# Weight sensor?

#1

I’m looking to add a weight sensor to my Cayenne project.

In short, I use a CO2 bottle for an aquarium, and while it has a guage, the nature of a liquid fill means the pressure holds very steady until about 5 minutes before the cylinder runs out.

One thing that will change is the weight if the cylinder as the CO2 is used up.

Can I modify some electronic kitchen scales to generate a signal? Are there alternative ways to return a signal based on the weight of an item?

All suggestions very welcome.

PS. I await the webcam facility with eagerness!

#2

i have the same issue with my CO2 tank… shows plenty until 5 min before its out. lol. I’m not sure about modifying a kitchen scale. Maybe if you found one somehow that uses resistance for its weight but would still have to plot out the weights. Checkout these, might be easier…

#3

So would the load cell bar hook directly to a raspberry pi and Cayenne could treat it as similar to a temp sensor - graphing the output over time. In which case this is ideal!

Liquid CO2 will stay liquid at around 50psi, so when full, the cylinder contains mostly liquid with a small gas head at 50psi. As gas is released, this is replaced from the liquid, but the head remains at 50psi. It’s not until the liquid is used up and only gas remains that the pressure in the cylinder falls below 50psi - and with cylinders being small, you probably have less than a litre of gas remaining!

Weight on the other hand decreases steadily!

#4

For greater accuracy, you need to know the max load, needed resolution and build in a tare function to zero the scale when unloaded.

Then you can select a load cell, and configuration that better fits your needs. If a coarse range is enough, then you can probably do it with a single load cell, but if you need more resolution and accuracy, then you’d get 4 of them and arrange in a wheatstone bridge configuration.

I am working on a project to modify a bathroom scale. For my application, my maximum is 100 lbs. My minimum is about 50 lbs, and my increments need to be about 1 lb. I want my resolution to be at least 4 times my needed increment, so I need at least 1/4 lb resolution. Thus the components in a bathroom scale are ideal for this application. Paired with an amplifier you can get from SparkFun.

Cheers,

Craig