Adafruit
MCP23017 - i2c 16 input/output port expander
Add another 16 pins to your microcontroller using a MCP23017 port expander. The MCP23017 uses two i2c pins (these can be shared with other i2c devices)...
Add another 16 pins to your microcontroller using a MCP23017 port expander. The MCP23017 uses two i2c pins (these can be shared with other i2c devices), and in exchange gives you 16 general purpose pins. You can set each of 16 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 8 unique addresses. That means 8 chips can share a single i2c bus - that's 128 I/O pins!
We used this chip in our RGB LCD + Keypad shield to both control an LCD and read a 5-way keypad and found it to be very reliable and easy to get up and running. We even have an Arduino library with example code written which will set pin state, read and write from individual pins, and set the pullups.
Jargon buster
Plain-language definitions for the technical terms used above.
- I2C
- I2C is a two-wire communication bus used by many sensors and small modules. It matters because several I2C devices can share the same two wires, but each device needs a compatible address and your controller must support I2C.
- I2C address
- An I2C address is the number a device uses so a microcontroller can tell it apart from other devices on the same I2C bus. It matters because two devices with the same fixed address may conflict if used together.
- LCD
- LCD stands for liquid crystal display, a screen technology that uses a backlight and liquid crystals to show images or text. It matters because LCD modules usually need a display driver and enough controller pins or a bus interface to send image data.
- microcontroller
- A microcontroller is a small computer on a chip that runs your program and controls connected inputs and outputs. For this product, it is the part that reads buttons and sensors, drives the display and speaker, and communicates over Bluetooth.
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