The default I2C address is 0x20.

Power Pins

• Vcc - 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.
• V+/+ - The DC power input terminal block for the solenoids is located in the center of the terminal block row on the top edge of the board. You can use 3V to 24V DC maximum to power the solenoids.
• GND - This is common ground for power and logic.
• GND pads - The ground pads (highlighted in white on the board's silkscreen) are available as discrete ground connections for the GPIO.

I2C Logic Pins

• SCL - I2C clock pin, connect to your microcontroller's I2C clock line. This pin can use 3-5V logic, and there's a 10K pullup on this pin.
• SDA - I2C data pin, connect to your microcontroller's I2C data line. This pin can use 3-5V logic, and there's a 10K pullup on this pin.
• STEMMA QT - These connectors allow you to connect to dev boards with STEMMA QT (qwiic) connectors or to other things with various associated accessories

Solenoid Terminal Block Outputs

Along the top edge of the board are two sets of 8 terminal blocks. These are the solenoid outputs from the N-Channel MOSFETs connected to the MCP23017.

• The outputs labeled + on the front of board and V+ on the back, are connected to the DC power supply input terminal block and connect to the positive input on your solenoid.
• The numbered outputs, labeled 0-7 on the front of the board and A0-A7 on the back, will connect to the negative input on your solenoid and are routed to the A port pins on the MCP23017 (A0-A7). 

Additional MCP23017 GPIO Pins

Along the bottom edge of the board are 8 additional GPIO from the MCP23017 B port. These pins are labeled B0-B7 and correspond to those same output pins on the MCP23017. You can use these pins as general purpose I/O for LEDs, button inputs, etc.

MCP23017 Port B Interrupt Pin

• INT - This is the interrupt pin (INTB) for port B on the MCP23017. You can use it to keep track of inputs connected to the port B GPIO pins at the bottom edge of the breakout.

LEDs

• Red LEDs - Directly below the terminal blocks are 8 red LEDs. These LEDs act as indicators for the 8 solenoid outputs. When a signal is sent to any of these outputs, the corresponding red LED will turn on.
• Power LED - On the left side of the board, above the STEMMA QT port, is the power LED. It is a green LED. 
• Power LED Jumper - This jumper is located on the back of the board, on the right. Cut the trace on this jumper to cut power to the green power LED.

I2C Address Pins

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.

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 Vcc.

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) should be high (closed) or low (open).