How to Use IO Expander MCP23017 Breakout: Examples, Pinouts, and Specs

The MCP23017 IO Expander Breakout, manufactured by Soldered (Part ID: 333007), is a versatile 16-bit I/O expander that communicates via the I2C protocol. It allows microcontrollers to extend their GPIO capabilities by adding 16 additional input/output pins. This breakout board simplifies the integration of the MCP23017 into your projects by providing easy access to all pins and connections.

• Expanding GPIO capabilities of microcontrollers like Arduino, Raspberry Pi, or ESP32.
• Controlling multiple LEDs, relays, or other digital devices.
• Reading multiple button inputs or sensors.
• Building complex projects requiring more I/O pins than the microcontroller natively supports.

• Communication Protocol: I2C
• Operating Voltage: 1.8V to 5.5V
• Maximum Current per Pin: 25mA
• Maximum Total Current: 125mA
• Number of GPIO Pins: 16 (organized as two 8-bit ports: GPIOA and GPIOB)
• I2C Address Range: 0x20 to 0x27 (configurable via address pins)
• Interrupt Pins: INT A and INT B for interrupt-driven applications
• Operating Temperature: -40°C to +85°C

The MCP23017 breakout board provides access to all necessary pins for operation. Below is the pinout:

1. Power the Breakout Board: Connect the VCC pin to your microcontroller's power supply (1.8V to 5.5V) and GND to ground.
2. Connect I2C Lines: Connect the SDA and SCL pins to the corresponding I2C pins on your microcontroller.
3. Set the I2C Address: Use the A0, A1, and A2 pins to configure the I2C address. Each pin can be tied to GND (logic 0) or VCC (logic 1), allowing up to 8 unique addresses (0x20 to 0x27).
4. Connect GPIO Pins: Use GPIOA0-7 and GPIOB0-7 as input or output pins, depending on your application.
5. Optional Interrupts: If needed, connect INT A and/or INT B to your microcontroller for interrupt-driven applications.

• Pull-Up Resistors: Ensure that the I2C lines (SDA and SCL) have appropriate pull-up resistors (typically 4.7kΩ to 10kΩ).
• Voltage Compatibility: Verify that the voltage levels of the MCP23017 and your microcontroller are compatible.
• Pin Configuration: Configure each GPIO pin as input or output using the appropriate I2C commands.
• Interrupts: Use the interrupt pins (INT A and INT B) for efficient handling of input changes without continuous polling.

Below is an example of how to use the MCP23017 with an Arduino UNO to toggle an LED connected to GPIOA0:

#include <Wire.h>
#include "Adafruit_MCP23017.h"

// Create an MCP23017 object
Adafruit_MCP23017 mcp;

void setup() {
  Wire.begin(); // Initialize I2C communication
  mcp.begin(0); // Initialize MCP23017 with default I2C address (0x20)

  // Set GPIOA0 as output
  mcp.pinMode(0, OUTPUT);

  // Set GPIOA1 as input with pull-up resistor
  mcp.pinMode(1, INPUT);
  mcp.pullUp(1, HIGH); // Enable pull-up resistor on GPIOA1
}

void loop() {
  // Read the state of GPIOA1
  int buttonState = mcp.digitalRead(1);

  // Toggle GPIOA0 based on button state
  if (buttonState == LOW) {
    mcp.digitalWrite(0, HIGH); // Turn on LED
  } else {
    mcp.digitalWrite(0, LOW); // Turn off LED
  }

  delay(100); // Small delay for debounce
}

1. I2C Communication Not Working:

   • Ensure SDA and SCL lines are correctly connected to the microcontroller.
   • Check for proper pull-up resistors on the I2C lines.
   • Verify the I2C address matches the configuration of the A0, A1, and A2 pins.

2. GPIO Pins Not Responding:

   • Confirm that the pins are correctly configured as input or output.
   • Check for loose or incorrect connections to the GPIO pins.

3. Interrupts Not Triggering:

   • Ensure the interrupt pins (INT A or INT B) are connected to the microcontroller.
   • Verify that interrupt functionality is enabled in the MCP23017 configuration.

4. Overheating or Malfunction:

   • Ensure the total current drawn by all GPIO pins does not exceed 125mA.
   • Verify that the operating voltage is within the specified range (1.8V to 5.5V).

Q: Can I use multiple MCP23017 breakout boards in the same project?
A: Yes, you can use up to 8 MCP23017 devices on the same I2C bus by configuring unique addresses using the A0, A1, and A2 pins.

Q: What is the maximum cable length for I2C communication?
A: The maximum length depends on the pull-up resistor values and the capacitance of the cable, but typically it is recommended to keep I2C lines under 1 meter for reliable communication.

Q: Can the MCP23017 handle analog signals?
A: No, the MCP23017 is designed for digital input/output only. Use an ADC (Analog-to-Digital Converter) for analog signals.

Q: How do I reset the MCP23017?
A: You can reset the MCP23017 by pulling the RESET pin low momentarily or by cycling the power supply.