The Role

You will own the firmware development for a rugged, cellular-connected display system for indoor and outdoor deployment. This role bridges the physical world of transit with cloud-based payment gateways, ensuring real-time transaction visibility in environments with unstable power and intermittent network coverage.

Key Responsibilities

Write, test, and maintain production-grade C/C++ firmware for ESP32 microcontrollers.

Develop and optimize rendering logic to drive HUB75/P10 LED matrix displays efficiently without flickering.

Integrate 4G LTE cellular modules (e.g., SIM7600) and manage persistent, secure cloud connections via MQTT.

Design and implement resilient Over-The-Air (OTA) update pipelines for remote fleet management.

Collaborate with backend engineering teams to consume payment IPNs and ensure sub-second display latency.

Implement aggressive watchdog timers and error-handling routines to ensure the board recovers instantly from network drops or voltage spikes.

Core Technical Requirements

Firmware: 2-3 years of experience shipping production C/C++ code for embedded systems, specifically using FreeRTOS and the ESP-IDF framework.

Connectivity: Deep understanding of IoT protocols (MQTT, TLS/SSL, HTTP/S) and experience managing cellular modems via AT commands.

Hardware Debugging: Ability to read schematics and use multimeters, logic analyzers, or oscilloscopes to debug communication protocols (I2C, SPI, UART).

Resilience Engineering: Proven track record of building state machines that handle edge cases (e.g., captive portals, SIM registration failures, power brownouts) gracefully.

Version Control: Strong Git hygiene and experience with CI/CD pipelines for embedded targets.

Bonus Points (Nice to Have)

Experience dealing with automotive electrical environments (load dumps, alternator noise) and testing firmware against physical hardware limits.

Familiarity with digital payment flows, POS systems, or FinTech API integrations.

Basic PCB design knowledge (KiCad/Altium) to collaborate effectively with hardware engineers.

What Success Looks Like in 90 Days

You have deployed a stable firmware build to a pilot deployment that maintains an active MQTT connection, successfully receives pushed payment payloads, drives the LED matrix without artifacting, and automatically recovers from cold reboots under 10 seconds.