Features

• 16 Digital Inputs/Outputs
• Control via the Raspberry Pi I2C port
• Stack up to 8 IO Pi boards on a single Raspberry Pi
• Solder pad selectable I2C addresses
• External 5V Input with isolation pad
• 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

Introduction:

The IO Pi Zero is a 16 channel digital expansion board designed for use on the Raspberry Pi Zero. The board is based around the MCP23017 16-bit I/O expander from Microchip Technology Inc. A MCP23017 expander is included on the board allowing you to connect up to 16 digital inputs or outputs to the Raspberry Pi.  The IO Pi Zero 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 Zero along with other expansion boards.

The I2C address bits are selectable using the on-board jumpers. The MCP23017 supports up to 8 different I2C addresses so with one MCP23017 device on each IO Pi Zero you can stack up to 8 IO Pi Zero 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 solder 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 or Vdd.  This gives 8 possible I2C addresses for each chip.  The IO Pi Zero contains one MCP23017 chip so you can stack up to 8 IO Pi boards on a single Raspberry Pi.  To simplify address selection on the IO Pi we have included a set of address selection pads which can be configured by applying a small solder bridge across the required pads. The table below show the recommended configurations for your IO Pi and the associated I2C addresses.

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

Default Configuration (IC1 = 0x20)

 Compatibility Chart

Model	Status
Raspberry Pi Model A	No
Raspberry Pi Model B	No
Raspberry Pi 1 Model A+	Yes
Raspberry Pi 1 Model B+	Yes
Raspberry Pi 2 Model B	Yes
Raspberry Pi 3 Model B	Yes
Raspberry Pi Zero	Yes
Raspberry Pi Zero W	Yes
ODroid C1	Yes
ODroid C2	Yes
Orange Pi	Yes
Asus Tinker Board	Yes

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

Installation

To install the IO Pi simply press the 40 pin connector down onto the Raspberry Pi GPIO pins with the board sat over the top (or below) 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.

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

Schematic

Click to download schematic PDF.

Mechanical Drawings

Click image to enlarge

Code Libraries and Demos

We have Python, Arduino, C, C++, Node.js and Windows 10 IOT libraries available for this expansion board.  You can download all of the libraries from github at:

https://github.com/abelectronicsuk/ or click on the logos below for your selected programming language