Wednesday, July 17, 2013

ADXL345 + Arduino!

As many Arduino enthusiast, I bought a ADXL345 accelerometer from RS components and I set it up to communicate with my board in order to use it in a wider electronic project. I did want to share my experience. If you want to try the accelerometer yourself, you have two choises: buy the sparkfun BOB, which comes ready to be used, or buy the accelerometer and a couple of passive components from your preferred distributor and make your own Break Out Board.
I opted for the second one! ;)
Of course you'll need some hardware stuff, and the results will not be as good as the assembled one, but the satisfaction will be over 9000. For the breakout board you will need some bypass capacitors to solder as close as possible to the VCC pin of the SMD, which is a LGA. After some hours of super focused, high level, ultra professional layout design with EAGLE, and after a couple of iron stains on my jeans, the result is the following:

ADXL345 on a DIY breakout board.

As you can see the result is quite obscene if compared to the red-fashioned ultra-small sparkfun edition, but this is a DIY and I love it!  In the image above the wire needed to provide power supply and I2C communication are already connected to my Arduino UNO. The second step of course was to google for some lines of code to read the accelerometer data. Internet is full of code for Arduino and this IC. Basically the code aims to: 
  1. Initialize the I2C communication setting the Arduino as Master & the IC as Slave.
  2. Wake up the device from its low power mode (sleep mode)
  3. Read out the X-Y-Z acceleration value. 

I left out the function code for "readFrom" and "writeTo" to keep the post as compact as possible. If you need it, just leave a comment and I will send you the entire project. The image below is a snapshot from the IC's datashhet and it shows the meanings of the bits in the Power Control Register, whose addres is 0x2D. As you can see from the code above, we first reset the register writing to 0 every bit, and than we set to 1 the bit "Auto Sleep Mode" and "Measure". The latter is the one who let the device start measuring. Of course we could set the bit with a single instruction, but since this is kind a tutorial, I thought it was better to leave the three different tokens.
Next step: Calculate position from acceleration. If I reach 10 comments, I promise I'll do it in one day! ;)

ADXL345 POWER_CTL Register configuration byte


  1. Hi, can you send me the whole code? Thank you!

  2. Hi, can you send me the whole code? Thank you!

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