How to get the best range out of an IR LED?

Hello, I'm using my Arduino as a universal remote and I've got everything working, but my IR LED isn't really strong.  I've read around the internet and all I've found are people using an IR LED with either a 33 Ohm or 100 Ohm resistor in front of it.

Currently I'm using this RadioShack High-Output Infrared LED
[Radiant Power Output = 16mW min
 Forward Voltage = 1.2V
 Forward Current = 100mA
 Wavelength = 940nm]

with a 100 Ohm resistor in front of it and only get a foot or two of range.  I'd really like to get out to about 20 feet but I could make due at 15/16 feet.  So I got nose-y and opened up my TV remote... it's all surface mount, but as best I can figure it the signal leaves an IC, goes through a 100 Ohm resistor and then goes into a transistor (labeled 2T) before heading out to the IR LED.  The third pin from the transistor snakes around to a bunch of other parts and I lost.  So I was wondering what to do to increase the range of my IR LED... change the resistor?  Power it via a transistor?  If I can use a transistor does anybody know how to wire it up?

Any help is much appreciated.

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You CAN put significantly more current into an LED than the spec says, but ONLY if you have a low duty cycle signal to it. If the duty cycle of the signal you are sending is 50% then you can push 50% more current than the spec through it. The limit is ultimately the fusing current of the bonding wires to the LED die.
Schmidtn (author)  steveastrouk7 years ago
Yeah, I went out and bought a bunch of different resistors... a 15 Ohm 1/2 Watt resistor got me over 20 feet and I'm guessing I didn't weld my LED shut because it's still working (although I did buy a backup IR LED, just in case). Thanks!
mick964 years ago
I'm kind of wanting to do the same thing. I have the adafruit ir LED running off my UNO and while it works, I need to figure out how to build some sort of an amp to power a cluster of ir LEDs to run the air conditioner, TV, DVD etc from a central location. I'm better at writing code than designing circuits and I'm not sure where to start. Does anyone know of a link to a similar project? Thanks!!
skyfly2004 years ago
That should need a minimum of 38 ohms for the spec 100mA, as stated above if you drive it with a <=50% duty cycle you could drive it at 150mA using a 25.4 ohm. (amusing a 5V arduino)
cncghost7 years ago
sorry correction on the website
cncghost7 years ago
well the ir led in a remote is ok but the better way to go is with 10mm, 200mw triple Infrared LED. they don't cost to much and if u can get about 12 wired together with a 10 ohm resistor in the lead then you will have the range you are looking for plus more. here this is were i get mine
trubshac7 years ago
Have a look at You don't have to use quiet so many LEDs if you don't want to!
framistan7 years ago
Older remote controls often have low output IR led's. I have several times replaced them with high output IRled's. The results are usually the remote can be pointed in almost any direction and it will operate correctly!!! Just remove the old LED and solder in the new one. You must observe polarity of the LED. If it doesn't work.... unsolder it and turn it around. If it still doesnt work, you probably BURNT IT OUT. So remove that one, and put another one in. This time, install the 2nd one the opposite way from the 1st one. Leds have ONE wire longer than the other one when new. also they have one side of the plastic is FLAT. other side is rounded to help you know which way to install. If you overheat the led you might burn it out. solder it quickly and get the iron off of it. You are already using a "high output" led... so something ELSE might be wrong. Maybe your resistor is not 100 ohms, maybe you misread it and it is 1000 ohms??? A really GOOD way to check the output LIGHTBEAM of any IR-led is to look at it with any kind of digital camera. You will be able to see the "beam" compare the beams intensity with other remote controls you have. good luck.
Agreed. The led should be run with an appropriate resistor based on the power supply. The arduino can handle a good 100mA of current on a pin, but not a lot more. I would recommend doing like the remote has -- output the signal through a transistor to drive the led. THEN you can have more power going to the led without worry of damage to the arduino pin. Lastly, you can run multiple leds on one transistor for extra awesomeness. If you're only getting a few feet of range, I'd guess your resistor is wrong.
Schmidtn (author)  framistan7 years ago
I used a multimeter and checked the resistor; it is 100 Ohm. I did the camera trick to compare them and I'd say the real remote is about 4 times brighter than the Arduino remote but it's kind of hard to judge it off of the camera's screen. It's definitely dimmer than the commercial remote though. Can I brighten it just by using a lower value resistor, or does the signal need to be amplified by semiconductors? Thanks, Nick