January 01, 2015

Under Pressure

Above is a shot of my "weather station" with a Bosh BMP180 barometric pressure sensor attached. The pressure sensor was a Christmas present from my Dad (thanks Dad!), and will allow me to report barometric pressure for my personal weather station page on Weather Underground.

The sensor itself is the small square in the middle of the red breakout board. It runs on 3.3V and uses an I2C or "1-Wire" protocol.
The recommended approach is to solder an IC header on, but I decided to just solder on some single core wires.
To test, I attached the wires to a breadboard. Sparkfun has a great tutorial on using the BMP180. I should have read this more closely, as I only really needed 4 wires, as my Arudino will supply 3.3V, and so the blue wire was superfluous.
Add in an EtherTen, the test code from SparkFun, and soon I was getting data.

Learning point for today: Barometric pressure is displayed on weather reports as at sea level. Of course the pressure changes with altitude, so you need to know your altitude. (About 40m above sea level here it seems.) The BMP180 library has a handy conversion utility to calculate the sea level pressure.

Once the correct altitude was entered, my sensor was reporting pressure readings very close to nearby weather stations, so I think we're good to go. (Interestingly, about 10% more than what our OS weather station tells us in the kitchen, so I think I need to read its instructions a bit more closely.)
Time to solder it on to the prototyping area that is available with my 433MHz receiver shield.
Not such a bad soldering job, given the board is already cracked.

OK, the antenna has been re-attached, and the shield re-attached to the EtherTen. My Weather Underground upload code will need a bit of work to add in the pressure. I'll let you know how it goes.

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