I builded a FTIR setup but apparently the leds doesnt illuminate enough and i dont know what to do.

This is a prototype im doing for the company i work for, so i used what they gave me, is not the best materials but i think this should work ok, but it doesnt, i hope someone can help me.

I used a 6mm acrylic, 1/2 inch aluminum bars for the frame with led holes every 5cm (that would be every 2 inches more or less), the generic IR leds they sell in an electronic shop because i couldnt find the osram leds that i read are the best (i live in Venezuela and here is difficult to find things) and they didnt know the specs of the leds, they just knew that are IR..., i connected the leds in parallel with a 510 ohm resistor and i give the circuit power through a universal adaptor, to pass the power from the adaptor to the circuit i used a protoboard (is called that way here so i will call it so, is the blue thing in the pic), here are some photos of my setup for you to see everithing.

I appreciate any help telling me why the leds illuminate very good in the protoboard and not so good when they are not on it and if im doing something wrong and how to fix it and why i dont get the IR light to reflect on my hand and i dont get blobs when i put my hand on the table

thank you very much

hi revai

are you using just the bare acrylic (no silicon layer on top)?
also, did you drill holes to put the leds in? (this might prove to be a problem if you did, because the holes might have a rough surface, preventing the light from getting into the acrylic)
and did you sandpaper the sides of the acrylic? (they must be nice and smooth in order for the light to get in)

these things might be the cause of your problems.
read up on cerupcat’s detailed guides and info here : http://nuigroup.com/forums/viewthread/1982/

yes, im using just the bare acrylic, but according to what i read it should work, ill have to press harder but it will work.

i drilled the holes in the alluminum to put the leds in, yes, if i dont do that how can i put the leds? and i polished a little the alluminum to elliminate all the leftovers

and the acrylic is pretty smooth but is not completelly transparent.

I’m pretty new to this forum and am still in the process of building my FTIR setup, but I’d have to wonder about the LEDs.  If you don’t have any specs for them, how did you decide upon which resistor to use?  It looks like you are using 23 LEDs and one resistor?  That is a big resistor, with that many LEDs hooked to it I would think that it would be pretty underpowered.  (Note, I don’t know much about circuits, just what I have been reading in the last few weeks and from looking at the LED wiring wizard.)

Also, are you putting in LEDs on the sides?  (Not just top and bottom.) My understanding was that I would need that to get enough IR light for good blobs.  What is the width and height of the acrylic?  I’m putting LEDs every 1inch instead of 2 like you.  (I haven’t gotten far enough to see if I’m detecting blobs though since I’m waiting on a camera.)

There are more experienced people here that can probably help better than me, but there is my 2 cents.

revai - 17 July 2008 03:39 PM

yes, im using just the bare acrylic, but according to what i read it should work, ill have to press harder but it will work.

i drilled the holes in the alluminum to put the leds in, yes, if i dont do that how can i put the leds? and i polished a little the alluminum to elliminate all the leftovers

and the acrylic is pretty smooth but is not completelly transparent.

the problem might just be the holes you drilled into the acrylic.
if you drill holes into acrylic, the hole tends to have a rough edge, which reflects more light than it lets in.

::edit::

sorry, i read wrong.
if you only drilled holes into the alluminium and not in the acryllic, ignore this.

Can you post your schematic(fancy name for a wiring diagram) with LED and Resistor specs?  That looks like a 1/4 watt resistor, and with that much power being drawn through it it should have gone pop by now.

Good Luck,

Alex

Can you provide a screenshot of what you’re webcam sees when you are pressing on the acrylic.  Can you also provide a screenshot of what the webcam sees when you point the IR leds straight at it.

Normally the camera is the issue.

Polish the edges until they are transparent!! Very important. A rough or cloudy looking edge will lose light instead of trapping it.
I think you should add two more rails of LEDs left and right.
Try to angle the LED rail a bit and see if that helps. 30 to 45 degrees works well enough. Better than 90 degrees.

Much like xeaplond said, your resistor has probably blown.  It’s not a good idea to have all the LED’s running in parrallel of one resistor try grouping 4 in series with 1 resitor for that group. Then run all of those groups in parrallel. Also more LED’s is better i have 80 in my setup on a 1024 x 768mm table about 1 inch apart and the blobs are bright without silicon. And polish the edges of the acrilic starting withe a 500 grit and then work up the grits to get a almost smooth fininish which then needs polishing with a buffing wheel on a drill or bench grinder.

Lots of Infrared
Polished Sides
good band pass filter on camera

: )

@ xelapond, like i said before i dont know the specs of the leds and the resistor is a 510 ohm resistor, thats all i know, i know is not the best way to do this but thats what i could find so i tried and tried until i found a way that works to connect everything…

@ Joobs, there are the screenshots:
imagen 001 is what the camera sees without the photo negative
imagen 003 is what sees with the photo negative
imagen 004 is what it looks when i point a led directly to the camera from aproximately 30cm, so as you can see, the camera does sees the IR light pretty good (i think)

@ Tinkerman and ajlovegrove, i talked with Taha and he told me to do that, to polish the edges of the acrylic and to angle the leds, that las thing i did and it improved a lot, the screenshots are with the leds angled already, before doing that the camera didnt see anything. And he also told me to put more leds, so ill polish the acrylic and put more leds in the left and the right and post my results here

ill also ask someone who knows about electricity and circuits to help me find the best way to connect the leds

thank you all for your help

Revai you havent removed the IR filter… in the last picture when you point the led at the camera it should be completely white, light should blanket the entire screen.

Taha

in all the pictures there is no IR filter because i removed it, in the first picture the photo negatives arent on top of the camera lens and in the 2nd and 3rd they are, aparently i have very weak leds, so ill have to find better ones and use more