Circuit wiring troubleshooting

Diagnose blank LCDs, missing DHT22 probes, and intermittent probe reads with a multimeter, serial logs, and a power-to-data checklist.

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

Intermittent readings usually trace to power, ground, or loose jumpers, not bad luck. Work methodically from rails to sensors before swapping the Arduino.

Symptom → likely cause

  • Blank LCD: Contrast pot, missing Vo, or wrong RS/E/D pins.
  • DHT22 timeout: Missing pull-up, swapped data/ground, or read interval too fast.
  • Ethernet dead: Shield not seated, bad cable, or SPI pin conflict with LCD wiring.
  • Garbled LCD: Floating data line or 3.3 V LCD on 5 V logic without level consideration.

Tools

Serial logging from Arduino IDE setup confirms firmware is alive. Multimeter checks on power rails confirm 5 V under load. Pin-by-pin review: pin wiring.

Sensor-specific help

Persistent DHT22 failures after wiring checks: DHT22 read errors and retries and data line wiring.