June 2008 Archives

This is a very short post compared to the ones that I write normally.

Anyway, I was looking around to find how I can achieve the great results that AlexP got in his laser multitouch. I really suggest you to read that link, Alex method is really cool!

So, basically I was guessing where I could find a suitable infrared laser to use for generating a very thin flat plane of infrared light just in front of the multitouch screen.

Googlin' around I found that the laser included in the DVD player/burner is not good as it is a visible red laser of about 650 nm of wavelenght. But the CD player/burner has a chance to be ok as it should be around 780 nm which is just below the visible spectrum that ranges from 380 nm (violet) to 750 nm (red).

Luckily I had an "ancient" SCSI CD burner in my drawer so, of course, I embraced my screwdriver and took it apart.

I was very happy to discover that I can't see anything coming out from the laser with my bare eyes but, once I looked at it with the infrared enabled camera that I use for the multitouch I saw a bright, coherent orange light!

I shoot a very short video:



So, it seems that the laser is really an infrared one. Now next steps may be to collect enough informations on it regarding its real frequency and power.

Further steps will be to understand how to drive it correctly, building a small voltage and current limiter circuit that may power it up without burning it.

Last steps, hopefully, may be to understand how I can get a cylindrical lens without dismantling a craftsmen leveler...
:o)

Look at this, isn't it wonderful?!?!

Yessss!!! It looks very very nice!
Anyway, of course it is still to be completed, I need to prepare all the braces for the circuit boards, the bracket for the webcam and, of course the infrared setup and the front mask.

So, let's start with this second part of the construction notes!

After bending all the parts, I had to refine them because, as I said, I abounded with measures because I was not knowing how much material I would loose with the bend. In this phase I discovered how useful is the circular saw for the Dremel instead of the electric hacksaw that I used to cut the parts before. The advantage of the circular saw is that it can make very straight cuts and you will have better result.

So, basically I cut again quite all the sides of all pieces of plexiglas refining them to the right size, then I started to try to put all together and see what was needing to be accomodated.

Once I got the situation where all pieces were complying well together I started with the holes for the screws. As I said in the previous post, I decided for the most difficult assembly solution: screws on the edge of the plexiglas.


There was a lot of difficulties: the first one is to keep the drill parallel to the edge all along the hole just using the hands, the second one may be to drill the hole without melt or break the polystirene ecc. Other than these issues, I had also a lot of oblique sides that means oblique holes!

I have to admid that it was really taugh but, luckily I had good results. I used a 1,5 mm drill bit for 2 mm screws. I made a lot of tests on spare polistyrene pieces to understand how I could drill it without melting it. At the end of the game I decided to don't care about the melting plastic!

I just regulated the Dremel to the slowest speed and made all the holes keeping the Dremel in position just by hand.

As you surely remember, three weeks ago I posted about my first test with an LCD panel for multitouch applications. I saw that it had enough chances to work out but I was so scared about the fact that the bare LCD panel is extremely delicate. So, as I was saying at the end of the post, I started to think, then work, to a case for this multitouch display.

Of course I thought about a case that should also look nicely, what's better than a plexiglas one?

So, after some weekends of work, this is how the case is looking today:

I designed it trying to keep its size as small as possible, so I went for a cut pyramid shape. The pyramid is (or better, it should) be deep enough to hold the webcam in a position that, using the wide angle optics, is far enough to capture the entire screen view.

I can honestly say that probably I choose a very complex shape to build, infact it took me several days to bring it to this stage. For this reason I'll talk about how I proceed and I think that this will fill at least 2-3 posts. Let's start!

First of all, reading also several modding forums, I undestood that plexiglas is quite difficult to work so I choose a similar material, the transparent polystyrene. It seems more tollerant to mistakes even if it is more easy to melt while working with electrical tools like drill or saw.

Anyway, all begins with a good drawing scheme of the whole case and the pieces that needs to be cut. I paid big attention in this trying to consider every factor like angles because there are very few square angles in my design, and exact polystyrene sheet thickness.

In addition, there are some bends in my design and I was not knowing how much material the bend was taking, so, basically, I was abounding with measures (3-5 millimeters more) impacted by bends and I considered to cut again the parts after bending them.

I used the electric hacksaw for cutting the polystyrene sheet but, keep in mind that it tend to melt very easily. So, to avoid that, I used a dimmer to regulate at very low speed the saw. Let's say a 2 saw movements per second under load. This useful also to be very accurate in cutting following a straight line.

I know, every single sencond that you spend working this kind of material you are tempted to take away the protective film but, I can say that it is very important to keep it on until the very end. In bad cases keep it in place with adhesive tape but don't remove it!


Then I cut some pieces of wood to use as mold for bending the pieces of polystyrene. Then I used those pieces to build a complete mold for every piece. It was a little bit of work more but absolutely essential to have a precise bent shape.


Once I had the molds, I started to heat the polystyrene. I used a heat gun, one of that tools that are useful to remove the paint. Basically it is a sorta like of hairdryer with a high temperature airflow.

I used it very gently, moving it very often, slowly but constantly to avoid any break in the plastic sheet. Despite this, one of the pieces broke and it was the last one (of course)!

The polystirene sheet that I used was 5 millimeters thick and it took about 2-3 minutes with the heat gun to soften enough.



When it was ready I gently pressed it on the mold and I used other wood sheet and small morsel to keep it in place. The polystyrene needs another 3-5 minutes to cool down enough to be hard again and, with the morsels it could take all the time it needs.


I paid particular attention to the angles. In order to have clear ones I used pieces of wood to press the polystyrend exactly on the edge.

I can say that the more you heat up evenly the polystyrene sheet, the best bending results you will have.


The last step that I will show in this post is regarding the piece for the back and bottom of the case. It was the most difficult one because it had two bends. Of course I had to create an ad-hoc mold just for it.

I'll continue to illustrate the case building process in the next posts, stay tuned!