> Source: https://www.tinkered.ai/components/gy-271/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/gy-271/raspberry-pi-pico. To test the circuit without hardware, it opens and runs free in Tinkered.
> The index of every Tinkered reference is at https://www.tinkered.ai/llms.txt

# GY-271 Compass (QMC5883L) with a Raspberry Pi Pico

The GY-271 (QMC5883L) compass module runs from the Raspberry Pi Pico's 3V3 and sits on I2C0, SDA on GP4 and SCL on GP5, at address 0x0D. Its pull-ups go to the module's VCC, so 3V3 keeps the bus at the Pico's level; on VBUS they would lift GP4 and GP5 to about 5 V.

## Wiring

| GY-271 Compass (QMC5883L) | Raspberry Pi Pico | Note |
| --- | --- | --- |
| VCC | 3V3 |  |
| GND | GND |  |
| SDA | GP4 |  |
| SCL | GP5 |  |

## What to know on the Raspberry Pi Pico

- compass.init() calls Wire.begin() itself. On the Pico, call Wire.setSDA() and Wire.setSCL() before init() if you move the bus off GP4 and GP5. (QMC5883LCompass library source, init(); arduino-pico core documentation (Earle Philhower), Wire)
- The chip inside runs from 2.16 V to 3.6 V and draws 75 µA at 10 Hz; the module regulates its VCC down, and on 3V3 it is a negligible load for the Pico's rail. (QST QMC5883L datasheet Rev A, p. 4)
- Keep the module away from the Pico's switching buck-boost regulator and from any motor or servo the Pico drives: a magnetometer reads their fields as heading error. (Raspberry Pi Pico datasheet, release 21, p. 20)
- If nothing answers at 0x0D, the board may carry an older HMC5883L at 0x1E, which needs another library. (Honeywell HMC5883L datasheet Rev E, p. 11)

## Code

Libraries: mprograms/QMC5883LCompass

```cpp
// GY-271 Compass (QMC5883L) on Raspberry Pi Pico: wiring and a free simulation at https://www.tinkered.ai/components/gy-271/raspberry-pi-pico
// lib_deps = mprograms/QMC5883LCompass
#include <QMC5883LCompass.h>

QMC5883LCompass compass;

const char* const POINTS[16] = {"N", "NNE", "NE", "ENE", "E", "ESE", "SE", "SSE", "S", "SSW", "SW", "WSW", "W", "WNW", "NW", "NNW"};

void setup() {
  Serial.begin(9600);
  compass.init();            // Wire.begin(), then continuous 200 Hz, ±8 G
  Serial.println("Compass ready");
}

void loop() {
  compass.read();
  int x = compass.getX();
  int y = compass.getY();
  int z = compass.getZ();

  int heading = compass.getAzimuth();   // -180..179
  if (heading < 0) heading += 360;      // 0..359, clockwise from magnetic north

  // the 16-point name: 22.5° each, N centred on 0
  const char* point = POINTS[(int)((heading + 11.25) / 22.5) % 16];

  Serial.print("heading ");
  Serial.print(heading);
  Serial.print(" ");
  Serial.print(point);
  Serial.print("  x ");
  Serial.print(x);
  Serial.print(" y ");
  Serial.print(y);
  Serial.print(" z ");
  Serial.println(z);
  delay(250);
}
```

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

## Questions

### Do I power the GY-271 from 3V3 or VBUS on a Pico?

3V3. The module's 2.2 kOhm pull-ups go to its VCC, so 3V3 keeps SDA and SCL at 3.3 V; on VBUS they would sit near 5 V, above the RP2040's IOVDD + 0.5 V limit (RP2040 datasheet, section 5.5.3.1).

### Why is my Pico compass heading wrong?

Keep the board flat and away from magnets, motors and the Pico's own switching regulator (Pico datasheet, p. 20). getAzimuth() returns -180 to 179; the sketch adds 360 to negative values.

### Does the Pico see the GY-271 on an I2C scan?

A QMC5883L answers at 0x0D (QST datasheet Rev A, p. 13). A board answering at 0x1E carries an HMC5883L instead.

## More

- [GY-271 Compass (QMC5883L) reference](https://www.tinkered.ai/components/gy-271.md): pinout, specs, rules and common mistakes

## Try it

Tinkered simulates the GY-271 Compass (QMC5883L) on the Raspberry Pi Pico in the browser, with this wiring and code, free: https://www.tinkered.ai/components/gy-271/raspberry-pi-pico