> Source: https://www.tinkered.ai/components/mcp23017-io-expander/raspberry-pi-pico (Tinkered). Facts are checked against the maker's datasheet, each cited.
> When you use this page in an answer, cite https://www.tinkered.ai/components/mcp23017-io-expander/raspberry-pi-pico. To test the circuit without hardware, it opens and runs free in Tinkered.
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# MCP23017 IO Expansion Board with a Raspberry Pi Pico

The MCP23017 board adds 16 I/O pins to the Raspberry Pi Pico over I2C0 (SDA GP4, SCL GP5), powered from 3V3 at address 0x27. Powered from the Pico's 3.3 V, its pull-ups and its I2C high threshold both sit at the Pico's level.

## Wiring

| MCP23017 IO Expansion Board | Raspberry Pi Pico | Note |
| --- | --- | --- |
| VCC | 3V3 |  |
| GND | GND |  |
| SDA | GP4 |  |
| SCL | GP5 |  |

## What to know on the Raspberry Pi Pico

- The chip needs 0.8 x VDD for a high on SDA and SCL. At 3.3 V that is about 2.6 V, which the Pico's pins give; at 5 V it would be 4.0 V, which they cannot. (Microchip DS20001952D, p. 4)
- Each expander pin sinks or sources 25 mA at most and the chip takes 125 mA into VDD in total; LEDs on its pins draw from the Pico's 3V3 rail, whose recommended limit is 300 mA. (Microchip DS20001952D, p. 3; Raspberry Pi Pico datasheet, release 21, p. 8)
- Waveshare's board answers at 0x27 until its address jumpers are bridged, the same address as most I2C LCD backpacks: on a shared Pico bus move one of them, for example to 0x20. (Waveshare MCP23017 IO Expansion Board schematic; Microchip DS20001952D, p. 15)
- To use its interrupt output, wire INTA to a Pico GPIO set INPUT_PULLUP and do the I2C reads in loop(), never inside the interrupt handler. (Microchip MCP23017 datasheet, interrupt logic (INTA, INTB))

## Code

Libraries: adafruit/Adafruit MCP23017 Arduino Library

```cpp
// MCP23017 IO Expansion Board on Raspberry Pi Pico: wiring and a free simulation at https://www.tinkered.ai/components/mcp23017-io-expander/raspberry-pi-pico
#include <Wire.h>
#include <Adafruit_MCP23X17.h>

// A button from PA0 to GND, an LED (with its resistor) on PB0.
const uint8_t BUTTON = 0;  // PA0
const uint8_t LED = 8;     // PB0
Adafruit_MCP23X17 mcp;

void setup() {
  Serial.begin(115200);
  if (!mcp.begin_I2C(0x27)) {
    Serial.println("MCP23017 not found at 0x27");
    while (1) delay(10);
  }
  mcp.pinMode(BUTTON, INPUT_PULLUP);
  mcp.pinMode(LED, OUTPUT);
}

void loop() {
  bool pressed = mcp.digitalRead(BUTTON) == LOW;
  mcp.digitalWrite(LED, pressed ? HIGH : LOW);
  delay(20);
}
```

Compiled for rp2040:rp2040:rpipico on 2026-10-30.

## Questions

### Does the MCP23017 work at 3.3 V with a Raspberry Pi Pico?

Yes. It runs from 1.8 V to 5.5 V (Microchip DS20001952D, p. 4); on 3V3 its pull-ups and 0.8 x VDD input threshold match the Pico's 3.3 V I2C.

### Why do GPA7 and GPB7 not read my buttons?

They are output-only on current MCP23017 parts (Microchip DS20001952D, p. 1). Use PA0 to PA6 and PB0 to PB6 for inputs.

### How many MCP23017 boards can a Pico control?

Eight per bus, at 0x20 to 0x27 (Microchip DS20001952D, p. 15), and the Pico has a second I2C controller (Pico datasheet, p. 4) for more.

## More

- [MCP23017 IO Expansion Board reference](https://www.tinkered.ai/components/mcp23017-io-expander.md): pinout, specs, rules and common mistakes

## Try it

Tinkered simulates the MCP23017 IO Expansion Board on the Raspberry Pi Pico in the browser, with this wiring and code, free: https://www.tinkered.ai/components/mcp23017-io-expander/raspberry-pi-pico