Positive Grid
Firmware development for Bluetooth and USB-connected guitar pedal controllers with MIDI support.
Services Provided
Technologies
Overview
Positive Grid creates innovative music technology products, including the Spark series of smart guitar amplifiers. NRB Tech developed the firmware for their Bluetooth and USB-connected foot controllers, enabling musicians to control amp settings, effects, and recordings hands-free.
The Challenge
The foot controllers needed to work reliably across multiple connection types (Bluetooth and USB), with broad compatibility across computers, tablets, and phones. The firmware platform also needed to be maintainable long-term—able to receive security patches and new features without full rewrites.
Future-Proof Platform
The firmware was migrated to the latest nRF Connect SDK and Zephyr RTOS, ensuring access to ongoing security patches, improved power management, and long-term stability from the semiconductor vendor.
A formal patch management system means SDK upgrades can be applied quickly—changes are 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—no drivers required. The implementation automatically negotiates the best available protocol, ensuring 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 configuration changes.
Reliable Updates in Any Environment
Firmware updates work via both USB and wireless OTA. USB DFU is particularly valuable for live performance venues where wireless interference is common.
The update system protects against failed updates:
- 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:
- High-precision calibration via the companion app
- Consistent response curves with configurable dead zones
- Extended battery life through intelligent sensor sampling
Consistent Behaviour Across Connections
The same features—Tuner control, FX Loop toggling, Looper commands—work identically whether connected via Bluetooth or USB. Musicians don’t need to learn different workflows for different connection types.
Release Infrastructure
An automated release pipeline ensures consistent, reliable firmware releases:
- Secure signing with hardware-specific keys
- Single build process generates packages for all hardware variants
- Hermetic build environments ensure reproducible binaries
- RSS feeds enable companion apps to discover available updates
Room for Growth
Memory optimisation tools enabled the addition of USB MIDI support without sacrificing performance on the constrained nRF52840 platform. Modular build configuration allows unused features to be excluded, leaving headroom for future functionality.