Introduction
You’ve connected your PIR sensor, uploaded the code, but nothing happens. Or maybe it’s triggering randomly. Don’t worry—most PIR issues are easy to fix. Here are 7 common problems and their solutions.
1. Check Power Supply
Symptom: Sensor doesn’t respond at all, LED never lights.
Solution: Verify that the sensor is receiving proper voltage. HC-SR501 needs 4.5V to 20V. Measure VCC and GND pins with a multimeter. If voltage is correct but sensor still dead, try another sensor.
2. Wait for Warm-Up
Symptom: Sensor triggers immediately after power-up and keeps triggering.
Solution: PIR sensors need 30-60 seconds to stabilize after power is applied. During this time, they may false trigger. Wait a minute and test again.
3. Verify Wiring
Symptom: No output even when motion is present.
Solution: Double-check connections. On HC-SR501, the pin order is often VCC, OUT, GND (left to right when facing the front with pins down). But some modules vary. Confirm with your module’s labeling.
4. Adjust Sensitivity
Symptom: Sensor doesn’t detect motion far enough, or is too sensitive.
Solution: Turn the sensitivity potentiometer (usually labeled “SENS”) clockwise to increase range, counterclockwise to decrease. Test after each adjustment.
5. Check Placement
Symptom: Sensor misses motion in certain areas.
Solution: Ensure the sensor is mounted at the correct height (1.5-2.5m) and not obstructed by furniture. Remember that PIR detects motion across its field of view, not directly below.
6. Avoid Heat Sources
Symptom: Random false triggers, especially when HVAC turns on.
Solution: Move the sensor away from air vents, radiators, windows, and direct sunlight. These can cause temperature changes that mimic motion.
7. Test with a Multimeter
Symptom: Still not sure if sensor is working.
Solution: Disconnect the sensor from your microcontroller. Power it up, wait for warm-up, then connect a multimeter between OUT and GND. When you move in front of the sensor, the voltage should jump from near 0V to 3.3V (or 5V). If it doesn’t, the sensor may be defective.
Still Having Issues?
If none of these steps help, your sensor might be damaged. Consider replacing it. For more specific problems, check our other troubleshooting guides.