HM55B Compass Module

Comments

• ellizard Posts: 106

  2007-01-29 09:39 edited 2007-01-29 09:39

  HI Nagelo,
  
  HM55B Compass Module, is like any other compasses sensible to the whole magnetic field present where it is located.
  "Whole" means the heart magnetic field toghether with the other disturbance fields
  (i.e. the magnetic fields generated by the electric wiring nearby, the presence of magnetic masses, etc.)
  this said, it's obvious that whenever you put the HM55B compass module in a place with differing magnetic disturbances,
  the calibration done is not anymore valid.
  So as a general rule: whenever the compass module is in a new environment, must be calibrated again.
  
  This is done on boats too any time the magnetic compass of the boat is changed (due to ageing or breaks),
  it's done also whenever in the boat are done engine substitution or other major electric wiring reworking.
  The compass reading are affected by three different magnetic influences;

  • general magnetic field of the heart (always pointing to magnetic north of the eart).
  • magnetic field direction present in specific parts of the eart surface (called DECLINATION)
  • magnetic field local perturbations due to influences in the proximity of the compass due to metal masses influences
    This perturbation is called DEVIATION

  
  This should be enough to claryfie the subject.................
  In the specific, it should be obvious that changing the electronic environment in wich the compass module is embedded,
  (Deviation) will alter the calibrations data.............
  for what concerns the Declination, it is valuable only when the travel is accomplished for long distances.
  
  hope to have clarified some of the aspects of the compass workings general rules......
  
  
  Saluti
  Stefano
• Bruce Bates Posts: 3,045

  2007-01-29 11:47 edited 2007-01-29 11:47

  Nagelo -
  
  Just to add a bit of clarification to Stefano's excellent response, please consider the following. Stefano wrote:
  
  "So as a general rule: whenever the compass module is in a new environment, must be calibrated again."
  
  By "new environment" we're speaking here of a new mounting environment or position, as opposed to a new geographic environment. When any compass is "swung" by hand, or electronically calibrated, that initialization compensates for any magnetic forces or fields in the local area of the compass, near its physical mounting.
  
  Regards,
  
  Bruce Bates
  
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• ellizard Posts: 106

  2007-01-29 13:22 edited 2007-01-29 13:22

  HI Everybody,
  
  The program Parallax suggested for the calibration routine and for the working with calibrated module keep data in the EEPROM so they wont be lost at power down.
  Remain however true that if the module is changed from a Boe on the desk to the Boe on the Bot, the Calibration data will no longer be up to date.
  
  One suggestion............
  
  make a compass module extension with a long arm (10> cm.) as to maintain the module away as possible from the electronic and iron masses as well from the motors.
  
  Somewhere on the Parallax Forums as been debated this topic.
  
  I did with one rigid copper wire between two six pin dil connectors thin wires for the electrical wirings and that's all, it's working fine, also with the laptop nearby.
  (Before it was impossible if the Boe was 40 cm. or less from the laptop).
  
  Saluti
  Stefano
  
  Post Edited (ellizard) : 1/29/2007 1:28:39 PM GMT
• nagelo Posts: 2

  2007-01-29 15:16 edited 2007-01-29 15:16

  Thanks Guys,
  thats helps to understand why I received the results I got. I will follow the recommendation from Stefano and build a bracket to move the HM55B away from the bot and the servos.
  
  Thanks again for the quick reply, it really help me a lot.
  
  Andreas