Sunday, November 8, 2009

laser table update

We ran into a problem with the lasers, or more specifically a problem powering the lasers a couple of weekends ago. Last weekend was still unable to solve it and was getting kind of frustrated... especially since construction time is limited to weekends and actually building this thing isn't nearly as interesting to me as starting work on the software/API.

I'd ordered a 3.3V/5V regulated breadboard power supply from sparkfun and a 5V/1A wall wart. After a couple of minutes of operation, the circuit would drop to 1.9V. Did some checking and found out that a heatsink on the thermal regulator could be applied, so we tried and got the lifetime up to 20 minutes. When I tried rewiring the lasers to share a parallel circuit to the power supply (like how I'd planned on rigging them up when it was time to deploy), the fsckers immediately started dropping voltage to 1.9 again.

Last night, we played a hunch and replaced the voltage regulator with a new one, and lo and behold, the lasers ran for 2 hours with nary a hiccup. We'd also swapped out the 22 gauge solid wire for 18 gauge threaded speaker wire, and hooked up each laser to a plug that could fit on the bread board. The end result is that all this can nicely be transferred to a PCB and mounted fairly easily. We also ended up replacing the 5V wall wart with a selectable voltage wall wart set to 7.5V... it just wasn't delivering the current at 5V for some reason.

On the actual acrylic side of things, I swung by Home Depot and picked up some 1x1x36 molding pieces, spray painted 3 sides satin black, and cut them down to size (along with a 45 degree angle on the corner) in order to use them as a safety rail for the lasers. The plan for calibration will be to use the modelling clay idea abratrarious suggested, and just glue the fsckers in place.

End result, the table looks more and more like some middle school shop project, but meh... that's what prototypes do.

Also started to notice that some of the superglued acrylic pieces are falling off. it's possible that I might end up having to just yank them entirely and bolt the table together. I think I see how this can be done without a problem now. I superglued the guard rails on to the acrylic, and we'll see how long those hold.

For the support, I'm thinking about just hacking together a dorm room table (some plywood, metal pipe, and metal fasteners), but instead of trying to cut a hole in the plywood, just flip the table upside down so the acrylic will be resting on the table's feet.

Finally, also worth mentioning the IR filter on the webcam. The webcam is a Logitech Quickcam for Notebooks, and it turns out that after you've remove the IR filter it's unnecessary to put your ambient light filter in the same spot. I was able to refocus the camera, and drop the little square of floppy disk material down into the lens well without having to remove it's assembly and wedge it into the other side.

The plan is for laser calibration in the clay on Wednesday (holiday), and maybe take a stab at building the support system. After that, it'll be testing the effectiveness of the camera to see light blobs, and then finally figuring out what to do about project. Was still considering the fresnel thing, but it turns out that it's hard to find a 15" LCD on a shelf these days... will probably start scouring used comp stores around here to see what they got.

Minus the PC and the aggravation so far invested, project is still under $200 for materials, if the fresnel thing works, could probably beat $500 for the total.

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