HMC5883L Magnetometer chip Possibilities.

[andybarrett1]

Hi

Have tided code.... And it does seem to work better now. But Degrees are reversed (360 to 0) Clockwise. Or am I reading the sensor upside down?

Azimuth is renamed Radians... the resulting calculation now used to give degrees.

Z... is not used at all... Maybe I can add or subtract the locale degree error (Unknown at time of writing) into code once degrees working the right way round.

Latest code show below.... Bear in mind I am not a software guy so any suggestions of further advice welcome.

'****************************************************************
'*  Name    : COMPASS_818.BAS                                      *
'*  Author  : [select VIEW...EDITOR OPTIONS]                    *
'*  Notice  : Copyright (c) 2014 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 24/08/2014                                        *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :                                                   *
'****************************************************************



' LCD should be connected as follows:
'       LCD     PIC
'       DB4     PortA.0
'       DB5     PortA.1
'       DB6     PortA.2
'       DB7     PortA.3
'       RS      PortA.4 (add 4.7K (10k)pullup resistor to 5 volts)
'       E       PortB.3
'       RW      Ground
'       Vdd     5 volts
'       Vss     Ground
'       Vo      5K potentiometer (or ground)
'       DB0-3   No connect

    adcon1 = 7     ' Turns Analogs off
    'DEFINE OSC 12	'Set oscillator in MHz
    OSCCON = $70
    DEFINE LCD_EREG PORTB
    DEFINE LCD_EBIT 6
    DEFINE LCD_RSREG PORTB
    DEFINE LCD_RSBIT 7 

' -----[ Pins/Constants/Variables ]-------------------------------------------
SDA            var      portb.1                  'transceives to/from SDA
SCL            var      portb.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 500                                     ' Give sensor needed power up time

  I2CWRITE SDA,SCL,WRITE_DATA,MODE,[Cont_Mode]  ' Send continuous output command

DO

  GOSUB GetRawReading                       ' Get RAW Compass reading

'RAW READX,READY,READZ data...
  
        'Lcdout $fe, 1 ' Clear LCD screen
        'Lcdout "X=",SDEC READX  ,"   Y=",SDEC READY 
        'Lcdout $fe, $C0, "Z=",SDEC READZ
        
'Calculate Azimuth

  GOSUB GetRadians

  'Calculated Heading in Degrees
  brads = Radians     'get angle
  degr = brads */360 'convert to degrees
  

Lcdout $fe, $C0, "Degrees =",SDEC degr

GOSUB GetHeading

LOOP
' -----[ Subroutines ]--------------------------------------------------------

GetRawReading:                                 'Compass module subroutine

    PAUSE 400                                  'Wait for new data to become available

    I2CREAD SDA,SCL,READ_DATA, X_MSB,[READX.HIGHBYTE]  'Read the data starting at x_msb 3
    I2CREAD SDA,SCL,READ_DATA ,X_LSB,[READX.lowBYTE]

    I2CREAD SDA,SCL,READ_DATA, Z_MSB,[READZ.HIGHBYTE]
    I2CREAD SDA,SCL,READ_DATA ,Z_LSB,[READZ.lowBYTE]

    I2CREAD SDA,SCL,READ_DATA, Y_MSB,[READY.HIGHBYTE]
    I2CREAD SDA,SCL,READ_DATA ,Y_LSB,[READY.lowBYTE]

RETURN

GetRadians:
'The output range of the HMC5883L is -2048 to 2047 and the input range of the ATN function
'is -127 to 127.

x = readx >>4  
Y = readY >>4
Z = readZ >>4

   'Lcdout $fe, 1 ' Clear LCD screen
   'Lcdout "X=",SDEC X  ,"   Y=",SDEC Y 
   'Lcdout $fe, $C0, "Z=",SDEC Z

Radians = x ATN -y

Lcdout $fe, 1 ' Clear LCD screen 
Lcdout "Radians =",SDEC Radians 

RETURN

GetHeading:
'Gives a heading in North, South, East and West.

    IF degr = 90 THEN
    'Lcdout "North"
    ENDIF

    IF degr = 0 THEN
    'Lcdout "East"
    ENDIF

    IF degr = 270 THEN
    'Lcdout "South"
    ENDIF
    
    IF degr = 180 THEN
    'Lcdout "West"
    ENDIF

RETURN

[towlerg]

Andy, you still have North and East reversed and South and West reversed as well, North is 0, East is 90, South is 180 and West is 270.
http://commons.wikimedia.org/wiki/File:Compass_Card.png Although I guess you'd be better off saying greater than 315 or less than 45 it's North.

George

BTW I'm trying and failing to get a 5983 (supposedly updated version) working with little or no success, I think I killed it!

[andybarrett1]

Hi George

I think the reversal on the last bit of the code is to do with headings and angles etc.. So not all that worried.
Is the 5983 the same layout as mine... If so will the code not crow bar into it ?

Am also not to sure about gain settings etc.... Have left mine at default.

BR
Andy

[towlerg]

My understanding (perhaps wrong) is that 5983 is an improved version of 5883. It is temperature compensated and will output at a greater rate appearently. I'm working on the assumption that it is software compatible - but you know what they say about assume.

George

[towlerg]

I can't edit my last post and I wanted to add

My understanding is that you want the gain as high as possible without saturating. X,Y and Z values are in the range -2048 to 2047 so I guess you're looking for something like -1500 to 1500.

I see you don't allow for declination, the difference between magnetic and true north. You can get your local declination from http://www.magnetic-declination.com/

I'm assuming the the X coordinate points North, although now I think of it I can't see why. the only reference I can find is "Arrow indicates direction of magnetic field that generates a positive output reading in Normal Measurement configuration" take from that what you will.

George

[andybarrett1]

Hi George

I agree with gain... Reading the datasheet seems to be way to go ... If it over saturates you get the -4096 figure.

I also am assuming that X is north... Certainly shows like that at in most of places I have looked.

Y seems to be either West (left) or East (right).... depending on what you look at... I did find a useful Honeywell document yesterday, will post a little later on.

There is certainly a shortage of info around as to how to use these devices with PicBasic

BR
Andy

[towlerg]

Are you using one of the break-out boards, GY0281 or GY282? Could you post a circuit diagram? The two break-out boards above both have 3.3v regulators on them, I'm curious as to what Vcc you run the PIC at and if you use level changers. If X is North Y must be West. George