making your own demux has got me stumped

Discussion in 'General Electronics Chat' started by ranch vermin, Sep 19, 2015.

  1. ranch vermin

    Thread Starter Member

    May 20, 2015
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    So a mux is fairly simple if its just reeling the parallel signals onto a single signal. But reverse has the problem that if you just do that you end up with pulses.

    So I guess maybe you go through some kind of accumulator capacitor/voltage doubler setup - to get a bit of voltage back on the dropouts.

    I guess thats what youd do. As long as it wasnt needed 100000 times maybe a few capacitors wouldnt hurt it. :)

    Since im planning on switching high voltage relays with the signal, its damn important i keep those switches closed and open when i need them to.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    If you want to keep the output of the mux constant when the output is not being addressed then you need a latch at that output.
    An addressable latch, such as the 8-bit CD4099, which has 8 latched outputs, should work for you.
    If you need more than 8 outputs you can cascade them, using the WRITE DISABLE input to disable writing to the chips not active.
    Are you using a microcontroller to generate the control signal?
     
    Last edited: Sep 19, 2015
  3. ranch vermin

    Thread Starter Member

    May 20, 2015
    85
    2
    Yes, its cpu based - coming out of an ordinary usb, so i need to split it parallel out - and mux it back in the read wire.
    ah addressed? do you mean using the pulses to set feedback flops - and using memory to do it. I didnt think of that.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,538
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    Are you muxing/demuxing analog signals or digital signals?

    ak
     
  5. crutschow

    Expert

    Mar 14, 2008
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    Not exactly.
    You give a 3-bit address to the CD4099 and then a data bit to set the latch at that address output.
    The latch is the memory.

    You could use a USB to parallel port adapter to generate the required parallel commands for the CD4099.
     
    Last edited: Sep 19, 2015
  6. ranch vermin

    Thread Starter Member

    May 20, 2015
    85
    2
    USB to parallel port adapter? that IS a demux. :)
    its a digital signal, but it closes an analogue voltage relay, given the right temporal pattern.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Depending upon the number of relays you want to control, that may be all you need. :D
    But you will need a program to generate the parallel port protocol and get the desired output signals.
     
    Last edited: Sep 20, 2015
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