benchtop CO2 laser

"Tom Del Rosso" wrote in news:qt3u9f$lno$ snipped-for-privacy@dont-email.me:

Better way? KEEP the laser power supply offline until switched on by the computer. Totally separate from the main supply.

But in this case the CPU obviously powered up with the IO pin on, so it would have turned the supply on.

There's a trap for young players there--most MCUs power up with all the pins defined as inputs, so you want the supply to be OFF when its enable pin is open.

Our current fave M0+, the LPC845, has a giant pin mux with nonvolatile configuration, so it's less of an issue.

Cheers

Phil Hobbs

That's the plan. Microchip just came out with the first pass of one of their ARM processors where this didn't happen. They're doing a re-spin of the chip to fix it.

Note that making all of the I/Os inputs (or tri-state in some cases) allows the user to define the power-on conditions with pullups or pulldowns.

As long as it's guaranteed that the CPU is powered on first.

Yup. We generally have the MCU control all the power supplies except its own, and sometimes even that, of course with a linear regulator off

Cheers

Phil Hobbs

So, the quick/dirty way to accomplish it is to have an AC signal required for activating the laser (four or five cycles through a charge-pump), or maybe use two I/O pins and only activate when they are in different logic states. Or, combine the two, and require a sequence of signals (like, POST success, and safety-switch check, and software BEAM_ON variable set, and software BEAM_SAFE_OFF unset), clocked into an addressable latch.

Somewhat more cumbersome, use a heat-activated shutter (Nitiol mechanism) so that it takes a few seconds of warmup before the eyelid over the laser opens.

One reasonable approach is to have an NMOS in series with the interlock, with its gate pulled down by a resistor.

Cheers

Phil Hobbs

When I did some kitchen-sink level anodizing, the coloring was bits of dye the process rather cleverly traps inside the porous aluminum anodize coating. First you generate the porous oxide coating, then insert the dye particles, then seal the pores to retain the dye.

I wouldn't think ablating the dye bits would bother the colorless hard coating, itself.

Cheers, James Arthur

John said that the laser "blasted off the blue anodize". A CO2 laser can't bleach an organic dye except by pyrolysis, whereas a UV laser can. So something like a nitrogen or excimer laser (or possibly a quadrupled Nd:YAG) might be able to nuke the dye without harming the anodizing much.

Cheers

Phil Hobbs

It depends heavily on what John means by "blasted off" :). I took it as figurative.

If John meant the laser literally blows away anodize, sure, bare metal would certainly be bad. But if he's just vaporizing dye bits and leaving the oxide, that wouldn't be bad at all.

An ohmmeter or maybe even a close inspection would answer the question.

Cheers, James Arthur

On Dec 17, 2019, whit3rd wrote (in article):

The classic appliance approach is a wax motor.

Dead simple, cheap, reliable, able to generate considerable force.

Joe Gwinn

Neat. I'd never seen those before. Thanks.

whit3rd wrote in news: snipped-for-privacy@googlegroups.com:

Damn things can latch up ON no matter what we do, right?

A HARD switch the user leaves off until run time. Not the main powers switch. The LASER SAFETY SWITCH.

snipped-for-privacy@yahoo.com wrote in news: snipped-for-privacy@googlegroups.com:

That would be "Chem Etch" or "Chem Film", not "anodizing".

Paulo got the idea from some other things he has that were similar, color anodize blasted by a CO2 laser. Some of that is years old and apparently OK.

No, you can do anodizing at home. You normally take the just-anodized piece out of the bath and just boil it in water with dye in it. Aluminum hydroxide forms, which plugs up the pores in the Al2O3 layer and stops further corrosion.

Cheers

Phil Hobbs

Okay, so probably the laser pyrolizes the dye without damaging the coating. Fun.

Cheers

Phil Hobbs