ADC lcd display help

[mackrackit]

http://www.picbasic.co.uk/forum/show...7177#post87177

[kevlar129bp]

Thanks for the heads up Mack,

I guess I was a bit confused by this in your ADC scaling tutorial:

Convert this to an 10 bit PIC® resolution.

10 bits ADC = 0 to 1023, 1024 steps.
At 5.0 volts one volt of input will will read 205. (204.6 actually)

Why would that read 205, instead of 204?
Thanks Mack, for helping a newbie trying to understand.

Chris

[mackrackit]

Why would that read 205, instead of 204?

Thanks for catching that and I apologize for the confusion.

I changed the article to

10 bits ADC = 0 to 1023, 1024 steps.
At 5.0 volts one volt of input will will read 204. (204.8 actually)
But we will use 205 for accuracy.
204 * 5 = 1020
205 * 5 = 1025

Hope that clears things up a bit..

[kevlar129bp]

Hey Mack,

I sketched this code in notepad after reading some other posts...
Does it look like I'm on the right track?

ADVal VAR WORD
Quanta CON 489	'VREF/1024 = 5/1024 = .00488 = 489
VoltageDivider CON 70
ADCVolts VAR BYTE
LCDVolts VAR WORD

ADCIN 0,ADVal
	ADCVolts=(ADVal/1000)*Quanta
	LCDVolts=ADCVolts*VoltageDivider
		LCDout $fe, 1
		LCDout $fe, 2,   "CURRENT READINGS ARE"
		Lcdout $fe, $C0, "A/D VDC = ",DEC1 ADCVolts/100,".",DEC2 ADCVolts//100
		Lcdout $fe, $94, "--------------------"
		Lcdout $fe, $D4, "ACTUAL VDC = ",DEC3 LCDVolts/100,".",DEC2 LCDVolts//100

Thanks again for your assistance,
Chris

[mackrackit]

Really close!!
But I think I would try it like this.

ADVal VAR WORD
Quanta CON 342     ' 350 / 1023 * 1000
LCDVolts VAR WORD
Z   VAR WORD     'DUMMY VAR
Z1  VAR WORD     'DUMMY VAR

ADCIN 0,ADVal
	Z = ADVal * 342
        Z1 = DIV32 1000
	LCDVolts = Z1

[fratello]

Need help ...with this math. Please !
I use voltage divider ; R1=1000 ohms; R2= 50 to 3500 ohms.
I read the voltage :

ADCON0 = %10000001 
		Pauseus 50			' Wait for channel to setup
	    ADCON0.1 = 1			' Start conversion
		While ADCON0.1=1:Wend		' Wait for conversion
		advalue.HighByte=ADRESH		' Read variable from ADC and save
		advalue.LowByte=ADRESL

I try to calculate the resistor(s) R2, assuming that I do not know values.
Formula is (?) :
R2= 1000 * advalue/(1024-advalue)
I wrote this code :

dummy =1000 * advalue 
resistor = div32 10
resistor = (resistor / (1024-advalue)) * 100

I want to display on Nokia 3310 :

'~~~~~~~~~~~~~~~~~ setting cursor for display the advalue
                LcdReg  =  %10000000 + 5       ' cursor  X
                call    PrintCtrlLcd
                LcdReg  =  %01000011            ' cursor  Y
                call    PrintCtrlLcd
'~~~~~~~~~~~~~~~~~ now display results 
   
               Char = (advalue dig 3)           
               call    PrintChar
                
               Char = (advalue dig 2)                      
               call    PrintChar                

               Char = (advalue dig 1)           
               call    PrintChar
               
               Char = (advalue dig 0)           
               call    PrintChar
.............
                Char = resistor dig 4          
                call    PrintChar
                Char = resistor dig 3          
                call    PrintChar
                Char = resistor dig 2         
                call    PrintChar
                Char = resistor dig 1         
                call    PrintChar

But I can not to display the last digit (from right) of values of resistors ...I have "50" instead "54" ; "140" instead "147" ; "1030" instead "1036" ...

Please, point me to the right direction ! Thanks in advance !

[HenrikOlsson]

Hi,
The result from the ADC ranges from 0 to 1023, not 1024. Try using 1023 in the formula and see if that makes it better.

With that said the whole thing is a bit convoluted....Why do you multiply by 1000 only to divide the result by 10 directly after?

What's the voltage at the top of the resistor divider and what's VRef?
If both are 5V then the highest voltage on the ADC input would be 5/(1000+3500)*3500=3.888V giving an ADC reading of 3.888/(5/1024)=796.
If you multiply 796 by 100 (multiply by 1000, divide by 10) the result will still overflow a WORD.

/Henrik.