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Under Pressure

…So this weekend I finally got around to doing something that I have been meaning to for some time – Building a test rig for the MPX5010GSX pressure sensors. You guys have already seen my temperature sensor test rigs in previous posts like Electromadness Continues, and I’ve had the pressure sensors for a while but have not actually done any testing with them yet. Instead I have been pondering how to proof the concept of pressure level sensing, and build accurate test circuits.

Pressure Sensor Test RigI built the mechanical portion, as shown in the picture. The 28 gallon (~100 L) kettle is included for a scale comparison. It consists of a plastic 1/2″ T, plenty of 1/2″ vinyl tubing, an old brass drain valve (long since replaced with stainless in on my kettles), and a wood support. This will let me test the pressure sensor with a very small amount of water, as opposed to filling up and draining 28 gallons at a time (not like that was ever even considered).

Sensor picThe circuit portion is going to require a little more time. First I need to find and purchase a 4 or 6 socket header that I can plug the sensor… I will run some wire back to a breadboard, and from there use my AD620 instrumentation amplifier IC to make it full-scale. I am thinking of taking it from the AD620 through a 12 bit SPI Analog to digital IC (MCP3202) and then to a 08M PICAXE chip. I haven’t worked out details, but I should have enough inputs and outputs on the 08M to bit-bang the SPI protocol and implement an interrupt / serial communication back to a master PICAXE chip when requested. If not, I’ve got a couple of the 14M chips that will definitely have enough power to do so – or I may even try playing around with the 28X1 and 40X1 parts that have native SPI support – haven’t really decided yet.

I also did some minor work on the VB.NET user interface – mostly getting the basic functionality for the “Designer” control to work. The biggest gap at this point dragging the pipe points around the screen, but I have a plan on how to do that. Cut/Copy/Paste is all working, the Zorder (bring forward/send back) is all working, as is shift-dragging and ctrl-dragging. Soon I’ll start work on the designer form (not just the control that displays and implements the changes). I don’t have any good / new screenshots to share, but I hope to complete a good quantity of work this week while on a business trip to Fayetteville. Once the workday is over and we’ve eaten dinner, I plan on locking myself in my room and working on the application rather than killing time, money, and brain cells in an overpriced and understocked pub. Seeing as Fayetteville is a military town, I do not have high hopes for the local craft brew scene.

Other things beer-related from this weekend:

  • I racked 10 gallons of Witbier to secondaries, 5 gallons of which went onto about 5lb of cubed mangos (the “Mango Mama” witbier).
  • I participated in the 2007 BUZZ-Off Competition and took 2nd place in the Belgian Dubbel category for Travellers & Tourists (TnT). My amarillo pale ale did well too (38.5), but did not place.
  • I carelessly broke my favorite belgian glass (a Dogfish Head tulip glass, given to me by Sam Calagione at a book signing) and they are not made any more – DRAT!

The unfortunate demise of my tulip glass is most tragic. You were good to me – RIP.

Goodbye old friend

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Categories: competitions, Tech geeks
  1. June 10, 2007 at 11:12 pm

    Sorry about your glass. Maybe you can get one used online?

  2. Arnie
    July 18, 2007 at 4:33 pm

    Garrett,

    I’ve just been reading the MPX5010 datasheet and it says
    “Media other than dry air may have adverse effects on sensor performance and long-term reliability.”

    It looks like you are running the head of water straight into it. What about inverting it like the sensor systems in washing machines where the sensor sits above the tun and a tube runs down to the bottom? This way the tube will fill with liquor to the level of the tun and exert air pressure on the sensor.

  3. July 21, 2007 at 5:49 am

    Yeah, I am making the liquid head exert the pressure. I know the sensor spec says that anything but air could foul it, but I am basing my design off prior art (Wicked Stone Brewing, Emile’s Home Brewing… both of which you are familiar with) where they also had the liquid exerting the pressure. They have years of experience with this setup, so I can only hope that I will get the same kind of life out of my sensor.

    I bought two of them, so if the test sensor dies on me, I have another to experiment with. I imagine the air pressure method could work, however you would want more a more sensitive sensor since the air will be compressible and a full kettle will not exert the same amount of air pressure that an equal level of liquid pressure would…. So the MPX5010GSX would most likely not be the ideal choice. I suppose you could amplify the signal with an AD620 or similar chip, but it would be better if the sensor range were matched to the application…

    IF you happen to run across one that is appropriate for liquid service and around 1 meter of head pressure (at full scale), please let me know…

  4. Arnie
    July 25, 2007 at 4:19 am

    I guess we are not using them constantly. Even if we brew once a week, that is probably no more than 6 hours of duty cycle per week and likely much less. It seems simpler to do it with liquid pressure as you have, so I’ll be bold and go for simple. I have a couple of samples, so nothing lost if one fails. I’d not gone back to Wicked Stone and Emile’s descriptions but thanks for the heads up.

    For a disctraction, check out my latest blog on a new and easy to use machine design. It is for my brewing friend Leah who has lost most of the use of one arm, so we have been trying to figure out a simpler way for her to make beer. See http://hermanmachine.spaces.live.com/blog/cns!FA0F18E537FC084D!317.entry

  5. July 26, 2007 at 7:02 pm

    I actually bought my sensors at like $18/ea. Man… free samples. That would have been nice.

  6. Arnie
    July 26, 2007 at 7:58 pm

    Yep, free and air freight from the States to Australia for free as well – ordered late on a Friday afternoon, arrived about 10am on Monday!!!

    Can’t complain about that.

    Now, after that stunning reference from your friend about the best beer he has ever tasted, does Sever.com offer the same kind of deals that Freescale do 😉

    Well done Garrett, keep making great beer.

  1. August 22, 2007 at 6:08 pm
  2. October 6, 2007 at 5:59 am

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