Dimmer

[Darrel Taylor]

You're right, I had the resistors wrong.
Making the change brought it up to 4.6V.
But, having the zeners in there adds about 40uS to the zero-cross signal.
It takes 35uS without the zeners, and 75uS with them.

Add in the interrupt latency for PBP type interrupts, time to do math in the handler, the minimum pauseus of 24us, and taking into account that a half cycle of 60hz is 8,333uS ... I'm sure the first step was quite a bit dimmer.

But the biggest problem is delaying inside the interrupt handler.
When 90% of the time is spent in the handler, the pause 10000 in the main loop takes almost a minute.

So here's my next attempt.
It uses Timer1 for the delays, so the main program can keep running in the foreground.
The handlers have been changed to ASM type to minimize latencies.
And the math is done in a separate subroutine that only runs once when you change the brightness, instead of having to do the math on every zero-cross.

It should be pretty close to the MAX/MIN dimming, but you may need to adjust the MaxBright/MinBright constants a little.
If you adjust them too far, it will start flashing.

INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System
INCLUDE "ReEnterPBP.bas"     ; Include if using PBP interrupts
Include "modedefs.bas"
@ __Config _XT_OSC & _WDT_ON & _PWRTE_ON & _MCLRE_OFF & _BODEN & _CP & _CPD

MaxBright                   CON 8250    ; maximum brightness
MinBright                   CON 200     ; minimum dimming 
Brightness                  var word
TriacDelay                  var Word
AlwaysON                    var BIT
AlwaysOFF                   var BIT
OffPeriod                   var BIT     ; used by timer1 periods
 
Triac	var	PortA.1 ' Output to TRIAC gate
ACLine	var	PortA.2 ' Input for the FullWave rectify AC line
Buz		var PortC.2

INTEDG  VAR OPTION_REG.6
TMR1ON  VAR T1CON.0
TMR1IF  VAR PIR1.0
Timer1  VAR WORD EXT
@Timer1 = TMR1L

TRISA = %001100
TRISC = 0
CMCON = 7
ANSEL = 0
PORTA=0
PORTC=0

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler    INT_INT,    _ACDetect,   ASM,  yes
        INT_Handler   TMR1_INT,   _T1Handler,   ASM,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM

@   INT_ENABLE   INT_INT     ; enable external (INT) interrupts
@   INT_ENABLE  TMR1_INT     ; enable Timer1 interrupts

Triac=0            ' disable Triac Gate
brightness=0       ' Set delay to minimum
gosub SetDelay

while 1
    pause 3000
    high buz: pause 500 : low buz
    brightness=MaxBright   : gosub SetDelay : pause 10000 :high buz: pause 50 : low buz 
    brightness=MaxBright-2 : gosub SetDelay : pause 10000 :high buz: pause 50 : low buz 
    brightness=4500        : gosub SetDelay : pause 10000 :high buz: pause 50 : low buz 
    brightness=4000        : gosub SetDelay : pause 10000 :high buz: pause 50 : low buz
    brightness=3500        : gosub SetDelay : pause 10000 :high buz: pause 50 : low buz
    brightness=MinBright   : gosub SetDelay : pause 10000 :high buz: pause 50 : low buz
    brightness=0           : gosub SetDelay : pause 7000
wend

SetDelay:
    Brightness = Brightness min MaxBright                    ; limit maximum brightness
    AlwaysON  = !(Brightness != MaxBright)                   ; MaxBright is always ON
    AlwaysOFF = !(Brightness != 0)                           ; 0 is always OFF
    if !AlwaysOFF then Brightness = Brightness max MinBright ; limit minimum dimming
    triacdelay = -(MaxBright - Brightness)                   ; calc delay time
RETURN

;------------------------------------------
T1Handler:
    if OffPeriod then            ; triac delay finished
        OffPeriod = 0
        triac=1                  ; turn on triac
        Timer1 = -50             ; load timer for 50uS
    else
        triac = 0                ; turn off triac after 50uS
        TMR1ON = 0 
    endif
@ INT_RETURN

;------------------------------------------
ACDetect:
    if AlwaysON then
        triac=1 ' Activate TRIAC
    else
        if AlwaysOFF then
            triac = 0
        else
            Timer1 = triacdelay  ; load delay into timer
            TMR1IF = 0           ; clear the interrupt flag
            TMR1ON = 1           ; start the timer
            OffPeriod = 1        ; tell T1Handler this is the main delay
        endif
    endif

    INTEDG = !INTEDG             ; toggle INTEDG to get both edges
@ INT_RETURN

Hope that works better.

[FromTheCockpit]

Thanks Darrel, I am on 50Hz, do I need to change any value in the code for that??

[Darrel Taylor]

There's another reason for the first step being much dimmer.

Half a cycle of 50hz, is 10,000uS.
So take MaxBright up to 9900.