This paper aims to enable schools to make their own low-cost temperature logging instrument and to
learn a something about its calibration in the process. This paper describes how a thermistor can be
integrated into a simple potential divider circuit which is powered with the sound output of a
computer and monitored by the microphone input. The voltage across a fixed resistor is recorded and
scaled to convert it into a temperature reading in the range 0–100 °C. The calibration process is
described with reference to fixed points and the effects of non-linearity are highlighted. An
optimised calibration procedure is described which enables sub degree resolution and a software
program was written which makes it possible to log, display and save temperature changes over a user
determined period of time.