Adding Sensors to Monitor Hive Health

The Digital Beehive uses Wi-Fi to broadcast a beehive’s weight, humidity, temperature, and battery voltage every minute to Spark Fun’s data channel service called Phant. The raw data can be seen here but you can view some prettier graphs of the data here on (sign-in required).
On a visit to Portland, Oregon, last summer my friend mentioned he had always wanted to put a load cell under a beehive to measure the weight of the hive over time. He thought it was a great project for Spark Fun and I immediately started thinking how it might be done. Fast forward through 9 months of testing and development and we’ve got live bee data!

First a disclaimer: This is a project that focuses on the technology and the lessons in the field, but I have only scratched the surface of beekeeping (apiculture). Spark Fun is fortunate to have a handful of employees who are either beekeepers or related to beekeepers. They were nice enough to do the bee tending, I did the tech.  Additionally, I am an engineer so data accuracy is important to me but the interpretation of that data should be left to research scientists. That said, check this out! A healthy hive can hit 400lbs (180kg), so we need to create a scale that can handle the hive’s maximum weight and also have the robustness to survive in the field.
There are a variety of 200kg bathroom and package scales available. The vast majority have a similar setup to the scale pictured above. There are four strain gauges (one in each corner) that are wired in a Wheatstone Bridge configuration to create a load cell. You can read more about load cells here.
This configuration of four gauges allows for low cost voltage measurement instruments to measure a very minute change in resistance. We’ll need to convert this voltage change to a digital reading. Scale manufacturers use specifically designed ICs to convert the analog voltage reading to digital, the HX711 is one such specialized instrument amplifier that is commonly used inside many consumer scales. So I whipped up a breakout board for the HX711 and started experimenting with this and other postal scales. What I found was discouraging.
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