The AB Electronics UK Knowledge Base provides support solutions, tutorials and troubleshooting guides.
This item has been replaced with the IO Pi Plus.
The IO Pi is a 32-channel digital development board designed for use with 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 development boards.
Features
- 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 onboard 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. You can use a separate high-current power supply to power the IO Pi, reducing the load on the Raspberry Pi. The 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 includes 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.
Note:
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 connects 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
Recommended Address Configurations
Configuration 1:
IC1 Port = I2C Address: 0x20
IC2 Port = I2C Address: 0x21
Configuration 2:
IC1 Port = I2C Address: 0x22
IC2 Port = I2C Address: 0x23
Configuration 3:
IC1 Port = I2C Address: 0x24
IC2 Port = I2C Address: 0x25
Configuration 4:
IC1 Port = I2C Address: 0x26
IC2 Port = I2C Address: 0x27
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, press the 26-pin connector down onto the Raspberry Pi GPIO pins with the board sitting over the top of the Raspberry Pi.
If you are installing more than one IO Pi on a single Raspberry Pi board, then you must 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.
Schematic
Click to view the schematic PDF.
Mechanical Drawings
Click the image to enlarge
Sample Code
We have Python libraries available for this development board. You can download all of the libraries from GitHub at:
AB Electronics UK GitHub Repository
To download the Python libraries to your Raspberry Pi, type in the terminal:
git clone https://github.com/abelectronicsuk/ABElectronics_Python_Libraries.git
Tutorials
Our Knowledge Base has several IO Pi and IO Pi Plus tutorials.
IO Pi Tutorials
Note: documents in Portable Document Format (PDF) require Adobe Acrobat Reader 5.0 or higher to view, download Adobe Acrobat Reader or other PDF reading software for your computer or mobile device.
