Serial debugging tips

Use the Arduino serial monitor effectively for DHT22 timing, Ethernet status, and HTTP trace logs during bench bring-up.

Arduino Uno wired to a DHT temperature-humidity sensor with three jumper wires
A minimal MCU-plus-sensor bring-up before Ethernet, LCD, and dual-probe wiring. Photo: Wikimedia Commons contributor. CC BY-SA 4.0

USB serial is the fastest feedback loop while the Uno still sits on the bench. Thoughtful logging, without flooding the monitor: shows whether failed reads, DHCP delays, or JSON formatting happen before you blame the website. These habits complement IDE setup and reduce ladder trips after deployment.

Laptop connected to Arduino with serial monitor showing timestamped log lines
Serial monitor at matching baud rate reveals sensor errors and network state during development.

What to log

  • DHT22 errors with probe index and retry count.
  • Ethernet link up/down and assigned IP after DHCP.
  • HTTP client connect/disconnect, not full JSON every second.
  • Watchdog pets only in debug builds to verify loop health.

Timing and baud

Match monitor baud to Serial.begin in firmware, often 9600. Remember main loop timing: verbose prints slow loops and can themselves cause DHT22 timeouts. Disable chatty logs in production builds.

After deployment

Serial is unavailable on the pole unless you USB again: switch to JSON curl checks and site-side stale debug. For network issues compare static IP versus DHCP logs from boot.