Detecting Sound Students often want to use ‘sound’ as an input within electronic projects. Unfortunately sound is not as easy to use as light and temperature, as there is not an instant ‘single component’ solution, as is the case with, for example, an LDR for light or a thermistor for temperature. The main problems with detecting sound are: 1) electret microphone inserts are low cost, but only produce a very small signal, which requires amplification 2) the background noise level can vary considerably, and so some form of calibration is required 3) some noises, such as a hand-clap, are very quick and so can be ‘missed’ with some electronic circuits (e.g. when using a microcontroller) Fortunately these problems can all be overcome at low-cost, by using an electret microphone with three common transistors. The circuit shown in Figure 1 will produce an analogue signal between 0 and 3V that can be detected, for instance, with the analogue input pin of a PIC microcontroller (e.g. 16F876). T...