Synchronized accelerometer DAQ System

Hello all,

I am planning to create a data acquisition system with 3 accelerometers recording values for 15 minutes at intervals of 15 days. My system will have internet access and power, however, I would like to be able to have the ability to make it "mobile", thus having a battery and a storage capacity (via a memory card I guess).

For the moment I am thinking of the following components for the configuration:

  • Teensy 3.2
  • SparkFun Triple Axis Accelerometer Breakout - ADXL345
  • LilyPad Coin Cell Battery Holder - 20mm
  • SparkFun Power Cell - LiPo Charger/Booster
  • SparkFun RJ45 MagJack Breakout
  • SparkFun Level Shifting microSD Breakout
  • Polymer Lithium Ion Battery - 6Ah

Please let me know what you think. I expect the accelerometers to be connected via ethernet to the main teensy component.

Any questions/suggestions are welcome!

Any idea?

I don't see how that list of parts gets internet access. The magjack breakout just gives you the ethernet wires. You need an ethernet interface chip to talk on those wires. Get a WiFi shield if you're in WiFi range, or an Ethernet shield.

The level shifting isn't required for the 3.3V Teensy to talk to a 3.3V SD card. Just get the plain breakout with no level shifter.

How do you intend to control the system? You put it in place and just let it run on its own schedule or do you need a "start" button?

I expect the accelerometers to be connected via ethernet to the main teensy component.

What? You mean you want to use the Cat-6 cable for the accelerometers? That's actually a bad idea. The ADXL345 is using either I2C or SPI communications and both of those are "single ended" meaning each signal is carried on one wire plus ground. That doesn't require twisted-pair cable. In fact, twisted-pair cable is bad for both of those.

How far away are the acccelerometers? I2C can have problems with wires as short as 10cm and will always require hard work to get it to go more than 2m. SPI will work at high speed up to 3m and by switching to lower speeds you can get 10m with no special effort on the wiring. Just regular ribbon cable works - not twisted pair. I've got a system of 4 ADXL345's on about 8m of wire in some very harsh conditions and I have had no problems since switching the SPI clock divider to 4. They're sampling one axis each at 400Hz.

One tip for the ribbon cable: put a DC wire between clock and data, such as ground. Adjacent wires will transmit high frequency interference between them. My long cables go: CS, MISO, 3.3V, MOSI, GND, CLK. I can share the design for the remote accelerometer PCBs if you want to get some made at OSHPark.