Hello Sergio,
     Thanks for the mail. 
>For the "junk characters" I would look at the software, in particular the 
>routines that convert you binary into displayable ascii. Is a big enough 
>buffer available? Can the routines cope with the full range of values you 
>might be giving them (can they cope with numbers bigger than 999 for 
>example)?

My display cannot exceed 900mV as I am subtracting my ADC values from 900. As mentioned earlier, my opamp sends 0V for a 900mV signal. I am having second thoughts about doubting my code. There seems to be regularity when I provide an input from a DC RPS.

>Regarding the strange random readings, could this be due to the wet probe 
>interacting with the oxygen in the air? Or maybe due to movement and a 
>faulty connection?

I had this doubt and I tested this by connecting to an oscilloscope. When I rub the probe with my hand, I see that there is an overshoot of voltages. 

Sairam



________________________________
From: sergio masci <smplx@allotrope.net>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sent: Sat, March 20, 2010 11:56:57 PM
Subject: Re: PIC ORP problem



On Sat, 20 Mar 2010, yamanoor sairam wrote:

> Dear All,

>               I constructed a PIC ORP(Oxidation Reduction Potential) 
> interface using the help of Mr.Marcel Du Champ from this list. I am 
> facing a problem with signal noise. The LCD display is showing a value 
> close to 200mV when I dip it in a solution of potential of 200mV (say 
> 203 to 207mV). When I remove my probe out of the solution, I see that my 
> display is indicating all possible values between 0 and 900mV before 
> returning to 0mV. I don't want my probe to pick up noises from the 
> environment. It is also displaying some junk characters before returning 
> to zero. How am I supposed to eliminate such erratic behavior?

For the "junk characters" I would look at the software, in particular the 
routines that convert you binary into displayable ascii. Is a big enough 
buffer available? Can the routines cope with the full range of values you 
might be giving them (can they cope with numbers bigger than 999 for 
example)?

Regarding the strange random readings, could this be due to the wet probe 
interacting with the oxygen in the air? Or maybe due to movement and a 
faulty connection?

Regards
Sergio Masci
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