FreeIMU

Posible to connect multiple freeimu's on one arduino ?

Asked by Hikmet

For motion capture issues , is multiple freeimu's could connect to one arduino ? [ ex. 16pcs ]

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Fabio Varesano (fabio-varesano) said : 		#1

Nope, you can't as the sensors would have to run on the same I2C bus thus you would have eg 16 accelerometers with the same address and communication wouldn't be possible.

In order to do so, connecting and communication with 16 FreeIMUs, you would need some kind of multiplexing on the I2C lines. This can be achieved in different ways, one of them being "I2C multiplexers" ad hoc devices for doing so. Read http://ics.nxp.com/support/documents/interface/pdf/an10216.pdf pag 43 for an introduction on I2C and multiplexing.

Note however that the effecting sensor reading bandwidth will then be shared amoung the 16 FreeIMU.. maning that if you are able to sample at 300Hz one FreeIMU, you'll be able of sampling 16 only at 18Hz.... so, not as easy as it seems.

A similar project is being under evaluation with some friends, however we will probably design an ad-hoc device with some kind of wireless communication.

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Hikmet (gumush) said : 		#2

Thanx for the great support.

I2c speed 100khz hz and a little tweak it runs about 400 Khz.
And after multiplying i2c's it still works 400.000 / 16 = 25khz per i2c device ?

Is there any option the change bus address for device's ?

We want to study on biomechs. Because of that size is very important. One central unit and 16 i2c sensors looks better than seperate i2c sensor + arduino pro + Xbee's ...

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Fabio Varesano (fabio-varesano) said : 		#3

Sorry, I missed your reply..

> And after multiplying i2c's it still works 400.000 / 16 = 25khz per i2c device ?

That's the bus speed, not the effective sensor sampling frequency. No matters how many devices you have, the bus will always work at that speed. But the effective will be inevitably lower.

> Is there any option the change bus address for device's ?

Only for the accelerometer and gyroscope. The FreeIMU comes with two solder switches which enable you to configure between two possible address for the 2 sensors. The problem is the magnetometer which doesn't provide this feature.

> One central unit and 16 i2c sensors looks better than seperate i2c sensor + arduino pro + Xbee's ...

Not when the sensors + arduino + wireless communication happens on an ad-hoc developed board.

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