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Topic: Measuring the weight of a beehive (Read 13 times) previous topic - next topic

LEGO-lars

Hi
This is my first ever post on the arduino forum, so be gentle ;)

I would like to use an arduino to measuring the weight of some beehives, and then have a gsm mudule send the result as an sms to my cellphone. Something like this:http://www.bienenwaage.de/englisch/beehivescales.html

The spec i need from the scale is:
1. Be able to measure weights from 0 - 150 kg
2. Have a tolerance on +- 1-2 kg
3. Sensor can be calibrated in the beginning of the season, and then stand for about five months without calibration or zeroing.
4. The sensor is placed outside so it have to deal with varius humidity levels and temperaturs from 0 - 35 degrees Celsius.
5. If the prototype works promising, I would like to build 20-30 scales, so the parts needs to be as cheap as possible.

My question is what kind of sensor can i use to achieve this specs? Is loadcells the only way to go? I thought loadcells had a problem with drifting during long time sessions(and they are a bit expensive ;))

Thank you for your reponses.

jackrae

Whatever method you use you could also produce a dummy beehive (to act as a reference weight) using the same type of sensor.  Then as the reference weight changes with the temperature, humidity, rain, wind, etc your dummy beehive's measured weight can be used to compensate your actual weight measurements.


PeterH

I suppose you could make a DIY weight sensor using springs and position sensors (potentiometer etc) but for beehives I guess you want the whole thing to be solidly mounted and not move around, which might rule out that kind of approach. If you fancy making and calibrating your own load cell, you can buy a strain gauge for just a few quid. Then you have to figure out how to mount it, read it, calibrate it, compensate for temperature drift and so on. It only needs time and effort rather than money, but I don't know how that sort of thing appeals to you.
I only provide help via the forum - please do not contact me for private consultancy.

radman

150kg is pretty heavy and +/- 1-2kg seems quite crude, are those figures correct?
I though you would be wanting to watch the honey come in a jar at a time  :)

Maybe I am going off at tangents. Bees probably don't mind a bit of movement, so perhaps the hive could be suspended from a spring balance and you just send a picture of several hives from time to time. Maybe you could convert weight to pressure, if that is cheaper/easier to measure.

Sorry just thinking out loud.

retrolefty

While load cells can be costly they are the best device for this kind of application. Some time you can find them surplus on E-bay for better prices. The idea of having a reference weight on one addition channel is a good one and would allow software compensation to all the other channels. Load cells are low level (millivolt) sensors and you will usually require external op-amps for proper amplification.


Lefty

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