Power

• VB (VBUS) - This is the micro-USB input voltage, connected to the micro-USB port on the Raspberry Pi Pico. It is nominally 5V.
• VS (VSYS) - This is the main system input voltage. It can range from 1.8V to 5.5V and is used to generate the 3.3V needed for the RP2040 and the GPIO pins.
• EN (3V3_EN) - This connects to the enable pin on the Raspberry Pi Pico, and is pulled high (to VSYS) via a 100kΩ resistor.
• 3.3V - This is the 3.3V output from the Raspberry Pi Pico. There is a long strip of connected holes for 3.3V power, noted by a line of white on the board silk.
• VREF (ADC_VREF) - This is the ADC power supply and reference voltage. It is generated on the Raspberry Pi Pico by filtering the 3.3V supply. It can be used with an external reference when ADC performance is required.
• GND - This is the common ground for power and logic. All GND pins are highlighted in white rectangles on the silk.

I2C Logic

• SCL - I2C clock pin on the PiCowBell. It is connected to your Pico I2C clock line, which is GPIO5. This connection is shared with the STEMMA QT port on the end of the board.
• SDA - I2C data pin on the PiCowBell. It is connected to your microcontroller I2C data line, which is GPIO4. This connection is shared with the STEMMA QT port on the end of the board.
• STEMMA QT - These connectors allow you to connect to dev boards with STEMMA QT connectors or to other things with various associated accessories. The port is located on the end of the PiCowBell.
• STEMMA QT Breakout Holes - There is an extra set of 4 breakout holes directly below the STEMMA QT port if you want more I2C connections or want to re-assign the I2C port.

Socket Headers and Duplicate GPIO Hole Pads

The PiCowBell has two 2x20 slim socket headers to plug in your Pico and have an extra row of sockets for each pin. There are also duplicate hole pads next to each pin for solder-jumpering:

• IO0-IO15, IO16-IO22, Reset, A0-A2, VR, 3V, EN, VS and VB. Ground pins that have a duplicate hole pad are highlighted in white rectangles on the board silkscreen.

Proto Area

In the center of the board, you'll find the proto area. This area on the board is made up of 12 3 hole-connected strips. You can cut the traces between the holes, but they're intended to be treated like a mini-mini breadboard.

Reset Button

At the bottom edge of the board is the reset button. It is routed to the reset pin on the PiCowBell and is labeled RESET on the board silk. You can press it to restart your program.