question for math wizards

[mackrackit]

Give this a try...
MiscEL

[aajgss]

Got It!

Thought it was a ! and not an l - old eyes no glasses. Often get told I need them - maybe I do


Thanks
aajgss

[mackrackit]

Got It!

Thought it was a ! and not an l - old eyes no glasses. Often get told I need them - maybe I do


Thanks
aajgss

I know what you mean... without mine I walk into walls .. try stairs with a new pair of bifocals

[mister_e]

I'm sure in the same boat... without mine I can't even say if it's an elephant ... or a supermarket

[Archangel]

Got It!

Thought it was a ! and not an l - old eyes no glasses. Often get told I need them - maybe I do


Thanks
aajgss

You mean you tried to read that text and type it ? !!!

Thank Jobs / Gates / Linus for copy/paste !

[aajgss]

Ok,

Lets forget I said the first bits easy!!!

Instead of converting to mmH2O and then converting that to Knots, I decided to go straight from ADC counts to Knots.

So the equation comes out to be (SQR(ADC Counts))* ( 484/79).

Excel comes up with the correct answer. for 1 ADC count the result comes out at 6.1266 knots. Doing the same calculation in a PIC the result is 6 knots. It appears that the result is the integer part only.

The numbers I am trying to get is in the table

mmH2O ________Knots
15_____________ 30
26.5 ___________40
41.5 ___________50
60 _____________60
81.5 ___________70
106.5 __________80
134.5 __________90
166.5 _________100
201 ___________110
239.5 _________120


How do I calculate the correct value and still heed Steves advice to be careful of Math Overflow?


Thanks
aajgss

[Archangel]

Hello aajgss,
What level of resolution are wanting to display, I mean how many decimal places ?
You could multiply up by 10, 100, 1000 and display using DEC modifier and "." .
I didn't notice which PIC you are using but 18Fs can use long variables which if I am not mistaken are 32 bit vars.

[aajgss]

Hi Archangel

Resolution I would like is to 1 decimal place. The project I am working on is an electronic manometer to check calibration of the Air Speed Indicator for gliders.
The limits are critical at 30 knots. The ASI must be within +/- 1.5 knots at 30 knots.

I am using an 18F14K50. I did try a LONG variable and multiplied the counts by 10000, but still got the same results. I looked like I was getting a 16 bit math overflow. Most likely cause was me not knowing what I am doing. Is it just a case of using a LONG identifier or is there something else I need to do. There is an option in MCS to use PBPL. Is PBPL another part of PBP, a different program all together or some type of addin? I find the documentation for this kind of simple info a bit difficult to locate.


Thanks
aajgss

[Acetronics2]

Hi,

Your answer is here :

Excel comes up with the correct answer. for 1 ADC count the result comes out at 6.1266 knots

you have to use a signal amplifier to get more ADC counts for the same outputted voltage ...

A logarithmic amplifier could be a nice idea to get a linear ADC input voltage Vs Speed.

I remember some really good work had been done here for Vu-meters ... ( a greek project ... )

CA3089 or NE 604 could be some interesting keywords to try ...

have fun

Alain

[Demon]

...I am using an 18F14K50. I did try a LONG variable and multiplied the counts by 10000, but still got the same results. I looked like I was getting a 16 bit math overflow. Most likely cause was me not knowing what I am doing. Is it just a case of using a LONG identifier or is there something else I need to do. There is an option in MCS to use PBPL. Is PBPL another part of PBP, a different program all together or some type of addin? I find the documentation for this kind of simple info a bit difficult to locate.
...

I see it at least in section 3 (pages 17 and on), and in section 4 on Variables (page 23) and Division (page 37). It could be in other places; no fast way to use SEARCH in a book besides the table of contents (no index that I can see).

(I really need to reread the manual, they've added important information in there)