The complete iButton datalogger starter pack includes one DS1921G iButton, a Blue Dot adapter, USB adapter and Windows-based software.

The measurement range for the DS1921 iButton’s temperature sensor is -30°C to +85°C in 0.5° increments, while the clock measures seconds to years accurately to +1 minute per month from 0°C to 45°C. Incredibly, the iButton can log data for more than 10 years, or up to 1 million temperature measurements.

As well as the datalogging memory, these devices also incorporate a further 512 bytes of user memory. This space could be used to store a product description, shipping manifest or even a student’s name, for example.

All iButtons include a unique 16-digit silicon serial number for identification. As described in our previous iButton article, this serial number can be read out using a simple PICAXE-08M circuit and BASIC program. Unfortunately, PICAXE BASIC does not include any commands that enable us to easily access the DS1921’s other resources over the 1-Wire bus.