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Calculating ARCTAN in Oshonsoft

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You can use Oshonsofts arctan function, but as I said before it is not accurate: arctan(1) gives ~ 41.5 degrees, should be 45
Have you defined arctn function in your program?
I don't see it in comp. jpg.

You used x_raw.hb, x_raw.lb in comp. jpg and they are defined as single variables in dim. jpg
Why?
 
Hi J,
I prefer to use the most acurate, so not Oshonsoft's 'Arctan' Function.

Is it possible to start again from here?

'arctn' and 'picalc' and x_raw and y_raw are all defined as SINGLE

Does this work without an actual ARCTAN function?

If x_raw < y_raw Then
If x_raw > 0 And y_raw > 0 Then
azi = arctn(x_raw / y_raw) * picalc '180/pi
Endif
Endif

(Again, sorry if I get mixed up)

C.
 
You need to define the function arctn(), which calculates the arcustanget, you have only defined a variable arctn as single.
You need x_raw, y_raw as word. You can't get the bytes from compass directly to a single variable.
Get the x_raw, y_raw as before, then make a single variable X = x_raw Y= y_raw and then calculate the angle.
 
Last edited:
Hi J,
I had to change the XZY by adding 'a' as they were reserved letters.
I made an attempt at the FUNCTION, which all compiles, but gives only AZI = 083456. 8

Here is Oshonsofts FUNCTION from the Manual:
Function square(arg1 As Word) As Word
square = arg1 * arg1
End Function
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Here's my DIMs

'READ COMPASS X
Dim x_raw As Word
Dim ax As Single

'READ COMPASS Z
Dim z_raw As Word
Dim az As Single

'READ COMPASS Y
Dim y_raw As Word
Dim ay As Single

Dim azi As Single 'word
Dim strazimuth As String 'For Screen
Dim picalc As Single
Const pi = 3.14159
picalc = 180 / pi
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Here's the section of program:

'READ COMPASS XZY REGISTER
SPICSOn
For i = 0 To 5 'READ XZY Xx2 Zx2 Yx2
compss = 0 'CHIP SELECT COMPASS ON
addr = 0x83 + i
SPISend addr
SPIReceive data
b(i) = data
compss = 1 'CHIP SELECT COMPASS OFF
Next i
SPICSOff

x_raw.HB = b(0)
x_raw.LB = b(1)
z_raw.HB = b(2)
z_raw.LB = b(3)
y_raw.HB = b(4)
y_raw.LB = b(5)

ax = x_raw
az = z_raw
ay = y_raw

'VVVVVVVV 2'S COMPLIMENT CALC VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
If ax > 32767 Then
ax = 65535 - ax
ax = ax + 1
Endif
If ay > 32767 Then
ay = 65535 - ay
ay = ay + 1
Endif
'AAAAAAAAAAAA 2'S COMPLIMENT CALC AAAAAAAAAAAAAAAAAAAAAAAAAAAA

If ax < ay Then
If ax > 0 And ay > 0 Then
azi = arctn(ax, ay)
Endif
Endif
l
l
l
l
END
____________________________________________________
'Azimuth CALC Function
Function arctn(ax As Single, ay As Single) As Single
arctn = (ax / ay) * picalc '180/pi
End Function

NOTE: There is a Z component. Should it be introduced now, or once the XY is working?
EDITED. EDITED.
C.
 
Last edited:
Use the approximation I gave in msg #2
Function arctn( .....
arctn= x/y / (1+0.285125(x/y)^2)*180/pi
End function

Edit: arctn= x/y/( 1+0.28125*( x/y )^2)*180/pi
 
Last edited:
Use the approximation I gave in msg #2
Function arctn( .....
arctn= x/y / (1+0.285125(x/y)^2)*180/pi
End function

Edit: arctn= x/y/( 1+0.28125*( x/y )^2)*180/pi
Hi J,
Thanks for the reminder and the edit.

This compiles, does it look ok? : arctn = x / y / (1 + (0.285125 * (x / y))) * x / y / (1 + (0.285125 * (x / y)))
I'll try it!
C.
 
Hi J,
Thanks for the reminder and the edit.

This compiles, does it look ok? : arctn = x / y / (1 + (0.285125 * (x / y))) * x / y / (1 + (0.285125 * (x / y)))
I'll try it!
C.
No, too many terms.
It has only (x/y)^2, not the whole expression^2
Use the edited arctn = ... in msg# 27
 
Using the equasion in #27. When module is turned CCW the output shows APP 1/20th of the correct reading.

C.
 
No, too many terms.
It has only (x/y)^2, not the whole expression^2
Use the edited arctn = ... in msg# 27
Hi J,
Oshonsoft doesn't support '^' so it needs some modification.

EDIT: Is this ok? arctn = x/y/(1 + 0.28125 * ((x / y) * (x / y))) * picalc '180/PI
It compiles!

C
 
Last edited:
It is ok.
Show values of x, y and the calculated angle
Hi j,
These are apporoximate!

At 1º AZI= 1 X= 10 Y= 510
At 10º AZI= 7.0 X= 64 Y= 506
At 20º AZI= 13 X=112 Y= 491
At 30º AZI= 19 X=158 Y= 472

If this doesn't look immediatelly ok, then I'll recheck the program to make sure it is READing correctly.
C.
 
Last edited:
Hi J,
It looks as though arctn= x/y/ ( 1+0.28125*( x/y )^2) *180/pi
would look like: arctn= x/y/ ( 1+0.28125*( x/y) ) * ( 1+0.28125*( x/y) ) *180/pi
Is this correct?
C.
 
Hi J,
It looks as though arctn= x/y/ ( 1+0.28125*( x/y )^2) *180/pi
would look like: arctn= x/y/ ( 1+0.28125*( x/y) ) * ( 1+0.28125*( x/y) ) *180/pi
Is this correct?
C.
No.
I don't understand.
(x/y)^2 means (x/y)*(x/y) = x*x/y/y
Msg#30 is correct.
 
Hi j,
These are apporoximate!

At 1º AZI= 1 X= 10 Y= 510
At 10º AZI= 7.0 X= 64 Y= 506
At 20º AZI= 13 X=112 Y= 491
At 30º AZI= 19 X=158 Y= 472

If this doesn't look immediatelly ok, then I'll recheck the program to make sure it is READing correctly.
C.
AZI is correct with those x, y values
Probably you get wrong x , y values from compass.
Hi j,
These are apporoximate!

At 1º AZI= 1 X= 10 Y= 510
At 10º AZI= 7.0 X= 64 Y= 506
At 20º AZI= 13 X=112 Y= 491
At 30º AZI= 19 X=158 Y= 472

If this doesn't look immediatelly ok, then I'll recheck the program to make sure it is READing correctly.
C.
AZI ~ correct with these x, y values.
x, y must be wrong.
 
AZI is correct with those x, y values
Probably you get wrong x , y values from compass.

AZI ~ correct with these x, y values.
x, y must be wrong.

EDIT: Hi J,
Am I correct that the AZI values are correct from the X an Y numbers, so the calculation is working but not giving the correct angle, because X and Y are not correct?
C.
 
Last edited:
Yes.
Calculation is ok.
You can check it with a scientific calculator.
Also on the web: https://web2.0calc.com
Hi J,
I've also get good results from the equation, so it must be something to do with either READing the module or Oshonsoft.

I'm going to try a different module. I'm now looking at MPU-9255 modules.

Thanks, C.
 
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