Better LED Rails, FTIR Attempt
by Peau on Nov.09, 2008, under Uncategorized
Earlier this week I ordered a piece of acrylic 12″ x 24″ x 1/4″ from www.usplastic.com It is about 6mm thick, where my LEDs are 5mm in diameter. I also got a new laptop charger off of craigslist to run the LED rails. Here are the specs of the charger:
Since it is 19vts (19.43 volts so says my voltmeter), I needed longer chains of LEDs in series (12 instead of the previous 8), and higher ohm resistors (12 instead of 1), all according again to ledcalculator.net.
Again, here are pics of my previous LED rails taken off:
And what the LCD looks like without any LED rails on it:
It’s basically the LCD crystal taped to a piece of thin acrylic with both masking tape for securing it down, and electrical tape on top of that to create a solid black frame.
I went to Home Depot and got some aluminum L beams to mount the LEDs more accuratly in and cut them to size:
I measured out the height needed to drill the LEDs at on the beam:
And then drilled the rails, insulated them with electrical tape, put the LEDs in, soldered them together, along with wires running to the new power supply, and put the power supply into the case.
(That’s the laptop power supply hiding behind the power strip in the corner)
And below in a Side DI setup, which is the same as FTIR, minus the acrylic:
Then I put some screws in the floor to hold the backlight in place:
I then began work on polishing the edges of the sides of the acrylic. I was told to get 800, 1000, and 2000 grit sandpaper and some polishing compound, but Im on a budget so I only got 800, 1500 and the polishing compound.
Initially I just hand sanded the edges, but the curve of my palm caused the edges to be curved instead of flat, so I wrapped the sandpaper around a deck of cards as a sanding block and that worked well. The edges came out a lot smoother.
Here is a video showing the initial performance of the FTIR setup:
It works okay, but I have to press harder than Id like to get the blobs to show up, so I posted to the nuigroup forum to try and get some answers on improving it. There also is very little capability of dragging, since applying pressure and dragging is hard to do.
What works really well is removing the piece of acrylic and using it again as a Side DI setup. The higher amount of LEDs and the more even distribution of them makes it for a perfect setup in Side DI. Also the height of when the blobs appear from a falling finger can be reduced to about 5mm, which is really good, but still not as good as a working FTIR setup, so the quest continues to find the best and most practical setup when on a budget and using an LCD.
November 14th, 2008 on 11:35 pm
How you solve the backlight problem for your FTIR setup?
November 16th, 2008 on 2:35 am
Backlight problem? I used the same backlight from the LCD to light it up.
December 7th, 2008 on 12:55 pm
Are you using a compliant surface of any kind?
December 8th, 2008 on 11:21 pm
Not in the video above and not currently…as I havnt tried to make one for an LCD FTIR setup as it is known to be difficult to not have the LCD image become dimmer or fuzzy with one on top.
July 9th, 2009 on 5:15 pm
hi
i want to know about the LED
are all the LED working with 19v?that right?
July 9th, 2009 on 5:20 pm
Using the LED Calculator (which you can find the link on the right panel of this blog), you just input the voltage you have. The laptop power supply that I used is about 19vts. The circuit I used is composed of 4 series circuits of LEDs, with each series circuit in parallel with each other.
July 20th, 2009 on 1:07 am
Thank you for a great blog, I will be sure to bookmark your site and check later… Usually I don’t leave a comment but I wanted to let you know that I really like your site
July 25th, 2009 on 11:40 am
yes!!my laptopt is broken!!the mother board die
i just want to know if i can use the LCD screen to make my first multitouche table
i have a question about your model.
i saw in the drawing that you put
1.the LCD
2.rosco
3.the acrylique
is that important to use LCD?
we can’t only use acrylique and rosco??
if i understand well you use LCD instead of Glass?
what is the diffuser?
why we use a mirror?we can’t directly project on the glass?or on the acrylique or on the LCD screen?
sorry but i have not seen a projector in your box?is there one?or you have connect your LCD with your computer?
thanks for replying
July 27th, 2009 on 10:26 am
If the laptop is dead, you would have to connect that lcd screen to a working version of that laptop.
The only thing important in an lcd setup for the layering is the lcd itself and a diffuser underneath so that the backlight evenly lights up the image.
See the nuigroup forums for specific questions.