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I'm not an expert about Arduino and I'm studying to create a project related to the bees remote monitoring.

I would like to monitor the internal humidity and temperature and the weight of the beehive boxes.

About the weight parameter my idea is to make a structure with 4 load cells.

I watched some video tutorials related to the creation of a weight scale with Arduino. I saw that it's necessary to calibrate the scale without any weight on the scale every time that Arduino will be started.

I'm not able to understand if there is a way to have this calibration in a different way: I mean,  I will place the beehives on my weight scales only one time and Is not possible to remove and put them back for each calibration step.

Is it really necessary or is there a way to have the calibration with the weight on the scales also?

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  • Once the cells are calibrated w/ no weight those values can be stored and used. It's possible there might be some drift over time (not sure) but for this use case it shouldn't be a huge issue, assuming you're after an approximate hive weight. I'd also imagine you're more interested in weight differential than absolute weight, e.g., "am I having honey tonight" or "where have my bees gone?!" Commented May 25, 2021 at 12:40
  • Can you share the source of your remark: "...I saw that it's necessary to calibrate the scale without any weight on the scale every time that Arduino will be started.". Commented May 25, 2021 at 12:44
  • (Also see github.com/sparkfun/HX711-Load-Cell-Amplifier, the calibration program makes note of applications where there's a "constant" weight on the load cells between power cycles, although your weight won't be constant. IIRC temperature can also affect readings.) Commented May 25, 2021 at 12:49
  • Problem completely solved by SparkFun: github.com/sparkfun/Beehive_WiFi Commented May 26, 2021 at 20:01

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It may be that in this application (beehive monitoring) it is not required to re-calibrate your load sensors before each use. When a person is observing a scale to measure their own weight they will be sensitive to the scale reading zero before each use. Even though being, say, a lb off is likely less than a 1% error when measuring their total body weight. This site talks about load cell calibration and "recommends a yearly recalibration interval". They also talk about temperature compensation.

As temperature and humidity will be monitored. And nonlinear load sensor response to weight can be compensated in software, consider testing your setup under different conditions to determine what considerations need to be taken into account to provide the desired accuracy.

This image is from https://www.futek.com/load-cell-calibration-services

This image is from https://www.futek.com/load-cell-calibration-services

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What I can find about calibrating load cells is that they are subject to "electrical influence, mechanical effects, instrumentation faults and loose cables etc."

In the case of beehives, I'd add temperature, water, ice, snow, dirt & dust, and debris from the bees. The calibration suggestions I found were to calibrate "periodically", which suggests to me that the suggestion to calibrate at every startup assumes that the calibration will be lost at every power-down. That does not have to be the case - it can be store in a non-volatile memory such as EEPROM.

What I do think you'll need to do is calibrate each cells at 0%, 10%, ..., etc., of its full load, probably to 120% or 130% to allow for wind loading and asymmetric loading within the hive, and at a range of temperatures, make a set of force vs. cell output and temperature, from which to interpolate to get the 4 partial hive-weights.

They probably will need to recalibrated periodically, but for your application, a tare-value, measured at a reproducible hive condition, may be sufficient, if all you need is a differential weight.

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