Introduction

An electret microphone produces an audio output signal in the millivolt range. To interface an electret microphone with a microcontroller (MCU), it is necessary to amplify the signal up to the 100-millivolt range so that it can be detected by an analog comparator in the MCU or converted to a digital signal by the MCU’s analog-to-digital converter (ADC). Conventionally, it has been necessary to add one or two operational amplifier (op amp) integrated circuits and several passive components to a hardware design to perform this amplification. An MCU containing the Analog Signal Conditioning (OPAMP) peripheral can be interfaced with an electret microphone using minimal external circuitry because the OPAMP peripheral is capable of linear amplification. In addition to the microphone, only one resistor and one capacitor are required. The OPAMP peripheral also provides the ability to adjust the gain under firmware control.