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Thanx alot HankMSpank and arrati, i did what you said and my problems have been solved.
I want to add something in this code, i want after the duty cycle being constant to giveout this duty cycle...

I want to incease the duty cycle until the volts on R4 is equal to three ( feedback voltage to the pic greater than 153) then at this volt i want to stop the duty cycle.
Problems
the duty cycle is...

I am doing my final year project on designing constant current pic controlled boost converter, boost converter which as the load resistance changed the output current still remained constant.

...

thaks in advance, am taking a time to concentrate with it and when i meet any difficult i will came back to you

up to now i dont need to continue to work with the comparator module because it fail to do as i want
i want to use adc but have already read the adcin command but how to use adc to compare the two...

thanx in advance Henrik. now i want to continue to output constant duty ratio when the comparator input are equal, is it possible to output that constant duty cycle which make input equal to Vref?

your right Henrik, input voltage at the RA2 is 3volts

/chitalula.
I will wire the circuit on the breadboard when the circuit do what i want. as you know that iam new on the world of programming....

sorry Henrik early i used that chip but was difficult to understand, i uploaded that by mistake, 16f877a it was difficult to me thus why i leave that and i have choosen to work with 16f628a, help me...

1. VRCON register is for internal Vref and is found within a data sheet
2. CM2:CM0=101 i found from the data sheet and is for "one independent comparator"
3. from the data sheet i found RA2 is the...

thanx in advance, i want to use external refence , am taking deep reading on the data sheet then if i see misunderstang i will come back to you

in this code i want to increase the duty ratio until the input volts at RA1 is equal to the Vref, after while loop is true to light the led at portb.5. the problem here is the output is not increase...

HenrikOsson my big problem was in CMCON register configuration, i leave my previous circuit and i took the circuit uploaded by sayzer. and i edit some code there by puting my own code

Thanx alot henrikolsson and sayzer for all of your suggestions, the problem was in configuration of cmcon, now it work as i want, thanx in advance

thanx for your suggestion. on stimulation if the input voltage equal to vref else statement always and if the input voltage is higher than or less than Vref else statement is executed too. it seems...

i tried to do as you told me but it didn't work as i want, led at portb.1 is always on even if the voltages at RA0 pin is changed. it seems the comparison is not working on the if statement, still...

sayzer i tried to run your but it didn't do anything, i don't know why. and i need a comparison in my code can you add too?

yah HenrikOlsson help me on that edit where necessary so that it can work as i want, iam a begginer in the pics progrmming, thanx indvance

i want to light the led at portb.0 when the output of comparator is high and to light led at portb.1 when comparator output is low, my code compiled successful and on running this code light a ked...

i want to light the led at portb.0 when the output of comparator is high and to light led at portb.1 when comparator output is low, my code compiled successful and on running this code light a ked at...

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

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...

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...

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)...

my aim is to control dc dc converter by using pic microcontroller, anyone to help me sample codes for controlling the dc dc converter