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Electronics & Test

Teardown: Fitbit Flex

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tekochip
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Platinum
Two Vendors?
tekochip   12/16/2013 3:48:37 PM
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I've got to say that was the most aggressive teardown yet and for the most diminuitive product; a bone saw and a Dremel?
 
Interesting that they used two different BLE parts for their product, I wonder why they didn't settle on a single vendor.


RichQ
User Rank
Platinum
Re: So many
RichQ   12/16/2013 3:37:28 PM
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Cadman, there is a wristband in the works that uses optical sensing to measure blood sugar and the like, although they recently backed off from that claim under FDA pressure. The Airo wristband is discussed here: http://www.engadget.com/2013/10/28/airo-wristband/

As to the guy dropping dead at 26, chances are that was not a heart attack (which is a plumbing problem) but sudden cardiac arrest (SCA - which is an electrical problem). Under SCA the heart loses its rhythm and so becomes ineffective at moving blood around. A defibrillator unit can restore the rhythm, and if done within a few minutes of the collapse can save the life often with no residual damage. SCA happens to all ages - my son was taken from me at 15 with it - and it's a big killer of student athletes but few know about it because it is often undiagnosed and is unrecognizable post mortem. Unlike a heart attack, which leaves a chemical trace, SCA leaves no clue that it is what has occurred. Check out the Sudden Cardiac Arrest Association for more info.

kenish
User Rank
Platinum
Re: Mega technology in a small package
kenish   10/14/2013 3:17:39 PM
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Also, when the pieces separate under X-acto pressure, some unintended finger surgery may be an unintended byproduct along with a possible tour of the local ER.  At least clamp the metal portion in the nice bench vise shown in images 10 and 14!

Cadman-LT
User Rank
Platinum
Re: So many
Cadman-LT   10/9/2013 2:19:01 PM
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By the way did I mention I don't care for fitness nuts? Ever hear about the guy....ran 20 miles every day...picture perfect of health. Just collapsed of a heart attack for no reason at age 26. It happens all the time. Then you hear about some 104 year old that says to live long "smoke, drink, and have a lot of sex" lol

Cadman-LT
User Rank
Platinum
So many
Cadman-LT   10/9/2013 2:15:12 PM
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They make all these things to track your fitness. Cause some of us are working out. I would like one to track my blood sugar level. I mean if they can measure all this other stuff, why not your blood sugar. Wear it on your wrist, poke you every 20 minutes or so and you don't notice...boom! Way better than "how many calories did I burn walking up the stairs?" 

rathomas
User Rank
Iron
Re: What FitBit measures and does not measure
rathomas   10/4/2013 1:38:58 PM
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The Fitbit Flex does not measure altitude, so it can't keep track of stairs climbed.  I've got a Flex and I like it, but in hindsight I'd have done as well getting the Fitbit Zip for $40 less.

I've also worked out the data dump (from tracker to computer) protocol; check libfitbit issue #46 at github for links to documentation.  Good news is the data is encrypted.  The bad news (if you are inclined to want to "own your data") is also that the data is encrypted.  I think I've worked out the basics of the encryption mechanism, but have no crack yet as I'm not a crypto guy :(

For now, I'm logging every data transaction in an effort to gather some statistical data on the keys used.

 

Ken E.
User Rank
Gold
Re: But how does it acquire physiological data from our body?
Ken E.   10/4/2013 12:15:33 PM
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Ambul8ory, thanks for so totally popping my balloon!  This would be a very expensive 'toy'.  Perhaps like some of the Polar wrist units, they plan on a heart monitor accessory.  (Polar also has an itsy bitsy bracelet similar to this.)

Why would 5-day battery life have anything to do with any of this?  I assume you are dumping the data regularly, and they merge all that together.

I can imagine a sensitive accelerameter, processor, and clever software attached to the wrist might be able to pick up the motions of a pulse on the wrist eventually, especially with a snug wristband.  You can take your blood pressure with wrist cuffs, so maybe you could get to heartbeat in a number of ways.  I never say 'can't' when it comes to electronics these days, what amazing things are done!

Tom Loughney AJ4XM
User Rank
Iron
What FitBit measures and does not measure
Tom Loughney AJ4XM   10/4/2013 12:08:32 PM
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FitBit in the ONE model measure 3 things: accelleration, altitude, and time. The FLEX does not have the altimeter but does have LED's that display progress twards a preset goal. They have different programming since the Flex is on your wrist all the time and the ONE goes on or in a pocket or on your Bra and only goes on the wrist when sleeping. Even though the battery lasts about 5-6 days you sync with your PC daily in normal use and it stores moinths (maybe years) worth of data.

It uses a 3-axis accelerometer to determine how many steps you take. This is quite different than a traditional pedometer that ataches to your ankle. You can make FitBit more precide ny inputting the normal distance taken with each step when walking or running. This is done with the PC software not on the device. Doing this will give you a more accurate indication of how many steps you take. If you do not do this it will use your height input and an average step length.

The ONE measures altitude with an almimeter that is based oin 1 story equaling 10 staris and count the combination of 10 steps and an increase in height as walking up 1 flight of stairs. This is reasonably accurate and gives a valid comparison. If you live, work or erercize where you have 12 smaller steps or 8 larger ones you can make some adjustment for that. It does a lousy job of measuring climbing ladders because the height is there bujt the forward motion is not and it uses both of those to calculate you are climbing a flight or stairs. I regularly go up a 30 foot extension ladder and it never sees that as climbing stairs becuase the angle is too steep. So that is a little refinement that needs to be done in their algorithms.

If you walk faster it sees that as higher activity level using the steps taken and the time it takes. If you run or jog it sees that as a still higher activity level the same way. It also uses the timer to measure how long you sleep. You start a counter (by bressing a small button) when you go to bed and then again when you get up. That gives you total in bed time. Attached to your wrist it measures when you stop moving around and equates that with sleep. If you toss and turn it sees that as awake time (even if you are not fully awake) and the next day when you sync with your PC it records that. You can also input or edit it manualy. It has a general setting and a more sensitive setting for people who use a CPAP or such. It does some basic math to give you an efficiency value and total time vs sleep time. It is not the most accurate way to measure sleep but for the price does give you some useful information.

It has a small vibrator that you can set as a silent alarm to vibrate on your wrist to wake you up with out waking up your partner. This work for some people. It has never woken me up and I turned it off which lengthens battery life. I like the idea and it was one oif the key reasons I got a FitBit but it is just too weak of a vibrator.

The other values that the software stores are mostly input manually. It does not measure your pulse/heartrate, blood pressure. glucose, etc. You still need traditional devices for that. I have a SportLine watch that does a great job for pulse rate which is essential for exercizing, and a MicroLife blood pressure automatic tester which is just superb and a fantastic compny to deal with that really stands behind their products.  I don't have a glucose issue so I do not test that.

You can use the FitBit ARIA scale which will communicate with the device to get your weight and BMI. It costs about $125 and seems way overpiced to me. I have a scale that gives that data and more but have to input it manually.

You can use the PC software to keep track of what you eat during the day and input it manually. It essentially just counts calories but it does total fat and a few ither basics. They have thousands of food items already in their database but mostly I still have to put in what I buy because the sources they use are not where I live except for a few restraunts which I do not eat at much. But once you start getting stuff in it is pretty easy to do it. Allow about 10-15 minutes a day.

Data is all stored online on their system so you can access it anywhere which has some advantages. I would definitely recommed the FitBit One (which I like better) or the Flex. It would have been nice to use Bluetooth 3.0 which is everywhere and not 4.0 which is mostly limited to the newer iPhones, iPad3 or some Samsung 3 and 4 models that do Bluetooth 4. I do not see any advantage they got from doing that.

ambul8ory
User Rank
Iron
Re: But how does it acquire physiological data from our body?
ambul8ory   10/4/2013 11:52:27 AM
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This device does not provide heart rate - it is just an accelerometer. There are a plethora of accelerometer based 'toys' since the power consumption of MEMs devices has fallen. It is possible to measure heart rate in free living and during sports or high intensity activity (do a web search for Actiheart).

Wrist worn accelerometers are useful for specific applications - the measurement of sleep basically looks at periods of inactivity and tries to decide if the person is sleeping. This means that if the person lies very still, the device will (wrongly) think that they are asleep. This field is called actigraphy and is very useful in the professional world for pre-screening of sleep and circadian rhythm disorders. However a device such as the fitbit is not really useful for this application as the battery does not allow any more than 5 days recording (and most likely less).

Also measuring steps and physical activity with a wrist worn accelerometer will provide dubious results at best. Think how your arms move as you walk (or if you keep them in your pockets). For calories, consider how many calories you burn while cycling - your wrist is not moving hence the device will grossly under-estimate this.

If you want a rough guess of these parameters then this 'toy' will provide it. If you want accurate, validated results then look elsewhere.

Ken E.
User Rank
Gold
Re: But how does it acquire physiological data from our body?
Ken E.   10/4/2013 10:32:15 AM
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From the article- "newest pedometer/heart-rate monitor/sleep-tracker wristband".

That said, the Fitbit web-site site doesn't claim heart-rate for the Flex, unless I missed it somewhere.  Regardless, the measurements they purport to derive are incredible.  Believable, accurate?  I hope so.

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