Hey all,

First time caller, long time listener.

I’ve been planning out a FTIR for the last month as a new hobby and need some help. I’ve picked up my plexi (24” x 18") and have my board and LEDs on order. I’ve read up on what types of LEDs and what to look for.

The LEDs I went with are 40 Liteon LTE5238A (High intensity Gallium Aluminum Arsenide LED @ 880nm). The specifications on them are as follows:

Forward Voltage: 1.3
Forward Current: 100mA
Viewing Angle: 40 degrees

My plan calls for 38 LEDs, 19 on the top and bottom. I’ve included a project plan below for the surface and the full LED specs in case any additional info is needed. What I’m having issues with is that I’m unsure about how to wire this up properly or power it via wall socket. If someone could offer some suggestions on possible resister placements and whether to go with 2 parallel arrays in a series or another way of doing this that would be better, I’d appreciate it.

Cheers,

tw!st

Well it all depends on how much voltage you supply… you should look at led series parallel array wizard http://led.linear1.org/led.wiz it’ll help you out.

Cheers
Taha

Hey Taha,

To be honest, I already have used it, but because it doesn’t offer specifics about my circumstances of 2 rows of 19, I’m not exactly sure how to move that to what I want to acheive. From my reading (which could be completely wrong as I’m new to electonics as a hobby) I could technically use either 5V or 12V based on how everything else is setup and how everything in the setup can be affected / changed by what voltage I use.

I’ve been trying to read and learn as much about this as possible, but it’s not going as fast as I’d like. =]

Thanks,

tw!st

Hmmm,

First time to try that LED wizard,but I’ve this solution based on
9 volts ,1.3V ,100mA ,38LEDs

Solution 4: 2 x 19 array uses 38 LEDs exactly
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms
+----|>|----|>|---/\/\/----+ R = 68 ohms

The wizard says: In solution 4:
each 68 ohm resistor dissipates 680 mW
the wizard says the color code for 68 is blue grey black
!! the wizard thinks the power dissipated in your resistors is a concern
together, all resistors dissipate 12920 mW
together, the diodes dissipate 4940 mW
total power dissipated by the array is 17860 mW
the array draws current of 1900 mA from the source.

Is that what it does :\ ?

cheeerz

I actually didn’t try it at 9V, but that looks like I’d need a resister every 2 LEDs? That might sound really stupid, but this stuff is really, really new to me.

I checked it out with the specs you posted, but that looks like 19 rows or 2… or am I interpreting that wrong?

What kind of power source would I use? I’m completely guessing, but I would assume there’s PSU out that use standard wall sockets but output 9V DC? Would I run them as 2 parallels in series or split off from the source or ...?

Thanks so much for baring with me…

tw!st

You can purchase different DC power adapters from various electronic stores, there are a large number of them available on ebay as well and they are cheap. What you need to keep in mind is the total current being drawn from the power supply and aswell the DC output voltage both of which always listed if not you can always ask the retailer/seller for the specifications.

Hope this helps
Taha

Hey again,

Won’t add a word to Taha’s reply .
and for the resistors use a “Resistor network” .

Thanks alot guys. I appreciate your patience with me…

tw!st

hi,

resister evry 2 leds is very stupid. and for 2 array (19+19 leds) you will be need 24,7 volt power unit.
normally power untis have 12 volt, so i drawed a picture for you with a 12 volt power unit.
its better if you wil use 36 leds, but 38 is also possibly.

you can also split the last 2 leds at the picture, but then you have to use antoher resister.

so here is the pic

Hmmm,

As far as I know ,I need the resistors as a current limiting element ,and since the application supposed to work for long hours ( I dunno ,am still a beginner here and new to MT world :S ) ,I need these to protect the LEDs .

hi,

every led is like a resistor (1.3V / 100mA = 13ohm per led). also the wire is like resistor, but here it´s unimportant becouse it is very small

the only necessary thing is that you get 100mA on the wire, where the leds are placed. by 12V to get 100mA on the wire you have to placed 120ohm resistor. 
9 leds get us 117ohm, then we only need 3ohm more. (i see now that i made a mistake in the picture, 13ohm shoud be 3 ohm, sorry)

i´m sure that this is correct.