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Advice on an IR amplifier

  1. May 28, 2006 #1
    Right now we have a projector and it is about 75 feet away. The remote, well, works pretty terribly to say the least. What I would like to do is build an IR amplifier to boost the signal so that the projector can pick it up much easier. What I plan to do is use some sort of buffer/driver IC to get some current gain. Ill have an IR receiver at one end that goes into the amplifier. Then the amplifier will output to at 75foot long cable with IR emitters on it aimed at the projector IR receiver. When I aim my remote at the amp, it should send it down the wire and shoot it out right at the projector.

    With this in mind, can you suggest a possible chip to use? I am not too familiar with my options and I can only mostly find chips with 80mA output (3-state) although I dont need a 3 state driver for this. Maybe even instead of putting the IR emitter on the long cable, I can just wire up 10 of them to the output of the driver to gain a better chance of getting a signal through.

    This is all I could find so far: http://focus.ti.com/lit/ds/symlink/tlv4110.pdf As far as I know, I would only need current gain, not voltage gain? Im thinking that since it is a digital square wave signal, you can't amplify the voltage or else everything gets out of wack.

    Thanks for you help
    Chris
     
    Last edited: May 28, 2006
  2. jcsd
  3. May 28, 2006 #2
    re

    The op-amp has to have a bandwidth of at least 50 KHz, tlv4110 has 2.7 MHz so thats more than ample. It can put out 300 mA, so thats good too.

    Find out how much current your each IR diode draws. You could hook up 4 or 8 in parallel or more. If thats not enough current, then don't bother looking for another op-amp, just use a transistor driver.
     
  4. May 28, 2006 #3

    dlgoff

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    Why not just use an optical fiber from the remote to the projector?

    Regards
     
  5. May 31, 2006 #4
    Another question, Instead of using an op-amp, can I use a bus driver/buffer of some sort?
     
  6. Jun 3, 2006 #5

    es

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    Although I am not sure of the specifics of your project (I think you are talking about modifying the remote itself) an alternate solution might be better. How about building a repeater box. Something that recieves IR at one end, copies the signal, and shoots out a new IR signal out the back via another LED.

    I think if you are able to build an op amp circuit, the repeater circuit would be trivial for you (especially using these parts http://www.solarbotics.com/products/index.php?search_id=124). You could build it small (easy to hide in the room) and power off batteries.

    Also, if you assume the engineers who designed your remote knew what they were doing (i.e. they picked the optimal power in/power out point for the LED) then you are probably going to get quickly diminishing returns for putting more current through the LED (See figure 3 in the LED datasheet linked to above, and that's one fine LED too).

    A second (important!) advantage to the repeater box is there is no risk of damaging the original equipment during experimentation leaving your whole system unusable.
     
    Last edited: Jun 3, 2006
  7. Jun 3, 2006 #6

    es

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    Oh! I did misunderstand your question. Sorry about that.

    I think you just want to know how to generate enough current for the LED. For this I would recommend using a LED driver IC such as http://focus.ti.com/lit/ds/symlink/tps61060.pdf. Just have the receiver drive the enable pin. Don't worry about the PWM input. Just tie it high (100% duty cycle) and set the bias current with a resistor.
     
  8. Jun 3, 2006 #7

    es

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    If you can get by with the lower switching frequency then another simple solution to boosting the output current is using the opamp to drive a bipolar transistor base current like figure two in this ap note.
    http://www.supertex.com/pdf/app_notes/AN-D14.pdf
     
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