I need help on the compare module

[chitalula]

I read compare module and i understand how it works that is it compare the two voltages on the input terminals.
comparator has two terminals, positive(Vref) and negative(input voltage on AN1 0r AN0)
Depending on which input has a higher voltage (analog value),
a logic zero (0) or logic one (1) (digital values) will appear on its output.

On my project i dont want to know whether the output is low or high but
i want to know exactly magnitude of output voltage, to know the magnitude of output voltage after comparison
I need someone to help me, anyone who is able to provide a sample code to overcome this problem

[HenrikOlsson]

Hi,
For that you need to use the Analog to Digital converter available in most PICs (but not all). It CAN be done with the comparators too by generating the VRef voltage with for example PWM and then sweeping the voltage from zero upwards while watching the comparator output. When the comparator output toggles you know the voltage. But the ADC is easier though....

Which PIC are you using?

[chitalula]

Hi,
For that you need to use the Analog to Digital converter available in most PICs (but not all). It CAN be done with the comparators too by generating the VRef voltage with for example PWM and then sweeping the voltage from zero upwards while watching the comparator output. When the comparator output toggles you know the voltage. But the ADC is easier though....

Which PIC are you using?

thanks HenrikOsson for your suggestion i hope it will help me, truely i have no anywhere to get the information on that issue, can you give me the reference book so that i can read to get enough concept on how to use ADC on comparators or can you give me sample code so that to be easy for me to understand.
I suggest to use PIC16F877, is it possible to work as i want, please Henrikosson help me

[HenrikOlsson]

Hi,
I'd suggest that you forget about the comparators for now, they COULD be used for what you want but the ADC will be easier for you.

To use the Analog to Digital Converter you use the ADCIN command. That command and all the others are decribed in the manual you shouldn've received when you bought PBP. If you have PBP3 then the manual even got installed as a.pdf on your system when you installed the compiler. If you have MicroCodeStudio a lot of information is available in the Help, the datasheet for your PIC is available from Microchips website and I'm sure that if you search the forum you'll find a LOT of info and examples showing how to use the ADC.

/Henrik.

[chitalula]

Hi,
I'd suggest that you forget about the comparators for now, they COULD be used for what you want but the ADC will be easier for you.

To use the Analog to Digital Converter you use the ADCIN command. That command and all the others are decribed in the manual you shouldn've received when you bought PBP. If you have PBP3 then the manual even got installed as a.pdf on your system when you installed the compiler. If you have MicroCodeStudio a lot of information is available in the Help, the datasheet for your PIC is available from Microchips website and I'm sure that if you search the forum you'll find a LOT of info and examples showing how to use the ADC.

/Henrik.

i have read the ADCIN command but i i do no how to link this command with the comparator, my aim is to design dc dc conveter with constant current by varying output voltage after comparison, So it's better for u HenrikOlsson to help me by giving sample code on that issue

[HenrikOlsson]

You can not use the ADCIN with the comparators. ADCIN is for the ADC.

On my project i dont want to know whether the output is low or high but i want to know exactly magnitude of output voltage

Again, you can not use the comparators for what you want without doing some tricks which I told you about in my first reply. The peripheral to use for measuring the actual voltage is the Analog to Digital converter (ADC) for which the ADCIN command works.

Why have you are you obsessing on the comparators? What am I missing?

[Acetronics2]

On my project i dont want to know whether the output is low or high but
i want to know exactly magnitude of output voltage, to know the magnitude of output voltage after comparison
I need someone to help me, anyone who is able to provide a sample code to overcome this problem

Comparator OUTPUT voltage is either LOW ( ~ VSS ) or HIGH ( ~ VDD ) ...

That's all !!!

as stated before ... if you need the difference between the two INPUTS , the A/D converter has to be used and difference CALCULATED ...

no problem here ... except your goal is " not so clear " ...

Alain

[chitalula]

thanx HenrikOlsson and Ailan, am taking a deep studies on that if i will meet with difficulties i will come back to you again