Which Accelerometer? - Page 1
Forum section: electronics / projects

author: fcb
author_rank: Super Contributor
timestamp: October 22, 2014, 12:41:40 pm
content: I'm working on a project at the moment (with a seriously compressed timescale), it needs an accelerometer to determine when it's being fiddled with. What's everyone's 'goto' low cost part?

author: dr.diesel
author_rank: Super Contributor
timestamp: October 22, 2014, 01:00:44 pm
content: You need something already on an breakout board, with say i2c for communication? Or just a chipset recommendation?

author: fcb
author_rank: Super Contributor
timestamp: October 22, 2014, 01:02:45 pm
content: Just the IC

author: penfold
author_rank: Frequent Contributor
timestamp: October 22, 2014, 01:05:10 pm
content: If its to determine whether the item is being fiddled with, would a tilt switch or vibration type sensor not also work, and perhaps be a bit cheaper?

author: fcb
author_rank: Super Contributor
timestamp: October 22, 2014, 04:10:01 pm
content: @Quote from: penfold on October 22, 2014, 01:05:10 pmToo big I suspect.Anyone used the MMA8653?

author: Rufus
author_rank: Super Contributor
timestamp: October 22, 2014, 04:30:27 pm
content: Quote from: fcb on October 22, 2014, 04:10:01 pmI have used the LIS3DH. One very low power design where an SPI interface is needed and another for vibration monitoring where SPI was needed for speed. The part seems OK, data sheet and design information is pretty shitty. I believe it is popular in mobile phones which may be a good or bad thing.A couple of years ago I got as far as prototyping with an analog output Freescale part - now it is obsolete, continued availability is a worry for all these new fangled MEMS things I think.

author: fcb
author_rank: Super Contributor
timestamp: October 22, 2014, 06:21:08 pm
content: The LIS3DH looks good, it's a bit more expensive than the MMA8653 but I suspect when you get into volume probably not much in it.

author: trevwhite
author_rank: Frequent Contributor
timestamp: October 22, 2014, 07:02:13 pm
content: MMA8653 is just awesome! Very easy and very sensitive and durable.

author: eneuro
author_rank: Super Contributor
timestamp: October 22, 2014, 07:04:38 pm
content: Quote from: fcb on October 22, 2014, 01:02:45 pmMaybe MEMS accelerometer & gyro in one: MPU6050?It looks like not to many additional elements including pullups for I2C, however do not hacked this module, so no schematics so far, but docs are quite good.Used it directly from PC Linux using custom made optoisolated I2C via RS232 serial portBTW: It is possible to make hardware sensors fusions and obtain quaternions to avoid gimbal issueshttp://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation

author: fcb
author_rank: Super Contributor
timestamp: October 22, 2014, 07:24:08 pm
content: That might be overkill & certainly blow the budget.The MPU-6050 is listed in Farnell (1000off) at £4.90, the MMA8653 (1000off) is £0.33. Nice part though.

author: dannyf
author_rank: Super Contributor
timestamp: October 22, 2014, 09:43:33 pm
content: You have to decide if you prefer digital interface vs. Analog interface. Digital interface, i2c for example, is easier for wiring but generally slower.another factor to consider is drifting: readings slowly change while the device is stationary. The mpu part is quite good there.another would be the parts support for interrupt: set a threshold level for the part and if it is exceeded, the part can alert the mcu.anyway, I would start with a small quantities, try them out first before buying in the thousands.

author: Rufus
author_rank: Super Contributor
timestamp: October 22, 2014, 10:27:10 pm
content: Quote from: fcb on October 22, 2014, 06:21:08 pmhttp://www.usinlife.com/index.php/blogs/item/90-accelerometers-in-phones-which-phones-have-whatLIS3 and I presume variants are well represented, also parts from Bosch and Kionix - nothing from Freescale. Like I said I don't know if that is an overall good or bad thing.

author: eneuro
author_rank: Super Contributor
timestamp: October 22, 2014, 11:24:23 pm
content: Quote from: fcb on October 22, 2014, 07:24:08 pmThis I2C accelerometer is really cool with its 2mmx2mmx1mm size and in many applications could be very usefull, but one need microscope to play with it on PCB, I guess

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 22, 2014, 11:31:41 pm
content: Quote from: fcb on October 22, 2014, 12:41:40 pmDoes it need to be sensitive to all directions, or have a linear output?A spring soldered to the PCB with a conductive weight at the end, contacting a via or a pad on the PCB. That's how toys do it, who knows how the manufacturing tolerances work out in production though.Mostly it's to detect spinning of a propeller on a toy helicopter. But it lights up when you shake it too.

author: fcb
author_rank: Super Contributor
timestamp: October 23, 2014, 08:00:42 am
content: Quote from: dannyf on October 22, 2014, 09:43:33 pmI'm pretty neutral about the interface. I didn't however come across any low-cost parts with analog 3 axis outputs.The accelerometer is in the product purely to inform the micro that the device is 'in-use' or has moved, so it can fire-up a GPS to determine if it is really on the move.

author: fcb
author_rank: Super Contributor
timestamp: October 23, 2014, 08:04:55 am
content: Quote from: Rufus on October 22, 2014, 10:27:10 pmGreat (&concise) article - thanks for the link. I suspect that the parts shown are potentially better than the part I've spec'd in, I just need to measure the 3 axis and determine if it's moved at all between wake-up's.

author: Rufus
author_rank: Super Contributor
timestamp: October 23, 2014, 01:50:35 pm
content: Quote from: fcb on October 23, 2014, 08:04:55 amMy low power LIS3DH design spends most of the time doing the same. When fully 'asleep' it checks if g on any of the 3 axis has changed by more than 'x' about once every 15 seconds. In that state the LIS3 supply current averages less than 1uA.