Displaying temperature using a -40 to 185F??

[skimask]

((Analog_value - 0.5V)/ (0.004883V))-40 = temp (in F)

won't work...
0-5v output, actually running from .5v to 4.5v, 10bit ADC, -40F to 185F range?

4v total range, 10 bit ADC, lowest value readable from ADC = 102.4, highest value is 921.6, range of 819.2

185+40 = 225 degrees total range thru 4v input offset by 40 degrees F

ADC value - 102 = the .5v offset at the input
ADC value * 225 / 819 = something like .275 degrees per bit

But the result so far is offset by 40, so...
IF result < 40 then
result = 40 - result
sign = negative
else
result = result - 40
sign = positive
endif
DONE....

So run a test case...
Input value from ADC is 921, corresponding to a voltage of 4.5v
921 - 102 = 819
819 * 255 / 819 = 225
The result is larger than 40, so sign is positive and subtract 40 from it,
225 - 40 = 185
sign positive 185
BAM done...

Another case at minimum...
Input value from ADC is 102, corresponding to a voltage of .5v
102 - 102 = 0
0 * 255 / 819 = 0
The result is smaller than 40, so set the sign negative and subtract it from 40.
40 - 0 = 40
sign negative 40
BAM done...


Not only that, but a search on temperature display here at this site would've most likely been a heck of a lot simpler and might actually net you some premade code just for this application....

[Darrel Taylor]

I understand the whole "Teaching a man to fish" thing.
But at the end of the day, the guy's gotta be able to catch a fish.

To help prevent starvation, I need to toss in a fish here. And maybe a loaf of bread to go with it.<hr>
The Slope Intercept formula for the given data points would be ...

Y = (0.2751 * X) - 68

to do this in PBP with 1 decimal place @ 10-bit resolution ...

ADCIN 1, TempF
TempF = TempF * 2751
TempF = DIV32 1000
TempF = TempF - 680
GOSUB ShowTemp

'...

' --- Display a Signed Word with 1 decimal place ---
ShowTemp:
    if TempF.15 = 1 then LCDOUT "-"
    TempF = ABS(TempF)
    LCDOUT DEC (TempF/10),".",DEC1 (TempF//10)
Return

Bon Appetite,

[skimask]

I understand the whole "Teaching a man to fish" thing.
Bon Appetite,

Hey, you're right.
I missed that 6th line in the 1st post about fractions...
My bad...
-40F to 185F... that temperature 'probe' sounds familiar... like something else I've seen before... might even have a greater range, just not documented... what is it... I can't put my finger on it...
Oh...yes...it's a...(click)....mmmmmmmmmmmmmmmmsssssssssssssss