Help with the conversion math

[Ioannis]

And this 65472, isn't the 1023 with left justification?

Ioannis

[Ioannis]

At page 157 of the Data sheet, it is shown that the PIC defaults to ADFM at 0 (zero), so it is really Left Justified by default. You have to make it a 1 for Right Justified result.

The register is the ADCON2 and bit 7.

Ioannis

[HenrikOlsson]

Just for grins I took a 10K resistor and fed the A/D input pin with 5 volts. The reading I got was 65472!

Yes, because you have the freaking thing configured wrong for the way that ADCIN works for crying out loud :-)
Just set the justification bit correct, as Ioannis shows AND as we've already discussed in the other thread where we went thru all this resolution and justification stuff last time.

OK, so it's a 0.07psi and not 7psi as I based my code around..... Well, then we need to change the scaling but lets see if it works at all first.

/Henrik.

[richard]

that works out pretty nicely every adc 100 count is almost exactly .01 psi

0=110 , 0.07 = 820 couldn't be easier


assuming I read the data sheet properly and that 0.07 psi = 4.0 volts and vref=5 v of course

[EarlyBird2]

that works out pretty nicely every adc 100 count is almost exactly .01 psi

0=110 , 0.07 = 820 couldn't be easier


assuming I read the data sheet properly and that 0.07 psi = 4.0 volts and vref=5 v of course

Not quite Richard. In theory

0=102.4 at 0.5 volts and 0.07=921.6 at 4.5 volts.

assuming as you say the vref=5 v.

102.4 is the zero offset and 0.07/(921.6-102.4) is the slope.

to convert to psi

psi=(reading-offset)*slope

psi=(reading-102.4)*0.07/819.2

psi=(reading-102.4)*0.0000854492.....

I do seem to remember this is for a depth gauge on a model submarine and am wondering what depth of water is 0.07 psi. The answer is 100 mm of water (99.54mm).

Giving

mm of water=(reading-102.4)*0.12207028.....

just to check at maximum reading = 921.6

therefore

mm of water=(921.6-102.4)*0.12207028

mm of water=99.9999

I am now wondering if this gauge is suitable?

[Acetronics2]

I am now wondering if this gauge is suitable?

0.07 psi gauge surely is a differential one ... so, one could reasonnably think it's for measuring SPEED with a pitot tube ...

just my two cents ...

Hi, Ed

Why not download that jewel ???
http://curveexpert.software.informer...nload/?ca13e51

Alain

[Ramius]

Hi! So if I understand correctly I need to use ADCON2 instead of ADCON1 with the same bit configuation? Yes Alian your are completely correct! It is a differntial sensor for my submarine. As the sub dives you need to subtract out the pressure at a given depth for the incoming pressure to stay meaningful.