I made a simple light and temperature logger a few weekends ago. It’s simple (I have built em lots of times) but this is the first one I actually soldered up. It uses a PIC24FJ64GA002 (Microchip) as its controller, a TSL-14S (TAOS) for the light sensor, and a MCP9701A (Microchip) as the temperature sensor. The data is stored in a 24AA1025 (Microchip) 1024Mbit I2C EEPROM. The firmware supports up to 3 more (4 total) 24AA1025s for expanded capacity. Just connect the EEPROMs to the I2C bus and tell the firmware about the expanded capacity and away you go.
All communications with the Logger are done using UART at 38400bps. The firmware provides a VT100-compatible terminal for easy data download and reconfiguration. There is an LED on the board that shows the current ambient light level (the brighter the room, the dimmer the LED), and another to show the memory status. The board will run for about 48hrs on 4 AAA, and records data once every 30 seconds (though that is easily changed in the code). The board also keeps track of up to 16 runs of data. Each time the board is reset, it starts a new run.
You can find a few photos below. And you can download the code (for Microchip C30 compiler), MPLAB project files and a complied binary.
