Saturday, 14 February 2015

Infrared black magic

Lately I have been fascinated by devices that use infrared. Quite old technology but fun anyways. IR remote controls are quite popular because that’s the cheapest way to remotely control a device. Negative sides? – Line-of-sight range.

So I stumbled across this thing called TV-B-Gone. It turns off/on every TV known to man. Quite cheap and popular thing. So I was interested to make my own little device using Arduino. Using sample sketches with libraries – easy.

Two TVs / Samsung and Philips


Next idea was to capture IR codes and then replay them. Transmission part stays the same but now we need input. I used commonly available IR photo-detector module. It has everything in one package. Again using a library – nothing fancy.


So my friend has a Samsung phone that has an IR blaster built in. That thing works great, a lot of apps and easy to use, works great. I don’t have that luck with me so I decided to build my own implementation.  So I thought using headphone jack. The sample rate should be at least 48 kHz. IR uses 38 kHz as clock so it SHOULD WORK in theory. Rather that reinventing the wheel I started searching for similar projects. Found a thing called “IRdroid”. Using one channel is out because it is 22 kHz. With some dual channel trickery it is possible to generate 38 kHz.


Usually they use two IR LEDs connected directly to a phone, that seemed too brutal to me. Found a schematic that seemed a bit safer + signal is amplified using transistors. I had my own idea first to use two LEDs and two transistors but this schematic was a more elegant solution.








With phone i found it to be quite fiddly, it depends also on the TV, how tolerant it is. Using a laptop it worked better.