Quick n dirty HPWM out of phase

[ChrisHelvey]

Assuming a PIC with at least 2 PWM channels, can someone suggest a quick way to output two PWMs exactly 180 degrees out of phase with each other?

I can do it by turning alternating pins on and off but there's no CPU left to do anything else without messing up the waveform.

Trying not to recreate the wheel...or maybe it's so obvious I can't see the answer.

Thanks

[Archangel]

Assuming a PIC with at least 2 PWM channels, can someone suggest a quick way to output two PWMs exactly 180 degrees out of phase with each other?

I can do it by turning alternating pins on and off but there's no CPU left to do anything else without messing up the waveform.

Trying not to recreate the wheel...or maybe it's so obvious I can't see the answer.

Thanks

Hardware ways, flip flop, inverter, transistor . . . since you do not want to burden PIC.

[Darrel Taylor]

Use a PIC with an ECCP (ENHANCED CAPTURE/COMPARE/PWM MODULE)
16F690 is one.

Put it in Enhanced Half-Bridge mode.
Outputs will be on P1A and P1B pins.
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[keithdoxey]

Assuming a PIC with at least 2 PWM channels, can someone suggest a quick way to output two PWMs exactly 180 degrees out of phase with each other?

How about a PIC with a Comparator. Feed the PWM into comparator and use the comparator output to give your out of phase signal.

Advantages...

No external components
no software overhead other than setting up comparator

Disadvantages...

You lose one comparator and a few pins on your PIC

[Darrel Taylor]

oooo, I Like it Keith.
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[keithdoxey]

oooo, I Like it Keith.
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Sadly I cant take the credit.

The idea was originally suggested by Melanie but it stuck in my mind because I have an device that uses the HPWM to generate an IR carrier which I then gate with a transistor. Too late to change my existing design but I will use the comparator to do the gating in a later revision of the board.

Not only does it save a transistor and a couple of resistors but has a better voltage swing as well!

[Darrel Taylor]

Darn Melanie. She's just too smart for her own "Britches".

Which is why I tend to envision her without them.

Oh wait, I'd have done that anyways.

At least you applied it to the right problem.
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[ChrisHelvey]

That is a very elegant solution - just what I was looking for.
Thanks, I will look in to this. The link to Melanie's post is very helpful. Since 0 Volts is "low voltage" it should work exactly the same - when the pulse goes low, the comparator output goes high.
Brilliance is always in the simplicity...