Home > BrewzNET, Rant, Tech geeks > Sod’s Law

Sod’s Law

…Or as we refer to it in the US, Murphy’s Law, was definitely in effect for my trip to Fayetteville. I won’t recount the whole experience, but needless to say I will never fly through Charlotte again if I can help it, particularly on US(eless)Air. I put some highlights of the business trip debacle at the end of this post, so you can read the good stuff and then listen to my whining (if you are interested in doing so). Man, do I hate business trips.

Proof of Concept - Point AlignmentSo at any rate, I did none of the things I wanted to on that trip. I am lucky to have just survived it. The past couple of nights I have worked out a demo for part of my missing pipe functionality – a routine that aligns the defining points for a pipe routing and will re-align everything if one of them is moved. In the screenshot, point 8 (in blue) is moved by either right-clicking in the new location, or holding down the right mouse button and dragging the mouse around. This will ultimately translate into clicking and dragging the pipe control points around (See Memorial Day Activities for some screenshots regarding the control points). I have made the VB2005 source code available if anyone is interested in trying it out.

Pressure sensor test standThis weekend I also got something working that I have been meaning to – the pressure sensor proof-of-concept circuit. I am stunned by how well the MPX5010GSX fits the system requirements – simplicity is a beautiful thing. For the test circuit, I ended up using a PICAXE 18X although I could have managed it with an 08M or 14M. I will have to decide how I want to implement when it comes time to print the circuit boards, but for now I’ll punish my 18Xs a little more. I did opt to test out the smaller 2-channel analog-to-digital chips (MCP3202) since the SPI communication protocol is a little different than for the 4 or 8 channel versions.

Pressure sensor circuitI included some captions in the picture so you can tell what is what… hopefully.
Pressure DataThe data sent back to the PC indicates that I probably won’t even need to use the AD620 instrumentation amplifiers. In the screenshot to the left, Channel 0 is the digital temperature sensor, and Channel 1 is the pressure sensor (as I am slowly letting the liquid level drop). I wouldn’t really need to amplify the signal more than 1.2 to 1.5X of what the raw reading is, and I’m not sure that the amplification would really buy me additional resolution. A simpler design means fewer things that can crap out when in use. Again – I *LOVE* these MPX5010GSX sensors.

Hot Liquor TankSo how do I plan on working the pressure sensors into my sculpture design? It just so happens that my test rig was put together with a very specific layout for one reason – it directly mirrors the physical orientation of my new 28 gallon Hot Liquor Tank. It has a site glass fitting (brass right now, soon to be replaced with stainless) that has a 1/2″ threaded plug on one end. I plan on drilling a hole in a stainless 1/2″ plug, and having the pressure sensor right there at the end of the site glass fitting. The circuitry will most likely be in a small sealed stainless project box, with only a wire/cable running back to the main control board.

And now, let the whining begin:

  • My flight from Philly to Charlotte was late in departing, and arrived at the gate 10 minutes AFTER my connecting flight was supposed to depart. That was OK though – the connecting flight was ALSO delayed.
  • Connecting flight to Fayetteville is cancelled after waiting 2 hours. We are told to go to the “Customer (Dis)Service desk and rebook.
  • 150 people in line before me at the US(eless)Air Customer (Dis)Service desk – Quick head math tells me I will talk to someone in about 4 hours, at which time no more flights out will be available (not to mention everything being booked solid from the other 150 people going first).
  • We quickly call our company travel agent and get booked on a flight to Raleigh. We fly into Raleigh without incident, and drive down to Fayetteville (about 60 minute drive, not bad).
  • We arrive in Fayetteville at 10:30pm, a full 5 hours later than anticipated, without our luggage, and immediately go to bed.
  • My luggage arrives in Fayetteville the following day, but my collegue’s bags get sent to Raleigh for some ridiculous reason. Baggage (Mis)handlers strike again!
  • I’m so tired on Tuesday from the previous day’s ordeal (and working a 10 hour day at the plant) that I eat a quick dinner and pass out at 8pm. I wake up at around midnight and realize no coding is gonna happen for my brew sculpture on this trip.
  • Wednesday our departing flight out of Fayetteville gets cancelled 10 minutes before we’re supposed to board. Fortunately this time around I didn’t try to check my bag, so we get booked out of Raleigh direct to Philly.
  • We go rent ANOTHER car (since we had turned in the previous one hour earlier) and drive to Raleigh, catch the flight in plenty of time, and get to Philly around 9:45pm.
  • Driving home on I-95, I hit the road construction around 476 (exit 7), and sit in bumper-to-bumper traffic as they squeeze 3 lanes down into 1.
  • I arrive home at 10 minutes to midnight, a full 5 hours after I was supposed to.
Categories: BrewzNET, Rant, Tech geeks
  1. Arnie
    July 9, 2007 at 10:35 am

    Well done Garrett,

    Is the pressure sensor calibrated for temp changes internally, or do you have to do that in code? Is it easy or difficult to calibrate?

    Sorry to hear about the crappy business trip. Keep brewing and inventing.

  2. July 9, 2007 at 4:58 pm

    My understanding is that the sensor is temperature compensated as part of the IC package. I will find out for sure once I start doing more tests, and if it requires additional software compensation it should not be too big of a deal.

  3. Arnie
    July 14, 2007 at 3:53 am

    You have inspired me and I’ve just ordered a couple of sample pressure sensors like the ones you have.

    I’ll let you know how I go with them.

  1. June 26, 2007 at 1:14 pm

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