asked on

Building a compass with MPU-9255 Magnometer

I have this module https://www.addicore.com/mpu-9250-p/ad280.htm

I have it sending me raw data for MX, MY, MZ (X,Y,Z,) from this data i am trying to create a compass.

this is example data i am getting

x = 3072
y=-6001

With these values and the script below it combines these variables to calculate a heading to location at= 209 degrees

The problem is when I rotate the compass the numbers are not linear... they jump around ate certain points.... 300, 600, 40, 180

I would like the compass to send me the correct degrees when i rotate it. Thank you for your help!

///JAVASCRIPT

var mx = msg.payload.mx;
var my = msg.payload.my;
var mz = msg.payload.mz;

//var heading = Math.atan2(my, mx) * 180/Math.PI;
//var heading = Math.atan2(my,mx)/Math.PI*180 + 180;

//var heading = Math.atan2(my,mx)/Math.PI*180+180;

//theta_rad = Math.atan2(my,mx);
//heading = (theta_rad/Math.PI*180) + (theta_rad > 0 ? 0 : 360);

angle = Math.atan2(mx,my)*180/Math.PI;
var heading = angle + Math.ceil( -angle / 360 ) * 360;


var lol2 = Math.ceil(heading);


msg.payload = lol2;

return msg;

Open in new window

David Johnson, CD

how are you getting the data points?
Here is the datasheet https://download.mikroe.com/documents/datasheets/ak8963c-datasheet.pdf

Gerald Connolly

From a quick scan of the spec, it looks like each axis should be linear (+32760 -> -32760) but it’s possible that the bytes are swapped .

Zeke Rich

ASKER

how are you getting the data points?

I have a code written in C running on a Arduino that generates the raw data that is sent serial to a javascript node:

/*
Raw data example
This example reads raw readings from the magnetometer gyroscope and the accelerometer and then
displays them in serial monitor.
*/
 
#include <MPU9255.h>//include MPU9255 library
#include <ESP8266WiFi.h>
#include <PubSubClient.h>



// Update these with values suitable for your network.

const char* ssid = "TP-Link_5A4E";
const char* password = "31801621";
const char* mqtt_server = "192.168.0.101";

WiFiClient espClient;
PubSubClient client(espClient);
MPU9255 mpu;


void setup_wifi() {

  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  randomSeed(micros());

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}



#include "mqtt.h";
 
void setup() {
  Serial.begin(115200);//initialize Serial port
 
  if(mpu.init())
  {
  Serial.println("initialization failed");
  }
  else
  {
  Serial.println("initialization succesful!");
  }


  //pinMode(BUILTIN_LED, OUTPUT);     // Initialize the BUILTIN_LED pin as an output.... CAN  NOT USE CREATS CONFLICT!!!
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
 
}
 
void loop() {

  if (!client.connected()) {
    reconnect();
  }
  client.loop();
  
  mpu.read_acc();//get data from the accelerometer
  mpu.read_gyro();//get data from the gyroscope
  mpu.read_mag();//get data from the magnetometer
 
  //print all data in serial monitor
  /*
  Serial.print("AX: ");
  Serial.print(mpu.ax);
  Serial.print(" AY: ");
  Serial.print(mpu.ay);
  Serial.print(" AZ: ");
  Serial.print(mpu.az);
  Serial.print(" GX: ");
  Serial.print(mpu.gx);
  Serial.print(" GY: ");
  Serial.print(mpu.gy);
  Serial.print(" GZ: ");
  Serial.print(mpu.gz);
  Serial.print(" MX: ");
  Serial.print(mpu.mx);
  Serial.print(" MY: ");
  Serial.print(mpu.my);
  Serial.print(" MZ: ");
  Serial.println(mpu.mz);
  */
  delay(100);

    char buffer [100];
    snprintf ( buffer, 100, "ax=%d,ay=%d,az=%d,mx=%d,my=%d,mz=%d", mpu.ax, mpu.ay, mpu.az, mpu.mx, mpu.my, mpu.mz );

    //Serial.print("Publish message: ");
    Serial.println(buffer);
    client.publish("lbicep", buffer); //outTopic, set the topic HERE
}

Open in new window

ASKER CERTIFIED SOLUTION

Zeke Rich

membership

This solution is only available to members.

To access this solution, you must be a member of Experts Exchange.

Start Free Trial