Senior ESP32 Embedded Systems Engineer for Gaming Machine Monitoring Device

We are building a real-time gaming/skill machine monitoring system using custom ESP32-based hardware. We are looking for a Senior Embedded Systems Engineer who can help develop both the hardware and firmware for the device. The system will connect to: Bill acceptors via RS-232 serial communication Machine motherboard/SAS ports for payout and credit monitoring Cellular modem for cloud connectivity The device will: Read money-in and money-out events Send encrypted event data to a cloud backend Buffer events locally if internet is unavailable Support OTA firmware updates Run reliably inside real gaming machine environments What we need help with: ESP32-S3 firmware development (C/C++) UART / RS-232 communication SAS protocol integration Cellular modem integration (SIM7080G or similar) MQTT or HTTPS event communication Event buffering using SPI flash memory PCB schematic and layout design Hardware debugging and testing Production-ready embedded system design Required skills: Strong ESP32 experience Embedded C/C++ UART / Serial protocols RS-232 voltage-level interfacing PCB design experience IoT device development Hardware troubleshooting Bonus experience: Payment terminals Bill acceptors SAS protocol Secure elements / cryptographic chips OTA firmware systems Project stages: Breadboard prototype Firmware development PCB design Prototype manufacturing Testing inside real machines Production optimization We prefer someone with real-world embedded product experience, not just hobby Arduino projects. Please share: Relevant embedded projects ESP32 work examples PCB examples if available Experience with serial communication or IoT hardware Availability and hourly/fixed pricing