Here is one more data-logger circuit, based on ATmega32. providing 8-channels with 0 to 5V voltage level measurement. The circuit also has on-board RTC (based on DS1307) to log the data with time-stamp. Data is logged via UART. The circuit has 3-pin UART connector, which can be used to connect to PC/laptop using UART(TTL) to USB serial converter.
Also, there is a thermometer IC, DS1621, which is connected via i2c (along with the RTC IC) and provides temperature measurement from -55 to +125 Deg. C. The temperature and the voltages are sent to the UART for logging in an ASCII string format, when a pushbutton provided for logging is pressed. Pressing the same button again stops the logging.
The circuit includes a 16x2 LCD (4-bit interface) for displaying the current date/time from RTC and the temperature, with logging status. The RTC date/time can be changed using three push-buttons provided on-board.
The detailed circuit description and operation with relevant pics/ schematic are shared on the link given below. Also, the source code (Atmel Studio 7 project folder), the simulation files and the schematic, layout and gerber files are available for download.