Accuracy of Fitbit Aria below 9kg?
March 21, 2015 4:22 PM Subscribe
I need to find a wireless connected scale to measure objects, none of them very heavy. The scale needs to have an API with which to retrieve the weight readings.
For various reasons, including system compatibility and short timescales, I'd prefer to use the Fitbit Aria if at all possible.
However, it looks like the minimum weight for accurate readings is 9kg. Can anyone tell me anything about how accurate the Fitbit Aria is *in practice* for weighing items lighter than this?
Response by poster: Not wishing to threadsit, but I need to clarify something important. The items will be left in situ and one item taken away or put back each time, which I would hope would trigger a new weight reading. Maybe the Fitbit Aria doesn't work like this at all, regardless of how heavy the items are. If I used something to increase the weight, that would also have to remain in situ.
posted by tel3path at 4:35 PM on March 21, 2015
posted by tel3path at 4:35 PM on March 21, 2015
Best answer: Yeah that won't work with most scales I know of, although I can't speak to the Aria in particular. They're usually triggered by someone stepping onto them, and it probably has to be a fairly heavy thing.
posted by RustyBrooks at 4:50 PM on March 21, 2015
posted by RustyBrooks at 4:50 PM on March 21, 2015
The Aria doesn't work like that. You step on to it to take a measurement and then it syncs to the cloud. You'd have to step off and then back on to trigger another reading.
posted by mmascolino at 9:03 PM on March 21, 2015 [2 favorites]
posted by mmascolino at 9:03 PM on March 21, 2015 [2 favorites]
Can you describe your actual use case? There are plenty of lab balances That can be connected to a computer that would probably do a lot better for you than a consumer- focused scale for people.
posted by rockindata at 11:07 AM on March 22, 2015
posted by rockindata at 11:07 AM on March 22, 2015
Best answer: rockindata is right. There are a ton of commercial scales that will talk to computers out of the box, and you can definitely find one appropriate to your application.
In terms of API, the ones that I've used have an RS232 serial interface that constantly streams (at 9600 baud or whatever) the mass being read. You could easily hack something with a pc or even like a raspberry pi with an RS232-to-USB converter.
posted by mr_roboto at 1:08 PM on March 22, 2015
In terms of API, the ones that I've used have an RS232 serial interface that constantly streams (at 9600 baud or whatever) the mass being read. You could easily hack something with a pc or even like a raspberry pi with an RS232-to-USB converter.
posted by mr_roboto at 1:08 PM on March 22, 2015
It's really impossible to give you useful advice here without knowing more about what you're actually trying to do.
No off the shelf scale indicator is going to give you a reading each time the weight settles to a new value. Some will, as mentioned above, give you a new reading if the weight returns to zero then settles on a new value. Otherwise you will be looking for continuous transmission, and you will have to write your own rules and implement the data collection. Pay attention to motion stability, a lot of programmers who dont' know scales forget this.
Realistically the only interface you are likely to see (especially if you're looking for something cheap) is RS232. Data packets vary widely in exactly what they contain so you'll need to be flexible about start and end packet characters, which part of the packet to parse the weight from, and other dangers like motion, wrong units, net instead of gross mode, etc.
You also need to determine whether your application needs to be legal for trade. If money will change hands -- even if it's determining that your bottle of BBQ sauce really contains 16 ounces, or printing the weight on a shipping document -- you have to conform to a bunch of anti cheating laws most people don't even know exist. You will need to use a platform and indicator (often sold separately in the industry) that are NIST certified, which about doubles the cost at the low end.
I recommend that you open the local phone book -- yes, that thing made of paper -- and look up "scales." There should be a few little businesses around doing local distribution for the national manufacturers. Get one of them to show you what's available, whether you can afford it or not, in the form factor and functionality you are needing. Then you'll be in a much better position to frame this question in a way that can be usefully answered.
You can memail me if you want more info. I have worked for one of those scale distributors myself for 30 years.
posted by localroger at 4:24 PM on March 22, 2015
No off the shelf scale indicator is going to give you a reading each time the weight settles to a new value. Some will, as mentioned above, give you a new reading if the weight returns to zero then settles on a new value. Otherwise you will be looking for continuous transmission, and you will have to write your own rules and implement the data collection. Pay attention to motion stability, a lot of programmers who dont' know scales forget this.
Realistically the only interface you are likely to see (especially if you're looking for something cheap) is RS232. Data packets vary widely in exactly what they contain so you'll need to be flexible about start and end packet characters, which part of the packet to parse the weight from, and other dangers like motion, wrong units, net instead of gross mode, etc.
You also need to determine whether your application needs to be legal for trade. If money will change hands -- even if it's determining that your bottle of BBQ sauce really contains 16 ounces, or printing the weight on a shipping document -- you have to conform to a bunch of anti cheating laws most people don't even know exist. You will need to use a platform and indicator (often sold separately in the industry) that are NIST certified, which about doubles the cost at the low end.
I recommend that you open the local phone book -- yes, that thing made of paper -- and look up "scales." There should be a few little businesses around doing local distribution for the national manufacturers. Get one of them to show you what's available, whether you can afford it or not, in the form factor and functionality you are needing. Then you'll be in a much better position to frame this question in a way that can be usefully answered.
You can memail me if you want more info. I have worked for one of those scale distributors myself for 30 years.
posted by localroger at 4:24 PM on March 22, 2015
Response by poster: Thanks, everyone. To be clear, I have already implemented a digital kitchen scale with a custom designed circuit board to output the weight readings. I programmed it to detect weight changes as a component of a larger system. I don't have any more of the circuit boards because they were made for a limited set of prototypes, and I don't have the ability to make any more myself. Now they want two more of these assemblies and they specifically want to know if the weight reading can also be done wirelessly.
The entire assembly, which consists of several other components, is manually powered on and off, but most wireless scales seem to be always-on and to detect weight changes by step on and step off. That means that there's probably no wireless scale that will suit our system in its present form.
posted by tel3path at 3:08 AM on March 24, 2015
The entire assembly, which consists of several other components, is manually powered on and off, but most wireless scales seem to be always-on and to detect weight changes by step on and step off. That means that there's probably no wireless scale that will suit our system in its present form.
posted by tel3path at 3:08 AM on March 24, 2015
Response by poster: My editing window got stuck. I have a couple of circuit makers marked in the yellow pages that could probably make me a couple of chips based on the circuit diagrams, but the complicating factor is that I don't trust the person who made the circuit diagrams. Additionally, they're not as accurate in the field as I want them to be. This is more reason for me to want to use something wireless.
And another reason for wanting to use a commercial off-the-shelf solution, especially one compatible with fitbit, is because the APIs we have for our endpoint have recently been made compatible with fitbit.
What I think I'm going to do is change the overall system design so that the scale can stand alone and doesn't have to be connected to the rest of the assembly, nor to have items left on top of it in situ. There are withings scales that are able to read below 9kg and are compatible with Fitbit, so I'm probably going to use one of those.
posted by tel3path at 3:13 AM on March 24, 2015
And another reason for wanting to use a commercial off-the-shelf solution, especially one compatible with fitbit, is because the APIs we have for our endpoint have recently been made compatible with fitbit.
What I think I'm going to do is change the overall system design so that the scale can stand alone and doesn't have to be connected to the rest of the assembly, nor to have items left on top of it in situ. There are withings scales that are able to read below 9kg and are compatible with Fitbit, so I'm probably going to use one of those.
posted by tel3path at 3:13 AM on March 24, 2015
Response by poster: So a follow-up is in order:
To answer my original question, and swapping the Fitbit Aria for a Withings (since Withings is compatible with Fitbit): I had high hopes for the Withings because it purported to be accurate from 0kg. However, I found that it wouldn't respond at all when I put lighter-weight objects on it. So the answer to my original question is: no.
Which is not to disparage the accuracy of the Withings scale, because if I picked up the lighter-weight object and stood on the scale, it was impressively accurate and consistent. It's just too bad that that was completely unhelpful for my use case.
Now, I acknowledge that even if the Withings had been able to register the lighter-weight objects, I would have had to redesign the overall system to make it fit my use case. However the answer to my question as originally posed is: nope.
So what I did was: I took the incomplete and ambiguous paper schematic that I had, scanned it, and added some shitty .jpgs of the original PCB in context. Then I shopped it around several custom PCB manufacturers, and picked the one that didn't charge for redrafting. I asked them to redesign the original PCB to make it more stable and robust, and so far they've done what they said they'd do: straight out of the box and a bit of crimping and soldering later, and we have a big improvement on the original prototype. It was a straightforward swap of old component for new.
If anyone wants more details feel free to memail me.
posted by tel3path at 7:54 AM on July 26, 2015
To answer my original question, and swapping the Fitbit Aria for a Withings (since Withings is compatible with Fitbit): I had high hopes for the Withings because it purported to be accurate from 0kg. However, I found that it wouldn't respond at all when I put lighter-weight objects on it. So the answer to my original question is: no.
Which is not to disparage the accuracy of the Withings scale, because if I picked up the lighter-weight object and stood on the scale, it was impressively accurate and consistent. It's just too bad that that was completely unhelpful for my use case.
Now, I acknowledge that even if the Withings had been able to register the lighter-weight objects, I would have had to redesign the overall system to make it fit my use case. However the answer to my question as originally posed is: nope.
So what I did was: I took the incomplete and ambiguous paper schematic that I had, scanned it, and added some shitty .jpgs of the original PCB in context. Then I shopped it around several custom PCB manufacturers, and picked the one that didn't charge for redrafting. I asked them to redesign the original PCB to make it more stable and robust, and so far they've done what they said they'd do: straight out of the box and a bit of crimping and soldering later, and we have a big improvement on the original prototype. It was a straightforward swap of old component for new.
If anyone wants more details feel free to memail me.
posted by tel3path at 7:54 AM on July 26, 2015
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I'd recommend finding something heavy and easily stackable. I'd probably use 2 25lb barbells and a wooden board. Then put what you want to weigh on top. Subtract the weight of your extra stuff from the readings later (in excel or a little script)
posted by RustyBrooks at 4:26 PM on March 21, 2015 [2 favorites]