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IR Buddy question. — Parallax Forums

IR Buddy question.

HIBITDACHIBITDAC Posts: 40
edited 2006-04-02 14:33 in BASIC Stamp
Is it possible to transmit a logic signal from one to the other without a basic stamp? I want to transmit a logic level signal, no data. I am using a IR LED and IR phototransistor right now but the sun is interfering with it (false triggering). I also need it to be as fast as possible and not add or shorten the length of the original signal. Any help is appreciated.

HIBITDAC

Comments

  • Tom WalkerTom Walker Posts: 509
    edited 2006-03-30 19:41
    One way to eliminate false triggering is to modulate your beam. A simple 555 circuit could create a modulated signal which can be "gated" by your logic level signal. Then on your phototransistor side, you would need a circuit to only "sense" the modulated beam.

    More info is probably required to get more detailed.

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  • HIBITDACHIBITDAC Posts: 40
    edited 2006-03-30 20:18
    On the sending side is the signal for the amount of time a motor needs to turn. On the other side Is the motor. I've had a RF setup, but it was limit in·the amount of times you could send a signal·and the pulse wasnt the same lenght, turning the motor·on longer·then it·was supose·to.·The RF receiver·needed a power source of its own·and opticlly ioslated because when the motor turned on it triggered the receiver. As of right now I have the IR phototransistor connected to a MOSFET that drives the motor. It works indoors and is instantaneous but when it meets the sun it turns it on. I dont know the spectral·sensitivity or spectral range·of the IR phototransistor im using but it is clear and I know thats affecting it some. Would use a black IR phototransistor work better?
  • HIBITDACHIBITDAC Posts: 40
    edited 2006-03-31 15:14
    Any thoughts?
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-03-31 15:28
    The problem is you are just detecting the level of IR light, and sunlight has alot of it. You need a different receiver, like this one: http://www.parallax.com/detail.asp?product_id=350-00014
    If you look at the pdf information file on page·3 you'll see its not just an IR detector, but it detects pulses of IR occuring at a specific flashing rate, the second diagram on page 3 shows it is designed to detect IR pulsing at 38 kHz. Sunlight and internal lighting doesn't flash like this so it doesnt detect them. Since you dont want a stamp in the mix, you will have to use a 555 like Tom said, to flash your IR LED at 38kHz, and turn on the oscillation of the 555 when you want the motor running, and turn it off when you dont. You can do this by using an AND gate, where one input is from the output of the 555, and the other input is the trigger signal, and the output of the AND gate is connected to the IR LED and current limiting resistor.

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  • HIBITDACHIBITDAC Posts: 40
    edited 2006-04-01 02:20
    Thank you for your help. Got it working, and it works great.

    Thanks Again

    HIBITDAC
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-04-01 02:54
    Your welcome, glad to hear you got it working.

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  • HIBITDACHIBITDAC Posts: 40
    edited 2006-04-02 14:33
    Just an update, instead of using an AND gate, I connect the signal to pin 4 of the 555. When its low it disables the 555, and when it goes high it enables it. Thanks again for the help.

    HIBITDAC
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