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IR sensor question — Parallax Forums

IR sensor question

vla7vla7 Posts: 79
edited 2008-11-12 18:58 in Robotics
I would like to attach a camera to a servo and have the the servo rotate to allow the camera to follow an object in the room as the object moves. ·The object would need to be about 20-30 feet away. ·What is the best way to go about this? ·I was thinking of attathing an IR emitter to the object and have several detectors near the servo so that the servo will rotate to an angle depending on which detector "sees" the ir signal. ·Is it possible to have a stand alone LED sending a signal and willl they reach 30 ft? ·If there is a better way to do this please let me know.

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-02 03:22
    What you probably need is one sensor on either side of the camera so that, if the object with the IR emitter moves to one side, the IR sensor on that side will see a brighter signal than on the other side and the servo can be moved to the brighter side. The sensors will need some kind of shield to narrow the field of view, like the IR opaque plastic tubes that Parallax uses for mounting their IR emitters, probably longer.

    The main problem I see is that the IR sensors are on/off sensors and Parallax changes the incoming IR light's modulation frequency to guess the range using the response curve of the IR sensor. If you use just an IR phototransistor as a detector, you don't get the benefit of modulated IR to reduce sensitivity to other light sources.

    If you were using something like a CMUcam, that has provisions for tracking an object with a servo, you'd just need a contrasting visible color for the object to be tracked. You could combine the CMUcam and a separate video camera or webcam on the bracket. Look at Parallax's webpage for their CMUcam version:
    www.parallax.com/Store/Sensors/CustomKits/tabid/134/txtSearch/cmucam/List/1/ProductID/29/Default.aspx?SortField=ProductName%2cProductName

    Post Edited (Mike Green) : 11/2/2008 3:34:58 AM GMT
  • vla7vla7 Posts: 79
    edited 2008-11-02 03:35
    How would I go about sending signal from the detached·IR emitters.· Are there ones that I can buy that constantly send a signal of a certain wavelenght without being connected to the stamp?
  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-02 03:55
    The "IR Remote for the BoeBot" tutorial from Parallax shows a 38KHz driver for an IR emitter in Appendix C that uses a 555 timer and a couple of resistors and capacitors.
  • vla7vla7 Posts: 79
    edited 2008-11-02 04:22
    won't the setup still need to be connected to the stamp?
  • ercoerco Posts: 20,256
    edited 2008-11-03 02:30
    Your camera will probably see the IR source easily as a bright visible steady light, even if it is pulsing at 38-56 kHz.

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    ·"If you build it, they will come."
  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-03 15:41
    Appendix C does show the 555 circuit connected to a Stamp, but this is for calibration purposes with the test program shown. Once the frequency is adjusted, the Stamp isn't needed. You'd just connect the point labelled P6 to Vdd to turn on the IR beacon as described in the Appendix.
  • vla7vla7 Posts: 79
    edited 2008-11-12 18:58
    Mike,
    How about the point labelled P7?· And with P6, can I just connect it to a battery instead of Vdd?
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