Weight Sensor Scale Kit - Is this ok?

Other Hardware Sensors
1

Hi,

has anyone experience with one of these kits? (http://www.elecrow.com/weight-sensor-scales-kit-20kg-p-714.html or http://www.aliexpress.com/store/product/Weight-Sensor-Scales-Weighing-Sensor-Kit-20KG-Range-Used-With-HX711-Amplifier/1306340_2004747557.html).
I think about using one of these to measure the weight of a CO2 bottle for my aquarium (to check how much CO2 is left in the bottle). The weight of the bottle including accesories is appr. 10Kg and it is filled with 2Kg of CO2. A resolution of 10gr would be great. 25gr would also be ok. I think most critical is the long term stability. One bottle last 6 to 9 months and I want to monitor when the bottle is empty a few days before it actually happens.

What do you think. Could I achieve this with a kit like that? The nice part about this kit is that it includes all the mechanics.

Thanks for your help in advance
Daniel

2

Looks good for your project. I have some experience with the HX711 and load cells of different ranges.

With most 5kg cells I get a resolution of around +/- 0.2g.
A 20kg load cell will give you roughly a quarter of that resolution then. Way more than you need.

Those strain gauges tend to shift with their output a little over time mostly depending on temperature fluctuations. I think that won't be in a range you need to be concerned about, but im not an expert on that matter. Maybe someone else can give some insight on long term use there.

3

That will work. I think it is expensive, it is a 20kg load cell with two metal plates.
The load cell itself is 6 dollars : load cell 20kg for sale | eBay
And you still need to buy a HX711 and try to make that work with an Arduino.

A good load cell should be compensated by design against temperature changes.

I think it measures different weights when the bottle is placed at the one end or the other.
So you would have to place it on the same spot, every time.

An other option is to buy a scale and only use the load cell that is inside it.
The hanging scales are very cheap.
Search Ebay for : digital hanging scale
That is 2.50 dollars, but it doesn't contain a "real" load cell. See the attached photo.

hanging-scale.jpg
hanging-scale.jpg600×800 53.7 KB

4

Thanks for your answers.
It is good to know that these sensors have such a high resolution. Temperature fluctuations shouldn't be a big issue in my case. The room temperature is relatively stabel (Max-Min no more then 4°C over the whole year).
The different measurement results when placing the load differently shouldn't be a big deal either. I plan to leave the CO2 bottle on the scale till it is empty. Therefore it won't move but it will be there fore a long time. A 2kg bottle lasts for more then half a year.
Regarding the price. I actually thought the price is ok. After some additional searching I also found some load cell for less then 10€ here in europe. But I would need to find somebody to make me the aluminium parts and therefore I don't think that I could safe more then 3 or 4 euros. And organizing that would take me hours. Therefore I think I will stick to the kit.

Thanks again
Daniel