Fire detection middleware: IEC 61508 compliance with Lean-Agile development

Apollo Fire Detectors is a leading global manufacturer of fire-detection equipment, providing commercial systems found in hotels, office buildings, and other large facilities. Their products must reliably handle hundreds of sensors (smoke alarms, call points, heat detectors, etc.) on a shared two-wire loop. Data is sent via small fluctuations in voltage and current (current modulation) that also power the devices.  

For this project, Apollo needed to unify a large range of legacy devices under a single, modern codebase while achieving stringent low-power and timing demands. Compliance with the IEC 61508 functional safety standard was essential for bringing their new generation of products to market. 

Creating the next-generation solution

Our role focused on delivering the embedded software that would unify Apollo’s diverse product line under one codebase. We developed critical software modules, working closely with Apollo’s existing architecture and ensuring that low-power consumption and tight timing requirements were respected.  

The client utilised a V-model approach to ensure architectural consistency and meet compliance obligations. We were able to integrate our Lean-Agile practices into this workflow, enabling early feedback, rapid adaptation, and a steady pace. 

Evidencing traceability 

To meet IEC 61508 requirements, we combined multiple safeguards throughout development. Automated unit tests linked to specific requirements were run with every commit, ensuring code could not merge unless all tests passed. We also enforced MISRA-C 2012 coding standards via linting and static analysis to catch issues early. Regular design and code reviews validated that each user story aligned with the approved architecture, while testers worked alongside developers from the outset, performing integration checks that caught problems swiftly. We maintained comprehensive test logs and generated detailed reports for both internal tracking and external audits, and biweekly demos with Apollo’s engineers and stakeholders offered transparency and timely feedback.  

This blend of rigorous technical processes and proactive project management ensured strong traceability and consistent proof of compliance. 

What we delivered

While Apollo retained control over top-level requirements and architectural decisions, we developed the critical embedded software modules, handled unit-level testing and supported integration. 

• Embedded middleware: We built a reusable software layer to handle Apollo’s proprietary two-wire communication protocol, which encodes data through voltage and current fluctuations—all within strict microamp-level power constraints. 

• Lean-Agile development: Building on Apollo’s existing V-model approach, we integrated sprint-based iterations, daily standups, and “three amigos” collaboration (developer, tester, product owner). This blend ensured frequent demos and rapid feedback loops. 

• Compliance documentation: We created and maintained a robust software development plan (SDP) capturing our approach to meeting safety standards. We also produced retroactive release documentation that satisfied both Apollo’s internal requirements and external audit obligations. Throughout the project, we generated detailed test reports to demonstrate continuous compliance at every development stage. 

• Design traceability: Using Enterprise Architect, we modelled each function in Unified Modelling Language (UML) to ensure end-to-end traceability from requirements through to final implementation. 

• Robust test harness: We developed a specialised harness that directly interfaced with the microcontroller pins on off-the-shelf MSP430 LaunchPad boards (the same chip used in Apollo’s devices). This setup emulated the two-wire loop protocol at a low level, enabling thorough validation of the software even before full hardware was available. By detecting issues early and often, the harness helped ensure a higher degree of reliability ahead of final integration with Apollo’s hardware. 

By combining advanced embedded engineering, Lean-Agile practices, and a deep understanding of IEC 61508, Bluefruit Software helped Apollo deliver cutting-edge, safety-critical fire detection devices on time, ensuring both business and end-user needs were met without compromise.