Hi, I’m doing a FTIR multi-touch for a university group project & I need some advice about possible LEDs…

Basically, since I am at university I can get LEDs for cheap but they only have two real IR possibilities, that I can find

This one or this one.

I have no idea about the specs of different LEDs but if someone could point me in the right direction I would gladly appreciate it.

The table will be about 80x60cm…

P.S. The company who sells the LEDs to the uni has a website here, if someone has spare time could they please browse down there and see if there are other options, cuz its all greek to me (I’m still learning ) but otherwise I would be happy with any helpful info.

P.P.S. I get charged the lowest rate (shown on the website) from the uni, in case your interested…

Well the 940nm one is a bit high in terms of the wavelength. Ideally you want something around 880nm because most ccd sensors on cameras start to become less sensitive above that. The first one is a bit small at 3mm, but it emits ir at 880nm and has a nice wide angle of 50 degrees - which would spread the light out nicely. So if I had to choose one out of the two then I guess I’d choose the first one.  My concern would be that at 3mm it’s too small and that it might not be bright enough, so I’d suggest that you wait for a few more qualified replies before making a decision. In terms of numbers you’ll probably need them every inch on at least two sides. Another option would be just to go with some of the standard shf485’s people have been using as they’re not that expensive.

The diagram below should give you an idea of why the wavelength is important.

Well it doesn’t look like I can get the sfh485 in South Africa (oh how hard it is to do stuff like this in Africa) but I’ll have to see what other people say. I was also thinking more towards the first one…