Connect Mobile App to Veeder-Root TLS-300 ATG

Job Title: React Native / Node.js Developer — Fix TLS-300 Serial Connection + Finish Fuel Tank Monitoring App Job Description: I’m building FuelCheck — a mobile/web app for gas station owners to monitor underground fuel tank levels in real time. Most of the system is already built; I need a developer with RS-232/serial hardware experience to solve the final connection issue and finish two remaining features. What’s already done: ∙ Full frontend app live at fuelcheckapp.com (HTML/CSS/JS) ∙ Firebase project set up (fuelcheck-prod) with tank structure, alert thresholds already saved ∙ Node.js backend live on Railway, connected to GitHub ∙ USR-TCP232-410s serial-to-ethernet converter installed on-site and connected ∙ Correct straight-through RS-232 cable installed in the TLS-300’s AUXILIARY port ∙ Backend is confirmed actively polling the TLS-300 every 5 minutes (sends inventory request command I20100, 8 bytes out) — but currently receives zero bytes back ∙ Serial settings matched on both ends (2400 baud, 7 data bits, odd parity, 1 stop bit) What I need you to do (3 milestones, $800 total): Milestone 1 — TLS-300 Diagnosis and Fix ($300) Diagnose why the TLS-300 isn’t responding to serial poll requests despite matched settings and confirmed cable/port. Likely causes: RS-232 physical layer issue, config mismatch, or the console gated behind technician mode. Remote diagnosis preferred — I can assist with on-site testing, photos, and readings as needed. Goal: live tank data flowing into Firebase. Milestone 2 — Firebase Auth ($250) Real email/password login. Each customer sees only their own tanks. Milestone 3 — Live Data Display ($250) Live gallons and fuel percentages showing in the app, pulled from Firebase in real time. Hardware details: ∙ Veeder-Root TLS-300 ATG ∙ USR-TCP232-410s serial-to-ethernet converter ∙ Serial connection: RS-232, DB9/DB25 Tech stack: ∙ Frontend: HTML/CSS/JavaScript (single file) ∙ Backend: Node.js on Railway ∙ Database: Firebase Firestore ∙ Auth: Firebase Authentication Budget: $800 fixed price Timeline: 1.5–2 weeks Please only apply if you have experience with: ∙ RS-232 serial communication and TCP/IP serial converters ∙ Veeder-Root or similar ATG/fuel monitoring systems (strongly preferred) ∙ Node.js backend development ∙ Firebase Firestore and Authentication ∙ Clear, proactive communication — flag blockers immediately rather than burning hours