Need some help regarding AD and float number

[Paulo Marcio Silva]

Hi everyone,

I didn't find this topic on the forum. I want to read an analogic value and make some maths with it and show the value in the LCD.
I have the 10 bit AD I want it to show the 0 - 5V value and not 0-1023. Do you know how should I do this? Heres the program I've made but it didn't work.

#chip 16F688, 4
#config WDT=off
#config MCLR=on
#config osc = INTRC_OSC_NOCLKOUT

#define LCD_IO 4
#define LCD_DB4 PORTA.2
#define LCD_DB5 PORTC.5
#define LCD_DB6 PORTA.4
#define LCD_DB7 PORTA.5
#define LCD_Enable PORTA.0
#define LCD_RS PORTA.1
#define LCD_NO_RW

#define ad AN7

dim advalue as word

PRINT "Hello World"

wait 1 s
main:
CLS
advalue=ReadAd10(ad)
advalue=5*avalue/1024
locate 1,0
LCDWord(avalue)

goto main

[Paulo Marcio Silva]

avalue is wrong. The right variable is advalue. I changed for it and I get just 0 in my LCD.

[mmotte]

Looks very close!

You need to define the port direction for the a/d

dir PORTC.3  in

only thing isee besides the "advalue" problem you found

GL

[Paulo Marcio Silva]

Really? I could get the 0-1023  A/D data before without using the port direction. But,  I'll try this tomorrow.
Thanks for the tip!

[gcha44]

Hi,
I think your program is correct but the precision is not good because you only obtain the entire value of advalue  .
You'l have a better precision if you multiply advalue by 10000 and then you could divide it by 10000 to display the remainder .
advalue=(50000/1024)*advalue   'The advalue never exceeds 50000  ( Word  )
50000/1024=48.828 . The entire value is 48 but you must multiply by 49 to have a better  result

You can call your subroutine Printdec like this
advalue=49*advalue                                                        'instead of advalue=5*advalue/1024
printdec advalue , 10000
print "V"

Sub PrintDec (number as word , factordiv as word )
dim entire , remainder as word
select case factordiv 'to avoid values that are different of 10,100,1000,10000
case 10
  nop
case 100
nop
case 1000
nop
case 10000
nop
case else
exit sub
end select
entire= number / factordiv
remainder=number %factordiv
print entire 'dispalys entire number
print "."
'you must display the number of "0" before the remainder 
'or else the result will not be true

select case factordiv
case 100
  if remainder < 10 then
    print "0"
  end if
case 1000
if remainder <100 then
   print "0"
end if
if remainder < 10 then
  print "0"
end if
case 10000
if remainder <1000 then
  print "0"
end if
if remainder <100 then
  print "0"
end if
if remainder < 10 then
  print "0"
end if
end select
print remainder
end sub

'ie: if advalue= 308
advalue=49*308
advalue=15092
the display will be :
1.5092V

Nota: the precision will still be better if your voltage reference is 2.56V because

25600/1024 = 25 exactly !

GC

[gcha44]

You can choose your voltage reference such as 1024*48=49152 =4,9152V  by adjusting voltage on Vref with a 10t potentiometer .
But you can choose any other value , the most important is the multiplicand is a entire number and the result is not greater than 50000 !
The PrintDec subroutine will be used to display any word value you want divide by 10 , 100 , 1000 , 10000

GC

[Nobody/Anonymous]

Hi!
tanks for the answer. I just didn't understand the use of this subroutine PrintDec. It's not doing anything is it?
I'll test it later but using this 2 lines should work ..
entire= number / factordiv
remainder=number %factordiv

[gcha44]

Hi,

I volontary choose an explicit example :
If entire =2 , remainder = 3 and factordiv=  10000 , if you don't use this subroutine (PrintDec)  you'll  display  result = 2.3  .
But it's false ,because the result is 2.0003  !

[Paulo Marcio Silva]

Understood.
Thank you very much for the support!

[gcha44]

I often use this subroutine ,and I added it to my included files .
To do that , you write your "Printdec" subroutine , you save it as "Printdec.h" in  "gcbacic / include / lowlevel"  directory .
Then you open the file named "lowlevel.dat" in "gcbasic / include " directory and you add "printdec.h"  at the end of list .
Each time you'l want to display a precise value of AD converting you'l call that subroutine
Example: if you want to convert 24017( mV)  in V  ,you'll write
PrintDec 24017 , 1000 :Print "V"
That's very easy to use , and the result will be  true and perfect !
Have a nice day
GC

[gcha44]

Hi again,

I think your program doesn't work for the same reason as in your last post "LCD 4 bits mode help me"
Before <goto main>  you must write  <wait 1 s>  to display the result ,or else it will be continuously erased
GC

[Tom Poulton]

Hi there.

How could this be adapted to work in the range of 0-25V? as Im using a potential divider on AN0 to give me 5V at 25V. I've tried altering GCHA44's code all ways i can think of, but all i seem to get is just 'V' on the LCD with nothing else but works fantastic to read 0-5V. I've tried altering the factor variable to be 4x greater, also tried modifying the AN0 figure before its put into the sub but to no avail

any advice would be greatly appreciated

Thanks

[gcha44]

Hi Tomlo,

The principle is the same but in this case  you work with a long word
If I muliply 25*10000 I obtain 250000 for a 25V potential
So, to find the entire value you must do (250000/1024)*Advalue = 244.14*advalue
You can work with 244*1024 to have a good result

I think you have just to dim entire as long , not word  ( see in GCBASIC.chm / syntax / variables). I have not tried this but I think it does work.
Regards

[gcha44]

Sorry not entire but advalue

[Tom Poulton]

Hi GC, thanks for the reply, I'll try it in a few minutes

[Tom Poulton]

I get an Invalid variable type: LONG when I try to compile :(

[gcha44]

Have you the last updated GCBASIC compiler?  See http://gcbasic.sourceforge.net/download.html (update.zip)

[Tom Poulton]

Cheers, that was what was stopping it compiling as I tend to use GCGB evvironment but in text mode

I've compiled it but still getting some odd actions, figure before the decimal point is all over the place, the 4 digits after the decimal point do seem correct though. Heres the code I am using now:

Dim Number As word
Dim entire , remainder As word
Dim advalue As long
Wait 1 s
loop:
advalue=ReadAD10(AN0)
advalue=(244*advalue)
'instead of advalue=5*advalue/1024
printdec advalue , 10000
locate 0, 2
print "V"
Wait 1 s
CLS
Goto loop
Sub PrintDec (number As word, factordiv As word)
    select case factordiv
    'to avoid values that are different of 10,100,1000,10000
    case 10
    nop
    case 100
    nop
    case 1000
    nop
    case 10000
    nop
    case else
    exit sub
    end select
    entire= number / factordiv
    remainder=number %factordiv
    locate 0, 4
    print entire
    'dispalys entire number
    print "."
    'you must display the number of "0" before the remainder 'or else the result will not be true
    select case factordiv
    case 100
    if remainder < 10 then
        print "0"
    end if
    case 1000
    if remainder <100 then
        print "0"
    end if
    if remainder < 10 then
        print "0"
    end if
    case 10000
    if remainder <1000 then
        print "0"
    end if
    if remainder <100 then
        print "0"
    end if
    if remainder < 10 then
        print "0"
    end if
    end select
    print remainder
End Sub

Snipped all the includes and irrelevant stuff out

[Tom Poulton]

Doh! just realised also that PrintDec I should have changed it to 'number as long' instead of word

Works great now, checked LCD alongside an DVM and its very accurate, its for use in a bench PSU im building for myself.

Thanks for all your help GCHA :)

[Tom Poulton]

Oops, forgot to ask, is there a way i can trim the figure after the DP to 2 decimal places?

[gcha44]

if you divide number by 10000 and to obtain 2 decimals after DP you just have to do

remainder= remainder /100

but for a better result  you must do :
dim remainder1 as word
remainder1= remainder % 100
remainder= remainder/100
if remainder1>50 then remainder=remainder+1

Regards

[Tom Poulton]

Thanks for the help, working perfectly now