GPIO I2C pHAT

Now you can use multiple HATs with the same I2C address!

The GPIO I2C pHAT is a manual I2C switch which mounts under your HAT to remap its I2C pins to 1 of 4 additional I2C buses.

By making use of the extra hardware I2C buses introduced on Raspberry Pi 4 (BCM2711) or software I2C (bit bang), the GPIO I2C pHAT offers a plug-in solution to overcome the limitations of the infamous “8 HAT limit” seen on many available HATs, without the need for a multiplexer or expander.

Simply attach the GPIO I2C pHAT to your Pi, select your preferred I2C bus and mount your HAT on top. Switching is controlled using a 4-position double-pole slide switch, which allows you to quickly switch between buses.

Multiple GPIO I2C boards can be stacked along with other HATs or pHATs, and it’s fully compatible with our HAT RACK mounting boards.

Includes a breakout header for the 4 extra I2C buses. These are always connected to the associated GPIO pins so can be used regardless of the switch position. Note: external pull-up resistors to 3.3V required.

Features

• Adds 4 additional I2C buses with breakout
• User selectable I2C GPIO pin remapping
• Hardware I2C compatible (Pi 4)
• Slide switch allows fast bus switching
• No-conflict solder jumpers
• Stackable design
• Immersion gold plated copper
• Compatible with our HAT RACK boards

Usage

Add required dtoverlay parameter(s) to /boot/config.txt and reboot.

Mount the GPIO I2C pHAT board to your Pi, use the slide switch to select your preferred I2C bus and stack your I2C based HAT on top.

Hardware I2C (Pi 4 Only)

dtoverlay=i2c3
dtoverlay=i2c4
dtoverlay=i2c5
dtoverlay=i2c6

Software I2C (Bit Bang)

dtoverlay=i2c-gpio,bus=6,i2c_gpio_sda=22,i2c_gpio_scl=23
dtoverlay=i2c-gpio,bus=5,i2c_gpio_sda=12,i2c_gpio_scl=13
dtoverlay=i2c-gpio,bus=4,i2c_gpio_sda=8,i2c_gpio_scl=9
dtoverlay=i2c-gpio,bus=3,i2c_gpio_sda=4,i2c_gpio_scl=5

Note: When using multiple software I2C buses, it’s best to add the parameters from highest to lowest, i.e., 6, 5, 4, 3.

Device Compatibility

The GPIO I2C pHAT is compatible with all 40-way Raspberry Pi models.

Dimensions

Schematic Diagram

Compliance

• UL 796 certified manufacturer
• RoHS compliant (lead free)
• CE & UKCA compliant (certificates)

Documentation

You can find this and our other Raspberry Pi projects on our GitHub page.

Gerber Files

Available for download here.

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