How can I connect the EFM32 Tiny Gecko MCU to a smartphone?
The EFM32 Tiny Gecko MCU can be connected with a smart phone using the audio jack interface of the phone. This way, the EFM32 can communicate and harvest power from the phone, which enables advanced smart phone accessories without needing batteries. Since the audio output driver in mobile phones is designed to play audio and not deliver a huge amount of energy, power through this interface is limited. This is what makes the energy friendly EFM32 well suited to audio jack connected, mobile phone accessories. Often the connected accessory includes the jack plug as an integral part of itself. For other accessories, it makes sense to have a cable between the phone and the accessory (see picture below).
Fig: Two different interface types - one fixed jack plug and one short cable solution
Communicating with the phone through the audio jack can be achieved in many ways. The simplest form of communication with an accessory is the passive approach, which operates by passing an analog AC-coupled voltage directly from a sensor in the accessory to the phone through the microphone connection. Information can also be passed in the other direction through the analog audio channel that is not used for energy harvesting.
Read the complete application note here for more details and an EFM32 software example.