Multiple Accelerometer used as angle meters, with wireless remote LCD display

Using Arduino Project Guidance
1

Hi All,

I'm working on a small project which involves being able to measure the angle of declination of a series of speakers mounted on a truss about 20m up in the air. The spec calls for a display of the angle on a unit at ground level to allow remote adjustment of said angle using an existing control system.

I know I can do this using Arduino and ADXL345 Accelerometers, as I have a PoC working. There are however a few issues:
There could conceivably be up to 14 speakers on the truss, which means that I cannot use I2C due to lack of different addresses.
I have not been able to see whether it is possible to use SPI over XBee, but I suspect it is not possible. At least with SPI, I can use shift registers to control the (possibly) 14 CS pins.

Would the best idea be to use 2 separate Arduino boards, one for the sensor side and one for the display side, and connect them using serial over an XBee (S1) link?

Also, what is the maximum length of wiring over which SPI will work reliably? The length of the truss could be 20m also, with speakers evenly spaced along it. If the sensor Arduino is placed in the middle of the truss, there could still be a 10m run to the outermost accelerometers, and I don't know if SPI can cope with this?

The sensing frequency of the active accelerometer will be below 10Hz, and the rest can go into low power mode when not in use. I was planning to use a LiPoly battery aloft to provide power for the 5 days the truss will be aloft, with a smaller LiPoly being used for the display unit.

I'm happy with the code to take the accelerometer output and converting it to an angle, but I'm interested in feedback on both using serial over XBee to communicate between the sensor and display Arduinos, and on using SPI over long distances (10m).
If there are better ways of approaching this project, I'd also love to hear it.

Thanks very much,
Stefan

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which means that I cannot use I2C due to lack of different addresses.

You can use a analogue switch to switch the bus to the different devices.
like this
Imgur

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Thanks for that, will have to investigate that as there are obviously less wires if I can use I2C.

Will see if I can get hold of one to play with, do you have any part numbers? I've found the NXP PCA9547 but doesn't seem easy to get hold of in small quantities after a cursory search.

Regards,
Stefan

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I've found the NXP PCA9547 but doesn't seem easy to get hold of in small quantities after a cursory search.

£1.48 each :-
http://uk.farnell.com/nxp/pca9547pw/ic-mux-8ch-i2c-16tssop/dp/2212121?Ntt=PCA9547

But why not a 4052?

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Hi Mike,

Thanks for those pointers, I'll get some of the 4052s and try them, that was a useful suggestion.

Thanks again, and I'll be back if I get stuck again.

Regards,
Stefan