Hysteresis.. How to do it??

[skimask]

[QUOTE=hoopstar;34279]

        if temp >= 80 then gosub fan1on         ' fan ON at 80 
        If temp <> 70 then gosub fan1off        ' fan OFF at 70

Look at your original code...it doesn't make any sense.
If the temp is above 80, the fan kicks on...BUT...
if the temp is anything EXCEPT 70, the fan kicks off...

Change it to:
if temp => 80 then gosub fan1on
if temp <= 70 then gosub fan1off

Which is basically what you had in the first place. But I think you are sampling far too often. And I'd also throw a counter in there somewhere...something like if the temp is below 70 and you've checked XX number of times, then turn the fan off. (same thing with fan on). That way it'll keep from clicking on and off too often when the temp is right at the switch point.

[mackrackit]

I think the answer to you problem would be to make fan1on a loop not a return.

Stay in that loop until the temp drops below the set point.

Move the ADC commands to a GOSUB and then you can sample from anywhere and have less code.

This example is using two probes on a 18F4320.

CHECK:
T1 = temp1*2
T2 = temp2*2
LCDOUT $FE,1,"INSIDE ",#T1
lcdout $FE,$C0,"OUTSIDE ",#T2
gosub getT1
gosub getT2
if T1 > T2 + 10 then BLINK
goto CHECK

BLINK:
LCDOUT $FE,1,"INSIDE ",#T1
lcdout $FE,$C0,"OUTSIDE ",#T2
high PORTD.0
LOW PORTD.1
pause 100
low PORTD.0
HIGH PORTD.1
pause 100
if T1 = T2 THEN DARK
gosub getT1
gosub getT2
goto BLINK

DARK:
low PORTD.0
LOW PORTD.1
goto CHECK
getT1:
ADCON0=$1 '%00000001 AN0
gosub getAD
temp1 = ADRESH
return

getT2:
ADCON0=$5 '%00000101 AN1
gosub getAD
temp2 = ADRESH
return

getAD:
pause 50
ADCON0.1 = 1
pause 50
return

end

[Ioannis]

Also you could use a variable as a hysterisis.

hyst_high var byte
hyst_low var byte

hyst_low=0
hyst_high=0

....
....

if temp >= 80+hyst_high then gosub fan1on ' fan ON at 80
if temp <= 70+hyst_low then gosub fan1off


fan1on:
hyst_high=5
hyst_low=0
...
...
return

fan10ff:
hyst_low=5
hyst_high=0
...
...
return

Ioannis

[hoopstar]

I think the answer to you problem would be to make fan1on a loop not a return.

Stay in that loop until the temp drops below the set point.

Move the ADC commands to a GOSUB and then you can sample from anywhere and have less code.

I do plan on using GOSUB's but at the moment I am using the demo version of PicBasic and can't really afford to step up to Pro (poor student) so am just qualifying my code/ideas within the line limit of the demo version.

I *really* appreciate all the help and input on this - thanks guys.


Hoops