BS2p Math

Archiver

I am reading a 12 bit A/D that is connected to a pressure sensor that
is trimmed up to 2.5V so that I can measure vacuum.

The pressure sensor outputs 150 mV/PSI and I want to then convert
this to inches of Hg which 1 PSI = 2.036021 inHg.

Right now I can zero out the reading by:

Zero = 2500 - CH_0

Which is a no brainer but ,

PSI = Zero/150

just gives me a whole number thats rounded off???

Once I have this PSI converson done I think I can convert to inHg
with this:

inHg = (PSI * 2) + (PSI ** 2361)

Need help with division.

Jason

Archiver

You have to excuse my previous brain fart.

If I take (Zero * 10)/15 then I get an acceptable amount of
resolution.

Unless any of you out there have a better way to do it.

Jason


--- In basicstamps@y..., "jbirnsch" <jbirnsch@v...> wrote:
> I am reading a 12 bit A/D that is connected to a pressure sensor
that
> is trimmed up to 2.5V so that I can measure vacuum.
>
> The pressure sensor outputs 150 mV/PSI and I want to then convert
> this to inches of Hg which 1 PSI = 2.036021 inHg.
>
> Right now I can zero out the reading by:
>
> Zero = 2500 - CH_0
>
> Which is a no brainer but ,
>
> PSI = Zero/150
>
> just gives me a whole number thats rounded off???
>
> Once I have this PSI converson done I think I can convert to inHg
> with this:
>
> inHg = (PSI * 2) + (PSI ** 2361)
>
> Need help with division.
>
> Jason

Archiver

Hi Jason,

I see you answered your own question. Here is another way to do it,
by working with the remainder from the first division:

PSI = ch_0/150*100 + (ch_0//150*100/150) - 1666
^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^ ^^^^
1st division remainder division offset

example, when ch_0=1234 then PSI= -844 to represent -8.44.

Note that division on the Stamp does not work right on negative
numbers, so if negative numbers might turn up, I always subtract the
offset _after_ doing the division. Your result ch_0 I think is
positive from the 12 bit A/D. 1666=2500/150*100 precalculated.

You trick for division is fine, using 15 instead of 150. The only
advantage of the "remainder" method above would come if your scale
factor happened to be, say, 153 instead of 150.

I hope that helps!

-- regards,
Tracy Allen
electronically monitored ecosystems
mailto:tracy@e...
http://www.emesystems.com


>You have to excuse my previous brain fart.
>
>If I take (Zero * 10)/15 then I get an acceptable amount of
>resolution.
>
>Unless any of you out there have a better way to do it.
>
>Jason
>
>
>--- In basicstamps@y..., "jbirnsch" <jbirnsch@v...> wrote:
> > I am reading a 12 bit A/D that is connected to a pressure sensor
>that
> > is trimmed up to 2.5V so that I can measure vacuum.
> > The pressure sensor outputs 150 mV/PSI and I want to then convert
> > this to inches of Hg which 1 PSI = 2.036021 inHg.
> > Right now I can zero out the reading by:
> > Zero = 2500 - CH_0
> > Which is a no brainer but ,
> > PSI = Zero/150
> > just gives me a whole number thats rounded off???
> > Once I have this PSI converson done I think I can convert to inHg
> > with this:
> > inHg = (PSI * 2) + (PSI ** 2361)
> > Need help with division.
> > Jason