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First Signs of Temperature Sensitivity

A project log for Honeybee Hive Monitoring

Recording weight, hive temperature, and weather data toward better management and understanding of honeybees.

ken-meyerKen Meyer 09/29/2014 at 01:140 Comments

After I got the HX711 working for the first time (after days of last-minute debugging code -- such a great feeling at the end!) I immediately walked away from the project and let it collect data for a couple of hours. The scale and Apitronics Bee were both sitting on my concrete basement floor, but since the scale has a metal housing, and the Bee is in a plastic box, the scale obviously responds to temperature changes much faster than the Bee.

When I looked back at the data, I was at first shocked at how unstable the weight reading was, but when I looked closer and compared the weight data to the temperature data, I found that the weight dropped and the temperature started to slide down just at the point where I turned the air conditioning back on because we were all roasting after cooking for a party!

Here's the temperature data (degrees C. on the vertical axis, time on the horizontal):

That elbow at 15:00 is right when the air conditioning kicked in. Now here's the weight reading (pounds on the vertical, time on the horizontal):

The weight of the hive was pretty steady after an initial rise that may be a combination of temperature and relaxation after loading the scale with 30 lbs, however, the sudden jump of 4 pounds when the A/C turns on is huge!

 If I'm interpreting the shift right, I've seen much more stable behavior in a more expensive scale, so I'm leaning toward using a large stand-alone load cell right away. I'm also quite unhappy with using an excitation voltage of only 2.8V for the postal scale when I could get almost 4X the signal (vastly improving the signal to noise ratio) by adding a regulator and bumping the voltage up to 10V.

Just in case I make it to the next round of the hackaday prize competition, I think I'm going to get a new HX711 board (I fear the current one may have been compromised by some excessive soldering work) and mount it properly in the Apitronics Bee. If I make it to the next round, I will spend the next month characterizing the system and try to compensate for temperature factors by the new deadline at the end of October so I can have data from a real hive, even if it's less accurate than I'd like.

If I don't make the next round of the hackaday prize competition, I think I'll step back, finish my design of the single-load cell scale, add the 10-12V regulator (paying careful attention to temperature sensitivity of the chosen regulator!) and significantly clean up the HX711 library so I can remove all the disclaimers about what NOT to do in a proper driver!

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