Geek Tip: Seeing Infrared

Infrared light is called "infrared" because it is invisible to the human eye. For this reason, TV remotes use infrared light to send signals to the television without bothering the humans in the room. Every such device has an infrared eye that should be kept clean to it'll work optimally.

There are some times when you want to see whether the TV remote is actually working or not. Sometimes the batteries are weak or dead and the remote doesn't have the power to send those invisible signals.

If you're a geek, you probably know that your smartphone camera has a sensor that is sensitive to infrared light. This means your camera can see what you cannot.

To see what I mean, have a friend aim the remote at you and push the power button and hold it down. If you've got a remote like I'm talking about (Some remotes use radio, those don't count.) there's a little LED light that to the naked eye doesn't look like it's doing anything.

Now, grab a smart phone or any digital camera, turn it on, and look at the remote through its display. If your remote is working properly, you'll see the LED light is flickering superfast.

Though the human retina is not sensitive to IR light, the camera's imaging sensor is sensitive to it. You can use this Geek Tip to see whether your remote's batteries are dead or not. Or just to entertain yourself if you're a Geek.

The Magic Raspberry

I got my Raspberry Pi put into an enclosure and doing great things running XBMC with my TV. I wasn't thinking and I picked up the TV Remote Control instead of the micro wireless keyboard. Instead of pushing the arrow buttons on the keyboard, I pushed the arrow buttons on the remote control.

It did what I wanted.

Then I stopped. Oh my gosh. How did that do that? That shouldn't have worked.

I'm an engineer. I understand things. If you push a button on a remote control, infrared light waves go speeding to an eye built into the TV. The Raspberry Pi has no eyes. It is blind to infrared light and everything else. It CAN'T respond to the remote!

Your eye does not work in the infrared. So, when you push the button on the remote control, you don't see anything.  Your smartphone's camera uses a sensor that is sensitive to infrared. So, when you aim a remote at it, you can tell whether it's emitting or not.
(If you're a terrorist worried about infrared targeting lasers from the US military, you already know this. I said I understand things.)

My wife held the remote up to the camera with the button off and the button pushed on so that we could illustrate this.

How in the world did my Raspberry Pi figure out that I'd pushed the button on the TV remote?

After a bit of Googling, I found the HDMI standard and read about a CEC (Consumer Electronics Control) connection. If you have the right kind of HDTV, it can send commands back down the HDMI cable from the TV. And if the thang, Blu-Ray player, cable box, satellite box, whatever, is smart enough, it'll respond to those commands. It's like freaking magic.

This has profound ramifications for use of a Raspberry Pi as a set top computer. You don't need to hook ANY MOUSE or KEYBOARD to it: Just power, HDMI, and Ethernet. No USB hub or even those cute little wireless dongles.

So, I got to thinking, let's try this on my other TV set. I did. No joy. HDMI CEC is not on every TV set, just a select few. Since Black Friday is coming up, you might want to know what to look for if you're going to be buying a TV.

According to Wikipedia, the Trade names for CEC are

• Anynet+ (Samsung); 
• Aquos Link (Sharp); 
• BRAVIA Link and BRAVIA Sync (Sony); 
• HDMI-CEC (Hitachi); 
• E-link (AOC); 
• Kuro Link (Pioneer); 
• CE-Link and Regza Link (Toshiba); 
• RIHD (Remote Interactive over HDMI) (Onkyo); 
• RuncoLink (Runco International); 
• SimpLink (LG); 
• HDAVI Control, EZ-Sync, VIERA Link (Panasonic); 
• EasyLink (Philips); and 
• NetCommand for HDMI (Mitsubishi).

Before you buy a TV from these vendors, look in the specs for these buzz-words. If you see them on the set you want to buy, you'll know its TV remote can control your Raspberry Pi XBMC application.