{"id":21759,"date":"2017-08-28T08:01:23","date_gmt":"2017-08-28T15:01:23","guid":{"rendered":"https:\/\/blog.digilentinc.com\/?p=21759"},"modified":"2023-04-17T11:43:55","modified_gmt":"2023-04-17T18:43:55","slug":"how-to-convert-magnetometer-data-into-compass-heading","status":"publish","type":"post","link":"https:\/\/digilent.com\/blog\/how-to-convert-magnetometer-data-into-compass-heading\/","title":{"rendered":"How to Convert Magnetometer Data into Compass Heading"},"content":{"rendered":"
\"Pmod
Pmod CMPS2 3-axis digital magnetometer\/compass.<\/em><\/figcaption><\/figure>\n

In two previous \u00a0posts <\/a>we discussed how to calibrate <\/a>magnetometer data in order to get accurate measurements, as well as how to acquire<\/a> data in the first place. In this post we will go through the last major step, how to convert the data from units of Gauss into a true compass heading using the Pmod CMPS2 <\/a>as an example. You can use an FPGA board like the Basys 3<\/a>, Nexys A7<\/a>, or Cora Z7<\/a> to host the Pmod.<\/p>\n

Data Conversion<\/strong><\/p>\n

The Memsic MMC34160PJ<\/a> magnetometer on the Pmod CMPS2 provides data for each axis in units of Gauss, but the information is generally more legible when presented as a compass heading. The method for converting Gauss units to a compass heading is provided below.<\/p>\n

    \n
  1. \n
    Calculate the real Gauss value for the X and Y axes from the amount of LSBs returned where the LSB value by default is 0.48828125 mG, resulting in 2048 LSBs per Gauss.<\/div>\n
    <\/div>\n
    <\/div>\n
    <\/div>\n
    <\/div>\n
    x<\/span><\/span>G<\/span><\/span>a<\/span><\/span>u<\/span><\/span>s<\/span><\/span>s<\/span><\/span>D<\/span><\/span>a<\/span><\/span>t<\/span><\/span>a\u00a0<\/span><\/span>=\u00a0<\/span><\/span>x<\/span><\/span>D<\/span><\/span>a<\/span><\/span>t<\/span><\/span>a<\/span><\/span>L<\/span><\/span>S<\/span><\/span>B<\/span><\/span>\u2217<\/span><\/span>0.48828125<\/span><\/span>\u00a0<\/span><\/span>m<\/span><\/span>G<\/span><\/span><\/span><\/span><\/span><\/div>\n
    <\/span>
    \ny<\/span><\/span>G<\/span><\/span>a<\/span><\/span>u<\/span><\/span>s<\/span><\/span>s<\/span><\/span>D<\/span><\/span>a<\/span><\/span>t<\/span><\/span>a\u00a0<\/span><\/span>=\u00a0<\/span><\/span>y<\/span><\/span>D<\/span><\/span>a<\/span><\/span>t<\/span><\/span>a<\/span><\/span>L<\/span><\/span>S<\/span><\/span>B<\/span><\/span>\u2217<\/span><\/span>0.48828125<\/span><\/span>\u00a0<\/span><\/span>m<\/span><\/span>G<\/span><\/span><\/span><\/span><\/span><\/div>\n<\/li>\n
  2. \n
    Calculate the direction\u00a0D<\/em>\u00a0by first checking to see if the X Gauss data is equal to 0 to prevent divide by 0 zero errors in the future calculations. If the X Gauss data is 0, check to see if the Y Gauss data is less than 0. If Y is less than 0 Gauss, the direction D is 90 degrees; if Y is greater than or equal to 0 Gauss, the direction D is 0 degrees.<\/div>\n<\/li>\n
  3. \n
    If the X Gauss data is not zero, calculate the arctangent of the Y Gauss and X Gauss data and convert from polar coordinates to degrees.<\/div>\n
    <\/div>\n
    D\u00a0<\/span><\/span>=\u00a0<\/span><\/span>a<\/span><\/span>r<\/span><\/span>c<\/span><\/span>t<\/span><\/span>a<\/span><\/span>n<\/span><\/span>(<\/span><\/span>y<\/span><\/span>G<\/span><\/span>a<\/span><\/span>u<\/span><\/span>s<\/span><\/span>s<\/span><\/span>D<\/span><\/span>a<\/span><\/span>t<\/span><\/span>a\/<\/span><\/span><\/span><\/span>x<\/span><\/span>G<\/span><\/span>a<\/span><\/span>u<\/span><\/span>s<\/span><\/span>s<\/span><\/span>D<\/span><\/span>a<\/span><\/span>t<\/span><\/span>a<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>)<\/span><\/span><\/span>\u2217(<\/span><\/span>180\/<\/span><\/span><\/span>\u03c0)<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/div>\n<\/li>\n
  4. \n
    If the direction D is greater than 360 degrees, subtract 360 degrees from that value.<\/div>\n<\/li>\n
  5. \n
    If the direction D is less than 0 degrees, add 360 degrees to that value.<\/div>\n<\/li>\n
  6. \n
    The compass heading can then be determined by the direction value D:<\/div>\n