Scales with bathroom load sensors

[clemens]

This thread is just for monitoring other projects that uses the cheap 3 wire load sensors – and fail – in the most cases.

We are talking about this around $ 9 cheap 50 kg load cells that are used in bathroom scales, e.g. the model sold by Sparfun:

Load Sensor - 50kg - SEN-10245 - SparkFun Electronics

The first trial to use this kind of sensor for bee scales is direcly from the founder of Sparkfun Nathan Seidle:

The Internet of Bees: Adding Sensors to Monitor Hive Health
https://makezine.com/projects/bees-sensors-monitor-hive-health/

It is interesting that he did not use the sparkfun load sensors but a hackt bathroom scale!

The results are not realy good, a long calibraion time, over days (!), and not really stable output leads to the conclusion that this model is not usable for a pofessional or even hobby grade bee scale.

The second trial is by Geo Meadows

nvestigations into low cost Load Cells
https://community.osbh.mirror.hiveeyes.org/t/investigations-into-low-cost-load-cells/133

Summary by Geo:

The evidence is that the cells are NOT SUITABLE for continuous beehive monitoring.

I think the original post is:

BeeBug Internet Hive Monitoring System

The third trial is

Beehive scale build details. finally

Beehive scale build details. finally

[lorenzo]

Maybe one exception -that works- using that kind of cells is be the BS4.

I did not test this device myself but got a discussion with his designer and he told me that as far as your expectations are to follow the overall weight of the hive, the performances were fine…

[clemens]

Hi Lorenzo, I have seen this “balance de ruche (balance apicole) Beescale4 (BS4)” also some month ago as you shared the link on The Beescale4 (BS4) by Jérôme Alphonse and I wonder what kind of sensors this are. i do not thinkt this are bathroom load sensors but a kind of weight or force sensitive mat. But I don’t know. So when you have contact to the designer and they are willing to share some details it would be nice they can give some information about the sensor.

[lorenzo]

Hi Clemens,
I remember he talked me about bathroom scale sensors.
If I link with him again I’ll invite to join as you suggest.

[clemens]

I had an interesting conversation with @iconize from the Beep project. They are also keen to develop a cheap as possible scale design.

So the guys did not rely on the bad information they found about long term weight on ultra low cost cells - as me ;-) - but did proof this information and tested different quality grade cells. Pim is confident that a new scale is doable with this kind of sensors.

I’d like to hear more about constrains. I think software based temperature compensation will be mandatory.

The design is super strong and flat. The only downside is that the film coated plywood is nicely waterproof but also expensive.

[iconize]

@clemens The two wooden plates for a 50x50 cm (Segeberger), or 48x38 cm (Spaarkast) scale are as expensive as €13,- including the cutting. We are also looking into injection moulding a series of 1000 pieces with a very nice design (to be continued), if these proto’s are doing their job well.

[Andreas]

Dear Pim (@iconize),

this sounds very promising. We will be very happy if you could share yet another prototype version with us - maybe the 11th one? We would really like to bring it online for the upcoming period as yet another source for data acquisition and prototype testing at the same location as our Labhive One, where we conducted our first tests. I believe @einsiedlerkrebs will also look forward to it.

Please don’t hesitate to let us know if you need some financial compensation for doing so. While we haven’t received any funding as a group yet, we will certainly find a way to support you.

Cheers from all of us and keep up the good work!

[clemens]

@iconize That’s great to hear. I paid for the wooden plates on my first prototype with “Siebdruckplatten” much more in the local DIY store. I think I bought 21 mm one. You milled some holes in the material for the microcontroller and the cable. What thickness did you use?

[I corrected a typo: we used 21 mm plywood, not 12 mm]

[iconize]

We used 18mm. The milling is done with a simple hand milling machine. Could be CnC’ed at series production

[clemens]

That project Peter Kočalka's Low Cost Bee Monitoring System uses this bad typ of sensors also and beelogger Aufbauanleitung: Waage mit Halbbrückensensoren - Arduino Datenlogger mit Stockwaage für Imker did is test also. Btw Beep switched to more reliable load cells in the meantime!

[clemens]

Btw Beep has changed their scale design and switched to a single load cell / single point setup!

[clemens]

@freedom2000 did a setup with this bathroom sensors also, see H frame or two bar frames? and was not really happy with fluctuation of the measured weight:

@freedom2000

I have assembled my first scale using woden bars and cheap half bridges load cells.

It is working but… there is a lot of drift due to temperature and many other factors not yet understood.
I have implemented temperature compensation which is flattening the curves but not completely. I can see ±500g of variation during a day (±10 °C). And this is still too much…

So I came to the conclusion that these chineese half bridge bathroom scales are more or less unusable for beehive monitoring.

[clemens]

@Tommy had also bad experiences with this setup: Keine stabile Gewichtsmessung mit 4 half-bridge load cells und HX711

@Tommy

The problem can be described as follows: The read values of the load cells prove to be unstable. The following two effects (a) and (b) can be observed:
(a) Measured values are not stable: For example, I zeroed the 4 load cells, loaded them with 4kg and then measured the load_cell output continuously. Within about 45 minutes it changed from -5.63 (beginning) to -2.12 (end). The measurement takes place at room temperature.
(b) Influence “human”: If I come close to the experimental setup during the measurement, then the values also start to pull out clearly (electrostatic influence?). Do the cables have to be shielded?