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pwm question

 
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Marc
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pwm question
PostPosted: Wed Jun 27, 2007 9:27 am     Reply with quote
I have a circuit which drives a led: a pic micro generates a pwm signal to the gate of a mosfet connected source-drain to a led and a resistor in series. I try to measure with adc the led current at the resistor pins but I see pwm waveform.
Iask how to know when pic generates pwm signal equal to 1 and when equal to 0 so that I can turn on adc when pwm waveform is 1.


Thank You
nilsener



Joined: 06 Dec 2005
Posts: 59

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PostPosted: Wed Jun 27, 2007 9:42 am     Reply with quote
Dear Marc,

the PWM is controlled by Timer2. Try to read the ADC in the ISR of Timer2. There is a 50:50 chance that the PWM signal changes from L to H when the Timer2 interrupt occurs. If it changes from H to L then it will not work.

Code:
#int_timer2                                        // ISR for Timer 2

void T2_ISR(void)
{

delay_ms(1);  // let LED current raise up
read_adc();

}// End T1_ISR()


Best Regards
Nilsener
Marc
Guest
another question
PostPosted: Wed Jun 27, 2007 10:13 am     Reply with quote
I do not know exactly how pics work but I think there should be a register in which it is written if pwm is 1 or 0 so that I can control that.
nilsener



Joined: 06 Dec 2005
Posts: 59

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PostPosted: Wed Jun 27, 2007 10:48 am     Reply with quote
which PIC do you use?
Marc
Guest
PostPosted: Wed Jun 27, 2007 10:50 am     Reply with quote
18f4580
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