Multiplexing 8 analog inputs using a CD4051B
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  1. #1
    Tech Guru Fatlimey's Avatar
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    Default Multiplexing 8 analog inputs using a CD4051B

    Here's a setup that allows 8 analog inputs to be read by a single analog expansion pin (plus three digital outputs). You'll need to make a few firmware changes to make it function however so it won't work out of the box, but it's not that big a change. I can make a .hex file or a new source drop available if there's enough interest.



    http://goo.gl/pIX5P



    http://goo.gl/0sIGD
    Last edited by Fatlimey; 01-20-2011 at 03:52 PM.

  2. #2
    Tech Convert
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    i´m very interested!!!

  3. #3
    Tech Student
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    Default o/+1

    sounds like exactly what I'm wanting to know about

    ~ct


  4. #4

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    that means more 8 knobs/faders/buttons on the remaining three expansion pins. if its possible i'l surely get one midi fighter righy away, no problem with soldering n coding a bit.

  5. #5
    DJTT Infectious Moderator photojojo's Avatar
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    So does that mean you could get 32 analog inputs and 12 digital outs on one MF board?
    Chris Jennings FHP

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  6. #6
    Tech Guru Fatlimey's Avatar
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    You have 4 pins of analog and 4 pins of digital.

    Each multiplexer takes three digital pins, but all the 4051s can share the same three digital pins. That would give you 4x8 = 32 analog POTs with one digital pin spare.

    Alternatively, you can use a pair of CD4052 which takes two digital pins and swaps four analog ins into two analog outs. That would give you 16 analog devices and two spare digital pins.

    If you can find a system that borrows or reuses pins, enough to get you three spare digital pins you can hook them up to a Latch-and-shift chip like the 74165 which can be daisy-chained together to give you multiples of 16 inputs, all read using three digital pins.

    Seriously, this stuff is not that difficult! Give it a try.

  7. #7
    Tech Mentor DjWindzOne's Avatar
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    :eek:
    Fatlimey. . .You're my hero!!!

  8. #8
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    Quote Originally Posted by Fatlimey View Post
    Seriously, this stuff is not that difficult! Give it a try.
    Hehe, Fatlimey you crack me up.
    Really not meaning to sound rude or anything here but most people here (myself included don't know much about electronics).
    In fact I probably shouldn't be allowed to play with a multi-meter and soldering iron.

    Now a technical question...
    When you do this multiplexing stuff I'm guessing inputs basically share pins with the midifighter working out which input is sending based on magic (it's the resistance or pulse isn't it?).
    Excuse my poor understanding I do have a point.
    Is it possible to trigger the wrong midi message by feeding in multiple inputs through the same pin at the same time?

    The reason I ask is I had a Reloop Digital Jockey 2 Interface Edition, and discovered that if you pressed three buttons at the same time it would trigger an extra unrelated midi message (the worst being pressing all 3 FX buttons would kill the bass on the deck).
    Was this issue related to multiplexing or just bad coding on Reloop's part?

  9. #9

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    Is there any way for multiplexing leds?

  10. #10
    Tech Guru Steve Zorilow's Avatar
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    Fatlimey,
    I'm not sure how bad the 4051 could be in this specific DC signal use, but I would suggest you to have a look at something.

    Some 4051 series have some "huge" crosstalk issues (CD4051 probably being the worst) 'Course you could trick it a bit in software, but it add some extra latency.

    74HC4051 are better, but still not perfect. If my memory serves me well, Maxim MAX4617 is a 4051 drop in replacement, sure more expensive but has better features (smaller Rdon and less crosstalk). On the long run they worth it.

    my 2 cents.

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