A resistor in strange place with IR sensor TSOPXX...

Discussion in 'General Electronics Chat' started by Willen, Jul 31, 2016.

  1. Willen

    Thread Starter Member

    Nov 13, 2015
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    12
    I have a device with TSOP IR sensor (there are no marking on the sensor though). So I guessed it is like TSOP. Because shape looks like same.

    It has same components around it like a 5V supply with 10uF and 0.1uF decoupling capacitors. IR output has 560pf filter capacitor to the Gnd. But there's a resistor 5k1 from 5V supply to IR output. What is this for? The sensor module kit and mainboard are connected with 30cm long ordinary wire (not shielded). And the black sensor has pretty small size, comparatively.

    - Is the resistor 5k1 there to drive 30cm wire to the board?

    - Seeing the tiny size of the black sensor, I also guessed that the sensor just have output transistor as built-in signal booster but do not have collector resistor. So they used it outside on their kit (board). However datasheets of other same type of IR sensor module has around 80k collector resistor as built in booster. But it has very low (5k1) external resistor.

    What you think? Please!
    I am talking about MX-KONKA618-IR V.4 tiny kit.
     
    Last edited: Jul 31, 2016
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,873
    369
    it's probably because the device has an open collector output.
    30cm of wire requires no special driving circuitry.
     
  3. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    As I see other have 80k internal collector resistor, this has just 5.1k. Does it work normally?
     
  4. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,873
    369
    Without a datasheet on the device any comment is little more than guesswork.
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    I think you are talking about the TSOP17XX, wich has an 80K resistor intern:

    TSOP17XX_block_diagram.png

    In the application diagram they say that the external resistor should be larger as 10K:

    TSOP17XX_application.png

    Bertus
     
  6. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,873
    369
    As this unknown device uses a 5k1 pull-up which would be beyond the specification for TSOP17XX then it probably isn't one of them. Or maybe the designer of this unknown device hadn't read the datasheet.
     
  7. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Hi bertus,
    Second circuit you uploaded looks same as I found found here (here's no series R) but with 5.1k. There's short description at the bottom. Maybe the 5.1k resistor there is needed to manage microprocessor input system, yes?

    Thank you for the attached pdf file. I am going to download.
     
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