I previously used a GY-652 module as the basis for a weather station. The module contains a BMP180 pressure/air sensor and a HMC5983 electronic compass. The weather station ran for about 4 months on 3 AAA batteries which was reasonable enough although the GY-652 had an unexpectedly large quiescent current of around 1mA.
Anyway, the batteries needed recharging and I decided it would be interesting to see if the HMC5983 could be useful in such an environmental monitoring test.
The Earth’s magnetic field varies from around 250 mG to about 650 mG. During solar storms, this can vary by as much as 170 milli-Gauss (source: http://www.spaceweather.gc.ca/svr-en.php). Daily variations in the magnetic field are of the order of 0.4 milli-Gauss. Are these measurable by the HMC5983 I wonder? According to its datasheet, the noise floor for the device is 2 mG so that probably rules out the detection of daily field variation. Storms are another matter however and these should be measurable by the device.
Batteries were recharged and code modified to make use of the HMC5983. The base-station for the weather station is now connected to a Raspberry Pi which relays the data up to Thingspeak. I’m going to leave it for a month or as long as the batteries hold out and, who knows, maybe it will spot a solar storm.
Click here to view the data on Thingspeak.
Update 20 January 2018
After a month or so in operation I think I *may* have seen some correlation between solar activity and magnetic reading variations. There is also some correlation between the magnetic field readings and temperature. The system had been using 3 rechargeable AAA batteries which have been drained twice (need to work on my low power mode :).
To overcome some of these shortcomings I’ve opted to move the sensor out of the attic and placed it under the stairs (unheated area, not too near any big electrical or magnetic fields). I’ve also replaced the AAA batteries with AA ones. Now just have to wait for a big solar storm…