The SHT21 is the Sensirion humidity and temperature sensor IC. This is a low power digital output chip that uses the I2C interface and has long term stability. The SHT21 is a 4C CMOSens® chip, that includes the capacitive relative humidity sensor and the band gap temperature sensor. The chip also contains an amplifier, A/D converter, OTP memory and a digital processing unit. This humidity and temperature sensing IC incorporates both of our remaining sensors with the benefit of lower power consumption than both sensors separately. The IC uses between 2 -5 μW while sleeping and 3 mW while measuring. The source voltage is between 2.4 – 5.5 V, but typically is 3.3 V which will keep us on par with our other sensor and well below the draw from the DE2 board. The environmental sensing module may be placed in some extreme conditions, for this reason it is fortunate that the SHT21 can operate within ±5% for relative humidity that ranges from 0-100%, and can operate within ±2℃ for temperatures ranging between -40 to 100℃. Of course these ranges are worse case, typical ranges can be seen below. The relative humidity reading do depend on temperature, and it is recommended that the SHT21 not be placed near any heat sinks and not measure more than twice per second. Light will not affect the SHT21. Again we chose to get the SHT21 on a breakout board. This made it easier to implement and came with the external pull-up resistors needed for the clock and data lines. As with the accelerometer, buying the breakout board was the same cost as buying the SHT21 alone.