Need some advice.

[cphillips82]

Hi everyone, I'm building a device which controls temperature. Currently I'm using an 18b20 to pick up the temperature and I also have to detect zero crossing on a 50hz ac waveform on portb.0 so I can fire a triac on cirtain 0-10ms periods. I'm using a 16f628 at 4meg. it is critical that the phase controling is not interupted while gathering the temp from the 18b20 however I'm having trouble due to the time being needed to access the temperature. Does anybody know if it is at all possible to do this using the interupt on portb.0 or am I just barking up the wrong tree using this 18b20 or should I use something like a 16f88 and an lm35 with some kind of voltage ref? thanks in advanced

[Acetronics2]

Hi,

No problem ... just poll the DS data line to see if conversion has ended.

'*****************************************************************************
' Start temperature conversion
'*****************************************************************************

mainloop: OWOut DQ, 1, [$CC, $44 ]

'*****************************************************************************
' Check for still busy converting ( ~ 4500 fois ... )
'*****************************************************************************

waitloop: 

		INPUT DQ
		If NOT DQ Then waitloop
	
'*****************************************************************************
' Read the temperature
'*****************************************************************************
	
	OWOut DQ, 1, [$CC, $BE ]		
	
    OWIn DQ, 0, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]

Here, you won't have a Waitloop, but, say, goto your regulating loop ...

AND remember heating has "a little" ( LOL !!! ) inertia, and some AC periods more or less won't disturb the system ...
the temp data will be updated each ~ .75 s ... that's all !!!

using a MOC 3041 to drive your SCR could miraculously simplify your program ...
just an idea ...

Alain

[sayzer]

From my side, I can say couple of things.

1. If the temp resolution (and consistency) IS NOT very critical, then you can use LM35 with 12F675, and if only turn ON/OFF is on the subject (no voltage control) then you can directly fire the triac from PIC pin using zero-crossing.

2. If temp resolution (and consistency) is critical then you can use DS18B20 with 12F675 and fire the triac from PIC pin using zero-crossing. You can check the "busy" feature so that you do not wait for temp conversation.

In both cases, sensitive gate triacs will be more suitable for PIC's current sink (25mA max).
If you use regular triacs, then gate will draw about 35mA, thus a MOC type will be appropriate as Alain mentioned.

[cphillips82]

thanks for your reply s. here is a piece of software I'm using just to see if I can get it working without the flicker of when temp hits 5000 and 10000, so far failed, I'm using a moc 3021 and a bt137 and bridge with a 1k feeding porta.0 and a 10k holding it low. I have been able to make a simple dimming program so I know this hardware works, I also have an lcd so I need a few more io that a 12f675

Define LCD_DREG PORTB
 'Set starting data bit
 Define LCD_DBIT 4 'rb4,rb5,rb6,rb7
 'Set LCD RS Port
 DEFINE LCD_RSREG portb
 'Set LCD RS Bit
 define LCD_RSBIT 3
 'Set LCD Enable Port
 Define LCD_EREG portb
 'Set LCD Enable Bit
 Define LCD_EBIT 2
 'Set number of LCD Lines
 Define LCD_LINES 2
 'Set Command Delay time in uS
 define LCD_COMMANUS 2000
 'Set Data delay time in uS
 define LCD_DATAUS 50

temp var word
temp = 0
temp2 var word
target var word
target = 3000
symbol fire = portb.1
symbol ac = portb.0

maxdelay var word
maxdelay = 8000

delay var word
delay = 4000

trisa = %00000011
trisb = %00000001

DQ	VAR	PORTa.0			' One-wire data pin
temperature VAR	WORD			' Temperature storage
count_remain VAR BYTE			' Count remaining
count_per_c VAR	BYTE

DS18B20_9bit CON %00011111 ; 93.75ms, 0.5°C
DS18B20_10bit CON %00111111 ; 187.5ms, 0.25°C <-- My favorite
DS18B20_11bit CON %01011111 ; 375ms, 0.125°C
DS18B20_12bit CON %01111111 ; 750ms, 0.0625°C (default)

OWOUT DQ, 1, [$CC, $4E, 0, 0, DS18B20_11bit]
 


lcdout 254,1
pause 100

on interrupt goto firetriac
intcon = %10010000

mainloop:
for temp = 0 to 10000
if temp = 5000 then
gosub startcon
endif
if temp = 10000 then
gosub readtemp
endif
next temp
goto mainloop 




disable
firetriac:
pauseus  delay
fire = 1
pauseus 10
fire = 0
intcon.1 = 0
resume
enable

startcon:
OWOut DQ, 1, [$CC, $44]       ' Start temperature conversion
return
readtemp:


waitloop: OWIn DQ, 4, [count_remain]	' Check for still busy converting
	IF count_remain = 0 Then mainloop    'was this what you ment about no waiting in the 'loop

	OWOut DQ, 1, [$CC, $BE]		' Read the temperature
        OWIn DQ, 0, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]

	' Calculate temperature in degrees C to 2 decimal places (not valid for negative temperature)
	temperature = (temperature >> 1)

	lcdout 254,1, dec temperature / 10 ,".", dec1 temperature , " c" 
    lcdout 254,192, dec delay 

return

[cphillips82]

what I want to do over all is to dim an incandescent light depending what temperature it is without an annoying flicker while fetching the temp.

[mister_e]

You may try to switch to asm interrupt or Darrel's instant interrupt to see if it works better.

A real schematic would help...

To generate 10uSec with PAUSEUS, you need at least a 10MHz crystal. If you're using a 4MHz, you'll need to use asm NOP or GOTO

A scope is handy for those things. 1 channel on the Main AC, the other on the PIC output... now you see if you're really in-synch. Be careful if you do that, unless we might see some smoke messages