Introduction
Large televisions, particularly older plasma screens, can emit significant infrared radiation and electrical noise that interferes with PIR sensors. This is a common issue in home theaters.
How Displays Cause Interference
1. Plasma TVs (Worst Offenders)
Plasma displays work by ionizing gas in tiny cells. This process generates significant heat and also emits IR. The picture content changes rapidly, creating varying IR patterns that can mimic motion.
2. Large LED/LCD TVs
Modern LED-backlit LCDs generate less heat, but the backlight can still produce IR. Some TVs use IR for remote control, which can also cause interference.
3. Electrical Noise
All large displays have switching power supplies that can generate EMI, coupling into sensor wiring.
Symptoms
- False triggers only when TV is on.
- Triggers correlated with scene changes or bright scenes.
- Sensor located near TV in home theater setup.
Solutions
1. Relocate Sensor
Move the sensor away from the TV. Even 1-2 meters can make a difference. Avoid pointing the sensor directly at the screen.
2. Use a Different Mounting Location
Mount the sensor on a side wall or ceiling, not facing the TV.
3. Add Shielding
Place a physical barrier between the sensor and TV that blocks IR but allows detection elsewhere. A small piece of cardboard can help diagnose if this works.
4. Reduce Sensitivity
Lower sensitivity may make the sensor ignore the weaker IR from the TV.
5. Use a Sensor with Better IR Filter
High-quality sensors have better rejection of near-IR, which may help with some displays.
6. Time-Based Solutions
If TV use is predictable, you could disable the sensor during known TV times – but this is a hack.
Case Study: Home Theater Motion Sensor
A motion sensor in a home theater triggered randomly during movies. The culprit was a plasma TV. Replacing the plasma with an LED TV reduced but didn’t eliminate the problem. Relocating the sensor to the ceiling above the seating area solved it.
Conclusion
Large displays can interfere with PIR sensors. Relocation is the most effective solution.