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advice on a simple pressure sensor?

Discussion in 'Electronic Basics' started by amorphia, Oct 13, 2005.

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  1. amorphia

    amorphia Guest

    Hi all,

    I'd much appreciate any advice on my search for a cheap and simple
    pressure sensor. I need to make a device which can measure how hard a
    baby is squeezing a tube, around 2cm thick. I figure the best way is to
    use a silicon tube, just above atmospheric pressure, and connect it via
    a pneumatic tube to a pressure sensor. So what I need is a pressure
    sensor that does not have to be accurate in absolute terms, but needs
    to be relatively sensitive, so it can measure changes in grip strength.
    I reckon if it went up to 1000 kPa that would be more than enough.
    Preferably it would come with an integrated USB interface and drivers
    which provided an API. Alternatively, if you know a good one but it
    just outputs a voltage, perhaps you could also recommend a good cheap
    and cheerful USB A to D converter?

    So far the best thing I've found is this, which you can combine with
    a USB interface from the same supplier:
    But I think it will only interface using their proprietary software -
    it's for classroom use, after all. But this gives you a basic idea of
    what I'm after.

    Other solutions to the basic problem also gratefully received!


  2. CWatters

    CWatters Guest

    Presumably you will also need to correct for temperature - The baby's hand
    will warm up the air in the tube causing the pressure to rise even if they
    don't squeze it.
  3. Guest

    1000kPa is ~145PSI! It's going to be one strong baby?!

    You're going to need a design but here's how I would go about it - I
    would connect the silicon tube directly to the sensor and seal the open
    end. Before use I would take a reading from the sensor without the baby
    squeezing the tube and uses this as a baseline (this would remove
    ambient conditions such as room temperature and altitiude), then get
    the baby to squeeze and take a reading then subtract the baseline
    reading from the measured reading. The trouble is babies are not always
    the most cooperative and like the other poster mentioned the heat from
    the hands would effect the readings if the tube was held too long. The
    wall of the tubing would have to be pretty thin so as not to damp the
    readings too much as I wouldn't think the baby will have a very strong
    grip. I have a sensor (but is is just sensor with a voltage o/p -
    nothing more) in mind but don't have the info to hand at the moment;
    will try to dig the info out tomorrow.
  4. Zak

    Zak Guest

    Fill the tube with a liquid: less expansion.

  5. Guest

    Sensor would need to be waterproof.

    The sensor I was thinking of was the motorola MPX2200A (0-29PSI) or
    similar (try googling for datasheet) - silicone tube would connect
    directly to the port on the sensor.
  6. Andy Baxter

    Andy Baxter Guest

    amorphia said:

    have 'quantum tunnelling compound pills', which work as pressure sensors -
    you could embed one or two in a piece of rubber and use that.

    you could also try

    who sell a conductive rubber that changes conductivity when under pressure.
  7. I seriously doubt if he'll get much of a reading at all from a silicon

    Silicone, maybe.

  8. Bob Eldred

    Bob Eldred Guest

    1000kPa??? That's about 10 Bar or 150 PSI. What baby is going to be able to
    create that pressure squeezing on a tube? You're going to have to be about
    100 times more sensitive than that, say 10kPa or 1.5 PSIG (gauge pressure)
    to be effective. That's about 100cm of water. Get a cheap pressure gauge and
    play around with it first before you try to instrument it.
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