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complex72
Joined: 10 May 2014
Posts: 11
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| Zero crossing detection and Triac firing with timer1 |
 Posted: Tue May 27, 2014 11:55 am |
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Hi I've worked before with zero crossing detection, what I would like assistance in is on using timer1 for handling the firing of the triac. I basically have a C# interface with a slider that sends me a 16bit number to the microcontroller 0-65535 and loads it to the timer. What I couldn't figure out is what time does this values represent.
For instance I know that the maximum time for firing depends on the wave cycle so using 60Hz freq the period would be T=1/60=16.67ms and Half a cycle is 1/2T=8.33ms so the maximum time I have for firing after the zero crossing is 8.33ms here is my code:
| Code: | ************************************************CONFIGURATION**********************************************************/
#include "18f4550.h"
#fuses HSPLL,PLL5,CPUDIV1,PUT,NOWRT,NOWDT,NOBROWNOUT,NOPROTECT,NODEBUG
#use delay(clock=48000000)
#use rs232(baud=9600, xmit=pin_c6, rcv=pin_c7, bits=8, parity=N)
#use standard_io(B)
#include <stdio.h>
#byte RD16=1
#byte TO8BIT=0
#define tirac_fire Pin_B2
#include <stdio.h>
#include <stdlib.h>
//------------------------------------------------VARIABLES-----------------------------------------------------------
int16 angle;
int x,y;
//--------------------------------------------------------------------------------------------------------------------
#int_RDA
void RDA_isr()
{
x=getc();
y=getc();
angle=make16(y,x);
}
#INT_EXT
void zero_crossing()
{
output_low(triac_fire);
set_timer1(angle);
}
#INT_TIMER1
void timer1()
{
if(angle>0)
output_high(triac_fire);
}
//--------------------------------------------------Main()------------------------------------------------------------------
void main()
{
setup_timer_1(T1_INTERNAL|T1_DIV_BY_2);
enable_interrupts(INT_TIMER1);
ext_int_edge(H_TO_L);
enable_interrupts(INT_RDA);
enable_interrupts(INT_EXT);
enable_interrupts(GLOBAL);
while(1){
delay_ms(100);
}
}
//***********************************************End************************************************************************** |
So basically I have to find values from 0-65535 that represent 0-8.33m and load them to timer1? is that a good approach? and how can I figure them out?
Thank you |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19504
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| Posted: Tue May 27, 2014 12:19 pm |
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Your timer1, runs off the master oscillator/8 (Fosc/4 /2).
So with your 48MHz clock, it is counting in 6 millionths of a second. So will count 49980 in 8.33mSec (8330*6).
However remember there will be latency in getting into the ISR and loading the value. Perhaps 20+ counts, so use 49950 as your maximum value.
There are problems with your 'angle' code.
INT_RDA, says _one_ character is available to read. You are reading two, so the code _will_ hang waiting for the second character in this ISR.
Then there is nothing to say when the number starts or ends. If a character gets missed at any point, the value will become invalid....
Suggest you just use a single character as 'percent'. Then when this is updated, multiply this by 499, to use in your angle code. Each character is then the complete 'message'. |
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complex72
Joined: 10 May 2014
Posts: 11
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| Posted: Tue May 27, 2014 1:36 pm |
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| Ttelmah wrote: | Your timer1, runs off the master oscillator/8 (Fosc/4 /2).
So with your 48MHz clock, it is counting in 6 millionths of a second. So will count 49980 in 8.33mSec (8330*6).
However remember there will be latency in getting into the ISR and loading the value. Perhaps 20+ counts, so use 49950 as your maximum value.
There are problems with your 'angle' code.
INT_RDA, says _one_ character is available to read. You are reading two, so the code _will_ hang waiting for the second character in this ISR.
Then there is nothing to say when the number starts or ends. If a character gets missed at any point, the value will become invalid....
Suggest you just use a single character as 'percent'. Then when this is updated, multiply this by 499, to use in your angle code. Each character is then the complete 'message'. |
Thanks Ttelmah, one last question how did you figure out the 6 millionths of a second, what if I where to use a 20Mhz clock..thank you |
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Mike Walne
Joined: 19 Feb 2004
Posts: 1785
Location: Boston Spa UK
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| Posted: Tue May 27, 2014 2:10 pm |
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[quote="complex72"] | Ttelmah wrote: |
Thanks Ttelmah, one last question how did you figure out the 6 millionths of a second, what if I where to use a 20Mhz clock..thank you |
He meant 6 million a second.
You're feeding the timer at 6MHz.
That's your 48MHz/4 then /2.
The /4 is because that's how 18F parts work and /2 because you've told the compiler to div_by_2.
It's all in the microchip data sheet.
Mike |
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complex72
Joined: 10 May 2014
Posts: 11
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| Posted: Tue May 27, 2014 9:14 pm |
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| got it...! Thanks Ttelmah and Mike |
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