This is a really simple but very flexible way to log data using a PICAXE microcontroller. Minimal parts, flexible data sampling, great battery life, and simplicity of data export to a PC were the important design considerations. This logger can read a voltage, a resistance, the internal temperature sensor, an external DS18B20 temperature sensor, or even monitor its own power supply. It is entirely controlled via the same serial cable that is used to program the PICAXE. The only parts are the PICAXE circuit, an LED to indicate that the logger is functioning, and a connection to the device being monitored (unless you use the internal temp sensor). Pretty amazing that you can monitor almost anything for just a few dollars.