Author Topic: IR LED Problems - Weak LED  (Read 16835 times)

Offline Iceman1979

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on: February 17, 2008, 12:00:55 PM
Hey guys,

I went to radioshack yesterday and bought some of their High-Output ir leds.
Forward Voltage = 1.2V - 1.6V
Wavelength = 940nm
Forward Currnet = 100mA

I'mn pretty sure I got the right ones but they are not bright at all. After I built my pen and tested it out and it seemed to work but not well. If the will was not within 2 feet of my screen it would not pick up the pen. This lead me to some investigation. I started watching some videos on other poeples pens to see what the desired characteristics were. I was noticing that when people were pressing the button on the pen the led was makeing a rather bright light on the camera. I break out my camera and do some tests and I can barley tell the led ligts up. Pointing the pen at the camera you could see it was lit but still it was dim.

I've tried energiser AAA, and rechargable AA batteries but nothing seems to make a differance. So far 2 of the same type leds have produced the same results.

any suggestions as to what I might be doing wrong?



Offline atomriot

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Reply #1 on: February 17, 2008, 10:46:28 PM
i had sort of the same problem. i could make the pens show up really well pointing at them but sideways there were not so great. On my pens i started putting something semitransparent on the end to stop the direct beam of IR light and diffuse it a little more. that helped a ton.

i still have not gotten something for my big mama jama black pen but my other two do very well with an end cap on them

Details, details. Things to do. Things to get done. Don't bother me with details, just tell me when they're done.
--
James Lionel Price



Offline SSpeare

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Reply #2 on: February 18, 2008, 03:37:26 PM
If I am understanding everything correctly (not sure yet!) the actual output of the LED is the mW rating, not the mA (forward current IF) rating. You can usually find the mW output on the packaging. The ones from Radio Shack are 16mW min. The ones Johnny recommends are TSAL6400 which are 25mW min. They also have TSAL6200 which are 40mW min.

(Please someone correct me if this is wrong)...



Offline Iceman1979

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Reply #3 on: February 21, 2008, 07:17:56 AM
Thanks for the feedback on this. The strength of the led is definately the problem. I guess I need to order some online.



Offline inio

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Reply #4 on: February 21, 2008, 10:43:42 AM
Are you using a resistor?  For a single-battery, single-LED setup that's probably not necessary.  Though you could blow the LED with an alkaline, rechargeable probably wouldn't have the voltage.



Offline Iceman1979

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Reply #5 on: February 21, 2008, 06:53:02 PM
nah, no resistor yet. I can see it with my camera on my cell phone its just really dark. I think SSpeare  is on to something with the 16mw comment. I think changing the led will make the difference



Offline gregorylouie

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Reply #6 on: February 23, 2008, 07:27:42 AM
Thanks for all your comments. 

I had already bought a Radio Shack IR LED, when I read your post. 

Since I have a low power LED, I want to try your endcap solution.  How far is your wiimote from your screen?  Would you describe your endcap in more detail please?

Thanks

Greg

i had sort of the same problem. i could make the pens show up really well pointing at them but sideways there were not so great. On my pens i started putting something semitransparent on the end to stop the direct beam of IR light and diffuse it a little more. that helped a ton.

i still have not gotten something for my big mama jama black pen but my other two do very well with an end cap on them



Offline Iceman1979

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Reply #7 on: February 25, 2008, 10:11:01 PM
Ok, so my TSAL6200 leds came in today and I wired one up to an led pen from walmart. Using my moded web cam I took a pic of the two sources pointing on the ground. I can't tell if its brighter or if its the differance in angles of the leds. The TSAL6200 is 17deg and 40mw the radio shack is 45deg and 16mw.

Here is a pic of it from the view of the webcam.
« Last Edit: February 25, 2008, 11:49:20 PM by Iceman1979 »



Offline inio

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Reply #8 on: February 25, 2008, 11:45:51 PM
Google pages doesn't allow external hotlinking.  Here's the image for the convenience of others:
« Last Edit: February 25, 2008, 11:51:21 PM by inio »



Offline Iceman1979

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Reply #9 on: February 25, 2008, 11:50:03 PM
Thanks for posting that. I was not aware of google not allowing hotlinking of images.

Thanks
John



Offline inio

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Reply #10 on: February 25, 2008, 11:51:54 PM
Also, assuming the webcam's response is linear (which it should be somewhat close to) the total energy is almost identical.



Offline Iceman1979

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Reply #11 on: February 26, 2008, 06:36:04 AM
Thats what I thought too.



Offline dice

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Reply #12 on: February 26, 2008, 09:42:18 AM
Could someone put together the best LED's to use and why they are the best.

Like
Radioshack led's are a waste of money or they are the best because...

I am a bit confused about what makes the best LED is it the wavelength, the wattage, or a combo of a bunch of things?

If someone could put a chart together that would be great.
Thanks
Dice



Offline inio

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Reply #13 on: February 26, 2008, 10:25:19 AM
I am a bit confused about what makes the best LED is it the wavelength, the wattage, or a combo of a bunch of things?

940nm is about twice the intensity as 850nm when viewed by the Wii Remote.

For a given wavelength (= given chemistry), max current is pretty much proportional to radiated power.  Running much above max current will kill the LED, so you have to be careful.  To do things right, use a higher source voltage and current limiting (don't connect it directly to a battery).  For example, for a 2.4V source (2x rechargeable AA batteries), and 1.2V (typical) 100mA (max) LED, the resistor should be at least R=V/I=(2.4V-1.2V)/100mA=1.2V/0.1A=12ohms.  If you want to get really fancy, measure the current (you can do this using a ammeter or by just measuring the voltage across the resistor and using I=V/R) and adjust the resistor until you're near your LED's rated maximum.

Power (wattage) isn't really that useful of a metric to compare unless the LEDs have the same current, angle, definition of power, and about the same wavelength.

For the Whiteboard project, you only care about angle if you want to be able to hold the markers more than about 1cm away from the board and not lose range.  If you do want that, you want the narrowest angle possible.

For marker's, the field is just too wide.

For non-marker applications, I like the following LEDs:

Panasonic LN52 & LN152 950nm, 100mA, approximately flat falloff over slightly less than a hemisphere, or a full hemisphere.  Not good for long range applications, but over short ranges (<4 feet) they work great.

Osram SFH 4231 940nM, 1A, approximately lambertian angular falloff.  Expensive though.  If you want to project IR points onto a screen, these plus some optics are you best bet.  The SFH4230 works in a pinch, but you'll get about half the intensity at the sensor for the same current. Powering these near their current rating is tricky - they need to be mounted to a heatsink to actually run at 1A, and merely supplying 1A to them could prove tricky as using a resistor for current limiting becomes problematic (if you don't understand why, don't try it).



Offline balam

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Reply #14 on: February 26, 2008, 04:50:01 PM
Hey guys,

I went to radioshack yesterday and bought some of their High-Output ir leds.
Forward Voltage = 1.2V - 1.6V
Wavelength = 940nm
Forward Currnet = 100mA

I'mn pretty sure I got the right ones but they are not bright at all. After I built my pen and tested it out and it seemed to work but not well. If the will was not within 2 feet of my screen it would not pick up the pen. This lead me to some investigation. I started watching some videos on other poeples pens to see what the desired characteristics were. I was noticing that when people were pressing the button on the pen the led was makeing a rather bright light on the camera. I break out my camera and do some tests and I can barley tell the led ligts up. Pointing the pen at the camera you could see it was lit but still it was dim.

I've tried energiser AAA, and rechargable AA batteries but nothing seems to make a differance. So far 2 of the same type leds have produced the same results.

any suggestions as to what I might be doing wrong?


agree
redioshack ones are weak.