HMC5883L Magnetometer chip Possibilities.

[andybarrett1]

Hi George

This is the exact one I am using ... The ebay link has Pics and Circuit... I am running it at 5v.. As the LCD needs 5v

http://www.ebay.co.uk/itm/1112141408...%3AMEBIDX%3AIT

BR
Andy

[towlerg]

So you are connecting the clock and data from the PIC directly to the break-out board pins? Do you have pull-ups? if so to 5 or 3.3?

george

[andybarrett1]

Hi George

I wondered about this

I have measured 2K2 to the 5v rail on the breakout board.

The Ic2 link seems to run OK so happy with that.

My issue remains to be the conversion from radians to degrees.

[richard]

I bought one to play with

after looking at the raw data I came up with this , works ok if device is held level , tilt compensation is elusive at this stage

'****************************************************************
'*  Name    : hmc5883l.BAS                                      *
'*  Author  : [select VIEW...EDITOR OPTIONS]                    *
'*  Notice  : Copyright (c) 2011 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 29/04/2011                                        *
'*  Version :                                              *
'*  Notes   :                                                *
'*          :  12f1822     
'*          :  
             '
'****************************************************************
 #CONFIG
cfg1 = _FOSC_INTOSC
cfg1&= _WDTE_ON
cfg1&= _PWRTE_OFF
cfg1&= _MCLRE_ON
cfg1&= _CP_OFF
cfg1&= _CPD_OFF
cfg1&= _BOREN_ON
cfg1&= _CLKOUTEN_OFF
cfg1&= _IESO_ON
cfg1&= _FCMEN_ON
  __CONFIG _CONFIG1, cfg1
cfg2 = _WRT_OFF
cfg2&= _PLLEN_OFF
cfg2&= _STVREN_ON
cfg2&= _BORV_19
cfg2&= _LVP_OFF
  __CONFIG _CONFIG2, cfg2
#ENDCONFIG
 

      osccon=$6A    '4 mhz
      anselA=0       'dig i/o
        
      trisA=1110
  
  
  
  
   pause 2000
  serout2 porta.0,84, ["ready",13,10]
  lata.0=1
  
  
   SDA            var      porta.2                 'transceives to/from SDA
   SCL            var      porta.4                  'sends clock pulses
WRITE_DATA     CON     $3C  'Used to perform a Write operation
READ_DATA      CON     $3D  'Used to perform a Read operation
MODE           CON     $02  'Read/Write Register, Selects the operating mode. Default = Single measurement
                             'Send $3C $02 $00 on power up to change to continuous measurement mode.
X_MSB          CON     $03  'Read Register, Output of X MSB 8-bit value.
X_LSB          CON     $04  'Read Register, Output of X LSB 8-bit value.
Z_MSB          CON     $05  'Read Register, Output of Z MSB 8-bit value.
Z_LSB          CON     $06  'Read Register, Output of Z LSB 8-bit value.
Y_MSB          CON     $07  'Read Register, Output of Y MSB 8-bit value.
Y_LSB          CON     $08  'Read Register, Output of Y LSB 8-bit value.
Cont_Mode      CON     $0
X              VAR      byte 'x sensor measured value
Y              VAR      byte 'y sensor measured value
Z              VAR      byte 'z sensor measured value
READX         VAR      WORD 
READY         VAR      WORD
READZ         VAR      WORD
brads          VAR      Word 'angle in brads
degr           VAR      Word 'angle in degrees
Radians        VAR      Word 'value calculated using X ATN -Y

' -----[ Main Routine ]-------------------------------------------------------
PAUSE 50                                     ' Give sensor needed power up time
  I2CWRITE SDA,SCL,WRITE_DATA,MODE,[0,1,Cont_Mode]  ' Send continuous output command
PAUSE 10 
DO
  GOSUB GetRawReading                       ' Get RAW Compass reading
  serout2 porta.0,84, ["x ",SDEC x," y ",SDEC y ," z ",SDEC z,13,10]
  
    brads = -x ATN -y ;
    degr = brads */360 'convert to degrees
   ;serout2 porta.0,84, ["xy ",SDEC Radians ,","]
    serout2 porta.0,84, ["xy ",DEC degr ,13,10]
     brads = -x ATN -z ;
     degr = brads */360 'convert to degrees
   ; serout2 porta.0,84, ["xz ",SDEC Radians ,","]
    serout2 porta.0,84, ["xz ",DEC degr ,13,10]
       brads = -y ATN -z
       degr = brads */360 'convert to degrees
    ;serout2 porta.0,84, ["yz ",SDEC Radians ,","]
    serout2 porta.0,84, ["yz ",DEC degr ,13,10]
    
   PAUSE 2000 
LOOP
' -----[ Subroutines ]--------------------------------------------------------
GetRawReading:                                 'Compass module subroutine
                                    'Wait for new data to become available
    I2CREAD SDA,SCL,READ_DATA, X_MSB,[READX,READZ,READY]  'Read the data starting at x_msb 3
  
    x = readx >>2  
    Y = readY >>2
    Z = readZ >>2
RETURN

[andybarrett1]

Hi Richard

Had put this on the back burner for a whilst....

Will revisit it later... I see you have done a few things differently!

Thank you for Ideas. Andy

[towlerg]

Hi Richard,

you need to add a 3-axis accelerometer to do tilt compensation, something like LSM303DLM.

George

[richard]

turns out that the premise of using this chip alone as a compass is basically flawed. it can't do its own tilt compensation because the earths magnetic field is not necessarily parallel to the earth .
as George says an accelerometer needs to be added to compensate for tilt. (read, complicated math probably needs floats for any decent accuracy)

no wonder they are so cheap , not a total loss it makes a pretty sensitive 3 axis hall effect sensor , nice colour

[towlerg]

Richard,

Not if your application will not be required to tilt or has some mechanical (gimbals) way to negate the problem.

George

[andybarrett1]

Hi both

Yeah.... I put your code in Richard ... Does pretty much same as before... So I think I need find a better chip
Or use a real needle

Thank you again for ideas .... Appreciated !

[gunayburak]

I bought one to play with

after looking at the raw data I came up with this , works ok if device is held level , tilt compensation is elusive at this stage

'****************************************************************
'*  Name    : hmc5883l.BAS                                      *
'*  Author  : [select VIEW...EDITOR OPTIONS]                    *
'*  Notice  : Copyright (c) 2011 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 29/04/2011                                        *
'*  Version :                                              *
'*  Notes   :                                                *
'*          :  12f1822     
'*          :  
             '
'****************************************************************
 #CONFIG
cfg1 = _FOSC_INTOSC
cfg1&= _WDTE_ON
cfg1&= _PWRTE_OFF
cfg1&= _MCLRE_ON
cfg1&= _CP_OFF
cfg1&= _CPD_OFF
cfg1&= _BOREN_ON
cfg1&= _CLKOUTEN_OFF
cfg1&= _IESO_ON
cfg1&= _FCMEN_ON
  __CONFIG _CONFIG1, cfg1
cfg2 = _WRT_OFF
cfg2&= _PLLEN_OFF
cfg2&= _STVREN_ON
cfg2&= _BORV_19
cfg2&= _LVP_OFF
  __CONFIG _CONFIG2, cfg2
#ENDCONFIG
 

      osccon=$6A    '4 mhz
      anselA=0       'dig i/o
        
      trisA=1110
  
  
  
  
   pause 2000
  serout2 porta.0,84, ["ready",13,10]
  lata.0=1
  
  
   SDA            var      porta.2                 'transceives to/from SDA
   SCL            var      porta.4                  'sends clock pulses
WRITE_DATA     CON     $3C  'Used to perform a Write operation
READ_DATA      CON     $3D  'Used to perform a Read operation
MODE           CON     $02  'Read/Write Register, Selects the operating mode. Default = Single measurement
                             'Send $3C $02 $00 on power up to change to continuous measurement mode.
X_MSB          CON     $03  'Read Register, Output of X MSB 8-bit value.
X_LSB          CON     $04  'Read Register, Output of X LSB 8-bit value.
Z_MSB          CON     $05  'Read Register, Output of Z MSB 8-bit value.
Z_LSB          CON     $06  'Read Register, Output of Z LSB 8-bit value.
Y_MSB          CON     $07  'Read Register, Output of Y MSB 8-bit value.
Y_LSB          CON     $08  'Read Register, Output of Y LSB 8-bit value.
Cont_Mode      CON     $0
X              VAR      byte 'x sensor measured value
Y              VAR      byte 'y sensor measured value
Z              VAR      byte 'z sensor measured value
READX         VAR      WORD 
READY         VAR      WORD
READZ         VAR      WORD
brads          VAR      Word 'angle in brads
degr           VAR      Word 'angle in degrees
Radians        VAR      Word 'value calculated using X ATN -Y

' -----[ Main Routine ]-------------------------------------------------------
PAUSE 50                                     ' Give sensor needed power up time
  I2CWRITE SDA,SCL,WRITE_DATA,MODE,[0,1,Cont_Mode]  ' Send continuous output command
PAUSE 10 
DO
  GOSUB GetRawReading                       ' Get RAW Compass reading
  serout2 porta.0,84, ["x ",SDEC x," y ",SDEC y ," z ",SDEC z,13,10]
  
    brads = -x ATN -y ;
    degr = brads */360 'convert to degrees
   ;serout2 porta.0,84, ["xy ",SDEC Radians ,","]
    serout2 porta.0,84, ["xy ",DEC degr ,13,10]
     brads = -x ATN -z ;
     degr = brads */360 'convert to degrees
   ; serout2 porta.0,84, ["xz ",SDEC Radians ,","]
    serout2 porta.0,84, ["xz ",DEC degr ,13,10]
       brads = -y ATN -z
       degr = brads */360 'convert to degrees
    ;serout2 porta.0,84, ["yz ",SDEC Radians ,","]
    serout2 porta.0,84, ["yz ",DEC degr ,13,10]
    
   PAUSE 2000 
LOOP
' -----[ Subroutines ]--------------------------------------------------------
GetRawReading:                                 'Compass module subroutine
                                    'Wait for new data to become available
    I2CREAD SDA,SCL,READ_DATA, X_MSB,[READX,READZ,READY]  'Read the data starting at x_msb 3
  
    x = readx >>2  
    Y = readY >>2
    Z = readZ >>2
RETURN

So according to your code , we get x , y , z raw readings as byte datas .... and xy xz yz calculations obtained using some trigonometry .. But what do those datas mean ? I think these xy xz yz readings are referring a direction but which one is what ? Does xy give me the magnetic north ? or is it xz or maybe yz ...

I'd be so happy if any of you guys could help me with that ...

Thanks ..

[richard]

maybe this will help

http://www.starlino.com/imu_guide.html

[gunayburak]

I still can't understand which vector shows me the magnetic north in this picture ... But as far as I read the datasheet of this IC , it mentions about a term called Hnorth which is the resultant force of X and Y vectors ... so which one is it then ? Is it XY calculation that shows me the north ?

[richard]

if the device is held so that the xy plane is perfectly!!!! level then the xy angle is magnetic north (sort of). if the device is tilted then the xy angle needs to compensated for that tilt . the device alone cannot really be used as a compass . the device output is a 3d vector as drawn by the black line in my previous post, as you can see the result is relative to the devices orientation , if that is unknown (and it is without an external reference ) then its virtually impossible to ascertain a direction from its output. even a small tilt creates substantial error.
furthermore magnetic field lines are not parallel with the earths surface they tilt into the earth or up to the sky depending on location. not to mention magnetic inclination/deviation etc
basically the concept of using this chip as a compass is unworkable see post 47

[richard]

I must add , the vector does not point north . it indicates the [ direction and magnitude ] of the magnet field relative to the device orientation.
the link I posted is for accelerometers but the math is the same . the big difference is that gravity always points to the centre of the planet so orientation can be established

[gunayburak]

if the device is held so that the xy plane is perfectly!!!! level then the xy angle is magnetic north (sort of). if the device is tilted then the xy angle needs to compensated for that tilt . the device alone cannot really be used as a compass . the device output is a 3d vector as drawn by the black line in my previous post, as you can see the result is relative to the devices orientation , if that is unknown (and it is without an external reference ) then its virtually impossible to ascertain a direction from its output. even a small tilt creates substantial error.
furthermore magnetic field lines are not parallel with the earths surface they tilt into the earth or up to the sky depending on location. not to mention magnetic inclination/deviation etc
basically the concept of using this chip as a compass is unworkable see post 47

That was a nice a explanation Richard ... As you've previously said , we can at least use this IC to observe the pitch then ... For example I'm intending to read XZ or YZ to see the pitch angle for the control of an inverted pendulum ... I personally thought it's a low cost way of doing it compared to an encoder ... Bye the way .. For my module , should I keep it horizontally flat just like in the picture or upside down , does it matter ?

Here is my module

[richard]

For example I'm intending to read XZ or YZ to see the pitch angle for the control of an inverted pendulum ... I personally thought it's a low cost way of doing it compared to an encoder

not sure how effective that will be , it would probably need to be calibrated every time you relocate it (or maybe even rotate it) . don't forget its own orientation is its only reference point . an accelerometer might be more appropriate

[gunayburak]

Well , Yeah actually I'm planning to calibrate it right before every operation with a quick push button click ... So that It can assume the present values as exact zero .. It's all about math I guess .... I'm also aware of that It won't be that accurate ... But I still wanna use it ... Thanks for your all prompt answers Richard ...

[towlerg]

For example I'm intending to read XZ or YZ to see the pitch angle for the control of an inverted pendulum ... I personally thought it's a low cost way of doing it compared to an encoder

Surely what you need is an accelerometer, you know that the period is always the same, it just moves faster when first set in motion (I'm not totally sure that's correct, my knowledge of basic physics is pretty ragged). If that's correct, there will be a relationship between angle and acceleration. With calibration you should end up with a look up table of acceleration/angle. Of course you'll only need to generate the table once.

Also I cant imagine how you would orient the magnetometer to even hint at the angle.

BTW anyway, you couldn't use an encoder if you want the pendulum to be "true", pivot must be frictionless.

Sounds like an interesting project, have fun.

George