I have for some time been wondering if it would be possible to use one of the new mini projectors for development like this. An example of this is the Samsung Pocket Imager. While many people think it’s not optimal for general usage I can see a lot of pros for this projector in multitouch screens.

1. At a size of 127.2 (W) X 94.5 (D) X 50.8 (H) in millimeters it is very handy to mount.
2. Consumes very little power(<25W) - no worries about cooling or noise (25dB).
3. Can be mounted vertically by Samsungs specs. This means you can put it under a table and point it straight up without risking any heat damage.
4. Has a minimum throw distance of only 50cm.
5. Has extreme lamp life, more than 10.000 hours.
6. Cheap.
(7. Can be run on a battery. I have no idea why but it sounds cool. )

Some of the cons would be:
a. Low brightness.
b. Low contrast.
c. Low resolution (800x600).

However, when you think about a and b, this might be solved by the fact that rear projection gives much better brightness and contrast simply because you basically look straight into the beam. This could actually be a good thing. When we built our first prototype at university we found out that the projector we used was actually too powerful for most diffusers. You got blinded by the intense light going through the screen. So, imagine that you could use a diffuser that was a lot thinner and blocked a lot less light. This way you could have a screen without getting blinded and track fingers easily at the same time. This is of course just my little theory.

I have not tried it yet as I don’t have the funds for it yet but I think it would certainly be interesting if anybody had the chance to test this. There are also other projectors on the market, e.g. the Toshiba FF1. Same concept but I don’t know the technical details of it. What do you guys think?

I’ve been looking at the LED based projectors as well… There are a lot of plusses in using them as you mentioned.  But as with any projector projected image size vs throw distance is the largest factor to take into account. 

Pocket projectors are (so far) all fixed zoom, so if your screen is 50cm across, there will only be 1 distance at which the projector will create that size image.

The other thing to take into account is keystoning (i.e. projecting the onto the screen at an angle will skew the image) Projectors can compensate for this either optically (for expensive projectors) or digitally.  Digital keystone correction will both degrade the image, and often require you to overshoot the image size so you don’t lose any screen real-estate in cropping/stretching.  Most LED projectors offer in the range of +/- 15 degrees of vertical keystone correction (many regular projectors are more in the range of +/- 30 degrees).  Bear this in mind.

Also, bear in mind that that keystoning offset is not necissarily measured from the centre of the screen, but wherever the manufacturer says.  (i.e. the projector’s middle point might be when the projector is in line with the bottom edge of the screen, or 1/3 of the way up)

Mirrors are a great way to get around some of these restriction but bear in mind it can make design tricky. 

Brightness of LED projectors is FAR FAR less then conventional ones, and are designed to make much, much smaller images.  RP requires far less brightness, but if your environment is bright, i’d suggest trying before you buy.

Google projection calculator and you’ll find most manuafacturers provide one, (or home theatre fans creat their own) use one of these to check things out… A CAD program will help a lot too.

Cheers

Mikie

Thank you for the reply.

I did not know about the zoom, that can be unhandy indeed. It will still have adjustable focus, right?

I don’t think keystone is that much of a factor unless you use mirrors, since the projector can be placed in any angle you want and be angled directly at the screen because of the short throw distance. Still worth mentioning though for people who do want to use mirrors.

Brightness is a downside but I don’t know how much yet since I haven’t seen one in real life yet. It only has 25 ANSI lumens which is incredibly little compared to normal projectors. I’ve heard that the new generation that should be due in not too long should be 4-10 times brighter so maybe it is worth waiting. It will still be relatively low though.

Have you done any research regarding projected image size vs throw distance? I guess it would be optimal to have the biggest image size possible at as short a distance as possible. Do you know any good projectors regarding this?

They do indeed have adjustable focus within the range they specify… i.e if they say their minimum throw is 2m or 1m, you might have trouble focusing on distances less then that.

In my case i’m trying to fit an 800mm diagonal 4:3 image onto the top of a 450mm coffee table, so i definitely have to take keystone/correction into account.

This is a sketch i’m basing my design on.  It happens to be based on the optics of the Mits. LED pocket projector.  You’ll notice the green line (’on axis’ line for the projector is not centred on the screen but 1/3 of the way from one edge.  I’ve used this to my advantage to get the projector to fit, and keeping my secondary mirror’s reflection within 15 degrees of the screen, i know i can correct with keystone correction.

What we are looking for is known as short throw projectors (or ‘extra’ short throw, ‘sooper’ short throw, ‘extreeme’ short throw, pick a wanky marketing term and go with it) sometimes expressed as a ratio of throw distance to diagonal screen size.  2:1, 1.6:1, 1.2:1, etc… the smaller the first number, the shorter the throw.

As for ANSI lumens, it ‘might’ be enough for rear pro don’t discount it yet.  I’m going to start hunting around shops to see if i can borrow one. (but as my acrylic, and RP surface won’t be here till next week, i’m not much help yet - sorry) Let me know how you go.

Cheers

Mikie

p.s. another advantage is there is no IR contamination from the proejctor, as the only light emitted is primary R,G,B.

I have no money atm so it will take some time before I get anywhere near what I want to do. I will of course post if anything happens.

I’ve only been able to find one short throw projector at a reasonable price here and it’s a Viewsonic:
http://www.viewsonic.com/pdf/us_eng/products/PJ358_ds.pdf

I’ll try and see if I in some way can find a way to test a mini projector, somebody has to have one.

Since I might want to use the table in my room I want as little noise as possible, so I still think I will keep an eye on mini projectors. I’m going to a computer conference on saturday so maybe I will have luck to find one. Let me know when something new comes up.

hi,

i just ordered the samsung pocket imager SP-P300ME mentioned in the first post. i’ll let you know my first experiences on friday (hope it arrives as promised).

in my setup there’s an IR-blocking foil on the upper side of my table. so only daylight comes in (nearly no more IR). on my camera there’s an IR-filter blocking daylight and letting through only IR-light. so the only light that’s left to be ‘seen’ by the camera is the frustrated IR.

now since i blocked out every light except for the frustrated IR that i want to have, the only source for noise would be the IR-light sent out by the lamp that standard projectors use. that’s why i decided to buy a LED-projector which doesn’t emit any IR light.

this setup should work even in bright sunlight (but i think the projector wouldn’d produce an acceptable image then).

waiting really keen on that shiny little led-thing…

sounds good tonius, looking forward for your results

Here’s an image of tonius samsung pocket imager SP-P300ME

some specs of the projector

Very glad to hear that, I hope you will get some nice results you can post.

tonius,

sounds like you are making some great progress - you are where we want to be about now. Looking forward to hearing how the projector goes in your setup. Is the IR film you are using working as a compliant surface as well?

rich - 08 March 2007 05:55 PM

tonius,

Is the IR film you are using working as a compliant surface as well?

unfortunalety not yet..

but luckily i got stunning news: a friend of mine works at osram in my hometown at the moment (germany, regensburg). she will be able to to give me some of the new ir-leds that are for experiental use only at the moment. the research-guys at osram here are experienting with some new ways of getting much more more brightness out of standard ir-leds.

and now the really stunning part:

the technical university of munich here in germany (architectural science) developed some new method to make glas blur just by putting a certain voltage on a special layer that can be integrated in most kinds glas windows. just imagine: have a standard plexiglas-like table that suddenly turns into a diffusing surface on which a projector can put its image on. these special windows for large buildings facades are mainly developed here near munich. i know some of the students who try to change these windows into ftir-like tables. the idea of just suddenly generating a surface on which a projector can put its image on, is really interesting. i will let you know as soon as can get hands on one of these special windows.

but first of all i’ll try to achieve some results with my new samsung pocket projecor this friday…

tonius,

that does sounds very cool - if the surface could be used as a rear project surface. Does it go opaque? Either way it sounds cool. Got another friend here who has caught the FTIR bug and is wanting to build a table that can do pretty much what you are exaplining (he wants to be able to totally blacken it when it is “off”.  It all sounds very interesting, now we have two bits of news we are hanging out for from you - how the projector goes and how these new LED’s and new surface may work…

This project really is very cool…

i’m really amazed by that little projector which arrived this friday. it is so small, it fits in my jacket’s pocket. i don’t have much experience with projectors, so i can’t do good comparisons. but on my 80x60cm table it gives a good and clear picture.
i spent most of this day playing around with the smokedemo and competing a friend in pong. works all great even in bright rooms. basically no need to re-adjust or re-calibrate configapp.exe when light situation changes! i was surprised by my very simple selfmade ir-filter. when put on the camera it completely ‘removes’ the projectors image out of the cameras sight. so my speculation on the completely non-IR light of this projector turned out to be true.

i won’t be home until tuesday, but as soon as i am i will post pics and videos of my touchscreen along with some more detailled explanations…

bye, tonius

sounds great so far - looking forward to the pics.

Very cool! How noisy is the projector?

Is the throw range short enough to not use a mirror?

great stuff tonius, can’t wait for the pics, still quite an expansive fucker though, quick search on google says 470 euro (one of the cheapest sites)

A company called iglass here in australia makes and LCD based coating.  It can be switched on/off and dimmed.  They are using it here in melbourne for some toilette doors (they go dark when they lock/close) and for rear projection at the melbourne museum.  It’s pretty neat stuff.  However effect on FTIR if applied to the top of the surface, or IR transmissiveness/cam frienlynes if applied to bottom would still be issues.

Mikie