Pretorian Technologies
Drop-in Bluetooth module replacement firmware enabling product continuity after component end-of-life.
Services Provided
Technologies
Overview
Pretorian Technologies designs and manufactures assistive technology devices that enable people with disabilities to control computers, tablets, and smartphones. Their products—including the APPlicator wireless switch interface, iSwitch accessibility buttons, and Blueline communication aids—are used by schools, care facilities, and individuals worldwide.
The Challenge
Pretorian’s product line relied on the RN42 Bluetooth module, a component that had been in production for over a decade. When Microchip announced the RN42’s end-of-life, Pretorian faced a difficult choice: either redesign all of their products’ MCU firmware—a costly, time-consuming process that would require recertification—or find a way to maintain compatibility while upgrading the Bluetooth hardware.
Drop-In Replacement Module
NRB Tech developed a custom Bluetooth module based on the Nordic nRF52832, designed as a direct drop-in replacement for the RN42. The replacement module:
- Replicates GPIO connections — The replacement module replicates the RN42’s GPIO signalling—connection enable, mode select, baud select, and connection status—so the host MCU controls it exactly as before
- Emulates the RN42 command interface — The module implements the RN42 serial command and data-mode protocol the host firmware relies on, so the host MCU sees no difference between the original module and the replacement
- Preserves the behaviour host firmware depends on — HID profiles, pairing, and device configuration continue to work as the host expects
This approach allowed Pretorian to upgrade their entire product line without touching a single line of MCU firmware.
Secure Field Updates
The new platform includes secure Over-the-Air (OTA) update capability built on Nordic’s Secure DFU:
- Cryptographically signed packages — Update packages are signed and verified during installation, preventing tampered firmware from being deployed
- Safe update process — A buttonless over-the-air entry path and secure bootloader let devices recover safely if an update is interrupted
- Future-proof architecture — New features and compatibility improvements can be deployed to devices already in the field
Products Upgraded
The same module firmware now powers several Pretorian products, with each host device configuring its own name and behaviour without firmware changes:
- APPlicator — Wireless switch interface that connects accessibility switches to iOS devices
- iSwitch — Bluetooth-enabled accessibility buttons in various sizes and activation forces
- Blueline — Communication aids for users with limited mobility
The module supports both standard HID operation and a data (MLDP) mode, so products that need a richer data channel as well as keyboard, mouse, and switch input are served by the same platform.
Long-Term Support
Assistive technology products have long lifecycles—users and institutions depend on devices working reliably for years. The Nordic-based platform provides access to ongoing security patches and Bluetooth stack improvements, ensuring these devices remain supported and secure.
“When we learned RN42 was being discontinued, we thought we’d have to redesign everything. NRB Tech delivered a drop-in replacement that let us keep our existing firmware and ship upgraded products within months. Our customers didn’t notice any change—except better Bluetooth performance.”
— Dave Gilbert, Director, Pretorian Technologies