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zenner diode in IR sensor — Parallax Forums

zenner diode in IR sensor

celestino_galancelestino_galan Posts: 44
edited 2005-06-17 09:17 in Learn with BlocklyProp
Why is there a zenner diode in the IR sensor?

Thanks

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-06-16 17:06
    Hello,

    ·· Which IR sensor are you referring to?

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • celestino_galancelestino_galan Posts: 44
    edited 2005-06-16 18:02
    One, I bought like one mounth·ago, from Parallax,·and , now I can't see.

    It has a resistor, a zenner diode?, an IR emmiter and an IR receiver.

    Post Edited (celestino_galan) : 6/16/2005 6:10:16 PM GMT
  • Aristides AlvarezAristides Alvarez Posts: 486
    edited 2005-06-16 19:06
    Hello Celestino,
    ·
    Please check the documentation at this link:
    http://www.parallax.com/detail.asp?product_id=28019
    ·
    If you are referring to that sensor, it was discontinued an that's why you cannot find it anymore.
    ·
    Regards,


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    Aristides Alvarez
    Education and Technical Support Manager
    aalvarez@parallax.com
    Parallax, Inc. www.parallax.com
  • Steve JoblinSteve Joblin Posts: 784
    edited 2005-06-16 19:58
    I am quite a newbie myself, so I may be way off base.· (by posting my response I am testing my own knowledge).· I need someone to confirm my hypothesis.

    I think the zenner diode is used to prevent voltage from going backwards in the circuit and destroying the I/O pin.· An LED can actually generate voltage when exposed to bright light (just like a solar cell does).· It is actually a fun experiment!· Tie a bunch of LED's in series to small motor or something, expose it to bright light and watch the motor spin!

    Again, this is only my hypothesis, so I could be totally wrong!
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-06-16 20:15
    Steve, you are correct, but zener diodes have an additional feature which they were designed for. Zener diodes are used in reverse polarity in a circuit (they are not designed for forward biasing, though they will conduct like a normal·diode when forward biased). Zener diodes breakdown (start to flow) when the reverse bias voltage exceeds a certain designed for voltage. This has the effect of clamping the voltage to the breakdown voltage of the zener diode. Zeners are different than normal diodes because they were designed to do this breakdown without damaging the diode, normal diodes are not designed for this and can be destroyed if you try to bias them with too great of a reverse voltage.
  • celestino_galancelestino_galan Posts: 44
    edited 2005-06-16 20:33
    Yes, Aristides Alvarez, is the one from the link.

    But I have it and I would like to know whay is that zenner diode in it...


    THANKS
  • Aristides AlvarezAristides Alvarez Posts: 486
    edited 2005-06-16 20:52
    Hi Celestino,

    In this case the zener diode is used to ensure the proper threshold level from the microcontroller reading the SSIR signal.

    This zener diode generated the right VDC drop when used in direct (not reversed) connection in series with the resistor and the IR-LED, with the current and voltage capabilities of the IR receiver.

    If you want to duplicate this circuit you can try with different diodes, from common ones to LEDs.

    Regards,

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    Aristides Alvarez
    Education and Technical Support Manager
    aalvarez@parallax.com
    Parallax, Inc. www.parallax.com
  • celestino_galancelestino_galan Posts: 44
    edited 2005-06-17 09:17
    Thank you
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