Strange ADC behaviour

[ruijc]

I still get behaviour no matter what i change...


except with Mister-e's code that works OK

Is it just a pbp version issue or is it something else ?

If it's a version problem...is there a way to get arround it ?

.

[Acetronics2]

Hi, Ruijc

I just re-wrote your code ... works fine ( I'm only talking of the PIC point of view - do not talk about precision ...)

Try to write carefully ( and readably) ALL your config sequence ( I know ... ~ 50 lines ! )... and it will work !!!

Just a tip:

instead of :

" temp = (va1*/500)>> 2 "

try :

" temp = val*125
temp = temp.highbyte "

Alain

[mister_e]

Mine did some averaging, not much. Read the sensor couple of time (10-16 times) then calculate the average of it, go to next channel, do the same, show the results.

I did it the 'bad' way

        for loopw = 0 to 15
            ADCIN 0, TEMPW
            VA1=VA1 + (TEMPW>>4)
            NEXT
            
        pause 500
        
        FOR LOOPW=0 TO 15
            ADCIN 1, TEMPW
            VA2=VA2 + (TEMPW>>4)
            NEXT

lost of precision and so on, now for something better, have a look at Darrel's routine.

Averaging 16 bit values without using 32 bit math?
http://www.pbpgroup.com/modules/wfse...hp?articleid=7

[Acetronics2]

lost of precision and so on, now for something better, have a look at Darrel's routine.

Hi, Steve

for precision ... measuring 150 or 200 mV on a 5 v full scale is a nonsense ...
we already had this discussion here with ruijc ...

Alain

[mister_e]

Yup i agree, an external Vref or op-amp should be used.

[ruijc]

Hi guys

thanks for all the help.

Mister-e...you mentioned an external Vref.

I have a 12v power down to 5v for this circuit.

Can i use 12v as reference ? How can i do this ?

I'm a bit confused...can i plug it directly to my 16F88 ?

.

[mister_e]

NO NO NO DON'T DO IT

Vref have to be lower than Vdd. Let's see you have a sensor who produce you a max of 1 volt. Then you select a Vref of ~1 Volt, then your ADC give you the full 10 bit conversion scale between 0-Vref. This is the use of it.

But yeah.. check out for the minimum Vref requirement...