Page 1 of 1

Strain gauge/load cell advice needed

Posted: Mon May 30, 2016 1:00 am
by Bee_Steward
I need guidance finding a RasPi3B-compliant sensor to take and report constant (OK, once every 15 minutes, but full 24/7 persistence) weight measurements of a stationary mass.

The “mass” is a fully-operational honeybee hive. I need to measure its weight and log its variation as these bugs gather nectar/pollen, cure the honey (evaporation), and then consume it (usually at night).

An inexpensive FSR sensor won’t do the job because ambient temperatures, the constant weight of the hive, etc. will cause these sensors to “drift” into unacceptable inaccuracy.

I suspect a strain gauge or load-cell is a better sensor choice. Does anyone have any experience with these?

Many THANKS!

Re: Strain gauge/load cell advice needed

Posted: Mon May 30, 2016 4:36 pm
by DougieLawson
Have you thought about using a Wii Fit as a Raspberry Pi weighing scale? There's a few "instructables" out there on hooking up a Wii Fit using BlueTooth to a RPi and getting sensible measurements from it.

Re: Strain gauge/load cell advice needed

Posted: Mon May 30, 2016 4:44 pm
by darkbibble
talking of bees I saw a neat rfid setup recently on the web where the guy had fitted all the bees in his hive with rfid tags to monitor them.

Sensing/logging weight variations in beehive

Posted: Mon May 30, 2016 4:49 pm
by Bee_Steward
I posted this yesterday in the General Discussion section and should have posted it into here instead.

-=-=-=-=-

A key "vital-sign" indicator of a honeybee hive's health is its weight or, to be more precise, its weight changes. So I'm attempting to harness the RasPi3B to the job of measuring and reporting a hive's weight.

I need guidance finding a compliant sensor to take and report constant (OK, once every 15 minutes, but full 24/7 persistence) weight measurements of a stationary mass.

The “mass” is a fully-operational honeybee hive. I need to measure its weight and log its variation as these bugs gather nectar/pollen, cure the honey (evaporation), and then consume it (usually at night).

A rising hive weight is almost always good news while a persistently falling one (except perhaps in the fall season when the bees are scaling down for the winter dormancy) is a sure sign the colony needs the beekeeper's attention.

Since weight-changes are the issue, there's no reason to get the gross weight of the hive; I propose to put one sensor under the rear of the hive (sloping the entire hive slightly forward) and simply monitor readings at that one location.

An inexpensive FSR sensor won’t do the job because ambient temperatures, the constant weight of the hive, etc. will cause these sensors to “drift” into unacceptable inaccuracy.

I suspect a strain gauge or load-cell is a better sensor choice. Does anyone have any experience with these in a constant-monitoring application?

I welcome your comments - and many THANKS!

Re: Sensing/logging weight variations in beehive

Posted: Mon May 30, 2016 5:17 pm
by rzusman
Among other things, I design pressure gauges, which have similar issues as scales.

First of all, you need to pick a load cell that has the right range for your hive. If you expect your hive to weigh 100 ± 25 lbs, it’s a bad idea to use a 1,000 lb. load cell - the amplifier errors and reduced ADC range will hurt your accuracy.

Secondly, find one that has the drift and temperature compensation specs you need. I would recommend buying the amp, instead of making it yourself. You can do the digitizer yourself, though.

A good load cell is going to be expensive, but it’s probably worth it to eliminate sources of error (you could machine your own, and glue a strain gauge to it, but then you would have to characterize it).

Also, when you design your mount, make it easy to remove and accurately replace the cell, so that you can do a calibration check on it periodically. Also, I would log the temperature, so that you can compensate for that if necessary.

Re: Sensing/logging weight variations in beehive

Posted: Tue May 31, 2016 10:48 am
by texy
Bee_Steward wrote:I posted this yesterday in the General Discussion section and should have posted it into here instead.
!
I've now merged the two threads - in future you can raise a report and request posts/threads to be moved.
Cheers,
Texy

Re: Strain gauge/load cell advice needed

Posted: Tue May 31, 2016 11:42 am
by tonywaite
Hi,
Following on from Dougie's post, another 'quick and dirty' approach:
How about buying a set of bathroom scales, sealing it from the elements using a ziplock freezer bag.
(For example scales, Google 'Salter Glass Digital Bathroom Scale')
Simply capture its weight readings via a Pi-Camera, with time-lapse snapshots.
This would give early data and an indication of feasibility.
Good luck!

Re: Strain gauge/load cell advice needed

Posted: Wed Sep 27, 2017 10:04 am
by connectororconductor
DougieLawson wrote:
Mon May 30, 2016 4:36 pm
Have you thought about using a Wii Fit as a Raspberry Pi weighing scale? There's a few "instructables" out there on hooking up a Wii Fit using BlueTooth to a RPi and getting sensible measurements from it.
Could you please share any links to the instructables. I need to connect a digital weighing scale to RPi by wifi?. The choices i have is however less. If there is a way that can connect through wifi it will be very much useful.

Re: Strain gauge/load cell advice needed

Posted: Sun Oct 01, 2017 4:41 am
by Gavinmc42
Hinge one end and support the other on springs.
Then use magnet and linear hall effect to detect spring compression.
A good i2c ADC and average the readings over time.
Things like TI's sensor tag have bluetooth.

Re: Strain gauge/load cell advice needed

Posted: Sun Oct 01, 2017 10:27 am
by DougieLawson
connectororconductor wrote:
Wed Sep 27, 2017 10:04 am
DougieLawson wrote:
Mon May 30, 2016 4:36 pm
Have you thought about using a Wii Fit as a Raspberry Pi weighing scale? There's a few "instructables" out there on hooking up a Wii Fit using BlueTooth to a RPi and getting sensible measurements from it.
Could you please share any links to the instructables. I need to connect a digital weighing scale to RPi by wifi?. The choices i have is however less. If there is a way that can connect through wifi it will be very much useful.
Is your local Google broken?
https://www.google.co.uk/search?num=100 ... spberry+pi