Reading Array values into variables

[Tom Gonser]

Exactly the problem.. I have 3 bytes that need to be put into one variable.. this is a 24 bit container that relates a number - the altitude in tenths of meters..

How to get this into ONE variable I can work with is the first issue..

Tom

[Acetronics2]

Hi, Tom

Let's have another view of the problem ...

You get an altitude measurement, ...but what is your sensor ??? and mostly what is its precision ???

I do not know lots of altitude sensors seriously able to give 1 cm on a hundred meters ... 1/10 000 precision, you sure ??? ... !!!

May be a little look here could reduce your number sizes ...and simplify you work.

24 and 32 bits arithmetics can be downloded from Melabs site ... if you really want to keep "ghost" centimeters !!!

Alain

[Ingvar]

Hi Tom,

What ranges are we talking about? Are you interested in altitudes higher than 21501 feet? If not, you can treat your input as a word(skip top 8 bits) and do your calculations on that. If you need to go higher, things will get more complicated but still possible. Higher than 65535 feet will get nasty ....

Do you really need 0.1m(0.3feet) resolution? Will 1m(3feet) enough?

Another thing .... you need to know how your inputdata(24bits) is formatted. My guess(based on your information) is that you are located at about 1096 feet. I'm assuming that "alt[3]" contains the most significant byte, 0,13,13 would be 000D0D in hex which is 3341 in decimal. 3341 tenths of a metre is 334.1m which is 334.1*3.28084=1096 feet.

/Ingvar

[Tom Gonser]

Thanks for the responses..

The precision is only tenths of meters. I don't know *why* the data is stored in 24 bits, it just is - not under my control, I am only trying to read it.

Regardless - the fundamental problem is that I have a 24 bit value stored in 3 bytes that I need to make into a variable I can do something with..... like read it digit by digit, and put a "." in the tenth's spot, and then multiply it by a factor to convert to feet..

TG

[Acetronics2]

Have a look to that thread :
http://www.picbasic.co.uk/forum/showthread.php?t=1217

here you have the solution to put your 24 bits into something usable ... just divide them as soon to reduce it to less than 16 bits ...

and that's all !!!

Alain

[Ingvar]

And the answers to my questions are ...... ? Can't help if i don't know.

/Ingvar

[Tom Gonser]

Oh- yes, sorry.

We are at about 300ft. Should be reading about 100meters or so. The GPS alt data 'wanders' so tenths of meters is a little silly, yes, but that is what is output.

The full range would want to support over 100,000ft in altitude.

TOm