The accelerometer will be played by an ADXL345 from analog devices. This is a low power 3-axis accelerometer which is accurate to measurement at ±16 g. The ADXL345 has a digital output through either I2C or SPI (3 or 4 wire) interfaces. This is fortunate for us as the Altera DE2 board is compatible with both I2C and SPI. For the environmental sensing module we will be utilizing I2C. It will require a supply voltage of 1.8 V to 3.6 V and will output in the X, Y, and Z directions providing little cross axis sensitivity. This will send a digital signal to the DE2 board that represents the acceleration felt by the sensor. This means any motion, shock, or vibration will be detected and recorded on the DE2 board. Several special functions are incorporated in the ADXL345 like active and inactive sensing, tap sensing, and free fall sensing. Active and inactive sensing works by comparing the acceleration on any axis with a user-set threshold, which means if you wanted to set an interrupt to occur when the ADXL345 either stops or slows; this is possible. Tap sensing is kind of like sensitivity, in that you can set the ADXL345 to wait and not record data on a single tap, this would allow you to account for slight bumping. Finally the free fall sensing allows the device to detect if it is falling. All of these functions can be mapped to one of two interrupt pins. For the environmental sensing module we decided to use the ADXL345 breakout boards. This is helpful because the ADXL345 is very small and we are not very good at soldering. The breakout board also already had the decoupling capacitors and was the same price as the ADXL345 alone. For the I2C interface we needed to add two pull-up resistors to the data line and clock line.