How paper tower hand out?

Discussion in 'General Electronics Chat' started by mpcotuong, Mar 1, 2011.

  1. mpcotuong

    Thread Starter Member

    Aug 26, 2010
    170
    0
    Hi All,

    When I go to bathroom, and there is auomatic machine give out the tower paper once I put my hand near to that machine. Does anyone know how it work? or any circuit relate to that?

    Thanks,
    Kevin
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Most of these units work by using reflective infrared sensors that when the emitted IR light is reflected back off of a person's hands, the dispensing motor is triggered to run for a predetermined hand.

    hgmjr
     
  3. mpcotuong

    Thread Starter Member

    Aug 26, 2010
    170
    0
    Thanks, hgmjr for reply. It does not call motion detection? How come it not detect too far. I have seen only work once very nera the unit.


    Kevin
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    That is on purpose since you want to avoid triggering the towel dispensing whenever a person just walks by the dispenser on his way to the bathroom facilities.

    hgmjr
     
    mpcotuong likes this.
  5. mpcotuong

    Thread Starter Member

    Aug 26, 2010
    170
    0
    Do you know, if infrared sensors detect about 20 inches far?
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    As a general rule, reflective sensors such as the type used in the paper towel dispenser have a limited range. That is because the sensor relies on the transmitted signal being reflected from a surface that can vary widely back to the detector.

    The range can be boosted by using multiple IR emitters together with a detector circuit that boosts the incoming signal. Still 20 inches would requires some fancy circuitry to carry off.

    hgmjr
     
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