Introduction
A PIR sensor that stays triggered (output HIGH) indefinitely can be annoying and render your project useless. Let’s troubleshoot why it won’t turn off.
1. Hold Time Too Long
If the hold time (delay) potentiometer is turned to maximum, the output may stay HIGH for up to 200 seconds. Wait a few minutes to see if it eventually turns off. If it does, adjust the potentiometer to a shorter delay.
2. Continuous Motion Detection
In repeatable trigger mode (H), the timer resets every time motion is detected. If someone is constantly moving in the detection area, the output will stay HIGH indefinitely. Test by having everyone leave the area and see if it turns off.
3. Stuck Relay or Load
If you’re using the PIR to control a relay or other load, the load itself might be keeping the sensor on (e.g., a relay that welds shut). Disconnect the load and check the sensor output directly.
4. Faulty Sensor
Internal component failure can cause the output to latch. Try power cycling the sensor. If it still stays HIGH with no motion, the sensor may be defective. Replace it.
5. Check with Multimeter
Disconnect the sensor from your microcontroller. Power it up, wait for warm-up, and measure voltage between OUT and GND. Wave your hand in front of it; the voltage should rise and then fall after the hold time. If it stays high regardless, the sensor is likely faulty.
6. Wrong Trigger Mode
In non-repeatable mode (L), the output will stay HIGH for the full hold time even if motion stops. That’s normal behavior. If you want it to reset immediately when motion stops, use repeatable mode (H) and ensure the hold time is short.
7. Ambient Temperature Too High
If the ambient temperature is close to human body temperature (e.g., in a very hot room), the sensor may have difficulty detecting the differential, potentially causing erratic behavior including staying on. This is rare but possible.
Conclusion
A stuck output is usually due to settings or continuous motion. If those are ruled out, consider sensor replacement.