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MIDI-Spark-Control-ESP32

Control your Positive Grid Spark amp with a MIDI controller, via a M5Stack Core with UBS host shield.

A program for the M5Stack Core (an ESP 32 platform) written in C++

What it can do

This has a configurable mapping of MIDI messages to commands to the Spark amp.
It currently responds to Note On and CC messages.

On the Spark amp it can:

  • change the hardware preset
  • send a custom preset (like the app can) - the preset it stored in a C++ structure (see below)
  • change an effect (eg change amp from Roland JC120 to Twin)
  • turn an effect on or off
  • change the value of a parameter (eg gain / treble for an amp)

This is pretty much every change the app can make.

Whilst this is focussed on MIDI the underlying code and class can be triggered by GPIO with some code changes.

Pictures

Spark Setups

Spark Setups

Installation instructions

M5 Board installations as per M5 instructions - for Arduino: https://docs.m5stack.com/#/en/arduino/arduino_development
USB Host: https://github.com/felis/USB_Host_Shield_2.0
Use the latest version of the USB Host Shield library - earlier ones seem not to work with some MIDI devices (Novation Launchkey 25 as an example)
I also installed ArduinoJson from the Arduino library manager, although the code doesn't use it - I may remove it at some point. It was used to read a JSON formatted preset but now I am using an internal C++ structure instead. To remove it comment out the #include <ArduinoJson.h> and void create_preset_json (const char *a_preset); in SparkClass.h and comment out all of void SparkClass::create_preset_json (const char *a_preset) in SparkClass.ino

API

Sending to Spark.

There needs to be a instance of SparkClass. Then we create a message and send it to the Spark;

Example:

SparkClass sc;
sc.change_hardware_preset(2); 
send_receive_bt(sc);

Set new hardware preset

This has the same effect as pressing the four preset buttons on the amp

void change_hardware_preset (int preset_num); // 0-3
      
Example: sc.change_hardware_preset (2);

Change an effect value

This has the same effect as moving the knobs on the amp - but you can access every parameter

The number for the parameter depends on the effect - for an amp they are:

0 Gain 1 Treble 2 Mid 3 Bass 4 Master

Note: the effect named must be the actual effect in use on the amp otherwise it will not work.

void change_effect_parameter (char *pedal, int param, float val);

Example: sc.change_effect_parameter ("RolandJC120", 0, 0.56);  / Change gain to 0.56

Turn an effect on or off

This can't be done physically on the amp at all!

Note: the effect named must be the actual effect in use on the amp otherwise it will not work.

void turn_effect_onoff (char *pedal, char *onoff);

Example: sc.turn_effect_onoff ("DistortionTS9", "Off");

Change an effect to a new one

The amp only allows amp models to be changed with the first knob

Note: the effect named must be the actual effect in use on the amp otherwise it will not work.

void change_effect (char *pedal1,  char *pedal2);

Example: sc.change_effect ("ChorusAnalog",  "Phaser");

Send a new preset

The preset is a C++ structure containing all the data required for a full preset.

void create_preset (SparkPreset& preset);

Example: sc.change_effect (preset);

SparkPreset preset{0x0,0x7f,"D8757D67-98EA-4888-86E5-5F1FD96A30C3","Royal Crown","0.7","1-Clean","icon.png",120.000000,{ 
  {"bias.noisegate", true, 3, {0.211230, 0.570997, 0.000000}}, 
  {"Compressor", true, 2, {0.172004, 0.538197}}, 
  {"DistortionTS9", false, 3, {0.703110, 0.278146, 0.689846}}, 
  {"ADClean", true, 5, {0.677083, 0.501099, 0.382828, 0.585946, 0.812231}}, 
  {"ChorusAnalog", true, 4, {0.519976, 0.402152, 0.240642, 0.740579}}, 
  {"DelayMono", true, 5, {0.173729, 0.233051, 0.493579, 0.600000, 1.000000}}, 
  {"bias.reverb", true, 7, {0.688801, 0.392857, 0.461138, 0.693705, 0.488235, 0.466387, 0.300000}} },0xa2 };

The preset format explanation is:

Description Example
Leave as 0 0x00
Preset number - use 0x7f 0x7f
UUID for preset - used an existing one "D8757D67-98EA-4888-86E5-5F1FD96A30C3"
Name for preset - use your own "Royal Crown"
Version - use 0.7 "0.7"
Description - use your own "1-Clean"
Icon - use "icon.png" "icon.png"
BPM - use 120.0 120.000000
Effects - see below
Checksum - use anything 0xa2

Effects are always in the order:

Noisegate (always "bias.noisegate"), Compressor, Drive, Amp, Mod, Delay, Reverb (always "bias.reverb")

Description Example
Name - use a effect name from the list in SparkPresets.h "Compressor"
On / off - true is on true
Number of parameters - needs to be the same as that effect has, can be discovered from other presets in SparkPresets.h 2
Parameter 0 0.172004
Parameter 1 0.538197
..... .....

Acknowledgements

All inspired by Justin Nelson and the marvellous #tinderboxpedal https://github.com/jrnelson90/tinderboxpedal
With thanks to gdsports on github for the MIDI USB host examples https://github.com/gdsports/MIDIDump