On the balloon we aim for data logging instead of real-time transmission. The balloon is to be brought down periodically to collect data. Data is collected using an onboard uLog. We use BMP085 to measure absolute pressure. This also provides the temperature value. BMP085 uses a Two Wire protocol for data transmission and operates at 3.3V. Analog Pin 5 is used for SCL and Analog Pin 4 for SDA. We use HH10D to measure relative humidity. A Two Wire interface is needed to read calibration coefficients from its onboard EEPROM. However we read it for once, record it in the sensor code, and never use the Two Wire interface thereafter. The data is output as encoded frequency and output through the middle pin. uLog is a Serial Logger. Data is send through the TX line of the microcontroller