Simple Maths Going Wrong

[wjsmarine]

Hi Folks,

Mainly for Darrel but happy to have input from all!

DT's example of averaging the direction (thanks Darrel) makes use of ATN from an 8 bit direction (0-255 = 0-359 degrees) and works well when I use this method with PBPro 2.60.

However this gives some inaccuracies and low resolution. I've acquired my direction with a 10 bit AD and converted down to 0-359 but no matter how I manipulate the numbers in DT's formula I get to about 270 deg's and then it rolls over with false values.

Is there a way to achieve the above or am I stuck with coarse direction? I'd like to have 1 degree changes if possible not the jumps 8 bit has.

Kind regards to all and thanks in advance,
Bill

[Ioannis]

As you have no code posted I can only guess that your vaariable are byte and not word.

Ioannis

[Darrel Taylor]

... makes use of ATN from an 8 bit direction (0-255 = 0-359 degrees) ...
... with a 10 bit AD and converted down to 0-359

Shouldn't it be converted to 0-255 (representing 0-359)?

ATN SIN and COS all use binary radians.
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[wjsmarine]

Hi Darrel and Ioannis,

Thanks for the help. I replied earlier but it didn't seem to make it, here goes again...

Ioannis the first thing I did when trying changes was to move to Words for the variables so was surprised when the numbers didn't crunch.

Darrel your code works well but gives 360/256 = 1.4 degree accuracy/resolution and I was hoping for better than this. I'm not strong at math so your comment about binary radians probably means I'm stuck with the original limits, which is probably okay for wind direction - but what do I do if I need greater accuracy for Tilt, etc?

Any suggestions and help is appreciated, thanks guys.
Bill

[Darrel Taylor]

If you need more resolution, you'll need to pull out the Big Guns ...

Cordic trig assembly code for PIC18f (scalerobotics)
http://www.picbasic.co.uk/forum/showthread.php?t=10528
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