesizer – Part 2.

If the XIAO ESP32-C3 is used, then an additional serial MIDI connection is required. This can be connected to the Grove UART connector (using the RX pin, and leaving TX unconnected) or the RX pin of the additional 8-way pin header on the expansion board. Then the code from this will work directly: XIAO ESP32-C3 MIDI Synthesizer – Part 5.

Adding a Display and Program Control

I already have some code that has done this for a XIAO on an expansion board here XIAO SAMD21, Arduino and MIDI – Part 6.

But for this to work usefully with the Synth module, I need to adjust the routing so that MIDI goes from USB to serial, but the program change messages are also sent via serial to the synth module. That has already been address in previous parts, to I just need to merge the code with that from XIAO ESP32-C3 MIDI Synthesizer – Part 4.

This is the result.

There is a bit of jitter on the analog pot, but that is only because I’m using the original fairly simplified algorithm to detect changes. If I was fussed about it, I’d reuse the averaging class from Arduino MIDI Atari Paddles. And to be honest, a capacitor on the pot would probably go quite a long way too…

As a test, I also powered the device from the Grove UART port connecting it as follows:

• Expander GND – GND Synth
• Expander 3V3 – 5V IN Synth
• Expander TX – RX/D6 Synth
• Expander RX – N/C

And this all worked fine. So I think a Grove to Grove lead would work fine if I had access to the Synth’s Grove port.

This does mean that the exact same code can work with the M5 Synth module using a Grove to Grove lead. The downside of this, even though it is a lot simpler in connectivity terms, is that there is now external audio out like there is on the XIAO Synth.

For completeness the same code can be used with the XIAO ESP32-C3 and serial MIDI, see the photo at the start of this blog.

To turn off all USB handling in the code, the following must be commented out:

//#define HAS_USB
//#define SER_TO_USB
//#define MIDI_USB_PCCC

For other parts of the code, the Arduino abstraction for A0 maps over to the ESP32-C3 fine. The only thing to watch out for is the increased analog resolution from 10 to 12 bits, but a call to analogReadResolution(10) drops that back to the expected 10 bits.

Oh and the Serial port to use is different:

• XIAO SAMD21: Serial1
• XIAO ESP32-C3: Serial0

Find it on GitHub here.

Closing Thoughts

If I can be bothered, it would be nice to actually display the General MIDI voice name on the display. The SAM2695 also has its MT-32 mode, so having some means of selecting that might be interesting too.

And so far I’ve largely only messed about with driving it on a single MIDI channel, so there is a lot more that could be done there.

Kevin

#controlChange #esp32c3 #midi #programChange #SAM2695 #samd21 #usbMidi #xiao

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https://vi.aliexpress.com/item/4000169610268.html?spm=a2g0o.order_list.order_list_main.10.75281802K6zj5w&gatewayAdapt=glo2vnm

Arduino Audio and MIDI Frameworks

I’ve been collecting bookmarks for interesting Arduino audio projects for a while now, and having now played with the XIAO SAMD21 I started looking back over my list for other things to try.  One thing that occurred to me is that there are a now a number of more powerful audio frameworks available for a range of microcontrollers, so in this post I’m doing an introductory “look see” at some of them, largely as “notes to self” to come back to them for some more detailed projects in the future.

Note: Many of these require a 32-bit processor, which is one of the reasons I’ve not looked at them so far.

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

If you are new to microcontrollers, see the Getting Started pages.

Mozzi

I’ve spent quite a bit of time with Mozzi of course, the synthesis library for Arduino that supports a large range of microcontrollers, including the “original” 8-bit Arduino ATmega328P, so I won’t go over that again here.

For a starting point with Mozzi, see: Arduino PWM MIDI Synthesis with Mozzi.  For using Mozzi on a 32-bit SAMD processor, there is more here and here.

But Mozzi isn’t the only game in town, especially if we’re expanding out to 32-bit microcontrollers.

The Arduino Sound Library

https://www.arduino.cc/reference/en/libraries/arduinosound/

This is an official Arduino library that supports SAMD21 based microcontrollers using an I2S digital to analog converter. It is designed for the MKR series of official Arduino boards.

Interestingly it appears to only support I2S audio devices for sound input and output.  That seems like a little bit of a missed opportunity to me in that the SAMD21 has a built-in DAC, but I guess analogWrite() deals with access to the DAC relatively easily.

It is designed for official Arduino SAMD architecture boards – so those in the MKR series.  It might work on other SAMD architecture boards, I haven’t looked into it in detail.

Phil Schatzmann’s Arduino Audio Tools

https://github.com/pschatzmann/arduino-audio-tools

This is a suite of open source code for audio stream processing, providing a range of audio sources (e.g. microphones, Internet streams, files, sensors, and so on) and sinks (e.g. DACs, PWM audio, MP3, codecs, audio modules, etc).

It can be used to build audio players, processors, effects, file processors, audio visualisers, networked audio tools, and so on.

I believe it supports the following microcontroller architectures:

• ESP32 (S and C variants)
• ESP8266
• RP2040 (MBED and non-MBED)
• AVR
• STM32
• SAMD

It supports several audio output boards too, including: ESP32-A1S based boards (ES8388 or AC101 codecs); VS1053 modules; and WM8960 modules.

I believe this is a library for audio processing, not necessarily audio synthesis.

Marcel Licence’s ML Synth Tools

https://github.com/marcel-licence/ML_SynthTools

This is a comprehensive synth library for producing synthesizers, organs and effects.  Most of the code is open source, but there are certain key elements that are provided only in pre-built library form.

It provides libraries for the following microcontrollers:

• ESP32
• ESP8266
• XIAO SAMD21
• Teensy 4.1
• Daisy Seed
• Raspberry Pi Pico RP2040
• STM32F407

As well as the synthesizer core oscillators there are modules for arpeggiators, effects, meters, scopes, and MIDI file playing.  Here are some example builds using the library:

• ML Organ (all platforms): https://github.com/marcel-licence/ml_synth_organ_example
• SAMD21 Synth: https://github.com/marcel-licence/samd21_mini_synth
• ML Synth (all platforms): https://github.com/marcel-licence/ml_synth_basic_example
• ESP32 FM synth: https://github.com/marcel-licence/esp32_fm_synth
• ESP32/RP2040 e-piano: https://github.com/marcel-licence/ml_epiano_example

Although it isn’t fully open source, this non-the-less looks like it would be worth taking a more detailed look.  The provided videos of Marcel playing are particularly excellent.

MIDI Controller Libraries

There are a number of Arduino libraries for building MIDI controllers. Here are a selection of some that I’ve found so far.

OpenDesk MIDI Platform – https://github.com/shanteacontrols/OpenDeck

This is a set of firmware and two official PCB designs for MIDI controllers. In addition to the official boards, it also supports many microcontrollers, including:

• Arduino Mega 2560
• Arduino Nano 33 BLE
• Raspberry Pi Pico
• XIAO RP2040
• Teensy++ 2.0

And many others. It includes a web-based configuration utility for defining the MIDI commands for the controls.  Official boards are available on Tindie and you can read more about them here: https://shanteacontrols.com/.

It supports a range of buttons, encoders, potentiometers, force sensitive resistors, certain touchscreens and can provided feedback using LEDs and displays.

Control Surface – https://github.com/tttapa/Control-Surface

This is a general purpose library for building MIDI input and output control devices.  It supports a wide range of microcontrollers, including:

• AVR (Uno, Mega, Leonardo).
• Arduino Nano Every and 33.
• Teensy.
• ESP8266
• ESP32
• Raspberry Pi Pico

It supports a range of MIDI transports, including serial, USB, “direct serial” (using Hairless MIDI) and MIDI BLE. It also supports a range of buttons, potentiometers, rotary encoders, switches, keyboard matrices, and so on and can provide visual feedback using a range of LEDS and displays.  It has built-in support for multiplexers, shift registers and LED drivers.

It includes a huge number of example projects to browse.

MIDIPal – https://github.com/pichenettes/midipal

This is a “MIDI Swiss Army Knife” that, with the additional of a display and rotary encoder, can provide a wide range of MIDI processing functions.  It includes an editor application for programming MIDI filters.

This is a “native” AVR application, not for the Arduino environment.

Notes and Volts MIDI Controller – https://www.notesandvolts.com/2016/04/arduino-midi-controller-buttons.html

This is provided for completeness as it is a fairly common codebase for people to find and use with an Arduino. It supports a range of potentiometers and buttons and makes the task of configuring them as a MIDI control device relatively straight forward.

Closing Thoughts

As I say, this post is really almost a bit of a “to-do list” of things that look interesting and that I might try to take a more detailed look at, at some point.

If you have experience of any of these frameworks or libraries; or have suggestions of others that might be worth a look, do let me know in the comments!

Kevin