Building an IR remote transmitter array

Discussion in 'The Projects Forum' started by timropp, Nov 3, 2011.

  1. timropp

    Thread Starter New Member

    Nov 3, 2011
    7
    0
    I'm trying to build an array of IR LEDs to control some model train stuff. I have an arduino programmed to generate the IR codes (pretty normal 38kHz stuff), and a basic circuit that works. However, the signal from the single LED isn't enough to reach everywhere that I need it. Therefore, I want to make a system with multiple LEDs that I can position wherever needed.

    Basic hardware design that I'm thinking: The arduino and 5V 2A power supply are in a small enclosure. I'll add a normal RJ45 jack to it and then I can run normal cheap ethernet cables around. Since they've got 8 wires, I'll use one as a common 5V rail and the other 7 to run 7 LEDs from. Cheap splitters (http://www.monoprice.com/products/product.asp?c_id=105&cp_id=10513&cs_id=1051304&p_id=7294&seq=1&format=2) will let me add an LED wherever I need, using a wall mount box (http://www.monoprice.com/products/p...=10517&cs_id=1051705&p_id=7069&seq=1&format=2) with a resistor and LED mounted in the small hole. Each LED will connect to a different one of the 7 remaining wires, so any one of them can plug in anywhere in the system.

    To do that, I need to drive 7 parallel LEDs. The LEDs I have are these: LTE5208A (there's a datasheet on that page; I know how much you all love a good datasheet!) Summary: 1.2V, rated for 100ma continuous. Since I'm not running continuous, I was planning for 200ma.

    My original plan was to connect the output pin of the arduino to 7 basic transistors (have a bag of pn2222s), with each one then driving one of the 7 lines out to the LEDs. That requires just a 22R resistor at each LED, which some people say is too low and I should switch to a constant current setup. I'm not familiar with that (and barely familiar with the design I've already done), so how would you do it?

    Summary: I want to drive 7 1.2V IR LEDs at 200ma each in parallel, controlled by an arduino output pin at 38kHz.

    One suggestion was to wire the RJ45 jack so that the LEDs are actually in series - would the fact that there'd be perhaps 30 feet of cat5 wire between LEDs matter? That would also require having all 7 connected all the time, or the series would be broken. It'd also require switching to a 9V power supply or higher. It also has the series resistor on the LEDs being very low again - like a 2.2R if I'm using a 9V supply. Actually, a 12V supply would be simple for what I've already got handy, so that would be 7 in series with a 18R 1W resistor, according to online calculators. Is that ok?
     
  2. timropp

    Thread Starter New Member

    Nov 3, 2011
    7
    0
    Ok, did more thinking about the series method and this is what I came up with:

    [​IMG]
    SeriesLEDs by mostlytechnic, on Flickr

    Does that all look ok? (there's some more circuitry in the box to handle the input controls, but that's all separate from this other than sharing the 5v and gnd)
     
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