Inverting the o/p of hardware PWM

[AndrewC]

Thanks Darrel, it's only a couple of extra lines of code so not too difficult. 3 PWM modules - perhaps I wasn't being clear, I didn't mean three times HPWM, but using the three different embedded PWM modules in a PIC such as 16F777 and addressing them directly.

Andrew

[Darrel Taylor]

perhaps I wasn't being clear, I didn't mean three times HPWM, but using the three different embedded PWM modules in a PIC such as 16F777 and addressing them directly

Yikes,

Then maybe my answer wasn't clear either, cause that's what I was talking about as well.

I could be more specific, if you were too.

What frequency are you running the PWM at?
What OSC?
Which version of PBP?
PM or MPASM?
<br>

[AndrewC]

Hi Darrel,

Basically following Bruce's example in this thread:

http://www.picbasic.co.uk/forum/showthread.php?t=1770

PBP: 2.46
20MHz
MPASM

Hopefully I'm not missing something obvious - it has happened before and will doubtless happen again A 16F777 has 3 PWM modules and I'll control them directly.

thanks, Andrew

[Dave]

AndrewC, Why not just use a transistor and a couple of resistors?

Dave Purola,
N8NTA

[AndrewC]

AndrewC, Why not just use a transistor and a couple of resistors?

Dave Purola,
N8NTA

To invert the signal or drive the leds ? These are Luxeon leds running at high power. They work best on constant current sources and buckpuks are great for driving them.

If I can do it with a simple line of code why add external parts ? Actually, my led drivers only go up to 1000mA and my leds can take 1500mA so I may just make my own constant current drivers (two transistors and a couple of resistors per channel) in which case 5V will be ON This particular project is for lighting a macrophotography stage - while focussing / adjusting I use the leds at constant low power but for actual exposures switch to a single high power pulse. Three channels for left, right and backlight.

[Dave]

AndrewC, I dont know what constant current has to do with inverting the control signal?

Dave Purola,
N8NTA

[skimask]

Question (maybe more of a comment) concerning taking pictures and using PWM to drive LEDs for lighting...

Won't your PWM frequency have to be REALLY high to keep the camera's shutter from seeing the flickering?
LEDs, unlike incandescent light bulbs, can actually turn on and off at those high speeds, whereas an incandescent light bulb will glow during the off time.
I'm thinking that even with a really fast shutter on a camera, the film (or CCD, or whatever) is going to see that 'flickering' caused by the PWM driven LEDs.

[Darrel Taylor]

Hi Darrel,
Basically following Bruce's example in this thread:
http://www.picbasic.co.uk/forum/showthread.php?t=1770

Oh,OK.
According to that, it's running the PWM at the absolute minimum frequency, which gives exactly 10-bit resolution.

From you're last post I see that it's not continuously changing the dutycycle. So I don't need to talk about "glitch-free" either.

So it looks like your original idea from post #1 is the way to go, with 1 exception.
Subtract from 1023 instead of 1024.
<br>