Monday, 2 March 2015

Pedalboard Controller MK2 Software

The last post described the hardware design and building of this:

This post describes the main features and the iPad app screens used to program patches.

For some context, here it is on the pedalboard:

Clockwise from top left: CV MK2, power supply, switch box, KOMA BD101, Ditto Looper, EHX Freeze, Moogerfooger Freq Box, Moog EP-2 expression pedal, 3-footswitch strip, Moogerfooger Low Pass Filter, Moogerfooger Ring Mod.

The 5V CV outputs are connected to the Moogerfoogers through TRS cables. The 9V CVs get to the KOMA through an Ethernet cable, broken out to TRS cables on a small board screwed to the pedal. This also connects the KOMA's sensor input to the CV box. The Freeze is controlled by one of the opto-isolated outputs connected via a stereo mini-jack cable (it has a spare opto output for future use). The expression pedal connects via its normal TRS cable. The 3-footswitch strip goes via an Ethernet cable, with the switches and LEDs wired separately (the CV box controls the LEDs, not the footswitches directly).

First, a bit about the overall design...

The idea is to have a variety of 'sources' that can be assigned to the CV outputs. This is the list so far:
  • Fixed level
  • Noise
  • LFO (sine)
  • Expression
  • Low Pass Filter envelope
  • Ramp
  • Arbitrary waveform
  • Bus combining other sources
The CV outputs can be connected individually to any of the sources, and their output level ranges can be set, and optionally inverted. For example, CV output 1 could deliver a sine wave from an LFO in the range 3V-4V. Or the expression pedal could change multiple parameters at the same time, perhaps in the opposite direction.

The sources all have their own set of configurable parameters, e.g. the LFO frequency, ramp time etc., and all are triggerable by a footswitch.

A patch is defined as the set of CV/source assignments and their parameter settings.

All of these features are implemented in the Arduino firmware (mostly C++), with the parameters and source routing being configurable through MIDI Control Change messages. These can be received from the iPad app and saved into the permanent storage attached to the Arduino.


iPad App


MIDI Designer is an app that can be used to build custom interfaces for MIDI control. You can place buttons, knobs, sliders etc. and have them send MIDI messages when they are changed. These are organised into pages taking up half of the screen.


5V CV Outputs


The page on the left is for selecting the source for each 5V CV output. The right is used to set the output voltage range. Sources with variable output (most of them) operate between the low and high levels, but each of these also has its own minimum and maximum value, so that it can be further modified by a different source, selected by the knobs. The 9V CVs have similar pages:


LFOs and Noise Sources


The left-hand page has the controls for two LFOs and two noise sources. The frequency range and Min control can be used to set the source to a fixed frequency. But the Control knob allows any other source to vary the frequency between Min and Max. In the screenshot, the expression pedal is used for that. The Trigger knob selects which of 8 programmable triggers starts the LFO running, or 'On' for a free-running oscillator. More on the triggers later.

The Noise source Rate control determines the time between new random values. The Amplitude control changes the amount by which the noise value can change at each step. This can be used to create wildy varying values or more subtle changes. Both Rate and Amplitude can be controlled between two values by any of the other sources.

The right-hand page is for configuring the triggers. This allows the footswitches to be used in momentary or latched mode (level or edge). The Env option can be used to generate a trigger when the audio signal exceeds a threshold. This could be used to trigger the Freeze pedal, for example.


Misc. Sources and Arbitrary Waveform Generators


The expression inputs can be inverted and enabled by a trigger. Expr 1 is the EP-2 expression pedal. Expr 2 is the KOMA's sensor output.

The Envelope State controls allow the levels and sensitivity of the Env trigger to be set.

There are two ramp sources with controllable rise/fall time.

The LPF's envelope output can be enabled or disabled, and boosted up to x3.

The Freeze settings determine which of the triggers controls the Freeze pedal(s).

The footswitch strip LED states are driven by selectable triggers.

Tempo is an experimental feature. In future, some things might need to be driven by a signal derived from a tempo - either a fixed BPM or tapped.

The Arbitrary Waveform Generator (AWG) has 8 'phases' that are run in turn. Each phase has a target level (the upper slider) and the time to reach that level from the previous one. This allows triangle, square, sawtooth waveforms to be created, and many other kinds of weird waveshapes. The overall rate can be fixed or controlled by another source.


Buses and Patch Control


The Bus 'sources' allow an output to be driven by a combination of two sources, with the balance between them being fixed or controlled by another source. For example, the expression pedal can be used to gradually change an output from an LFO to a noise source.

The page on the right has the buttons used to create and save patches in the Arduino. The other controls are mostly just useful during firmware development.


What Next?


I should really record some demos of the different features. Maybe one day.

The next addition is going to be a drum trigger. This will make use of a spare input connected to some kind of trigger attached to a tom. It'll be able to trigger any of the features in the box. For example, to 'duck' the guitar rhythmically, or start a ramp, or hit the Freeze pedal. Loads of possibilities.

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