ADXL335 Test

Triple Axis Accelerometer

Mitchell Knotts

Description and Use

                  The ADXL335 Triple Axis Accelerometer is a very small device that can sense accelerations in three different axis.  We are incorporating this instrument into our balloons payload so we can monitor the accelerations that the payload will experience. The accelerometer is very easy to use, it requires 1.8 – 3.6V and each axis has its own analog output pin. Each output pin will be connected to one of the analog input pins on the Arduino, finally the Arduino will interpret the signals from the accelerometer and output the acceleration values to the data logger.

                  This components interfacing to the Arduino requires more code than wiring, noted in the Testing section.  A pin out diagram as well as an overhead image can be seen below.

Triple Axis Accelerometer Triple Axis Accelerometer

Pinout definitions

Pin	Name	Description
1	ST	Self Test
2	X	X Axis
3	Y	Y Axis
4	Z	Z Axis
5	Gnd	System Ground
6	Vcc	Voltage In (3.3V)

ADXL335 triple axis accelerometer Data Sheet: http://www.sparkfun.com/datasheets/Components/SMD/adxl335.pdf

                   

Testing

                  Testing started out with connecting the Accelerometer to the Arduino. After the connections were made we had to read the data sheet for the ADXL335 chip and find out how the output values from the chip relate to useful units of acceleration. According to the data sheet the acceleration vs. voltage is a linear relationship. I started out by just programming the Arduino to read in the voltage from each axis. I then turned the accelerometer until the axis was parallel to the ground, meaning zero force of acceleration acting on the axis of interest. I recorded this value, the Zero Value, and moved to the next axis. After recording the “Zero value” for each axis I then twisted the accelerometer so that the axis in interest was pointed towards the ground, meaning the acceleration of gravity was acting on the axis in interest. I did this for all three axes and recorded the value. The value that was equivalent to one g force was 0.23V. Once I had this I plugged the values into the equation I had written in the code.

Accelerometer logic on the Arduino 

Once the code was uploaded on the Arduino I found that the accelerometer was functioning correctly! The values that the Arduino prints are in g’s, I decided to use g’s as units because I can easily multiply a g by whichever unit of acceleration I want like 9.8m/s^2.

 

Integration into Payload

This component will be soldered directly onto a printed circuit board that our team is designing. The printed circuit board connects all the instruments including the accelerometer and the Arduino. We will mount the printed circuit board to the bottom of the payload package, this will work well because the accelerometer will be reading the accelerations that the payload experiences.