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question about ir detectors and the bs2px — Parallax Forums

question about ir detectors and the bs2px

BadgerBadger Posts: 184
edited 2008-11-13 04:22 in BASIC Stamp
Hello

I was reading in nuts an volts when using a ir detector it had 3 wire lead. I have a radio shack ir detector number 276-142. Is it possible to use a 2 wire ir detector with the bs2px to make your own object detection system, like in the boebot. I will be using the BOE as is said there example uses a 3 wire mine is 2. Can this be done and if so How


thanks in advance

Badger

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-13 04:02
    No

    The RadioShack IR detector that you have is just a simple IR phototransistor that detects the presence or absence of IR energy. It does not do what the IR detector detector does that's included with the BoeBot. The BoeBot's detector has a phototransistor, an amplifier, a 38KHz filter, and a threshold detector all to detect IR pulses occurring at roughly a 38KHz rate. It does not respond to steady IR or to IR pulses at very different rates than 38KHz. The datasheet for this IR detector (downloadable from Parallax) has graphs giving the response curve (vs. pulse frequency) of the filter. A plain IR phototransistor is too sensitive to things like daylight or incandescent room lighting to be used for object detection. The 38KHz modulated IR detector is designed to reject this kind of interference (although it's sensitive to some compact fluorescent lights).
  • BadgerBadger Posts: 184
    edited 2008-11-13 04:09
    Mike Green

    Again I benefit from your knowledge. I was afraid of that. I now need to come up with 3 or 4 of those detectors.

    One more question. will the emitter work with this detector ???


    thanks Mike

    Badger
    Philip King
  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-13 04:16
    As always, read the datasheets involved. They usually say what wavelength light is predominantly produced by the IR emitter and usually have graphs of the light response of the IR phototransistor or detector. Most IR emitters work around 940nm and some work around 980nm. One of the phototransistors I looked at was specified for a 940nm wavelength, but its response at 980nm was about 90%. That's close enough.
  • BadgerBadger Posts: 184
    edited 2008-11-13 04:22
    Mike

    Thanks again. I did miss the hint on the data sheet. I am not having a good day here with the weather it is aggravating my arthritis badly. So between the pain meds and the weather I am not working at my peek let alone how late it is and such. I will read data sheet that is not a problem. I sometimes dont understand all of it but hey. I will look into one of the better detector/emitter pairs ..

    thanks again

    Badger
    Phil
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