Extending the Raspberry Pi GPIO with an I/O expander

As we have seen, making use of the higher-level bus protocols allows us to connect to more complex hardware quickly and easily. The I²C can be put to great use by using it to expand the available I/O on the Raspberry Pi as well as providing additional circuit protection (and, in some cases, additional power to drive more hardware).

There are lots of devices available that provide I/O expansion over the I²C bus (and also SPI), but the most commonly used is a 28-pin device, MCP23017, which provides 16 additional digital input/output pins. Being an I²C device, it only requires the two signals (SCL and SDA connections plus ground and power) and will happily function with other I²C devices on the same bus.

We shall see how the Adafruit I²C 16x2 RGB LCD Pi Plate makes use of one of these chips to control an LCD alphanumeric display and keypad over the I²C bus (without the I/O expander, this would normally require up to 15 GPIO pins).

Getting ready...