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Old 09-20-2011, 04:41 AM
btb125 btb125 is offline
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Default Using my Android Phone's TRS Port as an Infrared (IR) Emitter & Receiver for TV Sign

Hi, I'm new to this forum and was wondering if you could help me with a problem I've got...

I want to use my Android phone as an Infrared transmitter and receiver to control my TV. The idea came to me when I was lying in bed and my TV remote was on the other side of the bedroom, I thought this would be a great and simple little application to create. I went to Google how to create the infrared transmitter and receiver for an Aux port, and it seemed simple enough. I know there are apps on the Market for this already, but I wish to create my own both because I want it to do what I want, and my University final year project is coming up and I think this will be a great and somewhat unique project to undertake. Iím studying Computer Science so the programming side shouldnít be a problem, but what I thought would be a simple soldering session has definitely proven to be.

I've now spent days Google'ing the problem in aid for a solution with no success, and as a result Iím turning to you guys in the hope that you could enlighten me on what ridiculously fundamental mistake Iíve made.

The theory behind my project is that you solder IR bulbs to 3 or 4 pole 3.5mm AUX ports, record the IR light as a sound, and then playback the sound as IR light. This has been done, and Iím not so sure as to why I canít get it working.

Iíve tried using the phone as the recorder and the transmitter, but the light always seems too weak, and I was also worried that it made be cutting off the higher frequencies when it records. To overcome this I recorded the light-sounds as .wav files to my laptop using Audacity & SoundForge in hope that the sounds wouldnít be compressed, but when playing back the light-sounds it still doesnít work.

What I have noticed is that when looking at the brightness of the light being emitted from both the phone and the laptop, is that it was very weak (I tested this using a digital camera) in comparison to the remote control that I was recording from.

Iíve tried many different ideas, including searching this forum to see if there were any ideas, but I couldnít find the information here either.

I donít wish to keep going on for the sake of your sanity, but if you have any questions on what I have tried, or require any links to what I have read, please askÖ I hope my late night ramblings havenít made you give up, and I will be very grateful for any help you can offer.

Thanks for your time, B.
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Old 09-20-2011, 09:26 AM
DigitalReaper DigitalReaper is offline
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IR remotes send bursts of 38khz light pulses so you need to be recording and playing back at 76khz or higher. Look at the waveform in your editor, it should look like bursts of a square wave. Record the output from your phone with the PC and do the same to check playback.

The output from your phone may not be able to supply enough voltage and current to properly light an IR LED, these are typically driven at high currents but at a low duty cycle. You may need some sort of amplifier to drive the LED.

There are 3 terminal IR receivers that are tuned to 38Khz, I think they may strip out the carrier and give you a lower frequency digital output so those may be worth looking into as well (just remember you still need a 38khz carrier to transmit!).
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Old 09-20-2011, 01:14 PM
btb125 btb125 is offline
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Thanks for the reply, I'll give this a shot when I get a chance. Thanks again.
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Old 09-20-2011, 10:14 PM
btb125 btb125 is offline
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I'm now currently using only my laptop to record and transmit the signals.

Using [ ] as my receiver, I recorded 'Volume Up' as a series of short presses and long presses at 96KHz to produce the following:

I then tried to transmit the signal using a [ ]. Again, using my phone to see how powerful/bright the signal was, it was a very weak/dull signal/light (even though I used VLC @200% volume and the system at 100% volume). Also, when tested on the TV, it didn't work.

Is it a possibility that I am using the wrong bulbs for receiving and transmitting the information?

TY in advance...
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Old 09-21-2011, 08:43 AM
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bertus bertus is offline
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The links on this page of the EDUCYPEDIA will give you a lot information on the IR remote control signals:
IR remote control

You don't have to know everything, if you know where to find it.
When you do ask questions, you may look stupid.
When you do NOT ask questions, you will STAY stupid.

It would be nice to have the Timezone ( GMT +/- x ) in the location field in the profile.
(User CP -> Edit Your Details)

Last edited by bertus; 08-13-2012 at 07:57 PM. Reason: Updated link
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Old 09-21-2011, 03:21 PM
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radiohead radiohead is offline
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Does it work when you move it close to the TV? If so, concentrate on the amp for the distance as Digital Reaper said. If not, it's back to the drawing board.
If you don't want to stand behind our troops,
feel free to stand in front of them.
(GMT -5:00)
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Old 09-22-2011, 08:30 PM
btb125 btb125 is offline
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Originally Posted by radiohead View Post
Does it work when you move it close to the TV? If so, concentrate on the amp for the distance as Digital Reaper said. If not, it's back to the drawing board.
Unfortunately it doesn't.


Thanks for the link bertus, I'll give it a read and hopefully it will help.


Again, both of you, thanks for taking your time to help.
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