Data-logging interfaces connect to computers and can have sensors plugged into them. They convert the readings which they derive from the sensors into data which the computer can use. They convert continuous variable signals from the sensors to numbers using a circuit called an analogue-to-digital converter. These numbers are converted into real values and displayed by a computer programme. Some data-logging interfaces - called dataloggers - have their own memory and power supply and can record data without an attached computer.

A datalogger is a self-contained serial port interface which has its own power supply and memory to allow it to collect and store data over time. It can be connected to different types of computers to transfer data and instructions.

Some dataloggers must be programmed from the computer with specific instructions about what and when to record, and are then disconnected from the computer to carry them out. Dataloggers can be activated by the press of a button and begin recording with whatever sensors are plugged in, continuing to do so until they are deactivated. Some have small display screens to display data in graphical form as it is collected, a feature which enables students to see what is happening (and to reassure them that the device is working!). Some dataloggers can hold more than one set of data in memory at the same time and all can transfer their data to a host computer for analysis.

Battery life can be a problem. Dataloggers can be programmed to record data for weeks - as long as the batteries last (half as long as the manufacturers claim is a good rule of thumb). Use a mains power supply adaptor, if you can, to ensure that you'll have some data worth analysing after a long recording.

Predictably, the more features a datalogger has, the more it costs. It is worth considering whether you have a real need for all the advanced features of an expensive datalogger compared with a mid-priced serial data-logging interface.