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Ever Wonder About TV Remote Controls?

The remote controls in our home seem to be reproducing. 

I wondered if I should find out more about them before they completely take over the world.

When a couch potato like me pushes a button on a remote control, contacts underneath the keypad are touched, completing a circuit. Sometimes the contacts wear out or get gummed up. Some sites show how to clean or attach a new contact, but this did not seem to work so easily on mine.

Completing the circuit tells the headquarters in the remote control, an integrated circuit, to send the corresponding command to the light emitting diode (LED), which emits lights (in this case, infrared light) at a wavelength of about 940 nanometres. Infrared is a form of electromagnetic radiation, like visible light, so you can reflect the signal off shiny things and it will still work. It works best up to about 3 metres or so, but it doesn't go through walls or people—unlike the radio waves used in garage door openers.

Humans can't see infrared, but a digital camera can detect it. So, if you shine your remote into a digital camera and look at the image, you should notice flashes of light. The effect is enhanced if you have the camera in Night Mode. You can use this trick to check that a signal is actually being sent out if you're having problems with your remote.

The flashy message is sent at a frequency of about 38 kHZ and the receiver on the device to which you’re sending the message looks for information at this rate. This way, random infrared data from the sun or other sources don't interfere with the message.

Because the devices never know when you're going to send them a message, they always have to be on, drawing power even when they’re supposed to be off.

The message from your remote is in binary code. A flash is a one, and nothing is a zero. Each message includes four types of information: a start command, the actual command, the device address and the stop command, sent as a string of ones and zeroes. If the command is 7 bits, then you could have 2 to the power of 7 (2x2x2x2x2x2x2) = 128 different commands.

The device address is important so only the particular device you’re trying to control, gets the message. Universal remote controls either come with a list of codes for different devices and/or have a receiver built in so they can “learn” the signal from your original remote control. I tried to set up one of these but eventually gave up. It actually seemed simpler to have separate remotes for each device.

So the next time you're feeling remote and seeking control, sitting there flipping channels or looking for something to watch, you could also think about the wonders of that gadget in your hand.

Explore the science of infrared light further—visit Eureka! and take our infrared harp for a spin.