Because of the high hardware complexity of Thingy, the design requires additional GPIOs beyond the 32 GPIOs of the nRF52832 SoC.
To increase the number of GPIOs, a 16-channel, ultra-low power I/O expander is connected to the I2C bus. The I2C slave address for the I/O expander is 0x3E. Most of the GPIOs on the expander are used internally on Thingy, but some of the GPIOs are made available on a connector for the user to connect additional hardware. The I/O expander has an integrated LED driver that supports intensity control, blink control, and breathing control.
Figure 1. I/O expander schematics
