On-Off Keying receiver/demodulator

Discussion in 'General Electronics Chat' started by Kaspars, Jul 1, 2011.

  1. Kaspars

    Thread Starter New Member

    Jun 9, 2011
    17
    0
    Hello,

    I made a circuit that's output (blue colour (it's asynchronous)) and transmitted this signal by On-Off Keying (OOK) modulation type:
    [​IMG]

    But I'm trying to find some reveiver or demodulator circuit for more than day, but can't find...

    I have tried to use envelope detector circuit, that looks like this:
    [​IMG]

    It's ok for ASK, but it won't work for OOK. I have tried to simulate a lot of possibilities, but nothing worked well.

    Maybe some one have tried to do this and can send me some link or approach to solve this problem? Better if there were circuit (schematics) so I could simulate it in PSpice.

    P.S.
    Thanks for any help :)
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    It should work. A common mistake is to make the capacitor too large. What are you getting?
     
  3. Kaspars

    Thread Starter New Member

    Jun 9, 2011
    17
    0
    Thanks for your answer.

    Here is my simulation system:
    [​IMG]

    And here is what I get in bigger picture:
    [​IMG]

    [​IMG]

    I Use asynchronous system and there is very imoprtant to know the time when input signal changed his edge. But like you can see in picture after transmison and decoding using enveloped decoder, decoded signal (time events when input signal switched) are incorrect. I what this edge more accurate. Like you can see, for now the error ir about 0.1ms from real signal.

    Any suggestions? circuits? approach?

    Thanks :)
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    You definately need a Schmitt Trigger. It will clean it up.
     
  5. Kaspars

    Thread Starter New Member

    Jun 9, 2011
    17
    0
    Thanks for your help :)

    I tried to use Schmitt trigger with hysteresis with unipolar voltage source, but can't get appropriate levels, I want, that ir switch when it reach 0,09V (0.9V in picture) and 0.1V (in picture 1,7V) levels in my circuit:
    [​IMG]
    Maybe you can suggest exact circuit for that? Without using other voltage source, becouse I tried with comparator where I put 0,1V voltage source and then everything works fine, but this approch isn't suitable for my aim.

    Thanks :)
     
  6. mktechno

    New Member

    Jun 25, 2011
    2
    0
    you need to try a device called : ASK RECEIVER MODULE

    - look up a taiwan manufacturer called WENSHING.COM.TW

    _ search for this company on google

    _ click on link for ASK RECEIVER

    - it will work for OOK type modulation as well _ TRUST ME

    - try device with part no. RWS - 374 - 4

    - experiment with it on prototype board on your workbench ...

    - best of luck ..
     
  7. Kaspars

    Thread Starter New Member

    Jun 9, 2011
    17
    0
    Last edited: Jul 1, 2011
  8. Kaspars

    Thread Starter New Member

    Jun 9, 2011
    17
    0
    Thanks for your help :)

    I tried to use Schmitt trigger with hysteresis with unipolar voltage source, but can't get appropriate levels, I want, that ir switch when it reach 0,09V (0.9V in picture) and 0.1V (in picture 1,7V) levels in my circuit:
    [​IMG]
    Maybe you can suggest exact circuit for that? Without using other voltage source, becouse I tried with comparator where I put 0,1V voltage source and then everything works fine, but this approch isn't suitable for my aim.

    Thanks :)
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Designing a Schmitt Trigger isn't hard. Think in terms of voltage dividers when it is on and when it is off. You want to have the switching voltages you've set to match the divider voltages. Is this something you've never done?

    http://www.allaboutcircuits.com/vol_3/chpt_8/12.html
     
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