Can several MEMS accelerometers be connected (in serie?) in order to reduce self noise

[pedme]

Hello all

I am new at this forum and have almost zero knowledge in electronics but look at acceleration data on a daily basis (in the geophysics field).

My experience is that MEMS accelero are quite noisy, especially at "low" frequencies (<~1 Hz).

Just wondering if multiple MEMS can be connected together in order for the individual signals to be summed giving a sqrt(N) pure random noise attenuation.

I am thinking here about a hardware solution (e.g. N analog output sensors connected in serie, but is that that simple?), not a stack after individual sensor data digitalisation (something I could not afford for a number of reasons)

Your comments and advices will be much appreciated!

Regards

Pascal

[Miroslav BATEK]

How do you want to connect N analog output sensors in series?

It is not clear. Can you draw simple schematic?

[pedme]

Hello Miroslav

Thank you for answering.

Basically as one would do with batteries (see picture below) to output the sum of the voltage (but each battery would be a MEMS accelerometer).

This works with any passive analogue device (a geophone in my field), but wonder if the same applies easily with typical (active, i.e. requiring current to work) MEMS sensors.

Sorry if this is an obvious question.

Regards

Pascal

[pedme]

battery schematic attached

[Miroslav BATEK]

It doesn't work with our MEMS sensor, they are not floating, you can't do the serial connection.

[pedme]

Thank you Miroslav

Can you let me know why briefly?

They are not floating... what does that mean? what would be the proper keyword for a "floating" device?

and do you know if it is possible to find some?

Alternatively, do you see a affordable solution to produce such a stack?

My feeling is that summing the signal(s) (100+) after digitization would be expensive in particular because they would all need to be perfectly time synchronized. Or is that perfectly achievable?

Best regards

Pascal

[Harry Blake]

Hey, yes it is possible by using I2C mini modules you will be able to connect max 256 devices at same time like the one mentioned below in link

https://store.ncd.io/product/lis331hh-mems-motion-sensor-ultra-low-power-full-scale-3-axis-accelerometer-i2c-mini-module/

I am Only focusing on connection process and Like LIS331HH there many I2C module which will be access and monitor at same time from single micorcontroller

[Miroslav BATEK]

Connecting ST MEMS sensors in series is practically impossible. they need at least configuration from some microcontroler and all ground pins needs to be connected together.

I think, it feasible to do it with digital sensor, for example LIS2DW12 which has external synchronization feature, so you can trigger measurement of all sensors at the same time and then read them one by one. Or course connecting 100 sensors is not easy but definitely feasible.

[pedme]

Harry, Miroslav,

thank you very much for your comments/suggestions, it is very useful.

Looks like those NCD-I2C modules, with ready-to-use connnectors, could make my life much easier (to begin with at least...)

The LIS331HH however seems not sensitive enough for my application.

(ideally I would be after a +-1g range over 24 bit, with noise density < 1ug/sqrt(Hz) - that's not really the concern for the moment but plz let me know if you're aware of a user-friendly mems in such spec range!).

The AIS328DQTR (available as a NCD-I2C module as well) seems a bit better and also features this data-ready signal. Is such a feature just useful or actually required for accurate/simultaenous time sampling of all the channels?

Reading about the I2C bus:

• looks like one can be used to connect up to 2^7=128 "devices". Is it the max number of MEMS or the max number of channels (giving only 42 connectable 3C MEMS)?
• looks like each device/channel will need an indivudal/different address. How can I check if a sensor (the AIS328DQTR for instance) has a unique (or customisable) address?

Thank you again for your inputs!

Regards

Pascal

[Miroslav BATEK]

1) Sensor

the best what you can get from ST is LIS3DHH (+-2.5g, 16 bit, noise 45 ug/sqrt(Hz) but this device doesn't have possibility to do external synchronization (LIS2DW12 has this feature)

2) Interface

LIS3DHH has only SPI bus, but SPI bus i definitely better to use in case of many sensor connected to MCU. You can connect only two devices on one I2C bus. The address of the sensor cannot be changed.

3) Complexity

To do what you explained is not easy, I don't want to discourage but based on your question you will have hard time to make it functional.

[pedme]

Hello

thanks for the feedback - I agree it may be challenging for me alone but the idea is to figure out how complex this could be in order to discuss it with a more competent person who could help.

Coming back to the initial idea of summing the analog outputs, I found the following circuit schematic to stack multiple MEMS microphones:

https://www.analog.com/media/en/technical-documentation/application-notes/AN-1328.pdf

Could you explain why MEMS accelerometers (analog and single ended - I guess) could not be used instead of those MEMS microphones?

Best regards

Pascal