Retain power dial with smoothieboard

If I plumb the output pwm signal back through the 5V input to the pot, will I be able to manually control the power through the pot, up to the maximum output of the pwm?

Originally the K40 power pot alters a 5V line to control the output of the LPSU. If I take the 5V feed off, and replace it with the output from the Smoothie’s PWM pin, that should give the same effect, but while staying within the bounds of whatever PWM is outputting? Leaving the pot wired as it was originally, allows the pot to override whatever the smoothieboard is outputting - which makes the safety offered by going digital, moot.

I will need to level-shift the 3.3V PWM pin to 5V.

There is an easyer solution for that:

Just connect the pot as it originaly was and use the L pin of the LPS for PWM (connected to the mosfet minus connector of the smoothieboard). The mosfet pulls L to GND when PWM is on which enables the laser at the pot set power.

You actually want the pot to be able to override (actually it’s a added bias) the PWM.
This way as the tube wears it allows you to change the base power setting without changing job power parameters. I think of it as you would a contrast control.

But that would mean the pot overrides the output of the card.

My larger 130W laser dial adjusts power within the parameters currently being worked on, not outside, which would be the case if I retained the dial in its current configuration, wouldn’t it?

No, I really don’t. Any power adjustment needed can be done by changing the upper limit in software.

Not that I’ve seen a lot of diminishing of power over the years. Get a decent tube (Reci, EFR, SPT) and they last within 90% of rated power for thousands of hours. When they’re on their way out, I change them.

The pot doesn’t realy override the PWM value, it sets the maximum power for 100% PWM! (like the mini pot in a 100W Reci laser power supply to set the maximum current).

Limiting the power only by softare means to loose grayscale resolution. This is especially important for 8 or 10 bit PWM. Let’s say you have only 8 bit PWM resolution (as on Arduino GRBL) and want to engrve a picture with only 10% power. With software only, this would mean you reduce the different levels of power form total 255 to only 25. You will not get a decent grayscale with only 25 levels of power.

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