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!
Adafruit used this chip in Adafruit's 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. Adafruit even have an Arduino library with example code written which will set pin state, read and write from individual pins, and set the pullups.
- This board/chip uses I2C 7-bit address between 0x20-0x27, selectable with jumpers
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Documentation and Resources:
- I2C Bus and the Arduino
I²C stands for the inter-integrated circuit and refers to a communication protocol we are going to use to communicate between our Arduino devices. In the past we have investigated the SPI and Asynchronous Serial Communications protocols for this...
- The Maker Revolution
The Maker Revolution celebrates the creation of new devices and the modification of existing ones - the transition from a consumer buying goods to eventually having a major part in their creation. The Maker Revolution places strong emphasis on free (...
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