Freescale Semi

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  • Interfacing an Accelerometer with a Microcontroller

  • Created: Mar 06, 2015

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The capabilities of this project on measuring acceleration and orientation in space are described using Freescale's 3-axis FXLN8361QR1 xtrinsic accelerometer interfaced with a microcontroller. Accelerometers are recently developed solid-state electronics devices that makes it very easy to measure acceleration. They are completely modular and very tiny devices, which gives voltage proportional to acceleration. These types are called analog accelerometers, as their output is voltage. While other gives a PWM output or direct binary digital data, they are called digital accelerometers.

The project implements a microcontroller, which is powered at 3V from two AA batteries. The 3V power supply is also used as the reference input for the analog to digital conversion. A 6-pin ISP header is added on the circuit, necessary for programming the microcontroller through a standard ISP interface such as the USBtinyISP. Three wire jumpers are used to connect pins 20-22 of the microcontroller to power/power/ground. There are twelve pins on the FXLN8361QR1; five will be used for this design. The pins VDD and GND2 are connected to power and ground respectively, and pins XOUT, YOUT, and ZOUT for analog outputs. The analog output pins from the accelerometer are connected to the analog input pins 26-28 of the microcontroller. Having done so, L1-L6 output LEDs are added to indicate the acceleration values as the AVR reads them out. The big idea is that when there is no acceleration in the X-axis direction, both X-axis LEDs are off. When it detects acceleration one way, the red LED lights up (and brighter, the higher the acceleration is) and it lights up blue for acceleration in the opposite direction. Naturally, the other two axes work the same way.

Typical applications of FXLN8361QR1 include tamper detection, motion sensing in robotics integration and activity monitoring in sports and medical devices. This 3-axis accelerometer is widely used in modern devices such as automatic screen orientation changing in mobile phones. And those homebrew robots will be able to tell how far it’s been, which way it's facing, or which way is up.