Multitouch Display: testing LCD screen panel for FTIR

Quite a long time has passed since I did something more for my multitouch display. My last post on this topic was on November!

Unfortunately I did not any progress basically because I don't own a projector, so, everytime I should ask to someone to lend me a projector then I have limited time to do some tests with it. This is not exactly comfortable especially because I have very limited spare time and quite never in consecutive days.

So, in the last months, I was thinking more often that it would be nice to achieve the goal to use an LCD instead of a projected screen.....and I started to do it!

To be honest, I thought about using an LCD for a multitouch display since the very first moment. Infact, when I bought the webcam, the Fire-i from Unibrain, I bought also a wide angle, non IR coated lenses for the cam. This was exactly because I thought that, if all things worked out I could try with LCD and use the wide angle lenses to have a short distance beetween the camera and the display itself.

Ok, I was a little bit optimist at the first time but....at the end of the game it was definitively good!

Some days ago, at work, I was speaking with a great new colleague, Pietro, who read this blog and discovered all the works that I've done at home. I was very pleased to talk with him illustrating all the hints and techniques used with the multitouch display. Then I said "yes but I don't have a projector, actually I'm thinking about to buy an old used 14" LCD on eBay to sacrifce for the experiment". He had a great answer: "I have one abandoned in my cellar, I may give it to you"!!!

He was so gentle to give me this great LCD monitor for free!

So, last weekend, I started to disassemble the monitor to get out the bare LCD panel and test it with the infrared camera and the IR LEDs.

I was really surprised of how many pieces there were in the monitor! Kilos of screws, panels, the speakers in the basement, plastic covers and supports...

It took me more than two hours to fully disassemble it, especially because I didn't wanted to break something so I was very gentle trying to have a safe and, hopefully reversible, disassembling. At the end I had the bare LCD monitor panel and a little fear that this was a non-return point because I already forgot how to reassemble the monitor :o)

Of course the first step was to carefully inspect the backlight complex and its filters to understand what needed I needed to remove in order to have a monitor transparent to IR but not so transparent to the visible light (I need the backlight anyway to see the monitor image!).

I think I was really lucky because I needed to remove only the reflective white sheet that was in the back of the backlight, I kept the Fresnel lens and the diffuser. If I will have time I'll post some pictures of those layers for those of you that wants to understand exactly what I'm talking about.

Then I immediately put the LCD panel on the desk (keeping it vertical by two Fonera boxes :o). I reconnected all the electronics, double-checking the connections in order to be sure not to burn out the monitor on the first test. But, very soon, I realized that, even if the panel worked out, I could have a serious problem.

The problem is in the Flat Flex Cable (FFC) that is connecting the board on the right side of the display with the board on the bottom side. It is really too short and requires that both boards sits in the back of the panel, without the possibility to bend the boards out to free the view of the entire display surface from the back.

Anyway, I didn't care at that moment and switched on the monitor....all ok, it was still working!
Then, second test, I put the IR webcam on the back of the LCD and tested the IR remote of the TV: wow, I saw its IR light!

In addition the LCD didn't lost too much brightness with the removal of the reflective white sheet and the image was still clearly visible.

My last test was with a couple of spare Osram SFH485P IR LEDs that I had from my first multitouch: all ok, I was able to see very very clearly them by the webcam through the LCD display and I was able also to see the IR light reflected by my fingers. I took this as the definitive evidence that this setup could work greatly.

So, scared by the risk to break the very thin and delicate LCD panel, I put it apart in a safe place. I started to think about a good box to hold all the things together safely and steadily.

While brainstorming for the box, I found a great site that was selling spare parts for video projector and.....YES! On that magic site I found the right FFC extension! So the problem was solved!

I hope to post some news on this exciting new adventure very soon!

Stay tuned!