Need to demultiplex 24v 1 to 4 then multiplex 4 back to 1.

Discussion in 'General Electronics Chat' started by gixxerman1980, May 25, 2016.

  1. gixxerman1980

    Thread Starter New Member

    May 25, 2016
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    Every demultiplexer or multiplexer I've seen does not allow for the voltage I need to work with. I was wondering if anyone knew of any options that would allow me to do what they do, but still retain my 24v?
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    I don't know of any chips that do this, but it is not difficult to do with standard chips controlling switching transistors or transistor arrays.

    ak
     
  3. gixxerman1980

    Thread Starter New Member

    May 25, 2016
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    Good to hear. I'm looking to use an Arduino to trigger the switching, but as I am far from an electrical engineer, I'm not sure where to go with this. All the transistors I've looked at only open and close one valve, if you will. I haven't found a component that will, or figured out how to redirect current from out1 to out2 on a trigger.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    gixxerman,
    Please provide a detailed description of what you are trying to do..
    Schematics would help too..
     
  5. gixxerman1980

    Thread Starter New Member

    May 25, 2016
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    Ok, I attached a picture of what I am trying to do. I hope it makes sense. mux-demux layout.jpg
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    If the 24.15V is not changing, why do you need the multiplexer? Just generate the three voltages and switch alternately with transistors, preferaly each controled by a pin on the arduino, instead of a mux.
     
  7. gixxerman1980

    Thread Starter New Member

    May 25, 2016
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    I cannot generate three voltages as the one 24.15v signal is coming from a receiver that runs to a transducer and comes back to complete the circuit. As the pressure transducer is basically a dynamic variable resistor, I want to build a simulator that just uses known static values to test equipment. The receiver sends out 24.15v. When the transducer is connected, the circuit is closed and approx. 21.27v leaves the transducer back to the receiver. Consider that 0 psi. For the receiver to display about 2000 psi, it needs to have about 20.60v coming back to it from the transducer. I'd also like to see about 2200 psi, so the receiver would need to see about 20.45v coming back from the transducer. I figure, rather than just using resistors, it would be better to use resistor trimpots to fine tune the pressure I want to see.
     
  8. gixxerman1980

    Thread Starter New Member

    May 25, 2016
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    When speaking of using transistors, are you talking about using a Darlington Array?
     
  9. AnalogKid

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    Aug 1, 2013
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    If it is important to maintain 4-digit accuracy (24.15 V as opposed to 24.14 V), only a relay can come close. There are many relay boards and arduino expanders on ebay.

    PNP transistors can come close, with about 0.1 V of signal drop across them when on. Darlington's are much worse.

    ak
     
  10. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    You could use a mosfet which would have no voltge drop. What needs to be known is the input impedance of the reciever, I´d guess source impedance below 100 ohms might be ok.
     
  11. gixxerman1980

    Thread Starter New Member

    May 25, 2016
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    Wow! It just clicked. I was over complicating it. I'm on board with Kubeek now. Ugh! I feel dumb. LOL. Ok, so, I have some power MOSFETs (IRF520). From what I can tell with the datasheet, that should work. I think I just need to get my hands on some trimpots for fine tuning the resistance of each line.
     
  12. AnalogKid

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    Aug 1, 2013
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    The 520 is an N-channel FET, so you will need a gate voltage source that is 5-10 V above the signal being switched, or 34 V in your case. The alternative is P-channel FETs, which are turned on by pulling the gate down to GND. You will need a zener diode to limit Vgs to under 20 V. Not to be picky, but all solid state switching devices have a voltage drop across them. With a large power MOSFET it can be a very small voltage, but post #5 implies a 0.04% limit. That's not very much.

    ak
     
  13. BR-549

    Well-Known Member

    Sep 22, 2013
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    I am very leery of your monitoring strategy for that kind of pressure.
    Can we see a data sheet on the pressure transducer?
    AND a data sheet on the "receiver" that the ~ 20 v analog signal comes from.
    What are you doing?
     
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