A fun math problem

[Tom Gonser]

Oh, I see.

There is no PC connected to the unit, so there is no way to compute this. The PIC has to do all the work, and transmit the converted MB to Meters or Feet....

[Darrel Taylor]

Maybe I can try to translate from Canadian to English. (Just kidding Steve)

Steve's idea is to pre-calculate every value before hand using the PC. It could be done with VB or you could do it in excel if you wanted. Those values are then stored in an external eeprom as one great big look-up table.

Then later when the pic is running, when it needs to convert the numbers, it doesn't have to do any calculations. Just look up the answer from the eeprom. The PC doesn't need to be hooked up to the PIC during normal operation.

Assuming you wanted a range of 600-1100 milibars with 1 decimal place, you could store the whole thing in a 16kbyte eeprom. If you needed 2 decimals it would take a 128kbyte eeprom (yikes).

To calculate the given formula in real time, you would need at least 48-bit math (due to the decimals requested) so there really aren't many other options.

I even tried a 3rd order Power Polynomial formula to try to approximate the numbers, and it came up with an error of +/- 100 feet at the high and low ends. (Not too good)

HTH,
   Darrel

[Tom Gonser]

Now I get it!

Thanks folks for helping me see the options here. Since the number of feet between 0 and 30,000 would require me to store 30,000 locations, this does not seem feasable on a PIC.

I now understand how it would work however, and options might be to store 3000 locations and increment every 10, etc. However, for this application I think I will chalk it up to 'not in scope'..

Thanks,

Tom

[Darrel Taylor]

Not quite yet.

You would be storing them according to millibars not feet.

With a range of 600.0 to 1100.0 there are 5000 locations. Each value uses 2 bytes' for a total of 10,000 bytes.

If the range is 2 decimals 600.00 to 1100.00 there are 50,000 locations that would require 100kbytes.

Definately "Within Scope".

Don't give up yet.

Darrel

[Ingvar]

Hi Tom,

Ihelped a guy named Steve Turner once, he had the same problem. Since he made a pretty good job of explaining his project on his site, i will not do it again. Just follow this link .....

http://www.steveonweb.com/alt.php

/Ingvar