Arduino and Memsic 2125 Accelerometer Tutorial

Interfacing to the Memsic 2125 was one of my first Arduino experiences. This started because the Package Tracker from Sparkfun had me curious about IC-based accelerometers. I had last used accelerometers during the Cold War to ensure that US submarines were rugged and reliable. In my experience with laboratory accelerometers, they were elaborate electromechanical devices. Each accelerometer required a charge amplifier to normalize the device output before the output could be subjected to subsequent signal processing. Furthermore, the devices that I used measured the he change in velocity over time but did not sense the acceleration of gravity.

Nowadays, Micro-electro-mechanical systems (MEMS) IC-based accelerometers seem to include g, the acceleration of gravity. Device spec sheets differentiate the two by describing gravity as static acceleration, and the acceleration of motion as dynamic acceleration.

The Package Tracker uses an LIS302DL set up as a +/- 2g three-axis accelerometer. I was so intrigued by this device that I had to see one live in action. Luckily, my neighborhood Radio Shack carried the 2125. This is a +/- 2g two axis device, this would satisfy my curiosity quite nicely.
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Fig 1 – Breadboard with Memsic 2125 and Arduino

The Memsec 2125 uses a type of pulse width modulation to output its acceleration signal. I wired the circuit as it is described in the Memsic 2125 tutorial. It was simple and everything was straight forward. I powered the Arduino via the USB port and hooked an oscilloscope to the Y-Axis output. On a flat surface the signal looked like this:

zero

Fig 2 – Zero g output signal

As the spec sheet promises, we see a 100Hz, 5v square wave. In retrospect, I should have taken a closer look at the signal noise. I tilted the circuit so that the Y-Axis experienced the full effect of gravity. The following pictures and video describe the circuit operation as the Y-axis accelerometer swings between +/- 1g.

tip

Fig 3 – Circuit on End

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plus-1g

Fig 4 – (+ 1 g)

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minus-1g

Fig 5 – (-1g)
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Fig 6 – Zero to +1 g to -1g

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~ by ratdad on March 16, 2009.

One Response to “Arduino and Memsic 2125 Accelerometer Tutorial”

  1. HiraRO…

    […]Arduino and Memsic 2125 Accelerometer Tutorial « MAL's Adventures in Electronics Blog[…]…

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