Can I share this sensor with 2 computer modules?

Discussion in 'General Electronics Chat' started by gte, Apr 10, 2014.

  1. gte

    Thread Starter Active Member

    Sep 18, 2009
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    I'd like to share a temperature sensor with 2 different computers. Both computers use the same type of temperature sensor and work fine with 2 individual sensors, but practically there is not room for 2 sensors, so I would like to share a single sensors value to both computers.

    The sensor is a 5v thermistor 2 wire sensor that ranges from 4600Ω to 1Ω, with 4600Ω being very cold and 1Ω being very hot. Both computers provide the sensor 5 volts through the first wire and depending on the temperature, there is a varying voltage drop which is fed back through the second wire to the computer.

    Thinking about it, I believe I can feed the return wire voltage to both computers, does this sound correct? I can draw a diagram if that will help. Thanks!
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,360
    Try it and find out.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You are essentially using two supplies, although if using two PC's the 5v common is coupled via the earth grounded P.S. common.
    If using the devices in the device source mode, (supply connected to the device it may be prudent to use a diode in each 5v supply, alternatively, if both PC's will be on simultaneously, then one 5v supply may suffice.
    Max.
     
  4. gte

    Thread Starter Active Member

    Sep 18, 2009
    347
    4
    Hi, thanks for the replies.

    I did forget to mention that both PC's will be tied together via a common ground for their power supply.

    The reason I ask, is that the person that suggested this approach loosely mentioned something about needing a pull up resistor to make this work, and I cannot figure out a scenario where that would be needed?
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    A normal PC P.S. is usually connected to earth ground by default, so both commons would be connected, but best to connect by a dedicated connection.
    Where are you inputting? To the parallel port or?
    Max.
     
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  6. gte

    Thread Starter Active Member

    Sep 18, 2009
    347
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    It is wired directly into an external module, which I assume has a uC that measures the voltage drop inside of it.

    I wanted to make sure I wasn't overlooking anything, or that I didn't need a pull up because the functionality of this is somewhat critical and it would be foolish for me to jump into it cavalier like.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I can't quite seeing it needing a pull up if it is already connected from input to +5?
    A source device requires a connection or path to common, the module does not show the nature of the input?
    Max.
     
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  8. gte

    Thread Starter Active Member

    Sep 18, 2009
    347
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    No it doesn't. I tested it out hoping I wouldn't damage anything and I did not.

    After some probing, I believe what I need is a voltage follower. When I connect both sensor sources together to feed into the sensor, the voltage artificially increases by a percentage, for example when it was at 1.3v and I connected the second source, the voltage jumped to 2.1v. I was able to use a 1k pull down resistor to get it back pretty close to 1.3x volts but because the sensors resistance varies based on temperature, I cannot have a static pull down value. This leads me to believe I need some sort of comparator circuit and a voltage follower, would you agree?
     
  9. gte

    Thread Starter Active Member

    Sep 18, 2009
    347
    4
    Actually, I may need a "resistance follower" ... which I've never heard of but it has to be possible to make :)

    Time to google, any help or suggestions with that would be much appreciated.
     
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