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++
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.
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
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);
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);
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
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");
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");
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 |
| ..... | ..... |
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