Protective Casing Ideas

Discussion in 'The Projects Forum' started by Sparky49, Aug 1, 2011.

  1. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Hi all,

    I've got an idea to make a wireless air pressure sensor, but a problem I have encountered is that the sensing part of the pressure sensor IC, may become blocked by a runny, jelly-like substance.

    I've come up with an idea to protect the IC, involving covering the hole in the casing with a piece of muslin.

    Would this affect the sensitivity or accuracy of the pressure sensor?

    Are there better ideas?

    Thanks for your time,

    Sparky
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Anything permeable to air won't interfere much with the pressure reading, since the pressure will equalize quite quickly. If you're making "fast" measurements (eg. audio frequency), then it becomes an issue.

    Can't you just use gravity? I mean, just mount the sensor so that gravity keeps whatever goo you have away from the sensor. The mesh might not stop the goo. It might even attract it, and once it's covered, your pressure will go screwy.
     
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  3. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Thanks for the reply Wayne.

    Unfortunately, the substance is designed to prevent air from passing through it, and the sensor cannot be mounted, as it is in a sheepskin bag, which must remain airtight.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Huh? I thought muslin was cotton cloth, which means it'll allow pressure to equalize as long as it's not coated with goo.

    You might consider placing the whole thing inside a practice golf ball (like a whiffle ball) or other screen "cage" covered with the cloth. It would take a lot more goo to foul the entire surface.
     
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  5. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Sorry Wayne, I didn't make my sentence very clear, I meant that the whole unit would be measuring the air pressure inside the bag.:)

    I like the idea of using a practice golf ball. I'm planning to market this, so I'll have to come up without using an actual practice golf ball. haha.:p

    Perhaps this looks a wee bit better?
     
  6. Markd77

    Senior Member

    Sep 7, 2009
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    How about just making it very flexible. No air actually has to pass from outside into the sensor, imagine a pressure sensor in a sealed plastic bag.
     
  7. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Wouldn't it just measure the pressure inside the plastic bag, if it were sealed off?:confused:
     
  8. Markd77

    Senior Member

    Sep 7, 2009
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    The pressure inside will be the same as outside, if it wasn't then the bag would move until it was. The only cases it will be different are if the bag can't inflate any more or if it has significant weight (I suppose that might include being covered in a runny jelly-like substance).
     
  9. wayneh

    Expert

    Sep 9, 2010
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    What is this thing, a flatulence detector? :p
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Electronic bagpipes? ;) With extra jelly? :eek:

    You can measure the pressure in the bag with an "absolute" pressure sensor. It does not need to connect to the outside world.
     
  11. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Well, the cat's out of the bag (har de har har:D).

    I've kinda given up on the electronic bagpipe for the moment, and am considering making a pressure detector, to help me blow at a consistent pressure.

    Unlike other instruments, blowing harder or soften doesn't make the pipes louder or quieter, it makes them flatter or sharper. That's why it is important to keep a consistent pressure.

    The jelly like substance, (hehehe) is stuff we call seasoning, it's basically a mixture of lard and other sticky stuff which is melted down and poured into the bag to make it airtight. Although synthetic bags don't need this, there has been a recent surge in intrest for sheepskin bags, which do need seasoning to 'plug up' the tiny pores in the skin which would leak air.

    This seasoning is what I'm trying to prevent from clogging the sensor.:(

    If it doesn't need to be connected 'to the outside world' could it be plonked inside a re-sealable plastic bag which is then put inside the bagpipe, as in my picture?

    Sorry if I'm not getting what you guys are saying to me... I can be a little slow at times.

    P.S. I hope you enjoyed your little lesson on bagpipes today.:D
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Hah, so I was right about the flatulence after all! :D

    The sensor will work inside the bag - as long as it's sensor hole remains clear (use the cage idea) but you'll still need to connect to the outside somehow. Wireless is not impossible but would be a big step up in complexity for your project. Can you just run some wires?
     
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  13. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Cheeky bugger!;)

    The wires would affect the tone, so I thought wireless would be the way to go.

    After alot of research, I'm thinking of going down the Zigbee route, it's quite cheap and there is no licence fee to pay.

    Before I do that though, I'm going to have to learn abit more about wireless systems and programming (so the computer can project a graph of the pressure). I bought a book on C++ at Waterstones today - first steps towards great things I hope!

    That'll mean lots of questions for you guys in the near future, by the way.:D
     
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Putting the absolute pressure sensor inside a small bag will only work if the small bag is puffy. If it's flat it won't represent the large bag pressure. You could put the pressure sensor inside a small puffy balloon, or small puffy vacuum-sealed mylar bag might hold up better than the balloon which is porous.

    Maybe you should think about haing the sensor on the outside of the bag with a small tube to on of the fittings where the small tube can easily be inspected and cleaned.
     
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  15. wayneh

    Expert

    Sep 9, 2010
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    That's the way it would be done in most industrial settings. Just put a fistula in the wall of the bag, one that can be sealed when the pressure system is not in use. The first thing that pops into my head is the seal on a blow-up air mattress or beach ball, but I suppose there are better options.
     
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