Hello All,
       I am sorry that I was in a hurry to shoot a mail. I had posted the circuit while writing to the list on a previous occasion. The circuit is available at:

http://mechatronicscraze.wordpress.com/pic-orp/

One of the jpeg image contains the Express PCB file image that I had posted and the other image contains the eagle schematic that I had used for developing this ORP Probe interface. ( I would be happy if someone could offer an opinion on my PCB design skills).

The ORP probe is a glass probe which measures the oxidation reduction potential of a solution based on the potential of the solution. It is commonly used in aquariums by hobbyists and in water treatment plants to measure the dissolved ozone in water. 

Now the problem I am facing is that when I provide an input from a DC power supply, my display is providing me the correct voltage with an error of 3 to 4mV. When I dip my probe into a calibration solution of 200mV, it is displaying somewhere close to 203mV.  However, when I remove my probe from the solution, the displayed voltage has to get reduced gradually to zero. This is not happening. It is displaying all values between 0 and 900mV before getting reduced to zero. Some times it is displaying characters like "." "/" etc

I measured the input voltage to the op amp. My multimeter showed 215 mV and the voltage on the input got reduced gradually to zero when I removed the probe from the beaker of water. I measured the opamp output. The opamp output spans between 4.139V and 0V for 0mV to 900mV. My opamp also seems to be sending out the correct voltage. 

Could this be a problem with my code?
                  I did the following steps in my code using MikroC complier:
adc_rd = adc_read(0); // read voltage from AN0
t1 = 900-(float)(1.0625*adc_rd);//t1 is declared as float. I am doing this subtraction because my opamp gives an output of 0V for 900mV and 4.139V for 0mV.
t3long = (long)t1long;
//I am proceeding to LCD display section thereafter. 

Am I doing the scale conversion correctly or is there anything else that I should do for avoiding my PIC reading the noises.

Sairam



________________________________
From: Russell McMahon <apptechnz@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sent: Sat, March 20, 2010 6:08:46 PM
Subject: Re: PIC ORP problem

Sairam.

Congratulations on having got this far with your project.

While there are many things that MAY be causing your problems, and
while we MAY be able to suggest ones which are most likely, it would
be far better if you could provide a circuit diagram and also a
description of any aspects of the circuit which may not be shown well
on the diagram. For example the nature of the probe will affect the
result (and may be what is causing the problem) so knowing about it i
suitable detail will be useful.

The more useful detail that you can provide the more quickly and
easily we are liable to be able to help you.

   regards


              Russell McMahon
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist



      
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist