Ground loop avoidance

Prevent duplicate ground paths and noisy references when USB bench power meets barrel supply and long sensor cables.

Ground is not “just connect all blacks together.” When USB programming ground, barrel jack return, Ethernet shield chassis, and remote probe grounds meet at multiple points, small circulating currents add noise to the DHT22 one-wire reference. A deliberate **single-star ground** at the Uno keeps digital reads stable and LCD contrast predictable.

Wiring diagram showing star ground at Arduino versus problematic ground loops
Route all returns to one ground star at the MCU instead of chaining grounds through multiple paths.

Bench versus installed power

USB bench power shares ground with your laptop; adding a barrel supply without common planning can create loops. Before mount, verify power rails at one potential reference. After mount, disconnect USB when on barrel power if your enclosure design allows.

Remote probe grounds

  • Run GND alongside data from each probe—do not ground probes locally to building steel alone.
  • Avoid grounding shields at both ends of long runs unless using proper shielded cable practice.
  • See cable length limits for run geometry.

Diagnosis

If errors vanish when touching a wire, suspect reference issues. Cross-check circuit troubleshooting and DHT22 retries after fixing grounds before replacing sensors.