Senior Firmware Engineer

You will be the first in-house firmware engineer at ZWIM.

The hardware is built around a low-power ARM Cortex-M4 BLE SoC, a 6-axis IMU, and a precision force sensor ADC — all communicating to our mobile app over BLE 5.0. The firmware runs sensor fusion, power algorithms, calibration, persistent storage, and over-the-air updates.

You will own that stack — maintain it, improve it, extend it, and eventually help design what comes after it.

You will work directly with the founders, the full-stack engineering team, and our external hardware partners. No layers. No waiting.

KEY RESPONSIBILITIES
• Own the firmware stack. Embedded C on an ARM Cortex-M4 BLE SoC. You keep it stable, clean, and shipping.
• BLE architecture. Custom GATT services, characteristic design, connection stability, throughput, and reliability across iOS and Android.
• Sensor integration. IMU data processing, force sensor ADC pipeline, quaternion-based sensor fusion, and calibration workflows.
• Power and reliability. Low-power states, battery life management, graceful error handling, and production robustness.
• OTA DFU. Maintain and extend over-the-air update infrastructure. Athletes must always be on the right version.
• Manufacturing tooling. Production-line flashing, calibration fixtures, serial number provisioning, and factory test utilities.
• Certification support. Work with our regulatory team on FCC, CE/RED, BLE SIG qualification, and whatever comes next as we scale markets.
• Cross-disciplinary integration. Define clean contracts between firmware data and the mobile and game layers. Be the translator between atoms and code.

WHAT WE EXPECT IN THE FIRST SIX MONTHS
• Get deep into the existing codebase alongside our external firmware partner and own it with full confidence.
• Ship at least two meaningful firmware improvements — reliability, performance, or new capability — that athletes feel directly.
• Establish the internal development, testing, and release process so the team can iterate predictably.
• Be the person the rest of engineering trusts to answer "what does the firmware actually do here?"

REQUIREMENTS
Experience
•5+ years of professional embedded firmware engineering.
• At least one shipped consumer hardware product that real people bought and used.• Experience across the full cycle: prototyping through production, including manufacturing tooling and post-launch support.

Technical
• Strong embedded C. You write clean, readable, maintainable firmware — not just firmware that works once.
• ARM Cortex-M4 (or equivalent low-power embedded SoC), including working with a BLE SDK or embedded RTOS.
• BLE 5.0: custom GATT services, connection management, throughput and latency optimisation, iOS and Android interoperability.
• IMU integration and sensor fusion. You know the difference between raw data and useful data.
• Low-power design: sleep states, power rail management, and battery life engineering for a consumer device.
• OTA DFU — designing and maintaining reliable over-the-air update pipelines.
• Persistent NVM storage on embedded targets.

Practical
• Self-directed. You can take ownership of an unfamiliar codebase, build context fast, and start shipping improvements.
• Strong written and verbal English. You can explain a firmware decision to a product manager and a hardware engineer in the same sentence.
• Comfortable in a small team where everyone is close to the work and the user.
• Lisbon-based or willing to relocate.
• Right to work in Portugal. Ideally already in Portugal, or EU passport holder.

NICE TO HAVES
• Hardware debug tooling — JTAG/SWD, logic analyser, BLE sniffer.
• Regulatory certification experience: FCC, CE/RED, BLE SIG qualification.
• Factory calibration fixture design or production-line test scripting.
• Daily AI tooling (Claude, Cursor, Copilot) for code scaffolding, debugging, and documentation.
• Personal interest in triathlon, swimming, or endurance sports.

NOT A FIT
• Application or backend engineers who have never written embedded C targeting a microcontroller.
• Engineers who have only worked on high-power or mains-powered systems. Battery life matters here.
• Candidates who need a large team and defined process before they can ship. We move fast with a small team.
• Someone whose embedded experience is limited to side projects or academic work. We need production firmware — real hardware, real users, real consequences.• Remote-only candidates.

COMPENSATION AND BENEFITS
Compensation
Salary and potential equity discussed in our intro call once we understand your background, shipped work, and what you're looking for.

Time and Recovery
27 paid vacation days. Rest and recovery matter as much as performance.
Flexible hours for training and recovery. We trust you to perform your best in and out of work.

Day-to-Day
Meal allowance to fuel focus and performance.
Fitness partner discounts that support an active lifestyle.
Free access to everything we are building — train, test, and improve with the product.
Direct collaboration with athletes bringing real performance insight into how we build.
Team and community events where we train, celebrate, or just spend time together.