Positive Grid
Firmware platform for Bluetooth and USB-connected guitar controllers with secure updates, USB MIDI, and long-term maintainability.
Services Provided
Technologies
Overview
Positive Grid creates music technology products including the Spark series of smart guitar amplifiers. NRB Tech developed the firmware for Bluetooth and USB-connected foot controllers, giving musicians reliable hands-free control over amp settings, effects, and recording workflows.
The Challenge
The foot controllers needed to work reliably across Bluetooth and USB, with broad compatibility across computers, tablets, and phones. The platform also needed to stay maintainable over time, so security patches and new features could be added without repeated rewrites.
Future-Proof Platform
The firmware was migrated to the latest nRF Connect SDK and Zephyr RTOS, providing a more maintainable foundation with ongoing vendor support, improved power management, and a clearer upgrade path.
A formal patch management system means SDK upgrades can be applied quickly, with changes stored as versioned patches rather than manual edits scattered through the codebase.
Universal Connectivity
Full USB MIDI support allows the foot controllers to work as class-compliant controllers with computers and mobile devices, with no drivers required. The implementation negotiates the best available protocol automatically, maintaining compatibility with both legacy music software and modern digital audio workstations supporting high-resolution MIDI.
Musicians can use the same controller across Bluetooth and USB without learning separate workflows or reconfiguring the device.
Reliable Updates in Any Environment
Firmware updates work via both USB and wireless OTA. USB DFU is particularly useful in live performance environments where wireless interference is common.
The update system is designed to reduce field-update risk:
- Secure firmware signing prevents tampered updates
- Automatic rollback if an update fails
- Single update packages support multiple hardware revisions
Professional Expression Pedal Support
Expression pedal calibration delivers smooth, precise control for performance use:
- Extended battery life through intelligent sensor sampling
- High-precision calibration via the companion app
- Consistent response curves with configurable dead zones
Consistent Behaviour Across Connections
The same features, including tuner control, FX Loop toggling, and looper commands, work identically whether connected via Bluetooth or USB. Musicians do not need to learn different workflows for different connection types.
Release Infrastructure
An automated release pipeline supports consistent, repeatable firmware releases:
- Secure signing with hardware-specific keys
- Hermetic build environments ensure reproducible binaries
- Single build process generates packages for all hardware variants
- RSS feeds enable companion apps to discover available updates
Room for Growth
Memory optimisation tools enabled USB MIDI support without sacrificing performance on the constrained nRF52840 platform. Modular build configuration allows unused features to be excluded, preserving headroom for future functionality.