GSM-Enabled Automation Control PCBA

I am building a compact, production-ready PCBA that combines a low-power microcontroller with a quad-band GSM module to run stand-alone automation tasks in the field. Its core role is to read temperature, motion, and pressure sensors, make decisions locally, and trigger actuators or alarms while also pushing status updates or alerts over the GSM link (SMS, GPRS, or MQTT—whatever proves most reliable). Scope of work • Schematic capture and multilayer PCB layout, including antenna matching and power-supply conditioning for the GSM current peaks. • Firmware that handles sensor polling, on-board data processing, and a simple AT-command stack to manage the modem. I prefer clean, well-documented C/C++—an RTOS is fine if it keeps timing tight. • Complete manufacturing files: Gerbers, BOM with sourcing options, and assembly drawings. • A first-article test plan so I can verify that the sensors read correctly, the GSM link registers reliably, and the board survives brown-outs. Acceptance criteria 1. All three sensor types register within ±2 % of reference readings during bench tests. 2. A remote SMS command reliably toggles an output within 5 s. 3. PCB passes a 48-hour burn-in at 60 °C without modem dropouts. When you reply, focus on similar boards or firmware you have shipped before—practical experience carries the most weight here. If you have favorite toolchains (Altium, KiCad, Eagle, STM32CubeIDE, MPLAB X, etc.) just mention them; I am flexible as long as the files are industry-standard and editable later. I am ready to move quickly once I see a convincing track record.