Strange IR Receiver circuit

Discussion in 'General Electronics Chat' started by Laurens-Wuyts, May 6, 2015.

  1. Laurens-Wuyts

    Thread Starter New Member

    May 6, 2015
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    Hey everyone

    I have a digicorder (live TV) laying around from an old TV provider.
    I have recreated the schematics for the front PCB, which drives:
    - a 4 digit 7 segment display
    - 9 Buttons
    - 5 leds (2 bicolor)
    - an IR receiver
    By making these schematics, I saw a strange part in the circuit, which I don't quite understand.
    The Ir sensor is connected using 3 resistors. Like so:
    http://www.schematics.com/editor/ir-receiver-18561/

    Do anyone of you know why its done like this?

    thanks in advance

    Laurens Wuyts
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,137
    1,786
    How are we supposed to sign in to that !@#$%^& website?
     
    OBW0549 likes this.
  3. Laurens-Wuyts

    Thread Starter New Member

    May 6, 2015
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    Oops. Here is a screenshot.
    [​IMG]

    Laurens
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    If you want people to look at a schematic, then take a screen shot of it (provided it isn't copyrighted) and post that in your post here. Preferably as either a png or jpg image at a reasonable (a few hundred kilobytes at most) scale and resolution.
     
  5. WBahn

    Moderator

    Mar 31, 2012
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    Can you get a part number off of the IR receiver?
     
  6. Laurens-Wuyts

    Thread Starter New Member

    May 6, 2015
    4
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    SEK
    1FN1
    CE0OA

    Laurens
     
  7. hexreader

    Active Member

    Apr 16, 2011
    250
    82
    I suspect that an electrolytic capicitor (typically 4.7uF) is missing from the diagram. The 100R resistor and capacitor across the receiver power pins is typical for preventing interaction between main 5V power supply and IR receiver power pins.

    10K resitor is simply a pull-up resistor, since IR receiver is typically open collector output (with maybe weak internal pull-up resistor)

    100R resistor on output is the only slightly unusual component. Not sure exactly why it might be there, but it is a low value that could be considered inconsequential in normal operation.

    Hope I got it right, and hope it helps.

    Data sheet will probably give more definitive clues for the exact device that is fitted.

    If there really is no capacitor fitted - it probably will not matter. None of the component values are critical, and missing capacitor would probably only cause a small reduction in reliability of reception
     
  8. Laurens-Wuyts

    Thread Starter New Member

    May 6, 2015
    4
    0
    There are indead capacitors fitted onto the PCB. I don't have the values, but I have updated the schematics.
    [​IMG]
    Sound like what you said is true, because the outputted signal is inverted NEC protocol.

    Laurens
     
  9. hexreader

    Active Member

    Apr 16, 2011
    250
    82
    So take C2 to be 4.7 uF just to make me happy. Any value 1uF to 10uF probably would not matter much.

    I will take a wild guess at C1 being a low value such as 0.1uF or maybe 0.01 uF. Perhaps C1 and R3 reduce noise spikes - do not really know.

    I would ignore C1 and R3 completely, and just accept that "IR connector" pin outputs inverted 5V IR signal as explained well here:

    http://www.sbprojects.com/knowledge/ir/index.php
     
  10. hajivitra

    New Member

    Apr 7, 2015
    13
    0
    nice information
    thaks all
    [​IMG]
     
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