Why Is My Sensor Giving Random Readings?

Short answer: your sensor input is floating, noisy, or underpowered. This is almost always wiring or power, not the sensor itself.

Common causes

  • Floating input: No pull-up or pull-down resistor.
  • Loose wiring: Breadboard jumpers move or lose contact.
  • Power noise: Motors or servos share the same power rail.
  • Wrong voltage: 3.3V sensor on 5V logic or the reverse.

Fast fixes

  1. Add a pull-up or pull-down resistor or enable the internal pull-up.
  2. Shorten wires and re-seat all connections.
  3. Power sensors from a stable supply and share ground.
  4. Read the sensor at a steady rate and average a few samples.

Quick test

If your readings change when you touch the wire, the input is floating.

Pull-up and pull-down basics

Digital inputs need a defined state. Without a resistor, they pick up noise from the air and your hand. Use a 10k pull-up or pull-down, or enable the internal pull-up in code.

Power and grounding

Noise is the most common cause of random readings. If you run a motor, servo, or relay, use a separate power supply and connect grounds together.

Bottom line

Random readings come from floating inputs, bad wiring, or noisy power. Fix the wiring, add pull-ups, and separate noisy loads.

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