Let's Finish Off the Barometer Project.

In the last entry <link> I posted the code for my barometer; I took a simple program of a few lines and turned it into a monster that does everything imaginable.  Now, I should actually set it up to work and put it in service.  Yes, my XBee shield came in and worked fine first try, so I mounted the little breakout board on it and added four wires to connect the barometer chip to the Arduino pins and tested it.


Made a nice little package when I got it all put together, so I dismantled the Stephenson Screen on my fence and tie wrapped it inside.


I had the old temperature sensor in there for years with no problems, so I don't think I need to get any fancier than that.

One thing I did in the code that I didn't mention in the last post was how to correct the reading to adjust for sea level comparisons.  See, to make barometer reading useful around the world, weather folk adjust them for the altitude so that there is a common base for comparison.  There's some really good explanations for why and how to do this out there, so if you don't already understand this, do a quick search.

From our perspective, this is incredibly easy; just call a different routine to read the data:

float pressure = bmp.readSealevelPressure(altitude)/100.0;

This statement will get the pressure adjusted for 'altitude' and the division by 100 will convert it from Pascals to millibars.  If you want inches of mercury, just look up the conversion factor.  The Adafruit library has already got the code for the conversion, all you have to do is look up your altitude in Google Maps, or read it off a GPS at the location where you put the barometer.

I've already adjusted my house monitor code to use this device and if you look at my house display, the outside temp and barometric pressure are taken from the new set up. I was lucky enough to catch a small storm so I could compare it with the other stations in my area, and it was right on.  It's really great when a sensor does exactly what the datasheet says it will.

I really like this sensor; the temperature measurement is very stable as is the barometer.  It's a snap to read and only takes two signal wires for all of it.  Since there's room on the device for more sensors, I may think about luminance or something in the future.