microprocessor programming

We are currently developing a prototype to read data from a Toshiba TCD1304DG and process the result in an Atmega328p microprozessor (used with an external crystal oscillator at a baud rate of [login to view URL] MHz). Programming language is C. A single measure cycle contains: 1) led on 2) read line data from TCD 3) read temperature sensor (DS18B20 preferred) 4) led off 5) send data via UART for further analysis A single cycle may either contain one read of the TCD or an average of several cycles. We are looking to identify the point at the TCD where our light drops from high (light) to low (now light). Our setup only contains one change between high and low. We might have to define a smaller area of pixels to be measure from the TCD (e.g. start reading from pixel 500 until 2500).