The following code controls a Microchip Technology Inc.'s MCP9804 digital temperature sensor.

The following was developed on a Zipit Z2 running openWRT.  The distribution includes the nano text editor and picoc c language compiler.  Some of the following code was blatantly cut and paste from other peoples web sites and from many many internet searches.  

The first half of the code executes a user command and pipes the output of the command into an array of chars.  The user command that gets executed is:

i2cget -y 0 0xlf 0x05 w

• i2cget is a program which reads data from an i2c device
• -y option disables user intervention
• 0 designates which i2c bus to use for communication
• 0xlf is the chip address of the temperature sensor
• 0x05 is the memory address location of the temperature data
• w specifies that a word length of data is to be retrieved.

The second half of the code rearranges the order of the chars since they are received from the i2c sensor in a funny order.  After rearrangement, the array of chars is converted to an integer.  The most significant three bits are masked off.  The remaining integer can take a value from 0 to 8192 representing temperatures from -40 °C to 125 °C.