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What resistor(s) will I need for my IR LED Circuit?

I'm going on information obtained on the net so please bear with me! I'm intending to use eight 200mw triple IR Leds wired together using a nine volt power source (battery). What resistors will I need and how many? I've already seen a diagram on how to assemble the circuit but some confirmation would be greatly appreciated as the previous threads on the subject were somewhat debated.


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Find the data on the LEDs. Such as forward voltage and forward current. Then plug that info into this calc and it will show you a few options for wiring the LEDs up to your battery source. As steve mentioned a 9V battery may not be able to handle the load or at least the battery won't last very long. If you want to run it off 9V then use a set of 6x AA or AAA batteries.
Jman58 (author)  mpilchfamily5 years ago
Ok , Sounds good. I used the calc you gave me and with some LEDS I sourced from old IR remotes it gave me a test design. After wiring up the design it wouldnt light up the way the diagram showed. I used 4x 5mm IR LEDS sourced from old remotes. I also bought (what i thought to be) one of the same LEDS from radio Shack to have the specs because i cant find a data sheet on the remote to make sure. the led specs from the one i bought was 16mw, 1.2v, 100ma 940nm 5mm. so i thought the others would be the same they look identical. However They wouldnt light up and i confirmed with my phone cam. plz help sorry to be such a noob, perhaps as you stated even with 5mm IRs the source power is not enough? what power source should i use for this type of app?
There are literally millions of different LEDs and IR LEDs that look the same but have different specs. Type in the info on the LED you got from the shack and test it by itself. Then test each IR LED from the remotes by themselves with that same resistor. If it doesn't light then try a slightly smaller resistor. Keep in mind they will not light up as bright as regular LEDs. When looking at them through your camera make sure you turn the power on and off to make sure they are not on. Sometimes its hard to tell.
+1, there should be no debating. Get the info and go to the link above.
Datasheet for LEDs needed. And a 9V battery isn't going to have the output current you need by miles !!

Steve