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

[youtube http://www.youtube.com/watch?v=JIaN5j3LZXQ]

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.

[youtube http://www.youtube.com/watch?v=BBtoPneoi_4]

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.

IR_transmitter_schematic

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.

ir_boost

 

 

BREADBOARD TIME!

 



 

 

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.