The default I2C address is 0x20.

Power Pins

• VIN - This is the power pin. To power the board, give it the same power as the logic level of your microcontroller - i.e. for a 5V micro like Arduino, use 5V, or for a 3V micro like a Feather, use 3V.
• GND - This is common ground for power and logic.

I2C Logic Pins

• SCL - I2C clock pin, connect to your microcontroller I2C clock line. This pin uses the same logic level as the VIN pin, and there's a 10K pullup on this pin.
• SDA - I2C data pin, connect to your microcontroller's I2C data line. This pin uses the same logic level as the VIN pin, and there's a 10K pullup on this pin.

STEMMA QT Connectors

• STEMMA QT - These connectors on the left and right ends of the breakout allow you to connect to development boards with STEMMA QT connectors, or to other things, with various associated accessories.

Expander Pins

This breakout has a total of 16 I/O expander pins available.

• Along the bottom are the first 8 I/O pins for expanding your project. They are labeled below the pads, left-to-right as P0 through P7.
• Along the top are the second 8 I/O pins for expanding your project. They are labeled above the pads, left to right as 15 through 10 and P9 and P8.

Expander Power Pins

• Above the bottom set of I/O pins is the ground pins for the expander I/O pins. Highlighted in white on the silk, they are labeled to the left of the row with a - in a circle, and above the right end of the row with GND.
• Below the top set of I/O pins is the positive voltage for the expander I/O pins. Highlighted in white on the silk, they are labeled to the left of the row with a + in a circle, and below the right end of the row with VCC (same as VIN).

Address Pin and Jumpers

• On the back of the board are three address jumpers, labeled A0, A1, and A2. These jumpers allow you to chain up to 8 of these boards on the same pair of I2C clock and data pins. To do so, you solder the jumpers "closed" by connecting the two pads, in various combinations.
• On the front of the board are three address pins, labeled A0, A1, and A2. Just like the jumpers, these pins allow you to change the I2C address to connect multiple boards by connecting them to VIN in various combinations.

The default I2C address is 0x20. The other address options can be calculated by “adding” the A0/A1/A2 to the base of 0x20.

A0 sets the lowest bit with a value of 1, A1 sets the next bit with a value of 2 and A2 sets the next bit with a value of 4. The final address is 0x20 + A2 + A1 + A0 which would be 0x27.


So for example if A2 is soldered closed and A0 is soldered closed, the address is 0x20 + 4 + 1 = 0x25.


If only A0 is soldered closed, the address is 0x20 + 1 = 0x21


If only A1 is soldered closed, the address is 0x20 + 2 = 0x22


If only A2 is soldered closed, the address is 0x20 + 4 = 0x24

The table below shows all possible addresses, and whether the pin(s) or jumper(s) should be high (closed) or low (open).

INT Pin

• The INT pin is the IRQ output, which will automatically alert you when input pins change value.

On LED and LED Jumper

• On the left side of the front of the board is the on LED which lights up when the board has power. It is labeled to the left of the LED as on.
• Towards the right side of the back of the board is the LED jumper. It is two pads connected by a trace, labeled as LED to the left of the pads. If you'd rather not have the on LED lit up when the board has power, you can cut the trace between the two pads. To reenable the on LED, you can bridge the pads again with solder.

PCF8575 Chip

• The grey square to the left of center of the breakout is the PCF8575 I/O expander chip. This is what provides you with all of the expansion features of this board.