There have been quite a few complaints from iPhone 5s users that there may be a hardware issue with the device’s motion sensors. Several tests have concluded that the errors in the accelerometer and gyroscope results in discrepancies of as much as three or four degree when comparing the device with the iPhone 5 and iPhone 4s. The cause of this problem may have now been revealed. RealityCap, a developer of 3D APIs, has theorised that the bug could have something to do with Apple have changed its hardware vendors for the part. In a blog post, CEO Eagle Jones, referring to Chipworks’ teardown of the 5s, point out that while earlier iPhones made use of STMicroelectronics' accelerometers, the latest device comes with a new Bosch Sensortech part. This is a pertinent observation, though, as the accelerometers come with slightly different specs. Jones explains that these precision devices rely on two measurements that help to tell you how accurate they are: Variance and Bias. While the former tells you how consistent an accelerometer’s readings are, the latter describes a constant inaccuracy coming from a hardware manufacturing. While both the iPhone 5 and the 5s, according to tests run by the developer, show similar consistency in measurement, the Bosch device has a larger measurement “bias”.
The iPhone 5s issues could be due to a new accelerometer supplier
The end result is that the new accelerometer in the device will have a different “zero-g offset” which needs to be compensated for in the software. While talking about this, Jones said, “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.” This means that the overall equilibrium of the phone’s measurements is off, affecting everything from the level to how you might play racing games. Jones, while talking about this, has said that developers can compensate for the increased offset because it is unlikely to change much from one measurement to another. He does note that Apple could do a system-wide fix at the OS level to ensure accurate measurements in the future. There is no official word from Apple about this matter, though, so we may have to wait a while before these findings are validated.
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