Why would presence of a phone below a TV screw up an IR remote?

September 19, 2021 4:24 PM

We have a Roku tv in our bedroom with a table underneath it. If a phone is placed below the TV the remote, which I assume is IR based on needing line of sight, barely works at all. Moving the phone fixes the problem. Any idea what would cause this effect?
posted by Ferreous to Technology (7 answers total)

First thought: Is the phone an iPhone? Apple's Face ID technology projects a fairly bright pattern of infrared light in order to reconstruct a 3D model of your face. If that's getting activated for some reason, I can imagine it would interfere with the infrared signal from a more distant remote control.
posted by teraflop at 4:28 PM on September 19, 2021 [3 favorites]

The screen of the phone is reflecting ambient light into the IR sensor on the Roku, impacting It's sensitivity? Does it matter in your case which way the phone's screen is facing? Is the problem the same at any time of day?
posted by chudmonkey at 4:35 PM on September 19, 2021 [3 favorites]

Response by poster: Extra info: has happened with a pixel 4a, 5a and a moto z play. Time of day has been usually in the evening with only an overhead light. Have not tested with phone facing down but will do so.
posted by Ferreous at 4:43 PM on September 19, 2021

Our TCL Roku TV has a wifi-direct remote. I don't know if there's likely to be wifi interference, but check in your Roku settings if your remote is "paired." If it has a microphone or headphone jack, it's not using IR.
posted by Snijglau at 5:20 PM on September 19, 2021 [2 favorites]

the remote, which I assume is IR based on needing line of sight

Some Roku TV remotes are RF, not IR; the voice remotes (with a push-to-talk "microphone" button for voice search) are RF. What type of remote does my Roku® device use? A pairing button in the remote's battery compartment would also signify that it's an RF remote.

Does WiFi enabled/disabled on the phone make any difference?

(Roku employee, not speaking for my employer etc etc)
posted by We had a deal, Kyle at 5:23 PM on September 19, 2021 [4 favorites]

I'd have a feeling that the Roku remotes with the TV volume control may be IR. The old Roku stick basic remote I have is definitely RF and I don't remember any sort of pairing at all. Any idea what this pairing button looks like, I don't see anything in the battery compartment.

If it's IR, there will be a LED or some sort of window on the front to hide the LED. If there's no obvious LED/window then it's WiFi or RF.

iPhone's IR face recognition was my first guess as well, maybe WiFi, maybe reflections off the screen. I'm eagerly awaiting if turning the phone face down works, or if putting it in airplane mode works.
posted by zengargoyle at 8:39 PM on September 19, 2021

The above suggestions are probably most likely. Another possibility is radio frequency interference causing problems in the roku device, which could happen with either kind of remote. If blocking light doesn't work, consider turning off all all of the phones transmitters one by one: wifi, phone network, bluetooth, NFC, anything else that looks like it might transmit.

If one of those fixes it, and it's a problem you want to fix, putting some metal either between the phone and the receiver or around as much of the receiver as possible, or re-routing cables might be worth a try. Video cables tend to be pretty well shielded already. Analog audio and power cables often much less so. Taping a thick aluminum cookie tin lid to cabinet above the phone or below the roku device won't reduce the signal by much, but it's easy to try and might be enough to fix it. You could also try ferrite clamps on the cables, but I wouldn't be too optimistic. Good luck. And, do let us know what the answer is.
posted by eotvos at 9:32 AM on September 20, 2021