For audio input, Thingy is equipped with a digital output PDM microphone (U11).
The microphone's power and signal lines are routed through an analog switch (U12) to save power when the microphone is not in use. When the microphone is switched off, the GPIOs used for the PDM signal are available on two test points (TP3 and TP4). This allows the user to connect other hardware if the microphone is not in use.
Figure 1. Digital microphone schematic
