A codec is used in conjunction with the nRF51 DK to get the analog signal from the microphone to digital signals.
The codec used is the ES8218 analog-to-digital converter (ADC) from Everest Semiconductor. ES8218 is set up with the use of a two-wire interface. The microphone signal is transferred to the nRF5x DK via I2S interface.
Figure 1. Codec and appurtenant components
