Wednesday, February 19, 2014

Violet Blue Laser Pointer Build Part 2

Violet Blue Laser Pointer Build Part 2

Oh, one more thing:

Your visual safety is the most important factor to consider when undertaking a project of this kind. Please be cautious around lasers, and never allow a laser beam the remotest possibility of passing near or into an eye. I strongly recommend reading the "Laser Safety" portion of Sam's Laser FAQ. Also, parts of this project involved cutting and grinding metal, both of which create flying metal shards. Eye protection when operating cutting and griding equipment is an absolute imperative. 

Further, the post, posts, documents, text, photos, and any other media that are part of this series documents only my own project, and should not be regarded as advice to you. You undertake any project completely at your own risk. 

That said, here we go.

Project Execution, Take 1:

The PS3 Laser Lens assembly shipped from Monaco, of all places. It took far longer to arrive than I had anticipated, and the company I ordered it from was unresponsive to my requests for updates. I was literally one day from filing a charge back on it with my credit card company when it arrived.

The nondescript white box had me a little nervous at first. How could I know that I actually had a Blu-Ray component here? I would just have to carry on and find out when I power it up. But I couldn't power it up until I had it disassembled.

The lens assembly cover came off easily, and it was neat to see all of the laser lenses arrayed inside. Some of them were mounted on coils that could be moved around with small magnetic braces around them (coincidentally, this is also how the armature in your hard drive moves the read/write heads around on the platters).

The laser diode can be seen on the far left side of this photo, sitting horizontally with its soldered metal brace being the two metal points at the far left of the assembly. The laser is aimed through an initial lens block, and then through a splitter block, where the beam is apparently divided, perhaps by wavelength frequency (beam color).

The sheer number of lenses in this assembly impressed me. I've harvested laser diodes from CD burners and DVD drives, and they usually have very simple lensing compared to this. I suspect that blue lasers being a relatively new technology, the diodes aren't yet advanced enough to give quite the right beam properties straight from the component, and the beam needs a lot of work before it's ready for use in reading media. Thus, the extensive lensing.

It seemed to me that all of those cool lenses might be useful at some point, so when I got the diode free of the assembly chassis, I set the rest aside for more work at some future date.

This is a shot of the laser in its chassis, removed from the main lens assembly. The through hole ribbon cable connector was removed by locking a corner of the diode chassis into the desk vise, and then using copper solder wick to remove the solder and get the pins free so that the connector could slide off of them.

Below is a simple current limiting circuit we built to test things out with. We decided to start with high values of resistance and slowly ramp down to find where the diode would begin to light, and then lase. Once we had our ballpark, we would put a potentiometer on the circuit to help with fine tuning.

This was an early test circuit. I don't know resistor color bars on sight, but it doesn't really matter, because this one got the laser diode to glow like a dim LED, but it was nowhere near lasing. At any rate, it's good to see some of the breadboarding and testing process. You can add up the resistor values for yourself if you like.

This next photo is important to me, because it illustrates our first big mistake. What you'll see here is the laser diode, now removed from its metal housing, and put into the collimator sleeve (also metal, but thick and round). The original red laser was press-fit into the collimator sleeve. It was so snug in the sleeve that pressing it back out damaged the red laser diode can. I was loathe to damage the blue laser diode can by trying to fully press it into the sleeve, so instead I got it in as snug and straight as I could with my thumbnail and then hot glued it down.

Failing to press-fit the diode into the collimator sleeve was a mistake because the diode is intended to use the surrounding metal housing to sink heat away from itself. Without this precious thermal management, the diode is likely to fail even under normal operating power.

Further, the groove in which the diode is seated when it is press-fit is designed to align the diode can so that the beam travels into the collimator lens at as close to the ideal 90 degrees as possible. Simply placing it on the groove, or only pressing it in partway leaves the diode can both misaligned and physically further from the collimator lens than intended, leading to inefficient use of the light source and making beam tuning as intended impossible.

Our first powered tests produced only a dim LED glow from the diode, but as we ramped up power by decreasing resistance in our test circuit, we quickly brought the diode from a dim glow, to a bright glow, to dim lasing, to bright lasing.

We were so excited to see lasing that we turned off the lights in the room and took photos of the blue laser on a wall, but it's a classic "you had to be there" moment; the photos themselves are unspectacular. I won't post photos of a black background with a bright blue dot here for the sake of your sanity.

By this point, Eric had a good idea of the power range needed for the driver circuit, and he grew quiet as he thought about different design options. I left him to it and began work on the case for the laser.

So it's a black metal pen case. I pulled out the foam inserts and stared at it for a while to try to conceptualize the best way of mounting the laser guts inside. Once I felt I had an idea, I took the parts I had at hand and put them into the case to see if they'd fit as visualized. I didn't have a power circuit yet, so I arranged everything, leaving a big gap in the middle and asked Eric if he could commit to his circuit fitting there. He felt that the space provided would be ample, so I got to work on the cutting and drilling that the case would require.

You can see the dot I made on the case with a silver sharpie. To determine the right location for the hole, I simply popped in the collimator and lined it up with the natural front curve of the case. Where the lens ended up is where I needed my hole. I started the hole with a 1/16" drill bit, and then used an Irwin Unibit to step the hole up to 5/16" or so. I then used a Dremel grinding stone to deburr the hole.

Ergonomics are a factor with a laser pointer, so the momentary switch was next. Toward the front of the unit, next to the laser aperture seemed to make sense, so I made an outline for cutting to place the switch. The switch handily came with a collar (which, in a rare moment of brilliance, I had been smart enough to save), so all I needed to install it was the right sized square hole.

I traced the smaller, inner collar size onto the outside of the case with the sharpie and used that as my cutting template. I didn't worry too much about keeping it neat, as the larger, upper collar would cover any small sharpie fudges I made.

Dremel Note 1: Here I'll note that if you don't have a Dremel in your shop, you should really prioritize getting a good one for regular use.

My first "rotary tool" was a Black & Decker Dremel knock off, which I thought would be a good investment rather than a real Dremel because it took a VersaPak battery, along with several other tools I had at the time. Boy, did Black & Decker teach me a lesson. Dust Buster, yes. All other tools, no. They were right to kill off the VersaPak line, but it's too bad that I was suckered into buying any of that garbage in the first place.

Lesson learned. I buy quality tools now. My drills (well, one is an electric screwdriver) are DeWalts, and my Dremels are really Dremels.

Dremel Note 2: If you plan to do any kind of material cutting with Dremel's pressed sand cutting discs, make sure you keep a lot of the discs on hand. They shatter before they flex, and the shattering is just as soon induced by looking at them funny while in use as smashing them with a hammer. This makes eye protection doubly important, as cutting wheel chunks are relatively large, sharp and heavy, and the rotational speed launching them yields incredible velocity in flight. Goggles stop them easily enough, but you don't want your corneas doing that job for sure.

Part 3 Tomorrow!

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