What's a good choice for 6 DOF (accel + gyro) IMU chips today? - Page 1
Forum section: electronics / projects

author: IDEngineer
author_rank: Super Contributor
timestamp: April 08, 2021, 07:08:25 pm
content: We've brushed against this topic in a number of other threads - especially when complaining about how bad some IMU's are these days. But it's time for the rubber to meet the road.What is a GOOD CHOICE for an IMU chip these days?Background for new arrivals: MEMS IMU's are notorious for various problems. Lockup conditions that require a power cycle to recover (!) and documented as normal by the manufacturer (!!!), SPI interfaces going unresponsive, retired after just 18-24 months of production, the list goes on. A search here reveals numerous threads on the topic going back years.The latest problem is availability. A couple of years ago we settled on the Bosch Sensortec BMI160 as a reasonable compromise. Relatively new so less likely to stop production, deeply stocked by multiple distributors, reasonably reliable in extended testing as compared to competitors. We've consumed thousands of them and have an ongoing need. But as documented on this site in other threads, Bosch has seemingly fallen off the map in terms of production. Even their authorized distributors can't get answers and have stopped accepting orders for Bosch components. (Don't raise the topic on their support forums, though, or you'll get slapped hard for "spreading rumors" despite their own website documenting the facts. Guess how I know.)Previous to the Bosch part we used an STMicro chip, but it fell to the "retire after 18 months of production" problem. An STMicro part similar to the Bosch BMI160 turned out to be one of the most unreliable components I've ever personally tested - I could not in good conscience recommend that we use it in anything we shipped to customers.Which brings us to today. Bosch isn't discussing any schedules. Their distributors have no idea what is going on and have all but openly stopped carrying Bosch (no stock, no schedules, and won't accept new orders). We're tired of paying 4X list price for parts from the grey market. Meanwhile, the last STMicro part I evaluated was an utter disaster.So... what 6DOF IMU out thereactually worksand isavailable?!? I'm going revise our PCB to have twin footprints, one for the BMI160 and one for a new part, so we can stuff whatever is available. What is anyone else using that works well and isn't the MEMS equivalent of unobtainium? We can't be the only shop using these parts. Let's identify a good one, standardize on it, and drive up its demand so it 1) gets more time on the fab lines and 2) stays in production longer than 24 months.What are you using that works? Thanks!

author: phil from seattle
author_rank: Super Contributor
timestamp: April 08, 2021, 07:36:17 pm
content: I don't have IMU suggestions for you but if I were in your situation (and if the BOM cost can support it), I would create a standardized module set up that would plug into your base board. Maybe using castellated connections. Then as IMUs come and go you could keep the base board the same and use different IMU modules as you go along. Not sure how much it impacts your BOM cost but I would guess a couple of bucks or less. Maybe even come up with a scheme for IDing the IMU module so you can select it at run time.

author: IDEngineer
author_rank: Super Contributor
timestamp: April 08, 2021, 11:27:39 pm
content: A daughterboard would be a great idea on a larger project. But the PCB here is all of 2x2 inches total. No room to implement a daughterboard scheme.We did have a version a while back that had two footprints, like I'm considering now. But the second footprint was for the damnable STMicro LSM6DS3 that was so buggy I was embarrassed for ST's employees. We removed its footprint at the next minor board revision since there was no chance we wanted to become STMicro's Customer Support department by shipping anything containing that "component".Since I wrote the OP, I've found the TDK InvenSense ICM-42605. It has the same pinout, footprint, and power supply requirements so it's looking promising as a possible drop-in replacement. Modestly stocked at a couple of distributors, which is FAR more than Bosch Sensortec can claim. I need to go through the spec sheet and compare the internals, but as long as its WHO_AM_I doesn't overlap the BMI160's we can accommodate almost anything in firmware.EDIT: "Maybe even come up with a scheme for IDing the IMU module so you can select it at run time." As noted above, IMU's have a read-only WHO_AM_I value that allows you to identify them at runtime. A daughterboard would not need to do anything extra.Anyone have any experience, good or bad, with the ICM-42605?