Description The Spresense extension board is a board which extends the interfaces compared to the Spresense main board. The Spresense main board and the Spresense extension board are connected by a Board-to-Board (B-2-B) connector. The Spresense extension board has Arduino Uno pin compatible shape and pin socket locations. However, there are some differences compared to the Arduino Uno. For details, please refer to the Differences between Spresense and Arduino Uno. The Spresense extension board has the following connectors in addition to Arduino Uno compatible pin sockets. 3.5 mm headphone jack Micro SD card An extra USB port Multiple microphone pins