from Hacker News

iPhone 6: Comparing InvenSense and Bosch Accelerometers

by vishalchandra on 9/26/14, 5:13 PM with 12 comments

  • by hkmurakami on 9/26/14, 8:52 PM

    INVN was my former employer (~2013), so I'm quite familiar with the details of both of these chips. I'm not sure just how much I am allowed to talk about these parts, but imo the general consensus regarding power consumption being the killer feature that got Bosch the secondary accelerometer socket win seems correct to me. The likely accel only features are screen orientation, pedometer, and activity recognition, as the articles suggest. (I personally don't think that the 1ms vs 20ms start-up time matters much though)

    Also, (a) ST microelectronics parts always had quality issues so I'm not surprised that they lost the socket to Bosch, and (b) I expect Bosch to be selling the BMA280 at cost or even at a loss. Bosch was a late entrant to the consumer electronics accel/gyro world, and has always been keen on price dumping to win sockets and market share.

    edit: the more I think about this, the more I think that this is a situation where ST was the only loser. They had both the accel and gyro sockets before, but essentially lost the gyro socket to INVN and accel socket to Bosch. The integrated accel in the MPU-6700 is more of an add-on feature for low power on-chip sensor fusion that was not capable with the ST solution that was previously used (the DMP in the 6700 pre-dates the Apple M7 chip that was touted for low power activity tracking usage, but given that Apple has the M7, I'm not sure how much of its capabilities are being used. My guess would be that it is only the on-chip 6-axis SF that they are using). The ST socket was simply taken by Bosch.

  • by unwiredben on 9/26/14, 9:31 PM

    http://www.chipworks.com/en/technical-competitive-analysis/r... is the source URL, the EETimes article is a repost

  • by pstan on 9/27/14, 3:59 AM

    Civil engineering grad student here, BMA280 are much more stable and low noise than other sensor out there it features noise density of 120 μg/√Hz. Not sure about MPU-6700 but MPU-6500 is 250µg/√Hz. In my research on using consumer MEMS sensor to measure inclination, 16-bit resolution on MPU-6500 does not help a lot if the noise is much higher.

  • by i_am_ralpht on 9/26/14, 10:00 PM

    The Invensense has an autonomous mode (on Android devices it can count steps without bothering the host CPU) -- does the Bosch do this too?

    Apple have a separate Cortex-M3 which is branded as the "M7" or "M8" motion processor. Is this what they use for step counting when the A8 is suspended? Why not use the Invensense for that? Is the M8 + Bosch less power?

  • by newhouseb on 9/26/14, 9:43 PM

    A pipe dream here would be to use both accelerometers at the same time and filter out much of the random noise resulting in much smoother accelerometer readings that could be used to calculate displacement.

    (goes off and downloads Apple CoreMotion samples to see if they do this already)

  • by username3 on 9/26/14, 9:52 PM

    So that 1Hz is causing rotation lag.