MCP23008 8-Bit I/O Expander with Serial Interface – DIP-18 | Jaycar

You counted the pins on your microcontroller. You need eight more. You don't want to swap the whole board or redesign the layout. The MCP23008 solves that in one chip: three I2C lines in, eight configurable GPIOs out. It idles under 1 µA so it won't drain your battery, runs from 1.8 to 5.5 V, and talks at up to 1.7 MHz over I2C. The interrupt pin is configurable — active-high, active-low, or open-drain — so it slots into whatever logic you've already got. Fourteen pages of data sheet back it up if you need the full spec. Wire three pins, gain eight. Sorted

• Expands 3 I2C pins into 8 configurable GPIO inputs/outputs
• 1.8–5.5 VDC operating range, under 1 µA standby current
• 1.7 MHz high-speed I2C interface
• Configurable interrupt output: active-high, active-low, or open-drain
• External reset input for clean board recovery
• DIP-18 package, straightforward breadboard and PCB fit