I2C port extenders or expanders are extremely useful devices, and I use quite a lot of them in my projects. My go-to device is definitely the PCF8574, mainly because it is sort of “breadboard friendly”. The MCP23017, with the existing breakouts available locally, are not. I have thus decided to design my own version of a breadboard friendly MCP23017 breakout board.
The Breakout Module PCB and its features
While this was definitely one of my easier projects, It still took a bit of time to get it just right and add some essential components and features directly onto the PCB.
The main features of this breakout:
– DIP12 Layout – with all pins broken out, address pins to jumper headers…
– Proper decoupling capacitors, as close as possible to the MCP23017 chip.
I had to make use of the back layer of the PCB to do this, not exactly ideal, but with proper power and ground planes, and nice thick tracks, I believe they will be just fine.
– Address selector jumpers – The breakouts that are available locally, do not have these.
– Breadboard friendly layout – 33.020mm x 20.320mm [board size], with 15.240mm vertical spacing between the rows of pins, ensures that you can easily fit it onto your breadboard, while still having space to add jumper wires to the pins. Horizontal pin spacing is standard 2.45mm.
The Schematic
The schematic is plain and simple. A few points to note though:
– The address selection header, as well as the io pin headers are not shown on the schematic.
– I2C pullup resistors are set at 1k but can be replaced with more suitable values as required in your circuit
Using the breakout
I have previously written two very detailed articles on using this chip. They are linked below:
Using the MCP23017 with the standard Wire.h library
Using the MCP23017 with the Adafruit MCP23017 library
Manufacturing the PCB
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