So in my mechanical engineering class right now we have to create a product that will demonstrate some learning principal to younger students (somewhere in the K-12 range). In my last group our project was to build a glove that would measure acceleration as you threw a ball, at the time I had tried to use the arduino but was having problems with getting it, the accelerometer, and labview to interface correctly in time, so I ended up using a DAQ unit instead.
This time around, my new group and I have to rebuild another project from the last cycle, showing changes in size of a balloon (or another like apparatus) in a vacuum/pressure chamber. This seemed a whole lot less interesting to me, so to make it fun I want to computer control the **** out of it.
The chamber we were given from the last group wasn't even worth recreating in concept, so we are going to start over entirely. This time we will probably either modify a pressure cooker or an air tight food storage container for our vacuum/pressure chamber. Either way the volume of the chamber should be from 1-2 ft^3. I haven't decided on the pump yet, it would be nice to find a single unit that could provide both adequate vacuum/pressure levels, but for cost/availability reasons we might end up with separate vacuum and pressure pumps. If anyone has input on this I would appreciate it. Also limiting this would be my idea to use a computer power supply which would give several convenient voltage choices (3.3v, 5v, and of course 12v). Though according to the wikipedia page http://en.wikipedia.org/wiki/Power_supply_unit_%28computer%29
the maximum draw allowed is 18A at 12V, so the pumps would have to fall within that spec (since both pumps will never be running at the same time, they can both draw up to 18A). I will also need a pressure/vacuum sensor, and a solenoid valve to regulate pressure, something of which I have been looking into, but am hoping for someone with experience to chime in here as well.
All of this will be controlled by an arduino uno with labview software, to control the pumps (with relays, of course) by using the readings from the pressure/vacuum sensor.
There are a lot of engineering problems with this, a few of which I can think of (besides the actual construction of the chamber itself) include:
If by using the pumps alone will I be able to accurately achieve the desired pressure/vacuum levels? I imagine they will not, so I might have to program it to "overshoot" the desired pressure/vac level and use the solenoid valve to adjust to to correct levels. Which means I will need a valve that can act quickly enough to bring within range (hopefully within 1-2in Hg).
Also as an apparatus, the balloon is pretty poor, since rubber is especially porous. Not really ideal for any sort of scientific measurement, but probably adequate for its intended purpose. I'd prefer something else, it just has to be reasonable to the vacuum/pressure levels achieved.
Another issue is cost, which is not too big of a deal since the school is paying for all of it. It just needs to be reasonable.
As far as what reasonable is, your guess is as good as mine.
Also something else was that my professor mentioned something about using a cell phone camera to track the size differences in whatever apparatus we use. I really haven't thought much about this as it is more "end game" right now, but I figured I would just mention it here anyway.
I'm sorry my questions on here are pretty vague, I am just hoping for some experienced input on ideas and feasibility on the different aspects of this. I love to overdo projects like this, and learning more on the arduino and electronics is a plus.