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IR sensor

Discussion in 'Sensors and Actuators' started by vick5821, Sep 13, 2012.

  1. vick5821

    vick5821

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    Jan 22, 2012
    Hey friends, I am abit of confuse in the working principle of IR sensor.

    I know that the transmitter will always give out infrared light and a receiver is connected near to the transmitter. So when a white line/white paper is put on top of the transmitter and receiver sensor, the transmitted ray will be reflected to the receiver. So, what next ? The receiver get the infrared ray then what it does next ? Provide 5V output ?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It depends on the sensor.

    In many cases you'll get a very small current or voltage that you have to amplify.
     
  3. BobK

    BobK

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    Jan 5, 2010
    How about a link to the sensor?

    If you are talking about an IR remote control sensor, they work by looking for a specific frequency (the carrier frequency, usually about 38KHz). They have a logic output that indicates that the carrier is dectected. Information is then transmitted serially by a sequence of on / off intervals.

    Bob
     
  4. vick5821

    vick5821

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    Jan 22, 2012
    Just a normal transmitter and reciver LEDs
     
  5. BobK

    BobK

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    If you can't be more specific, we can't help.

    Bob
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Often you have 2 devices that look like LEDs.

    One is an IR LED, the other is a phototransistor or photodiode.

    When the photodiode sees IR light, it produces a small voltage/current

    When a phototransistor sees IR light, the transistor turns on (maybe just a little)

    It is probably more likely that you have a phototransistor.

    If you have a circuit that uses (say) an LDR to detect light and dark, you *may* be able to replace the LDR with the pototransistor. The resistor that forms the other leg of the voltage divider will probably have to change -- generally by making it much larger. If the circuit uses an op-amp (as opposed to transistor(s) then this is far more likely to work.

    Beware that the photopransistor will see IR from more than just the LED. The sun is a particularly good source of IR, so you need to shade it from that.

    Phototransistors are much faster than a CDS cell (and photodiodes are much faster again). Often you modulate the signal to the photodiode so it can easily be detected from the amplified output of the phototransistor.
     
  7. vick5821

    vick5821

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    Jan 22, 2012
  8. davenn

    davenn Moderator

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    A photo diode/transistor operates just like a transistor without a base connection
    that is.... with a normal transistor you supply a small current to the base and that turns the transistor on and it conducts between collector and emitter. with a photo transistor
    there is no base, instead the presence of light turns the transistor on and it conducts between its collector and emitter. A photo diode works on pretty much the same principle
    ... the diode is biassed on in the presence of light and will conduct

    Dave
     
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