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Let me start by saying that I am a newbie on this, trying to do some hobby stuff. I am a software professional trying to interface with hardware (maybe getting into Arduino).

Using this information I was able to build an IR transmitter for an audio device (like my Samsung Galaxy Ace).

Using this information I built a receiver for the computer, captured some input from my TV's remote and built the .wav file to play it in my phone with my transmitter.

It works. Kinda. The range is very short (maybe 3 feet).

Also, I have read somewhere of people adding a resistance because there is a risk of burning the sound card.

I have an old set of computer speakers that have their own amplifier. I am considering connecting them to the output of my phone, and connecting my transmitter to the output of the amplifier. I wouldn't mind if the amplifier died in the experiments, but I am trying to prevent my cell from getting killed in the process.

So the question is, how do I protect my laptop (when recording with the IR receiver) and my cell phone (when playing back with the IR transmitter) from getting burnt?

Thanks.

IR Receiver IR Transmitter

Note: I know I can just buy the transmitter for the cell phone, but there is no fun on that. This is a hobby project.

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    \$\begingroup\$ This question could be improved by incorporating the information from the links provided. I'd suggest drawing a proper schematic of what you've built and including it in the question. \$\endgroup\$ – Phil Frost Jan 30 '13 at 13:40
  • \$\begingroup\$ So, is this what you are trying to do: "Remote Control -> PC via sound card" then, you will save the audio file and then, you will replay it using the "PC sound card -> IR LED" so that you will copy one of the buttons (functions) of the remote control? \$\endgroup\$ – abdullah kahraman Jan 30 '13 at 13:42
  • \$\begingroup\$ @PhilFrost: I will. \$\endgroup\$ – rufo Jan 30 '13 at 13:45
  • \$\begingroup\$ @Abdullahkahraman: yes, that's what I have actually done it. It works, with the very limited range, and my uncertainty if I am going to burnt something. I could also use a way to boost the signal. \$\endgroup\$ – rufo Jan 30 '13 at 13:45
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    \$\begingroup\$ @rufo Do not connect amplifier's output to the IR LED, you may damage it. Also, amplifying the sound is not the way to increase the distance. You have to give more current to the IR LED, not more voltage. But, if you are insistent on connecting the amplifier's output to the IR LED, then use a resistor in series. Value and size of the resistor depends on the voltage levels on the amplifier. Anyways, this was a very very complicated comment, I know. Don't worry, someone will explain it in detail in an answer, in a way that you will understand, if not I may write an answer later on. \$\endgroup\$ – abdullah kahraman Jan 30 '13 at 13:51
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Interesting design - literally the simplest thing that could possibly work.

The risk of damage to the audio devices from this setup is pretty minimal, as there's no external power supply involved. The only question is the current tolerance of the output of the cellphone headphone driver. Make sure all your exposed wires are insulated from one another (tape, heatshrink etc).

Adding an amplifier to the system is an idea in the right direction, although now you're at risk of destroying the LED driven by it - extremely likely with an audio amp of any power.

I would suggest building a standard transistor LED driver (e.g. Driving LEDs from audio signal ). Use a visible LED first to check it's working then swap it out for the IR one.

It's also worth applying volume normalisation to the WAV file you recorded and playing it back at maximum non-distorting volume.

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  • \$\begingroup\$ Ok. That sounds fine, I need to find out a schematics for an stereo LED driver (the one you referenced is only using one channel). BTW: I forgot to mention that I am actually planning on controlling a RC helicopter, that means that I will send signals continuously for relatively long periods (6-8min). Thus my concern on breaking my cell phone (or computer). \$\endgroup\$ – rufo Jan 30 '13 at 18:13
  • \$\begingroup\$ Your schematic above is only really using one channel (well, the output is a slightly odd push-pull arrangement). \$\endgroup\$ – pjc50 Jan 31 '13 at 9:51
  • \$\begingroup\$ it is using both channels. That's because you need to generate a 38khz signal, and audio usually doesn't get that far, so somebody found out a way to "sum" the signals. In my original links there is the complete logic behind it (I am yet to study and really understand it). The case is that my .wav file is stereo, with two inverse signals. \$\endgroup\$ – rufo Jan 31 '13 at 13:14
  • \$\begingroup\$ As the LED circuit is not impedance matched with the output of the audio PA, power may be reflected and may damage the PA! \$\endgroup\$ – Chetan Bhargava Feb 16 '13 at 21:19

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