The MacroPad is packed with onboard hardware, but what if you want to use it with even more hardware? The answer is to use the STEMMA QT port, located on the back left-hand side of the MacroPad underneath the OLED screen.
The STEMMA QT port is best for use with I2C devices. You can use any of the Qwiic-compatible I2C breakout boards available by plugging them into this port and coding them with either the available CircuitPython or Arduino drivers and libraries.
An I2C to GPIO Expander board may be added for more discrete GPIO pin availability if more than two GPIO are needed. An example:
You can use either of the SCL and SDA pins from the STEMMA QT port as discreet GPIO, as long as they are not sharing a bus.
For example, you could connect a button's input to SDA and an LED's anode to SCL, with the STEMMA port's GND connecting to both components. In CircuitPython, these pins are accessed with
board.SCL. In Arduino, SDA is pin
20 and SCL is pin