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Author Topic: Measuring the weight of a beehive  (Read 11534 times)
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Norway
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Hi
This is my first ever post on the arduino forum, so be gentle smiley-wink

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 smiley-wink)

Thank you for your reponses.
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SW Scotland
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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.

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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.
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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  smiley

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.
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Left Coast, CA (USA)
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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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Norway
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Thank you for all the good ideas. keep them coming smiley-lol. I like the idea of a dummy beehive and the diy spring scale. One problem whith the spring idea is that the scale has to be placed directly under the beehive so it is not in the way when I work. to prevent the hive from lean over and tip in the wind I would need some short and hard springs. Then i would have to mesure very tiny contraction of the springs, maybe in tens of a millimeter. I am not sure how to do that.

@radman
A full hive can weigh up to around 100 kg. the extra 50 kg is just to be at the safe side.
The goal of the weighing is to check if the bees have enough food, having to little space, to see were the bees collect most honey(so i can move more bees over there), and to detect swarming(when the bees leave the hive).

@retrolefty
It looks that mabye load cells is the way to go. A beefy shear beam load cell, right under the hive should do the trick. On eBay there is a lot of el cheapo 20 dollar load cells, but none of them goes as high as 150 kg. In that weight class, i can only find industrial 300 dollar load cells smiley-sad
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You can get carbon impregnated foam material whose resistance changes when compressed. You could put the hives on that, but accuracy, range and rain may be an issues. I suppose the foam could be placed inside an impermiable coating.
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Norway
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Hi.
A little update.
After a bit research, a load cell seems like the best solution. I just have to find one cheap enough smiley-wink

My plan so far is to in each beefarm have one control box(master), and several scales(slave) that will communicate with each other using wireless transcivers.

The control box will be powered by a lead acid battery, and contain an microcontroller, a GSM module, a RTC, a wireless transceiver, sensors for measurment of temperature, humidity and rainfall and maybe a load cell with a fixed load for using as a referance.

For the hive scales I was tinking of using a single load cell made for platform scales. For the op-amp I was thinking about the ina125 http://www.ti.com/lit/ds/symlink/ina125.pdf since it got an onboard voltage referance and a sleep mode.
For communication I have looked at various NRF24L01+ transceiver module since it is cheap and have a low power consumption.

To power the scale I was thinking of using a small solar panel to charge up a supercapasitor. when the supercapasitor is charged up, the atmega will wake up from sleep, measure the weight of the hive, transmit it to the master, and then go back to sleep. I only need 5 or 6 samples during the day, so the atmega and radio, will be in sleep mode for 99% of the time.

Does this sounds manageable solution? I do not have much experience with op-amps, and I have never used wireless transceivers. So if someone has any opinions regarding to these, I would be very grateful
« Last Edit: July 11, 2012, 04:23:43 pm by LEGO-lars » Logged

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Hi.
A little update.
After a bit research, a load cell seems like the best solution. I just have to find one cheap enough smiley-wink

My plan so far is to in each beefarm have one control box(master), and several scales(slave) that will communicate with each other using wireless transcivers.

The control box will be powered by a lead acid battery, and contain an microcontroller, a GSM module, a RTC, a wireless transceiver, sensors for measurment of temperature, humidity and rainfall and maybe a load cell with a fixed load for using as a referance.

For the hive scales I was tinking of using a single load cell made for platform scales. For the op-amp I was thinking about the ina125 http://www.ti.com/lit/ds/symlink/ina125.pdf since it got an onboard voltage referance and a sleep mode.
For communication I have looked at various NRF24L01+ transceiver module since it is cheap and have a low power consumption.

To power the scale I was thinking of using a small solar panel to charge up a supercapasitor. when the supercapasitor is charged up, the atmega will wake up from sleep, measure the weight of the hive, transmit it to the master, and then go back to sleep. I only need 5 or 6 samples during the day, so the atmega and radio, will be in sleep mode for 99% of the time.

Does this sounds manageable solution? I do not have much experience with op-amps, and I have never used wireless transceivers. So if someone has any opinions regarding to these, I would be very grateful


Well it sounds like you have a good grip on what is required to perform what you have defined needing to be done. As far as manageable, that would depend on your experience and ability to keep plugging away at it. I would suggest you approach the project in steps. I would recommend you first work on getting the wireless network working between the master and the number of slaves you will be using. Wireless (software & hardware) can be very taxing to get going from basic components, it's never as easy as it first sounds. Once that is mastered and working well then you can make the higher cost investment in the load cells and support components and the mechanical packaging, etc.

Good luck
Lefty
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Artisan's Asylum, Somerville, MA, USA
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Just as a thought, have you tried looking at cheap digital bathroom scales as a source of load cells?  The ones I've seen typically can deal with weights up to around 300lbs, which sounds like the range you are after...

It does sound like an interesting project, I might be interested in it myself, as I'm also a small scale beekeeper (2 hives)

ex-Gooserider
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Norway
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Thank you for all the help. Now I feel this project is a bit more doable. I have ordered some cheap NRF24L01+ modules from eBay, as well as some small solar cells and supercaps. Now I will learn to use the transceivers, and testing their range and differend master/slave setups.
Looks like i have som work to do with the atmega328P also. I would like it to run in the same voltage range as the NRF24L01+ (1.9 - 3.6V) which means I have to use a slower clock. I would also like to remove the arduino bootloader so I avoid the bootloader delay waste a lot of power during powerup.

@ex-Gooserider
I have been thinkin about using bathroom scales as well. But I am under the impression that the load cells in these scales are of a very bad quality. And for some reason it feels a bit wrong to buy 30 bathroom scales, remove one component and then throw avay the rest. smiley-razz
But if i can't find anything else, it's worth a try. smiley

LEGO-lars
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Hi ,

I am busy on a similar project. with :
-2 strain gauges from a bathroom scale ( there are 4 in each lowcost bathroom scale) mounted in weadstone bridge on a ad620 precision  amp ( cheaper than the texas ina125 )
-4 ds1820 temp sensor
-HD44780 LCD
-DS1302 RTC
-sd slot for data storage ( tested appart and working but not implemented yet in this specific project )

the objective is to read temp + weight each 24 hours and  to store or send it
accuracy is 100gr , but one of my biggest problem was until now to keep the weight readings stable

Maybe we could share our respective experience ?
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Norway
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Hi xavier smiley

Nice to hear about other peaple having the same project. Do you only store the data from your scale, or do you have some method for reading the weight remotely?

An update on my work:
I made a prototype using this load cell:http://www.aliexpress.com/item/100kg-200kg-300kg-weighing-scales-load-cell-for-platform-scales/624403255.html  and the ina122 amplifier. This setup gives me a great accuracy and almost no temperature drift. However, the ina122 is getting a bit unstable when I am powering it with a 3v battery, so I am going to try some other amplifiers like the ina333 or AD8553.

LEGO-lars
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Ontario
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Most of the applications I have seen with load-cells call for periodically re-taring or zeroing out the reading.  Just comparing the reading with a similar load cell at a known load doesn't really tell you that much.  You have to un-load THIS load cell and take a reference reading, then load it again, to get a good useful reading from a given load cell.

So in my project, which is for measuring the weight of a 300lb LPG tank, or for the present project, to weigh a beehive, a critical requirement is that the propane tank or beehive is going to want to sit on the load cell for weeks or months at a stretch, and you still want decent readings -- say within 1 part in 100.  No one's going to come around and lift off the hive every few hours to zero out the load cell -- it has to remain accurate under constant load, day in, day out.

For this type of application, I have imagined two approaches:

(1) build a balance-lever linkage system that enables a load cell to be presented with 1:1000 of the load.  Have the small load spend most of it's time against a stop.  Once in a while, when a reading is needed, use a servo or similar mechanical linkage to push the load cell against the load to move it away from the stop.  Take your reading, retract the load cell.  This way the cell spends most of its time un-loaded, so fatigue and creep don't affect it, and it is always neatly tared to zero before each reading.

(2) build a pneumatic balloon system under the load, like a hot water bottle.  Inflate it and seal it up, then just measure the pressure in the balloon.  If its hard to keep the balloon inflated all the time, then let the weight rest at the bottom and make a contact closure.  When  reading is needed, pump air into the balloon until the contact closure opens, take pressure readings for a while, then kill the pump and let the weight settle back against its stop.

I'm not super enamored of either, really, but they're the best solution I can up with for the re-tare problem.
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Norway
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Most of the applications I have seen with load-cells call for periodically re-taring or zeroing out the reading.  Just comparing the reading with a similar load cell at a known load doesn't really tell you that much.  You have to un-load THIS load cell and take a reference reading, then load it again, to get a good useful reading from a given load cell.

So in my project, which is for measuring the weight of a 300lb LPG tank, or for the present project, to weigh a beehive, a critical requirement is that the propane tank or beehive is going to want to sit on the load cell for weeks or months at a stretch, and you still want decent readings -- say within 1 part in 100.  No one's going to come around and lift off the hive every few hours to zero out the load cell -- it has to remain accurate under constant load, day in, day out.

For this type of application, I have imagined two approaches:

(1) build a balance-lever linkage system that enables a load cell to be presented with 1:1000 of the load.  Have the small load spend most of it's time against a stop.  Once in a while, when a reading is needed, use a servo or similar mechanical linkage to push the load cell against the load to move it away from the stop.  Take your reading, retract the load cell.  This way the cell spends most of its time un-loaded, so fatigue and creep don't affect it, and it is always neatly tared to zero before each reading.

(2) build a pneumatic balloon system under the load, like a hot water bottle.  Inflate it and seal it up, then just measure the pressure in the balloon.  If its hard to keep the balloon inflated all the time, then let the weight rest at the bottom and make a contact closure.  When  reading is needed, pump air into the balloon until the contact closure opens, take pressure readings for a while, then kill the pump and let the weight settle back against its stop.

I'm not super enamored of either, really, but they're the best solution I can up with for the re-tare problem.

The need for zeroing of the load cell was a consern for me too. However my 200kg load cell have been standing on my kitchen bench with a constant load for over a week, and it is only drifting like +/- 20g (a little worse when the temperature changes, but not to bad).
If I had zeroed my scale before each measurement (and had higher resolution on my ADC), I would mabye get ten times better accuracy. But it all comes down to if you really need that extra accuracy. In my case I did not. smiley

LEGO-lars
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