Ignitron, a DIY based footswitch for the Spark

Ignitron logo large

An ESP32 based foot pedal to communicate with the Spark Amp and Spark App via Bluetooth LE. Also works as a control device for a Looper app on the mobile.

Ignitron gives you full control over your Spark Amp:

  • Switch between the four hardware presets
  • Switch between custom saved presets organized in banks
  • Toggle effects for the selected preset
  • Load new presets via the Spark App (iOS only)
  • Delete stored presets
  • Control Looper apps (and other apps which support bluetooth keyboards)
  • Firmware can (rudimentarily) be updated via OTA Web interface.

Adding new presets to Ignitron can easily be done as it can also act as a Spark Amp. Simply connect to Ignitron with your Spark app and load new presets directly from ToneCloud (or your downloaded presets) to Ignitron.

One big advantage of Ignitron is that it communicates with your Spark Amp using the Bluetooth LE protocol. This means you can still connect your mobile with your Spark Amp as an audio speaker and play along your favorite songs while you control your effects.

The current active preset and effects are indicated via LEDs.
In addition, the built-in display provides information on

  • selected bank and preset number
  • selected preset name
  • operation mode (Preset, Manual/FX, Looper)
  • activated pedal types in the FX chain
  • show Bluetooth connection status to Spark Amp and Spark App and WiFi connection status

This work was inspired by the Sparkpal project and the Python Spark Parser project helped me to understand the messages being sent to and from the Spark Amp.

The following sections explain how to build and operate the pedal.

Building Ignitron

Software: click here

Hardware: click here

Ignitron with Spark Ignitron preset mode Ingitron FX Mode2 Ignitron full wiring

Operating Ignitron

Table of contents

Operation modes

Ignitron has two operation modes, APP mode and AMP mode.
In APP mode (default mode on startup), Ignitron connects to a Spark Amp and behaves like the Spark App towards the Spark Amp. It can then be used to switch between saved presets, toggle FX pedals, and even connect it to a Looper app on a mobile. AMP mode can be used to manage the presets stored on Ignitron, presets can be added from the app or be deleted from Ignitron.
To enter AMP mode, hold the Preset 1 button during startup.

APP mode

In APP mode, the foot switches can be used to either switch between pre-saved presets (Preset mode), control all single effects in the selected preset (Manual/FX mode), or switch between presets while controlling an app on your mobile, e.g. a Looper app (Looper mode). You can easily toggle between Preset mode and Manual/FX mode by long pressing the Bank-Up button. To toggle between Preset mode and Looper mode, simply long-press the Bank down button. When selecting Preset mode, four buttons are used to select presets the other two buttons are used to navigate through different preset banks. This way the user has access to a huge number of saved presets. When pressing the foot switch of the current active preset, the effect configured in the DRIVE section can be enabled and disabled. In Manual/FX mode, the user has direct access to all effects of the selected preset. When Looper mode is activated, you can swtich between presets of the current selected preset bank and use the Bank down/Bank up buttons to control your Looper app, e.g. to record on two separate loops.

Each switch controls a different FX pedal type:

Button commands in APP mode:

Preset mode

Button Press pattern Function
Bank down Short Navigate bank up
Bank up Short Navigate bank down
Preset 1 Short Select preset 1 / Toggle Drive
Preset 2 Short Select preset 2 / Toggle Drive
Preset 3 Short Select preset 3 / Toggle Drive
Preset 4 Short Select preset 4 / Toggle Drive
Bank down Long Switch to Looper mode
Bank up Long Switch to FX mode
Preset 2 Long Restart Ignitron

Manual/FX mode

Button Press pattern Function
Bank down Short Toggle Noise Gate
Bank up Short Toggle Compressor
Preset 1 Short Toggle Drive
Preset 2 Short Toggle Modulation
Preset 3 Short Toggle Delay
Preset 4 Short Toggle Reverb
Bank up Long Switch to Preset mode
Preset 2 Long Restart Ignitron

Looper mode

Button Press pattern Function
Bank down Short Toggle recording on Loop 1 (can be freely configured in app)
Bank up Short Toggle recording on Loop 2 (can be freely configured in app)
Preset 1 Short Select preset 1
Preset 2 Short Select preset 2
Preset 3 Short Select preset 3
Preset 4 Short Select preset 4
Bank down Long Switch to Preset mode
Preset 2 Long Restart Ignitron

Note: In Looper mode, Ignitron is connected to your mobile as a bluetooth keyboard. If supported by the respective app on the mobile, the Bank down/Bank up buttons can be freely configured to any function offered.


AMP mode

In AMP mode, Ignitron acts like a Spark AMP and can communicate with the Spark app running on a mobile. New presets can be stored on Ignitron and existing presets can be deleted. In this mode, Ignitron's firmware can also be updated OTA via a web browser.

Note: With the current version of Ignitron, it is only possible to connect the iOS version of the Spark app with the pedal. The Android version of the app uses Bluetooth classic to connect to the amp which is currently not supported by Ignitron.

Connecting the Spark app with Ignitron

  1. Start Ignitron in AMP mode (hold Preset 1 button during startup).
  2. Open the Spark App on the mobile
  3. For the first connection, make sure to have your real Spark Amp powered off to avoid the app connecting to it.
  4. Hit the connect button in the app (or the + button in the connection overview)
  5. Once the connection is established, you can give the connection a name in the app so you can distinguish from your regular Spark Amp connection.

Storing a new preset (a preset from the app needs to be loaded)

  1. Start Ignitron in AMP mode (hold Preset 1 button during startup).
  2. Connect the Spark App with Ignitron (see above)
  3. Select a preset in the app (either saved in the app or from the ToneCloud).
  4. The preset name should appear in the bottom line of the display
  5. The Preset/Bank buttons on Ignitron can be used to navigate to the desired preset position.
  6. Press the Preset button to mark the position for storing
  7. The LED of the selected preset position should start blinking
  8. Hit the same Preset button a second time to confirm storage (Hitting any other Preset/Bank button will revert the state back to navigating)
  9. The preset will be saved to the selected position, other presets will be pushed back

Button commands (case: preset has been received from Spark app)

Button Press pattern Function Remark
Bank down Short Navigate bank up
Bank up Short Navigate bank down
Preset 1 Short Select preset 1 Press twice to store received preset
Preset 2 Short Select preset 2 Press twice to store received preset
Preset 3 Short Select preset 3 Press twice to store received preset
Preset 4 Short Select preset 4 Press twice to store received preset
Bank down Long Unload preset Removes loaded preset
Preset 2 Long Restart Ignitron

Deleting a preset (only possible when no preset from the app is loaded)

  1. Start Ignitron in AMP mode (hold Preset 1 button during startup).
  2. Use the Preset/Bank buttons on Ignitron to navigate to the desired preset position
  3. Long press the Bank Down button to mark the selected preset for deletion
  4. The LED of the selected preset should start blinking
  5. In the display you should see a prompt if deletion should be executed
  6. If you want to cancel the deletion, simply short press any other button
  7. Otherwise, long press the Bank Down button again to confirm deletion. (Hitting any other button will cancel the deletion and return back to navigation)

Button commands (case: no preset has been received, slot is empty)

Button Press pattern Function Remark
Bank down Short Navigate bank up
Bank up Short Navigate bank down
Preset 1 Short Select preset 1
Preset 2 Short Select preset 2
Preset 3 Short Select preset 3
Preset 4 Short Select preset 4
Bank down Long Mark preset for deletion Pressing any other button in that state will cancel the deletion
Bank down Long Delete marked preset Only if preset was first marked for deletion
Preset 2 Long Restart Ignitron

Manually creating presets

This method is only recommended if a preset cannot be transferred via the Spark app or if the preset files have been received/generated in a different way.

  1. Create a preset file in JSON format as shown above
  2. Make sure the file name does not exceed 31 characters (including the .json suffix)
  3. Put the file name into the data folder
  4. Insert the file name (including the .json suffix) to the desired prefix location in the PresetList.txt file
  5. Place the PresetList.txt file into the data folder (if not already there)
  6. Upload the data folder to Ignitron via the Arduino IDE (or other tools)

Preset format

Ignitron stores presets in a JSON format using the SPIFFS file system. Each preset is stored in a separate file and presets are organized in a separate text file called 'PresetList.txt'. This list simply stored the file names of the presets, the order defines the way the banks are filled. An example preset file would look like this:

{"PresetNumber": 127, "UUID":"DEFBB271-B3EE-4C7E-A623-2E5CA53B6DDA",
"Name":"Studio Session" , "Version":"0.7", "Description":"Description for Acoustic Preset 1", "Icon":"icon.png", "BPM": 120.0000,
"Pedals": [
  { "Name":"bias.noisegate",  "IsOn": false,  "Parameters":[0.5000,0.3467] },
  { "Name":"BBEOpticalComp",  "IsOn": true,   "Parameters":[0.7583,0.2585,0.0000] },
  { "Name":"DistortionTS9",   "IsOn": false,  "Parameters":[0.1396,0.4073,0.6898] },
  { "Name":"Acoustic",  "IsOn": true,   "Parameters":[0.6398,0.3851,0.3834,0.5994,0.5195] },
  { "Name":"ChorusAnalog",  "IsOn": true,   "Parameters":[0.8417,0.2275,0.9359,0.3513] },
  { "Name":"DelayMono",   "IsOn": false,  "Parameters":[0.2240,0.2112,0.4909,0.6000,1.0000] },
  { "Name":"bias.reverb",   "IsOn": true,   "Parameters":[0.7228,0.3262,0.2758,0.3607,0.3439,0.4860,0.4000] } ],
"Filler":"23"
}

As a guidance which effect and amp names can be used and in which order the parameters of each effect have to be given, please refer to

FX parameter reference

In order to know which effects are available with paramters, see below table. This data can be used to build own presets in JSON format (see above). Use the Technical Name information in the JSON files. Parameters marked with Switch can only have values of 0 or 1, others can have any value between 0 and 1.

Standard Tones
Type App Name Technical Name Parameter 0 Parameter 1 Parameter 2 Parameter 3 Parameter 4 Parameter 5 Parameter 6 Extra Info
Noise Gate Noise Gate bias.noisegate Threshold Decay
Compressor LA Comp LA2AComp Limit/Compress Switch Gain Peak Reduction
Compressor Sustain Comp BlueComp Level Tone Attack Sustain
Compressor Red Comp Compressor Output Sensitivity
Compressor Bass Comp BassComp Comp Gain
Compressor Optical Comp BBEOpticalComp Volume Comp Pad Switch
Drive Booster Booster Gain
Drive Clone Drive KlonCentaurSilver Output Treble Gain
Drive Tube Drive DistortionTS9 Overdrive Tone Level
Drive Over Drive Overdrive Level Tone Drive
Drive Fuzz Face Fuzz Volume Fuzz
Drive Black Op ProCoRat Distortion Filter Volume
Drive Bass Muff BassBigMuff Volume Tone Sustain
Drive Guitar Muff GuitarMuff Volume Tone Sustain
Drive Bassmaster MaestroBassmaster Brass Volume Sensitivity Bass Volume
Drive SAB Driver SABDriver Volume Tone Drive LP/HP Switch
Amp Silver 120 RolandJC120 Gain Treble Middle Bass Volume
Amp Black Duo Twin Gain Treble Middle Bass Volume
Amp AD Clean ADClean Gain Treble Middle Bass Volume
Amp Match DC 94MatchDCV2 Gain Treble Middle Bass Volume
Amp ODS 50 ODS50CN Gain Treble Middle Bass Volume
Amp Blues Boy BluesJrTweed Gain Treble Middle Bass Volume
Amp Tweed Bass Bassman Gain Treble Middle Bass Volume
Amp AC Boost AC Boost Gain Treble Middle Bass Volume
Amp Checkmate Checkmate Gain Treble Middle Bass Volume
Amp Two Stone SP50 TwoStoneSP50 Gain Treble Middle Bass Volume
Amp American Deluxe Deluxe65 Gain Treble Middle Bass Volume
Amp Plexiglas Plexi Gain Treble Middle Bass Volume
Amp JM45 OverDrivenJM45 Gain Treble Middle Bass Volume
Amp Lux Verb OverDrivenLuxVerb Gain Treble Middle Bass Volume
Amp RB 101 Bogner Gain Treble Middle Bass Volume
Amp British 30 OrangeAD30 Gain Treble Middle Bass Volume
Amp American High Gain AmericanHighGain Gain Treble Middle Bass Volume
Amp SLO 100 SLO100 Gain Treble Middle Bass Volume
Amp YJM100 YJM100 Gain Treble Middle Bass Volume
Amp Treadplate Rectifier Gain Treble Middle Bass Volume
Amp Insane EVH Gain Treble Middle Bass Volume
Amp Insane 6508 6505Plus Gain Treble Middle Bass Volume
Amp SwitchAxe SwitchAxeLead Gain Treble Middle Bass Volume
Amp Rocker V Invader Gain Treble Middle Bass Volume
Amp BE 101 BE101 Gain Treble Middle Bass Volume
Amp Pure Acoustic Acoustic Gain Treble Middle Bass Volume
Amp Fishboy AcousticAmpV2 Gain Treble Middle Bass Volume
Amp Jumbo FatAcousticV2 Gain Treble Middle Bass Volume
Amp Flat Acoustic FlatAcoustic Gain Treble Middle Bass Volume
Amp RB-800 GK800 Gain Treble Middle Bass Volume
Amp Sunny 3000 Sunny3000 Gain Treble Middle Bass Volume
Amp W600 W600 Gain Treble Middle Bass Volume
Amp Hammer 500 Hammer500 Gain Treble Middle Bass Volume
Modulation Tremolo Tremolo Speed Depth Level
Modulation Chorus ChorusAnalog E.Level Rate Depth Tone
Modulation Flanger Flanger Rate Mix Depth
Modulation Phaser Phaser Speed Intensity
Modulation Vibrato Vibrato01 Speed Depth
Modulation UniVibe UniVibe Speed Vibrato/Chorus Switch Intensity
Modulation Cloner Chorus Cloner Rate Depth Switch
Modulation Classic Vibe MiniVibe Speed Intensity
Modulation Tremolator Tremolator Depth Speed BPM On/Off Switch
Modulation Tremolo Square TremoloSquare Speed Depth Level
Modulation Guitar EQ GuitarEQ6 Level 100 200 400 800 1.6k 3.2k
Modulation Bass EQ BassEQ6 Level 50 120 400 800 4.5k 10k
Delay Digital Delay DelayMono E.Level Feedback DelayTime Mode BPM Switch Modes: 0.3 (50ms) - 0.4 (200ms) - 0.6 (500ms) - 0.72 (1s)
Delay Echo Filt DelayEchoFilt Delay Feedback Level Tone BPM Switch
Delay Vintage Delay VintageDelay Repeat Rate Intensity Echo BPM Switch
Delay Reverse Delay DelayReverse Mix Decay Filter Time BPM Switch
Delay Multi Head DelayMultiHead Repeat Rate Intensity Echo Volume Mode Selector BPM Switch Modes: 0 (Head 1) - 0.35 (Head 2) - 0.65 (Head 3) - 0.95 (Head 4)
Delay Echo Tape DelayRe201 Sustain Volume Tone Short/Long
Reverb Room Studio A bias.reverb Level Damping Dwell Time Low Cut High Cut Selects Reverb Type 0.0
Reverb Room Studio B bias.reverb Level Damping Dwell Time Low Cut High Cut Selects Reverb Type 0.1
Reverb Chamber bias.reverb Level Damping Dwell Time Low Cut High Cut Selects Reverb Type 0.2
Reverb Hall Natural bias.reverb Level Damping Dwell Time Low Cut High Cut Selects Reverb Type 0.3
Reverb Hall Medium bias.reverb Level Damping Dwell Time Low Cut High Cut Selects Reverb Type 0.4
Reverb Hall Ambient bias.reverb Level Damping Dwell Time Low Cut High Cut Selects Reverb Type 0.5
Reverb Plate Short bias.reverb Level Damping Dwell Time Low Cut High Cut Selects Reverb Type 0.6
Reverb Plate Rich bias.reverb Level Damping Dwell Time Low Cut High Cut Selects Reverb Type 0.7
Reverb Plate Long bias.reverb Level Damping Dwell Time Low Cut High Cut Selects Reverb Type 0.8
Hendrix Tones

Note: You can easily store tones using Hendrix gear on Ignitron. As the effects are licensed and purchased In-App, you need to connect your mobile Spark App to the Spark Amp after switching on the Spark Amp. When you then disconnect the Spark App and connect Ignitron afterwards you should be able to use presets using below gear.

Type App Name Technical Name Parameter 0 Parameter 1 Parameter 2 Parameter 3 Parameter 4 Parameter 5 Parameter 6 Extra Info
Compressor/Wah J.H. Legendary Wah JH.Vox846 Auto Wah Mode BPM Mode Switch ms (BPM Off) Bar (BPM On) Sensitivity Auto Wah Mode: 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 - Bar: 0.0 (1/8), 0.25 (1/4), 0.5 (1/2), 0.75 (1/1)
Drive J.H. Axle Fuzz JH.AxisFuzz Volume Drive
Drive J.H. Super Fuzz JH.SupaFuzz Volume Filter
Drive J.H. Octave Fuzz JH.Octavia Level Fuzz
Drive J.H. Fuzz Zone JH.FuzzTone Volume Attack
Modulation/EQ J.H. Legendary Vibe JH.VoodooVibeJr Speed Sweep Intensity Mix (Vibrato/Chorus)

OTA Updates

When in AMP mode, the firmware can be updated Over-the-air by using a web interface. In order to enable this, you need to rename the file Credentials.h.template to Credentials.h and enter your WiFi SSID and password before compiling the code. Once installed manually for the first time, subsequent firmware versions can be uploaded by opening a web browser and connecting to http://Ignitron.local and uploading the compiled Ignitron.bin file. The Ignitron should restart automatically after the upgrade finished successfully.

More information on the Ignitron Github page

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