compass_bn880

Overview

The compass_bn880 node interfaces with the BN-880 module, a dual-purpose board combining a u-blox GPS receiver with a QMC5883L 3-axis magnetic compass. This provides both geographic position and magnetic heading in a single module. The compass data is read via I2C while the GPS data comes through UART, giving you latitude, longitude, altitude, magnetic heading, pitch, roll, and field strength.

Properties

Output

{
  "latitude": 51.5074,
  "longitude": -0.1278,
  "altitude": 11.2,
  "heading": 247.5,
  "pitch": 2.3,
  "roll": -1.1,
  "magneticField": {
    "x": 0.182,
    "y": -0.054,
    "z": 0.423
  },
  "declination": -0.8,
  "timestamp": 1640000000000
}

Wiring (I2C + UART)

  BN-880            Raspberry Pi
  ------            ------------
  VCC  ──────────── 3.3V (Pin 1)
  GND  ──────────── GND  (Pin 6)
  SDA  ──────────── SDA  (Pin 3 / GPIO 2)
  SCL  ──────────── SCL  (Pin 5 / GPIO 3)
  TX   ──────────── RXD  (Pin 10 / GPIO 15)
  RX   ──────────── TXD  (Pin 8  / GPIO 14)

  Note: SDA/SCL = compass (I2C)
        TX/RX   = GPS (UART)

Example: Drone Heading and Navigation

Combine GPS position with magnetic heading for drone autopilot navigation and waypoint tracking.

// Function node: Navigate to waypoint
var lat = msg.latitude;
var lon = msg.longitude;
var heading = msg.heading;

// Target waypoint
var targetLat = 51.5080;
var targetLon = -0.1260;

// Calculate bearing to target
var dLon = (targetLon - lon) * Math.PI / 180;
var lat1 = lat * Math.PI / 180;
var lat2 = targetLat * Math.PI / 180;

var y = Math.sin(dLon) * Math.cos(lat2);
var x = Math.cos(lat1) * Math.sin(lat2) -
        Math.sin(lat1) * Math.cos(lat2) * Math.cos(dLon);
var bearing = (Math.atan2(y, x) * 180 / Math.PI + 360) % 360;

// Calculate turn needed
var turn = bearing - heading;
if (turn > 180) turn -= 360;
if (turn < -180) turn += 360;

// Distance to waypoint
var R = 6371000;
var dLat = (targetLat - lat) * Math.PI / 180;
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
        Math.cos(lat1) * Math.cos(lat2) *
        Math.sin(dLon/2) * Math.sin(dLon/2);
var distance = R * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));

msg.payload = {
    position: { lat: lat, lon: lon },
    heading: heading,
    bearingToTarget: bearing.toFixed(1),
    turnAngle: turn.toFixed(1),
    distanceToTarget: distance.toFixed(1),
    arrived: distance < 5
};

return msg;

Example: Compass Calibration Check

Monitor magnetic field consistency to detect when the compass needs recalibration due to magnetic interference.

// Function node: Calibration quality monitor
var mag = msg.magneticField;
var fieldStrength = Math.sqrt(
    mag.x * mag.x + mag.y * mag.y + mag.z * mag.z
);

var readings = flow.get('magReadings') || [];
readings.push(fieldStrength);
if (readings.length > 100) readings.shift();
flow.set('magReadings', readings);

// Calculate variance
var sum = readings.reduce(function(a, b) { return a + b; }, 0);
var mean = sum / readings.length;
var variance = readings.reduce(function(acc, val) {
    return acc + Math.pow(val - mean, 2);
}, 0) / readings.length;

var quality = "good";
if (variance > 0.05) quality = "needs_calibration";
else if (variance > 0.02) quality = "moderate";

msg.payload = {
    heading: msg.heading,
    fieldStrength: fieldStrength.toFixed(4),
    variance: variance.toFixed(6),
    quality: quality,
    samples: readings.length
};

return msg;

Common Use Cases