Monday, May 20, 2002, 5:05:58 PM, Jinx wrote:
>> Here is probably an easier way to do it:
>>
>> 1) multiply your 16 bit number by 100*360/65536 = 0.54931640625

> The gyro is claimed to have 0.05 degrees accuracy at 14 bits,
> although noise does seem to be a problem, despite sending
> regular zero/integration commands and ignoring the LSbs. There's
> still work to do sorting that out, as it's the core of the project.

> Even if it's a little slower to do I want to keep the maths as
> precise as possible so that any calculation errors are insignificant
> compared to the jitter from the gyro. I don't think 16-bit maths will
> be good enough to get 3dp fractions from a 16-bit source will it ?

Well, it seems you need to display only 2 decimal digits after the
point, which is only a +-0.01 degree error. So, I'm not really sure
why you want 3 decimal digits. It is not really necessary for
rounding, because you need only 1 extra bit for that, to tell if
fractional part is less than 0.5 or not. And this extra bit is already
there after multiplication by 100*360, that is bit 15. In pseudo code
that would look like:

        //multiply sensor output by  100*360
        temp = sensor * 36000;

        //round (increment integer part if bit 15 is set)
        if(temp & 0x8000) temp += 0x10000;

        //divide by 65536
        temp >>= 16;

You could still use the multiplication code generator for this, just
tell it to use rounding and a 0% error.

http://www.piclist.com/cgi-bin/constdivmul.exe?Acc=ACC&Bits=16&endian=little&Const=0.54931640625&ConstErr=0&round=yes&Temp=TEMP&cpu=pic16

> I'm using this conversion routine, around 48us

> http://www.piclist.com/techref/microchip/math/radix/b2a-16b5a-rl.htm

This one is probably better, since it gets a digit at a time and can
be called while LCD is still receiving the previous digit. But the
other one seemed to take a few less cycles overall.

Good luck!
 Nikolai

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