neddie
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pic 24 motor control conumdrum :0)
Hi to all.
I hope this explanation makes sense. I'm using a pic24fj256ga104 to control an AC motor using a triac. Speed control is achieved by varying the firing of the triac
with respect to the zero crossing. Phase control I think it called. It is all working as expected.
The issue I have is I'm sure I've made a "mountain out of a moll hill" with the coding. I'm sure the peripherals on this chip are powerful enough
do do this almost without processor intervention , just modifying the OC1R and OC1RS registers to adjust the firing angle.
My current implementation is as follows.Processor running at 16Mhz.
I have a zero crossing detector that gives me a 50% dutycycle (50 Hz) into the micro. That is connected to IC1 , configured to interrupt on both edges.
I get interrupted every 10mS , at zero crossing.(or close enough)
My output compare module is set for mode 5(Dual compare , continuous pulse).
I've set the OC1 clock source to Timer4. Timer4 clock is prescaled by 8 and a period (PR4 of 15000 = 7.5mS)
I've set the OC1 Trigger/Sync to timer 4 as well.
On interrupt from the IC1 module I clear timer 4 (TMR4 = 0) , Start timer 4 (T4CONbits.TON = 1) and set up the OC1R and OC1RS registers to the values I want.
I just send a quick pulse (50us) to the opto to fire the triac , I don't leave the triac drive on. I can then set a pulse that can occur from just after the zero crossing up
to 7.5ms after zero crossing , depending on the OC1R and OC1RS registers.
When Timer 4 interrupt occurs (15000 counts or 7.5mS later) , I turn off Timer 4 (T4CONbits.TON = 0).
On the next IC1 interrupt , the cycle repeats. Hope you get my explanation.
I'm sure I'm doing this all wrong and there is a more efficient way of doing this. I shouldn't be turning timers on and off ect. I'm sure the trigger/sync etc should
handle all of that automatically.
Anyone got any better ways of doing this.
Cheers
Neddie
Hi to all.
I hope this explanation makes sense. I'm using a pic24fj256ga104 to control an AC motor using a triac. Speed control is achieved by varying the firing of the triac
with respect to the zero crossing. Phase control I think it called. It is all working as expected.
The issue I have is I'm sure I've made a "mountain out of a moll hill" with the coding. I'm sure the peripherals on this chip are powerful enough
do do this almost without processor intervention , just modifying the OC1R and OC1RS registers to adjust the firing angle.
My current implementation is as follows.Processor running at 16Mhz.
I have a zero crossing detector that gives me a 50% dutycycle (50 Hz) into the micro. That is connected to IC1 , configured to interrupt on both edges.
I get interrupted every 10mS , at zero crossing.(or close enough)
My output compare module is set for mode 5(Dual compare , continuous pulse).
I've set the OC1 clock source to Timer4. Timer4 clock is prescaled by 8 and a period (PR4 of 15000 = 7.5mS)
I've set the OC1 Trigger/Sync to timer 4 as well.
On interrupt from the IC1 module I clear timer 4 (TMR4 = 0) , Start timer 4 (T4CONbits.TON = 1) and set up the OC1R and OC1RS registers to the values I want.
I just send a quick pulse (50us) to the opto to fire the triac , I don't leave the triac drive on. I can then set a pulse that can occur from just after the zero crossing up
to 7.5ms after zero crossing , depending on the OC1R and OC1RS registers.
When Timer 4 interrupt occurs (15000 counts or 7.5mS later) , I turn off Timer 4 (T4CONbits.TON = 0).
On the next IC1 interrupt , the cycle repeats. Hope you get my explanation.
I'm sure I'm doing this all wrong and there is a more efficient way of doing this. I shouldn't be turning timers on and off ect. I'm sure the trigger/sync etc should
handle all of that automatically.
Anyone got any better ways of doing this.
Cheers
Neddie
