Like one that would take like 10lbs to depress? I’m thinking about making a dog food low indicator. Thx
I haven't, but for 10 lb you could probably use a pressure mat. Look up the projects people have done for things like couch occupancy or doormat sensors with one of these hooked up to an Ecolink contact sensor (or others with the ability to connect external sources). I'm not really sure a button would work well here anyway--most probably won't fare well with a normal state of depressed (it would need to send something on release but also not, say, drain the battery while it waits for "you" to let go).
Thx, the problem is I don’t want it to report less than 10lbs. Those things “close” at like 5 lbs
Yeah, it depends on the mat. Mine is supposed to close at more than 1 psi, which is good for telling if someone is sitting on my (cheap...thin cushions) couch. There are "pet resistant" models with a higher threshold, but then I'm not sure they'll be sensitive enough for this case. There may be some in-betweens.
Can I ask where you found it?
My exact mat is this one from Amazon: https://www.amazon.com/gp/product/B00GUNX7WY. It works fine for my purpose (coupled with a Monoprice contact sensor; I'd have done the Ecolink if I did this again), though I can't help but wonder if people with larger couches or heavier cushions might want a "pet resistant" one.
I am not sure these would be useful to you. But, I thought that I throw in some idea that may help.
@ogiewon played around with pressure sensor in his Hubduino. There is a way to adjust that project with smaller sensor for lighter weight measurement. This is a good solution for DIYer.
There is also a way to use scale. There are a couple path to do this. Again, you can build one which you can plan and design on how you would connect to Hubitat. I make my own sensor. I had played around on interfacing to a scale once.
If you are looking to purchase one, unfortunately, there is not specifically Hubitat friendly connection. But there are plenty Bluetooth scale like below.
There are more availability if you can use Human weight scale.
Going from Bluetooth to Hubitat still have some DIY aspect that you need to do. I started to make my BLE gateway so that we can connect Bluetooth devices to our hub.
Most of the electronic scales on the market are not designed for continuous measurements, but rather instantaneous readings before they power off in about 10 seconds. It is also worth considering that they also self-zero on power, so leaving something on it will not work.
I'm shocked that a DIY project isn't out there already to stick force sense resistors under furniture legs or a small platform for detecting occupancy or weight. I was using them to detect when the hot end nozzle of my self-designed 3D printer touched the glass so that the controller could self-calibrate, and was just thinking that the same basic scheme could be used to monitor BBQ propane tank levels or even the remaining water bottle capacity on my 5 gallon bottom-loader water cooler.....
Another approach is going back to high school physics and lever theory. Instead of dropping the object on a switch directly, drop it on a lever and slide the switch towards/away from the fulcrum until you find the sweet spot for your target alarm weight.....
This is a good point about load cell and scale in general. But, there are some countermeasure to minimize the need to tare/re-zero. Here is a good tutorial about load cell design. It is an interesting reading. If you go step by steps, at the end has what we call "full bridge" setup. It should be quite stable and repeatable.
In addition, since we have our hub, we could have some businness logic (AI model) to automatically auto "tare" the scale. For example, as the OP case, when the bowl is taken out for cleaning, there should be a jump on measurement to value close to zero (but perhaps not 0). We could write an application to automatically tare the scale by monitoring this type of jump. This is one of smartness that you can add to the scale.
On a lark I found this USB Scale Wedge Keyboard Wedge Software | USB Scale Wedge Best Keyboard Wedge Software | TALtech. Might be able to get it integrated.