Why this ADC value flickers?

[jayanth.devarayanadurga]

I am using Analog Comparators as ADC as mentioned in AN700 application note. I am not getting a stable value. Why? I am attaching mikroC PRO PIC files + Proteus Simulation file. I am testing in hardware and also Proteus. Video of hardware attached. In the real hardware power supply is like this.

100 nF Ceramic at I/P and O/P of 7805.
1000 uF 25V at O?P of 7805.
200 nF Ceramic between VDD and Vss pins of PIC.
10 uF 10V between VDd and Vss pins of PIC.
External oscillator of 4 MHz with 2 * 33 pf Ceramic.

How can I improve the stability of readings?

 

[chippevijaya]

How many ADC sensors did you connected?
And what is the PIC you are using , What else interface's it is doing apart ADC's?

Try these:
- by keeping decoupling resistor's at the Analog source supply, so that noise will reduced....
- you have used the ADC libraries in mikroC Pro, but try writing your own ADCread function(u will get in MPLAB examples) in that change Vref+, Vref- voltage using registers in that particular PIC datasheet

 

[jayanth.devarayanadurga]

I am not using any ADC. I am using Analog Comparator to work as ADC. PIC16F628A doesn't have ADC and I am not using ADC_Read() function of mikroC. I have just used the code from AN700 and used inline assembly in mikroC PRO PIC to do the project.

 

[Venkadesh_M]

by putting 1k instead of 39, there is a small range of variation, but its still exists......

 

[chippevijaya]

try to keep the decoupling(104) capacitors at the signal and ground of potmeter will reduce some flickering.