Wrong values with COSINE!

[Eng4444]

Hello,

i am working on a very serious project and i chose to use PicBasic Pro.
but i just encountered a serious problem:

in a certain part of my program i got a certain value "alpha". I needed to get cosine alpha.
but the problem is that:

"COS returns the 8-bit cosine of a value. The result is in two’s complement
form (i.e. -127 to 127). It uses a quarter-wave lookup table to find the
result. Cosine starts with a value in binary radians, 0 to 255, as opposed
to the usual 0 to 359 degrees."

but i need the usual 0 to 359 degrees!! and this is so essential in my program!

Now i am getting: cos 0 = 127 ! i just need to get back the normal values example: cos 0 = 1, cos 90 = 0, cos 70 = 0.342

Please any help??

It's so URGENT... write a code if possible and i'll be more than grateful...

[Melanie]

You're not going to get an answer any faster if you post it once or if you post a dozen times... but if you keep doing it, it'll be considered spamming and they'll all be removed!

PICBasic only handles integers. Like it or not, you won't get a fractional result.

[Eng4444]

I wasn't talking about integers... i noticed that you wre only concentrating on me sending many posts.. why not concentrating about the contents of posts?

the cosine and sine functions are not giving the basic answers...they are giving results in twos's complement!

for example, instead of giving a "1" for "cosine 0", it is giving 127!!

i need to go to the normal numbering system... anyone has a hint?

[Melanie]

>> i noticed that you wre only concentrating on me sending many posts..

That's what System Admins are supposed to so...

>> why not concentrating about the contents of posts?

You'll have a solution about an hour after despositing US$5K in my Bank Account... there's around a couple of dozen people on this forum that also have the skills and could probably get it down to thirty minutes... Somebody may do it for free if you're lucky and post it on the forum, but until then be patient... a lot of people only look at this list once or twice a week.

[Eng4444]

>> i noticed that you wre only concentrating on me sending many posts..

That's what System Admins are supposed to so...

>> why not concentrating about the contents of posts?

You'll have a solution about an hour after despositing US$5K in my Bank Account... there's around a couple of dozen people on this forum that also have the skills and could probably get it down to thirty minutes... Somebody may do it for free if you're lucky and post it on the forum, but until then be patient... a lot of people only look at this list once or twice a week.

-----------------------------------------------------------------

Well,

i'll wait as you advice me but i really need a quick answer...i posted this msg in several websites and even sent a mail to picbasic pro community.. i hope i'll get at least one good answer!

[BigWumpus]

Uuuhhhh...

Super-Mel is right, don't cry as a angry kid !!!!


Use your brain, or source it out !

Transfering a value of 0-360 to 0-255 ?
What a heavy task !
perhaps: x*255/360 ?

And now, the final:
Converting a number -127..127 to -1..1 ?
perhaps: x/127 ?

Have a nice day, coding the FP-math. And after that you will see, it is not necessary, because your real problem has another - slim - solution.

Or use some of these f******* C-dinos around us.

[Luciano]

...i just need to get back the normal values example: cos 0 = 1, cos 90 = 0, cos 70 = 0.342

The sample in the link will print the values as you are asking in your first post.
Please explain that again with a real example with numbers.

Luciano

[Eng4444]

Thanks for your interest , i will try to provide more details and hope they will be helpful for you.

But first, in that link, i am not using "ATN and HYP", nor "X and Y", nor arctan or arcos or logarith or interpolation...

all my work is that i am getting Power. It is given as you know by:

P = V x I x Cos alpha.

and i am using PIC 16F876A with PicBasic Pro.

I solved the matter of V and I by applying sensors. and for the phase between them, i used a PLL. now i am inserting all 3 variables as inputs for the PIC and i need it to give me the correct power but i discovered that it is giving very wrong values!

i found out that it's from the "cos" because as it is stated, the cosine give value in 2's complement from -127 to +127 and not in the traditional way from 0 to 359 degrees...

But for us, we use the traditional numbering system.... so i need to use it! But it is not working... i can do it with a table but i need to find out if there is a mathematical way to use the same function "cosine" , already provided..

thanks again and i hope you will be able to help me.

[BigWumpus]

all my work is that i am getting Power. It is given as you know by:

P = V x I x Cos alpha.

And out of this silly task you are able to make such a lot of dust ?

P=V*I 16 Bit
X=COS(Alpha*255/360) 8 Bit 2-komplement
Minus=X.7
P=P*(X and %01111111) 32 Bit !!!
P=Div32 127
It's quick-n-dirty, maybe there is an error inside....

And all the way without using this boring 0,xxx, only integers !
Ha, the good old times are back, where programmers must understand what they are doing and counting the bits...

Just USE YOUR BRAIN, not your mouth !



Hello Mel,
Yes, I ruin you prices and your time....
but I inserted 1 mistake, so this code will not work right. But some postings ago, there was the right hint. Maybe we could train his brain....

[Eng4444]

And out of this silly task you are able to make such a lot of dust ?

P=V*I 16 Bit
X=COS(Alpha*255/360) 8 Bit 2-komplement
Minus=X.7
P=P*(X and %01111111) 32 Bit !!!
P=Div32 127
It's quick-n-dirty, maybe there is an error inside....

Just USE YOUR BRAIN, not your mouth !



Hello Mel,
Yes, I ruin you prices and your time....
but I inserted 1 mistake, so will not work right. But some postings ago, there was the right hint. Maybe we could train his brain....

--------------------------------------------------------------------


It's just that you like to show up... i wonder if you succeeded because for me you were just acting like a clown... trying to be nice to mel just by making fun of me.

i wonder what you get from all this - stupid... and moreover, you wanna train my brain? lol and you submit and error on purpose???!

i came here because i didn't know how to do it so do you really find it worthy to take all your advantages and try to make fun of me?? or just to appear the intelligent?? you are idiot! keep your knowledge for yourself.

In case someone else has an idea about my question i'll be grateful.



By the way Mel,

Did you made this forum just to make fun of people with your friends?
thanks a lot for your kindness.

[Melanie]

It's not my forum. I just make sure folks don't abuse it (or each other) too much...

From your first post, I gather this is a serious project with a serious problem... unfortunately I only answer the frivolous ones - serious I leave to other people - unless there's money involved.

But really, to join a forum just in order to ask folks to drop what they're doing and IMMEDIATELY write code for you because you need it URGENTLY is really the height of bad manners - and you should expect a little fun to be made from it.

My original post pointed you to the fact that you CANNOT have fractions with PICBasic... ONLY INTEGERS. If you are capable of doing the circuit you describe, then you are also capable of a little high-school mathematics in converting degrees to radians. Then feeding that figure into the provided COS function and converting the resultant into the required COSINE but scaled-up because we must always work in INTEGERS.

You have been shown how to convert degrees to radians and how to get your Cosine function... a little bit of experimentation on your part will complete the code and you will have a working program. So make an effort, try to understand what's been written (thank you BigW), and don't expect everyone else to do it all for you...

See... this is why we're not getting rich on this forum... somebody always does it for free... *sob*