Knowledge Base

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Created 11/05/2016 | IO Pi Expansion board

This item has been replaced with the IO Pi Plus.

The IO Pi is a 32 channel digital expansion board designed for use on the Raspberry Pi computer platform. The board is based around the MCP23017 16-bit I/O expander from Microchip Technology Inc. A pair of MCP23017 expanders are included on the board allowing you to
connect up to 32 digital inputs or outputs to the Raspberry Pi.  The IO Pi Expander is powered through the host Raspberry Pi using the GPIO port and extended pins on the GPIO connector allow you to stack the IO Pi along with other expansion boards.


  •  32 Digital Inputs/Outputs
  • Control via the Raspberry Pi I2C port
  • Stack up to 4 IO Pi boards on a single Raspberry Pi
  • Jumper selectable I2C addresses
  • External 5V Input with isolation jumper
  • Based on the MCP23017 from Microchip Technologies Inc
  • Configurable interrupt output pins - Configurable as active-high, active-low or open-drain
  • INTA and INTB can be configured to operate independently or together
  • Configurable interrupt source  - Interrupt-on-change from configured register defaults  or pin changes
  • Polarity Inversion register to configure the polarity of the input port data

The I2C address bits are selectable using the on-board jumpers. The MCP23017 supports up to 8 different I2C addresses so with two MCP23017 devices on each IO Pi you can stack up to 4 IO Pi boards on a single Raspberry Pi giving a maximum of 128 I/O ports.

The IO Pi includes a 5V port that can be isolated from the Raspberry Pi via an isolation jumper so you can use a separate high current power supply to power the IO Pi reducing the load on the Raspberry Pi. Use of an external supply is recommended if you plan on connecting more than one IO Pi to your Raspberry Pi.

I2C Address Selection

The MCP23017 contains three address select pins which can be tied to Vss, Vdd.  This gives 8 possible I2C addresses for each chip.  The IO Pi contains two MCP23017 chips so you can stack up to 4 IO Pi boards on a single Raspberry Pi.  To simplify address selection on the IO Pi we have included a set of address selection pins which can be configured using the included jumpers. The illustrations below show the four recommended configurations for your IO Pi and the associated I2C addresses.

Disconnect the IO Pi from the Raspberry Pi before changing the address pins.  The address pins are tied to Vdd (high) via a 10K resistor so the jumper is used to tie a pin to ground (low).

Default Configuration (IC1 = 0x20, IC2 = 0x21)

When you purchase the IO Pi the address selection jumpers will be pre-configured to the following addresses. IC1 Port = I2C Address: 0x20, IC2 Port = I2C Address: 0x21

Default I2C config

Recommended Address Configurations

Configuration 1: 
IC1 Port = I2C Address: 0x20
IC2 Port = I2C Address: 0x21

Config 1

Configuration 2: 
IC1 Port = I2C Address: 0x22
IC2 Port = I2C Address: 0x23

Config 2

Configuration 3: 
IC1 Port = I2C Address: 0x24
IC2 Port = I2C Address: 0x25

Config 3

Configuration 4: 
IC1 Port = I2C Address: 0x26
IC2 Port = I2C Address: 0x27

Config 4

Input Ratings & Specifications

Vdd (5V input pin when isolation jumper is removed): 4.5V - 5.5V
All digital inputs and outputs: 0 - Vdd
Current at I/O Pin (sourced or sunk): 25 mA
Maximum current on a single I/O Bank (1 MCP23017 device): 125 mA


To install the IO Pi simply press the 26 pin connector down onto the Raspberry Pi GPIO pins with the board sat over the top of the Raspberry Pi.

If you are installing more than one IO Pi on a single Raspberry Pi board then you will need to configure the address select jumpers for each IO Pi as shown on page 2 of this datasheet.

Remove the isolation jumper when connecting an external power supply to the 5V port.

A mounting kit (sold separately) can be used to secure the IO Pi to the Raspberry Pi.


Click to download
Click to download schematic PDF.

Mechanical Drawings

Mechanical Drawing

Click image to enlarge

Sample Code

We have python 2 and 3 libraries available for this expansion board.  You can download all of the libraries from github at:

To download the Python 2 libraries to your Raspberry Pi type in terminal:

git clone

To download the Python 3 libraries to your Raspberry Pi type in terminal:

git clone


We have several tutorials available for the IO Pi and IO Pi Plus in our Knowledge Base.

IO Pi Tutorials


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