How do the sensors maintain a connection?

Discussion in 'Apple Watch' started by Luba, Mar 25, 2015.

  1. Luba macrumors 6502a

    Luba

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    Apr 22, 2009
    #1
    I believe I read two of the sensors are LED so if the LED light in the sensor isn't being blocked AW thinks it's not on the wrist? Or perhaps the sensors are "feeling" the heat from your skin?

    If AW needs constant full contact (touching the skin), then AW would be very finnicky unless you wear it tightly on your wrist. I don't wear my watches tightly. If I rest my arm on the table I can see half the watch would not have full skin contact. Hopefully, that won't break the AW connection.
     
  2. DreamPod macrumors 65816

    DreamPod

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    Mar 15, 2008
    #2
    The watch is designed in such a way that the sensors are pressed into your wrist, you'd have to wear it *really* loose to keep losing connection.
     
  3. betabeta macrumors 6502a

    Joined:
    Jun 28, 2013
    #3
    It will be very interesting, I know the heart rate app I use is super finicky, and that's on a simple spot with little movement.

    Really on the top of the wrist seems much harder, I mean I don't care I'll shave my wrist if I have to:D
     
  4. Multiverse223 macrumors regular

    Joined:
    Mar 16, 2015
    #4
    My question is, how do people expect to wear a smartwatch, loosely? This isn't an anolog device that you don't interact with. You use the touchscreen, and how do you use a touchscreen if the watch is flopping all over your wrist when you're trying to? Do you really want to have to stabilize the watch whilst interacting with the touchscreen, every time you do? Makes no sense to me.
     
  5. Luba thread starter macrumors 6502a

    Luba

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    Apr 22, 2009
    #5
    Well, there's loose like a wearing a bracelet. I don't
    mean that way.

    The sport band and the leather loop have rigidness built-in so you could wear it loosely. Sometimes you have to. For a band with notches, it's either real tight or you adjust the band one notch bigger and it's loose. The whole backside of the watch would not completely touch your wrist.




     
  6. tgwaste macrumors 6502a

    tgwaste

    Joined:
    Sep 18, 2013
    #6
    I know exactly what you mean. I wear my watches lose too and I've also had the same concern. Well just have to wait and see how it works.
     
  7. Newtons Apple Suspended

    Newtons Apple

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    Mar 12, 2014
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    Jacksonville, Florida
    #7
    Unless you wear your watch pretty tight the sensor will not do well at all. It uses the same principle as other HR sensors and it must contact the skin tightly to be accurate.
     
  8. marvz macrumors 6502a

    marvz

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    Berlin
    #8
    For workouts you should wear Apple Watch more tightly and some 1-3 finger widths from your wrist so that the HR sensors work best.
     
  9. zacheryjensen macrumors 6502a

    zacheryjensen

    Joined:
    May 11, 2009
    #9
    If you want this watch to work properly, you're going to wear it differently. You're going to wear it the way a watch is supposed to be worn, tight to the wrist. It will have to be tight enough that it doesn't slide around on its own. That's the best guide.

    I've been wearing watches a LONG time and sometimes I have them looser, but, I find when I tighten them up to the point the the Apple Watch will require, it feels too tight... for about a day, but, then I get really used to it and prefer it greatly over a loose floppy watch. It's not to be able to rely on the watch facing being in the same spot relative to my arm position at all times.

    If you're a watch wearer, maybe you should adjust it accordingly and start getting used to the feeling now, assuming you have a comfortable band.

    With regards to the rubber band with notches, if it's anything like the rubber band I have on my wrist-worn HR monitor, it will be stretchy enough to cope with a wrist that seems sized "between" notches. Just start by stretching it tightly as you can then notch out until it no longer feels like you're getting your blood pressure taken :)
     
  10. Julien macrumors G3

    Julien

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    Jun 30, 2007
    Location:
    Atlanta
    #10
    Where are you guys getting this info about the band needing to be tight on the wrist from? I have not seen any info produced by Apple about the need to have the watch tight. Here is a pic from the Apple site that shows a good bit of slack in the band. Look at the slack in the bottom strap.

    [​IMG]

    [​IMG]
     
  11. kovey macrumors 6502a

    Joined:
    Apr 10, 2011
    #11
    That looks like a render. If you expect to tell how tight the watch is by looking at that, reddit has some mysteries for you to solve.
     
  12. Julien macrumors G3

    Julien

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    Atlanta
    #12
    It may be Photoshopped but it is done by Apple to accurately represent the wearing of the :apple:Watch. This is not some uniformed 3ed party pictures.
     
  13. kovey macrumors 6502a

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    Apr 10, 2011
    #13
    It doesn't matter. To somehow use that picture to determine how tight you must wear the watch is ludicrous.
     
  14. Julien macrumors G3

    Julien

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    Atlanta
    #14
    I'm not claiming to know. I'm questioning how others KNOW it must be worn tight without any source as proof. I'm simply offering anecdotal evidence that it may not need to be worn tight. Here is a NON Photoshopped image of someone who SHOULD know how it must be worn and it is NOT tight.

    [​IMG]
     
  15. kdarling macrumors demi-god

    kdarling

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    #15
    The heart rate sensors shine an LED into your skin and look at the amplitude change of the reflected light over time. This change is very tiny, btw.

    ppg-blood.jpg

    So to see if it's still on a wrist, it's probably using one of the sensors to just check for any reflection at all, somewhat like the phone's face proximity sensor, (but probably much less often in order to conserve power).

    That way, the watch can be worn pretty loose when you're not interested in pulse reading.

    We'll find out soon enough, when someone tests it by putting something under the watch body and seeing if it can be removed without the watch noticing :)
     
  16. Newtons Apple Suspended

    Newtons Apple

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    Jacksonville, Florida
    #16
    It uses the same technology as other HR devices and the watch will HAVE to be tight against the wrist for at least 15 seconds.
     
  17. Julien, Mar 26, 2015
    Last edited: Mar 26, 2015

    Julien macrumors G3

    Julien

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    #17
    I have been skeptical about the optical HR sensor since it was announced. If it is on par with other wrist based optical HR sensors then it will be totally worthless for fitness (especially running) monitoring no matter how tight you have the band. See CNet test for just how BAD and inaccurate they are.

    http://www.cnet.com/news/how-accurate-are-wristband-heart-rate-monitors/

    However the QUESTION is has Apple perfected the optical HR sensor the way they have done with other technologies, like Finger Print ID (though acquired tech) or Force Touch on the new MacBook?

    Apple has stoked expectations that it won't just be another crappy optical HR sensor, but will be a bonafide accurate fitness tracker. If Apple has done this then we CAN'T say it must be worn tight.

    If it IS just another optical HR sensor then there will be many disappointed athletes who will feel duped by all the fitness accuracy hype Apple has promoted.

    I plan on comparison testing on April 25 to find out (although we will probably see fitness reviews when the embargo is lifted).

    Here is a post I made in Sep. http://forums.macrumors.com/showpost.php?p=19930433&postcount=2

     
  18. kdarling macrumors demi-god

    kdarling

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    #18
    I embarked on a crash course to learn about wrist based pulse sensors, and it's fascinating how many papers have been written on various methods / attempts to make them more accurate. It's like attempting to find the Grail of cheap sensors.

    Here is some of what I've learned:

    The way these things work is that they shine either red + infrared LEDs (for pulse and oximeter readings), or more recently a green LED (pulse only) into your skin.

    Each LED is pulsed anywhere from 25-500 times a second, along with a dead period to check for ambient light as a base reference.

    A photodiode reads the amount of light reflected back by the blood in the arteries under your skin. IR reflects most from hemoglobin with little oxygen, Red reflects most from oxygenated blood. Green doesn't go as deep and is better with darker skin and ambient sunlight IR.

    The main problem with using the top of wrists is that it's not reading arteries with a true pulse (like at the end of your fingertip). Instead, it's reading from tiny capillaries, where the actual blood pulse has been dampened and spread out, which is why wrist readers are usually quite inaccurate at higher rates.

    Also, movement adds difficulty. Not just mechanical movement where the sensors aren't tight against the skin, but blood movement within the body caused by the person moving their arm around or even breathing heavily.

    Again, here green LEDs help somewhat because they don't read as deep. Also, offset sensors can be used to help cancel out signal noise. Which might explain the slightly odd arrangement on Apple's device.

    The upshot is, everyone from major companies to students writing for a Master's degree, have tried to crack the wrist nut, and so far has succeeded only in pieces. So it'll be interesting to see if Apple's hired guns have done any better.
     
  19. Newtons Apple Suspended

    Newtons Apple

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    #19
    There is no magic when it comes to this type of sensor. How it works is simple but until someone comes up with a different method that will fit in a watchit will have to do. I predict it will be quite inaccurate. To get a good reading you will have to hold it against the arm for about 15 seconds so it can settle down.
     
  20. Julien macrumors G3

    Julien

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    Atlanta
    #20
    There are a couple of companies (Valencell and Mio) that licenses a lot of the optical technology used in the optical HR monitor industry. It's fairly certain Apple has developed their own proprietary system in house.

    While Apple is famous for sprinkling fairy dust on existing technologies, it is always at least a mature/acceptable technology before receiving Apple's 'magical' interpretation. Usually if the technology is not perfected Apple will ignore it, avoid it or dramatically improve it.

    I just can't see Apple releasing an optical HR sensor that is as mediocre as the rest of the industry. It seems like they would have avoided it altogether or added a standard BT HR strap for when exercising. Relegating the optical for every day general use monitoring.

    Instead Apple is full on hyping the accuracy of the fitness aspect of the :apple:Watch without stipulating the need for a HR strap. No doubt Apple is painting themselves into a corner and it MUST be a breakout improvement or risk embarrassment.

    One thing is for sure. In September we were looking at a long void in finding out how the optical will work. Now we are down to a few weeks.
     
  21. kdarling macrumors demi-god

    kdarling

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    #21
    A lot of the smartwatches being made these days use a Texas Instruments heart rate sensor chip, which controls the LEDs / detectors and includes software to calculate the rate.

    Mio claims to have super accurate sensors, and at first I thought they must have figured out the magic, until I read reviews saying it wasn't accurate and/or you had to wear their band way up on the arm.

    Yes, often that's true.

    I dunno, Julien. Compare the way that they use "precise" all over the place... EXCEPT when it comes to the HRM, where that overused word disappears and is replaced by the much more vague sounding "helps".

    Example: Apple marketing descriptions of non-HRM items:
    Then what they say about the HRM:
    So to me, they're avoiding talking about HRM accuracy, and instead making it sound helpful.

    Consider: if they had made an accuracy breakthrough, wouldn't they be shouting it from the rooftops? I mean, they overuse "precise" and "accurate" for things that are usually that way, yet avoid those words for the HRM.
     

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