This is a collection of alt firmware made for Sitka Instruments Gravity using the open source libGravity library. This library helps make writing firmware easier by abstracting away the initialization and peripheral interactions. Now your firmware code can just focus on the logic and behavior of the app, and keep the low level code neatly tucked away in this library.

https://git.sitkainstruments.com/awonak/libGravity

NOTE: Make sure your Gravity module is disconnected from
the eurorack power and the MIDI expander before flashing.

WARNING: Flashing this firmware will erase any saved data
from your previously installed firmware!

ALT-GRAVITY#

This version of Gravity firmware is a full rewrite that leverages the libGravity hardware abstraction library. The goal of this project was to create an open source friendly version of the firmware that makes it easy for users/developers to modify and create their own original alt firmware implementations.

The libGravity library represents wrappers around the hardware peripherials to make it easy to interact with and add behavior to them. The library tries not to make any assumptions about what the firmware can or should do.

The Alt-Gravity firmware is a slightly different implementation of the original firmware. There are a few notable changes; the internal clock operates at 96 PPQN instead of the original 24 PPQN, which allows for more granular quantization of features like duty cycle (pulse width) or offset.

ENCODER:
     Press: change between selecting a parameter and editing the parameter.
     Hold & Rotate: change current selected output channel.

BTN1:
     Play/pause: start or stop the internal clock.

BTN2: 
     Shift: hold and rotate encoder to change current selected output channel.

EXT:
     External clock input. When Gravity is set to INTERNAL or MIDI clock
     source, this input is used to reset clocks.

CV1:
     External analog input used to provide modulation to any channel parameter.
CV2:
     External analog input used to provide modulation to any channel parameter.

Euclidean#

The Euclidean firmware is an alternative sequencer for the Gravity module that generates polyrhythmic Euclidean rhythms instead of traditional linear sequences. The dual CV inputs can be assigned per channel to dynamically modulate clock divisions/multiplications, Euclidean steps, or the number of hits in real-time. It also includes a menu system accessible via the encoder and buttons, allowing control over playback, muting, clock routing, external sync, and saving/loading patterns and settings to hardware EEPROM slots.

ENCODER:
     Press: change between selecting a parameter and editing the parameter.
     Hold & Rotate: change current selected output channel.

BTN1:
     Play/pause: start or stop the internal clock.

BTN2: 
     Shift: hold and rotate encoder to change current selected output channel.

EXT:
     External clock input. When Gravity is set to INTERNAL or MIDI clock
     source, this input is used to reset clocks.

CV1:
     External analog input used to provide modulation to any channel parameter.
CV2:
     External analog input used to provide modulation to any channel parameter.

Comparator#

The Comparator firmware transforms the Gravity module into a CV rate dual-window comparator for analyzing CV signals. It utilizes CV1 and CV2 as separate inputs, offering an intuitive OLED visualization of both comparator windows spanning a -5V to +5V bounds. You can quickly toggle between adjusting the Shift and Size of either comparator using the buttons and rotary encoder. The module provides six distinct logic outputs based on the voltage windows: individual Gates for each comparator, combined boolean logic (AND, OR, XOR), and a Flip-Flop state.

Additionally, press rotate the encoder to toggle between Comparator, Settings, and CV Calibration modes. Setting menu allows changing encoder direction and parameters for increasing cv accuracy. Turn off hystresis and cv display for audio rate cv input. CV calibration mode for improving the accuracy of the input’s voltage tracking. Exiting calibration mode automatically saves your calibration settings and will persist across power cycles.

ENCODER:
     Press: edit the currently selected parameter.
     Hold & Rotate: switch between comparator, settings and calibration mode.
CV1:
     Analog input for Comparator 1 in the range of -5V to +5V.
CV2:
     Analog input for Comparator 2 in the range of -5V to +5V.

BTN1:
     Toggles between editing Comparator 1 and Comparator 2 values.
BTN2: 
     Toggles the active parameter between the Shift and Size of the selected 
     Comparator window.
BTN1 + BTN2:
     Switch between Comparator mode and CV input calibration mode.

CH 1 (Gate 1): 
     Outputs +5V while CV 1 is actively inside Comparator 1's bounds.
CH 2 (Gate 2): 
     Outputs +5V while CV 2 is actively inside Comparator 2's bounds.
CH 3 (AND Logic): 
     Outputs +5V only when Gate 1 AND Gate 2 are active simultaneously.
CH 4 (OR Logic): 
     Outputs +5V when either Gate 1 OR Gate 2 (or both) are active.
CH 5 (XOR Logic): 
     Outputs +5V exclusively when either Gate 1 or Gate 2, but not both, 
     are active.
CH 6 (Flip-Flop Logic): 
     Rising edges of the XOR signal toggle the flip-flop on or off.

Parametric Rhythm#

The Parametric Rhythm firmware is an alternative sequencer for the Gravity module that generates complex drum patterns by traversing 2D interpolation density maps, similar to Mutable Instruments Grids. The dual CV inputs can be assigned globally to dynamically modulate Kick, Snare, or HiHat densities, the amount of generated Chaos, or the X/Y interpolation positions in real-time. CV can also be routed to completely alter the selected pattern preset A-E.

It includes an intuitive menu system accessible via the encoder and buttons, allowing control over playback, clock routing, external sync, pulse out subdivisions, and saving/loading pattern density settings natively to the hardware EEPROM. Press and hold the encoder button and rotate to select different pattern presets.

ENCODER: 
     Press: change between selecting a parameter and editing the parameter value.
     Hold & Rotate: change between the Global Settings menu and Pattern Presets A-E.

BTN1 (PLAY): 
     Play/pause: start or stop the internal clock and reset output gates.

BTN2 (SHIFT): 
     Reset: sets all gates low and returns the sequencer back to the first step.

EXT: 
     External clock input. Advances the sequencer by the selected PPQN amount. When
     Gravity is set to INTERNAL or MIDI clock source, this input is instead used as
     an external sequencer reset.

CV1 & CV2: 
     External analog inputs used to provide real-time modulation to any pattern 
     parameter, or dynamically jump between loaded pattern preset slots A-E.

FAQ#

My computer does not recognize the Arduino when I connect the USB cable#

Some Arduino clones require older CH340 drivers to communicate with the serial port. Follow these instructions: (https://learn.sparkfun.com/tutorials/how-to-install-ch340-drivers/all)

All 3 lights on the back of the Arduino are lit up - RX, TX, and POW - and it’s not doing anything at all#

Unfortunately this means that the Arduino is bricked. Some of the cheap Arduino clones do not have reverse voltage protection, and will damage the Arduino if any modules in the case have the power connector reversed.

Feedback#

This is a beta release which may contain bugs, or have room for improvement. Your feedback is crutial to help ensure the new firmware is well received when it is officially published. We need your help to make this a success!

You can help by submitting Gitea issues here for bug reports, feedback, or any ideas you’ve got.

https://github.com/awonak/alt-gravity/issues

If you don’t want to submit feedback on the public Gitea site, feel free to shoot me an email at adam.wonak@gmail.com.