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4 Channel PWM output with PIC16F690

March 4th, 2009 | Uncategorized

picI wanted to “pulse” four seperate LEDs on each of the four PIC16F690 PWM output channels. The correct mode to use is the enhanced PWM output – single output mode with pulse steering. Sounds hard, but it’s really not. Here is a link to the source: pic16f690_PWM_ex.c

The source code should be self-explanatory. To set up the correct mode you use:

/* use pulse steering with single output mode */
CCP1CON = 0b00001100;

To work out PR2 and T2CON you use this website: http://www.micro-examples.com/public/microex-navig/doc/097-pwm-calculator.html

You set the each of the following registers to 1 to turn on that output port:

STRA (pin5), STRB (pin6), STRC (pin7), STRD (pin14).

And then you just make a loop that varies CCPR1L  from 0 to 0xff and back down to 0 again.

Easy as pie. Have a look at the source code for a more detailed explanation and a function for pulsing the LEDs. Leave a comment if you have any questions.

7 comments ↓

#1 Ryan on 04.15.09 at 9:20 am

Hi
How do you select and output individual pwm channels? i have 3 pots and i want to use them to control the colours the rgb led will output. I am quite stuck. If you could help it would be much appreciated.

Many thanks

#2 psichron on 04.16.09 at 6:41 am

”
Use registers STRA, STRB, STRC, STRD to turn on/off each of the 4 channels
STRA = pin5
STRB = pin6
STRC = pin7
STRD = pin14
”

So you can turn on/off the channel output on pin5 by setting STRA = 1 (on) or STRA=0 (off).

#3 Ryan on 04.16.09 at 6:47 am

Hi
I have tried this but it only dims or brightens the led, doesnt actually change the colour? The colour stays red??

Thanks

#4 psichron on 04.16.09 at 6:50 am

Do you have a link to the datasheet of the LED?
Because STRA, STB, etc is how you enable/disable output of the channels, so you have the same signal coming out of all the enabled channel pins.

#5 Ryan on 04.16.09 at 9:12 am

Is it possible to have different signals coming out of the 3 pwm pins? i.e pin5 – 100Hz, pin6 – 200Hz & pin7 – 500Hz or something like this?
Is this how the led colour changes or am i wrong?

Many thanks

#6 Ryan on 04.16.09 at 9:25 am

Unfortunately i dont have the datasheet but its the standard common annode 4 pin rgb led. Basically i want to manually control the colour output from the led with 3 pots.

Many thanks

#7 psichron on 04.16.09 at 12:36 pm

No, not with the 16F690’s PWM generator. You’ll have to use your own timing functions and switch the pins on/off manually.

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