Add another eight pins to your microcontroller using a MCP23008 port expander. The MCP23008 uses two I²C pins which can be shared with other I²C devices, and in exchange gives you eight general purpose pins. You can set each of eight pins to be input, output, or input with a pullup. There's even the ability to get an interrupt via an external pin when any of the inputs change so you don't have to keep polling the chip.

Use this chip from 2.7-5.5V (good for any 3.3V or 5V setup), and you can sink/source up to 20mA from any of the I/O pins so this will work for LEDs and such. Team it up with a high-power MOSFET if you need more juice. DIP package means it will plug into any breadboard or perfboard.

You can set the I²C address by tying the ADDR0-2 pins to power or ground, for up to eight unique addresses. That means eight chips can share a single I²C bus - that's 64 I/O pins!

• 8-bit remote bidirectional I/O port
• High-speed I²C interface (MCP23008)
• Hardware address pins
• Configurable interrupt output pin
• Configurable interrupt source
• Polarity Inversion register for input port data polarity config.
• External reset input
• Low standby current: 1 µA (max.) • Operating voltage:
  • 1.8V to 5.5V @ -40°C to +85°C I2C @ 100 kHz SPI @ 5 MHz
  • 2.7V to 5.5V @ -40°C to +85°C I2C @ 400 kHz SPI @ 10 MHz
  • 4.5V to 5.5V @ -40°C to +125°C I2C @ 1.7 kHz SPI @ 10 MHz

• Datasheet
• Bourns EAW - ACE GitHub