iPhone 5s accelerometer bug linked to new chip

iPhone 5s accelerometer bug linked to new chip

Summary: There's an issue with the iPhone 5s accelerometer and a developer has pinpointed a change in hardware suppliers as the potential culprit.

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TOPICS: Apple, Hardware
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iPhone 5s accelerometer bug linked to new chip - Jason O'Grady
(Image: Gizmodo)

Several outlets have been reporting on an apparent hardware bug in the iPhone 5s accelerometer/gyroscope (see CNETGizmodoExtremeTechApple Support Communities, and MacRumors). The defect manifests itself in accelerometer-based apps and Apple's Compass app, which show discrepancies of as much as 8 to 10 degrees compared to the iPhone 5.

In the gifimation above, Gizmodo discovered that EA's Real Racing 3 (running on a level plane) immediately registers a phantom leftward tilt when you start a new race on the iPhone 5s.

RealityCap, a developer of 3D APIs, theorizes that the bug may be in the new Bosch Sensortech accelerometer, a new part supplier in the iPhone 5s. In a blog post RealityCap CEO Eagle Jones points to the Chipworks teardown of the iPhone 5s, which identifies a Bosch Sensortech BMA220 accelerometer in the new flagship iPhone 5s. The iPhone 5 uses a STMicroelectronics LIS331DLH part according to iFixit.

Apparently all accelerometers aren't created equal. Jones poured over the ST and Bosch datasheets and drew these conclusions:

Accelerometers have two key numbers that tell you the quality of their outputs. Note: in the spec sheets, and the next couple paragraphs, the abbreviation mg refers to milli-g, or one one thousandth of standard gravity, not milligram. The first key spec is the noise density (ST) or output noise (Bosch). This tells you how much random jitter you will see in measurements. At first it looks like the spec for the Bosch part is much worse, but this is deceiving as these numbers are reported for a specific measurement rate (bandwidth), and the ST datasheet doesn’t specify that rate. In our measurements, the noise output of the accelerometer in the iPhone 5S is reasonably similar to that of previous iOS devices.

The second key spec for accelerometers is the zero-g offset, or bias. This indicates the range for a roughly constant offset that will be added to every output sample of data due to manufacturing variance. This can also change over time due to mechanical stress or temperature variation. This is where we find the problem: the typical bias for the ST part is +/- 20mg, while the Bosch part lists +/-95mg. This almost 5x greater offset range is confirmed by our measurements, and is absolutely consistent with the failures being reported by users and the media. Specifically, a +/- 20mg offset range would translate to around a +/-1 degree accuracy range in tilt detection, and a +/-95mg offset translates to +/-5 degrees in tilt.

Jones notes that both parts cost about one dollar in quantity making it unlikely that Apple switched suppliers to save money. His theory is that Apple chose the Bosch part based on its lower power consumption (in normal mode the Bosch part uses 450μW and the ST part uses 625μW), concluding that it's a poor tradeoff for the inherent inaccuracy.

Unfortunately, hardware defects can't be patched with a simple iOS dot release. Luckily, Jones thinks that developers can work around the chip flaw by incorporating a calibration procedure into their apps - like the Compass app does when you first launch it. This would allow the app to determine the accelerometer bias which can then be subtracted from the data coming from the accelerometer to get a correct reading.

I compared Compass.app my iPhone 5s to my wife's iPhone 5c and they were pretty close, which appears to validate reports that both new iPhones use the same Bosch part. (I don't have an iPhone 5 on hand to compare them to). There's a 70-page thread discussing the issue on the MacRumors Forums, if you'd like to follow the blow-by-blow. 

Topics: Apple, Hardware

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10 comments
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  • You're moving it wrong.

    Just waiting for the Apple explanation...
    dodonfred
    • There is nothing wrong with the device.

      You can calibrate the level by simply touching it. It will reset itself to the level after turning red and will level off at 0* green. Now you are calibrated.
      Simple.
      kpdaman
  • Hardware only fix

    Ugh, and I was just about to trade-in my iPhone 4S for the 5S ... oh well, guess I'll have to wait for the 6.
    Rob Ainscough
  • That's why I don't buy iPhones

    It isn't that the previous iPhones haven't been generally decent hardware devices for the most part. It's that your choice of buying an iPhone today and the resulting costly investment into that ecosystem locks you into buying future new iPhone hardware without ever being able to evaluate them first to ensure that the hardware and software continue to conform to your particular evolving needs.

    You're expected to assume that iPhones will always have the screen size and other hardware features that you will need in the future despite the fact that they only make one new model at a time over a period of a year or two. Frankly. that's illogical. You're expected to assume that Apple's build quality will remain unchanged and their phones won't get more fragile as they make them thinner and thinner simply because they're selling their $200 worth of hardware at the highest prices in the marketplace. Only foolish people assume that highest prices automatically means highest quality...and I make no apologies for saying this. Time and time again, I'm seeing increasing signs like this one above of Apple's blatant failure to adequately test their phone hardware and software updates before public release. This is something that should NEVER have been missed by a company that only designs one measly new phone a year and charges a massive premium for them. How can you call yourself a premium company and insist that you be paid premium price while making novice slip-ups like this defective accelerometer hardware with the one phone update you've been working on all year?
    eMJayy
    • iPhone Premium.. you've got it in one!

      Apple give the illusion of being a premium brand.. it's in the way they market.. it's in their pricing.. Apple is cool.. right? Ok, if they are so cool.. why is the iPhone pretty much the ONLY premium phone without gorilla glass? And as eMJayy rightly says, Apple takes a full Year to develop a phone and they still get it consistently wrong.. remember antennagate? And there have been lots more examples. Everyone I know who has an Apple phone has it in a cover.. why? Because it's too fragile to not put in a cover is the answer I get.. I don't want a phone I have to cover up to protect it. I've tried Apple and I won't go back.. give me Android or windows phones any day.. at least the manufacturers aren't full of excuses..
      ursulus
    • You are expected?

      So, after your first iPhone purchase, Apple came and put a gun on your hear, telling you -- every next smartphone you buy, must be an iPhone, no questions asked?

      Why not stop assuming things and start thinking with your own head?

      By the way, the accelerometer in the new iPhones is not defective. It is even better in some aspects. However, being new component, those developers were "surprised" -- perhaps, they are trying to use some undocumented trick that used to work with the previous part and works differently with the new? The article even mentions everything is ok, if the app self-calibrates.
      Big deal!

      Anyway, don't let facts stand in the way of your agenda.
      danbi
  • I am so glad I never invested in Apple

    eco-system and I never will.
    Rob.sharp
    • Good for you

      I'm glad I didn't buy an iPhone 5s as the iPhone 5 works perfectly without the accelerometer issues. Oh wait, did I just make your post look like the ranting of an iHater? Whoops.
      athynz
  • accelerometergate

    The *gate stuff never ends.

    Then, one day that great developer finds the bug in their own code. Will there be public apology for the misinformation?
    danbi
  • Apple might have made a mistake

    If something didn't break, don't change or fix it.
    Yaarov Skimaan