We have developed firmware for gathering data using sensor nodes based on the open Arduino platform (see http://mobilab.eecs.umich.edu/mpod.html). This firmware controls sensor data collecting, data transmission, and all the other on-board components. This firmware is compiled and tested under the Arduino environment V0022 (http://arduino.cc/en/main/software). It can be uploaded to Arduino BT based systems via bluetooth interface if a bootloader is pre-installed. Otherwise, it can also be uploaded using an Atmega AVR programmer via the 6-pin programming header on board. The code is available here.