HPWM question

[sjmusic2]

I am trying to write a program for my aquarium to control a 'sunrise' effect for high power LED lights. I am good with the driver side of the circuit but need a little help with the pic pwm signal.

I have read about the HPWM function in PBP, but don't really understand how to set up the configuration. I have a 16F887 (with 4 channels) and want to use something like...

DutyCycle var byte
TRISD= $00000000 ' for P1B output pin, or TRISC if P1A

For DutyCycle=0 to 255
HPWM 1,DutyCycle,1250
Pause 15000
DutyCycle=DutyCycle+1
Next

End

Will this produce a gradual increase in perceived brightness up to the max after around an hour, then maintain the max output until power is turned off ?

Are all declarations made ?

Is it possible to use a different output channel, ie. P1B instead of P1A, how would this be coded ?

Thanks.

[mister_e]

The best way to know is to try, that for sure ;)

Your code would work... but you're not going to have a 60 minutes ramp up but ~32 minutes instead. Remove the

DutyCycle=DutyCycle+1
line and you'll have a 64 minutes ramp-up.

Wanna make sure the PIN stay high? No big deal,

CCP1CON=0
HIGH PORTC.2

And nope, you can't use an alternative PIN alone, check the datasheet under CCP1CON section (pdf p126) & Enhanced Mode p134.

[sjmusic2]

The best way to know is to try, that for sure ;)

Your code would work... but you're not going to have a 60 minutes ramp up but ~32 minutes instead. Remove the

DutyCycle=DutyCycle+1
line and you'll have a 64 minutes ramp-up.

Wanna make sure the PIN stay high? No big deal,

CCP1CON=0
HIGH PORTC.2

And nope, you can't use an alternative PIN alone, check the datasheet under CCP1CON section (pdf p126) & Enhanced Mode p134.

Thanks for the quick reply, so is this the right placing of your suggested code...

DutyCycle var byte
CCP1CON=0
TRISC= $00000000

For DutyCycle=0 to 255
HPWM 1,DutyCycle,1250
Pause 15000
Next

HIGH PORTC.2

End

[Acetronics2]

Hi, SJ

The light changes are perceived in an exponential evolution ...

1,2,4,8,16 ... etc

so, just multiply the Dutycycle per 2 for each loop instead of adding 1 ...

May be you'll have to use little trickery to increase the allowable steps number. i.e use LONGs and scale them down to 8 or 10 bits ( HPWM10 from Darrel's goodies ! )


the changes will then be smoother ...

Alain

[Bruce]

Have a look at Darrels' MIBAM code;
http://www.picbasic.co.uk/forum/showthread.php?t=10564

This will give you a very smooth fade in/out effect, and it's easy to use.

[sjmusic2]

Guys, thanks for the replies - I now have my 16F887 pwm ramping an led just the way I want it !!

A follow-up question...

Keeping in mind this is for an aquarium, I would like to be able to have the pwm start at a specific time every morning and turn off at a specific time at night (probably with a ramp-down, prior to shutdown). The timer on/off times will be coded in the program (and not require external input).

I have read close on 20 different timer-related threads and I'm struggling to see how you can have a timer running concurrently with the pwm code.

Any help, much appreciated.