The ADXL335 is a 3-axis analog acceleration measurement sensor. That's a mouthful. Basically, this gizmo can detect speed of movement, also known as g-force, in three directions: up/down (z), forward/backward (x), and sideways (y). The axis directions change depending on how we position the sensor IC.
The ADXL335 has a measurement range of ±3 g minimum for each axis. When you are standing still, the earth exerts a gravitation force of 1g. This sensor outputs signals in the form of voltage changes ranging from 0 to 3.3V. At zero gravity, the voltage value of the Z pin is right in the middle between 0V and 3.3V = 1.65V.
The accelerometer can measure the static acceleration of gravity (1g) as well as tilt-sensing applications and also dynamic acceleration resulting from motion, shock, or vibration. Which axis of the ADXL335 reports 1g is dependent on how you position the chip.
THE ADXL335 GOES MOBILE
I drive a Toyota Yaris, a good car as far as reliability and fuel economy but not known for its luxury suspension system. This is perfect for my purposes. A high-end suspension system may dampen road bumpiness possibly generating weaker and inconclusive ADXL335 sensor readings.
POWERING THE ADXL335
This particular ADXL335 breakout board must be powered by a 3.3V source. It's also configured to provide updates 50 times per second. That's plenty of resolution for our road condition sensing device.
Since the Arduino Uno can handle reading 3.3V signals without conversion, we can wire the ADXL335's X,Y,Z outputs pins (3.3V) to Arduino Uno's analog input pins (5V) directly.