ESP32 Modbus To Google Sheets

I need a small firmware-ready solution that lets my ESP32 (with a MAX485 transceiver) poll a Selec UCI 500 PID controller over RS-485/Modbus RTU, grab the temperature once every 60 seconds, hop onto the local Wi-Fi network via a simple on-device web interface where I enter the SSID and password, then push the reading to a predefined Google Sheet through an Apps Script HTTP endpoint.

The reading has to reach the sheet as a single CSV line so it drops neatly into the next free row. Reliability matters more than fancy graphics—I just want to see the numbers stacking up.

Please use clean, well-commented code (Arduino IDE or PlatformIO—your call) and keep memory use modest so OTA updates remain possible later.

Deliverables
• Complete, compilable firmware with clear build instructions
• A wiring diagram showing ESP32 ↔ MAX485 ↔ RS-485 A/B and power connections
• Quick setup notes that walk me from flashing to entering Wi-Fi details and watching data land in Sheets
• A short demo video or screenshots proving a successful 60-second polling cycle feeding the live spreadsheet

Acceptance criteria: after following your guide I can wire the board, flash the code, open the captive-portal style web page to input Wi-Fi credentials, and see consecutive CSV rows appear in my Google Sheet without manual intervention.