Thanks in advance to those who reply. Very much a newbie with electronics, so apologies up front.

I am planning an LED light project using an Arduino microprocessor. My plan calls for 8 banks of 5 LED Lights. These are very small LED lights.

In each bank, the LED's are spaced 5 yards apart, for a total circuit length of 150 feet (all the way around). Is it even possible to run 12v power through a circuit that long?

I think I have to run 12V because I hope to run them underwater in a swimming pool, and that sounds much safer to me.

Also, I believe that a series (rather than parallel) circuit is the way to go with LED's. Correct?

What additional information can I provide?

Thanks!

-Ryan

 

Hi, and welcome.

What type of LED, red, green, blue, white...?

What type of wires?

What is the uC doing?

About that "under water". This needs some more explanation. Could be dangerous.

It's always good to post a schematic.

 

Thanks to you both. I'll try to put in a little more details here. I don't have a very good working knowledge of electricty specifics (Amps, etc)

1) Here is the LED I am thinking of using. Nothing major:

Red LED from Radio Shack
Peak emission wavelength: 660 nm
Light output: 5000 mcd @ 20mA
Forward voltage: 1.85V

Absolute maximum ratings:
Forward current (continuous): 30 mA
Forward voltage: 2.5V
Reverse voltage: 4V
Power dissipation: 75mW

2) Also, the function and arrangement of my project works much better if I can wire the LED's in parallel.

3) I'm learning about transistors, so I can see how that would work.

I'm going to try to make an illustration of what I want to make and I will post here. It will be easier to explain the underwater component that way.

Thanks again!

-Ryan

 

5 or 6 in series would come out to be a perfect match to a 12V supply if you don't mind driving them close to their max rating which really shouldn't be a problem with higher brightness LEDs. On top of that if they're under water they'll have plenty of cooling.

12V doesn't travel well in water, even pool water, but some silicone seal on the connections would certainly be in order to help prevent the eventual corrosion that will occur. Length of the wire is no big deal, you're only talking 30 mA even at the max ratings so even plain #24 AWG telephone twisted pair wire would work fine but you can buy that landscape wire cheaply enough from Home Depot which would be far more durable.

I'd just wire them in series, it's easy to break one of the two conductors in a wire pair and solder an LED in there. You eliminate having to have any sort of dropping resistors or regulation that way if your power source is stable enough.

BTW: What are you intending to power this with? They make highly isolated 12V supplies for that landscape lighting too that aren't too expensive if you don't need much current. I was an idiot a couple of years ago, Home Depot was closing out a brand of outdoor lighting they had been selling and had some 12V 100A supplies on sale for $99. Couldn't think of a valid reason to charge a couple off on my business account then once I did and went back they had already sold them. If you buy one of most any size you'll not only have plenty for all your LEDs (unless you're using 100s of them) so the extra could be used for a few of those little outdoor fixtures someplace around the pool.

 

Thanks guys for your responses. I really do appreciate it. I've spent the morning working on some diagrams. I'm probably not using the symbols all correctly, but hopefully it will help illustrate. Let me explain what my project is, and then I'll show you the diagram.

I am a youth swimming coach - have been for 15 years. I would like to make an LED chaser-string that I can submerge underwater so that my swimmers can see it while they are swimming. I will then set the LED's to light up in sequence at a desired "swimming pace" so that the kids can race the light that they see underwater.

A pool is 75 feet long. I'm going to space the LED's just under 2 feet apart. I am using 8 banks of 5 lights (40 LED's total) because it will use much less wire than running 40 individual circuits, and much less circuit controls.

The reason I am using 5 "tubes" is because it needs to be convenient to pull the lights out of the water and store them. A 75 foot tube isn't convenient, but five 15 foot tubes that can be connected and unplugged is much more useful.

Marshall - I did this diagram before reading your post. My hesitance with wiring in series is that if one LED goes out, I'll lose the entire bank. But, if that is the best way to do it, I'm sure I can work with it. This diagram was done showing it in parallel.

URL to Diagram: http://tinyurl.com/2auet4u

Thanks again!

-Ryan

 

Brilliant idea - I think it would be fun for anyone to "race the light", where the pace is something meaningful to the swimmer, like last lap pace, personal best pace, or something like that.

Not to bash the Shack, but if you're buying a bunch of LEDs, you'd do better with the e-bay crowd. Or, if you want higher reliability in each LED, you can get brand recommendations from folks here. I bought a bunch of several colors out of Hong Kong and I've been very happy with them. In general they're much brighter and cheaper than what the Shack offers. I don't think twice if/when I roast one - they're just pennies.

One thing you might want to experiment with before buying a bunch of them, is angle of dispersion. Some are tightly focused and others not so much. Off hand I can't predict which would work better for you. If you're not able to "point" them up towards the swimmer, I suppose a wider angle LED or any LED with a diffuser will get more light to the swimmer's eyes. I also suspect that different colors may look very different when submerged. For instance, maybe a red LED will wash out whereas a green will be brighter for a given current, or vice versa. Just a guess.

 

Wayneh - Thanks! I've looked at some on ebay, and that's probably how I will go in the end. Same with all of the components. Our Radio Shack is stupid-expensive.

What do you think about the configuration of the banks spread over 5 tubes and using the connectors between tubes?

 

I'd be reluctant to place any connection under water, unless they are purpose-built for that application. They'll be exposed to movement, people stepping on them, waves, pulling them in and out, coiling, etc. Really tough to maintain a seal, and a solid connection, I would think.

I agree that modularity is good, and especially if some of your LEDs are in series. Nothing worse than long strips going out. (I'm kinda thinking of all those XMAS light strings I've had to diagnose this season.)

FWIW, I bought my LEDs from here, via their e-bay store:
http://www.hkcitylights.com/

 

Again thanks to everyone. Based on the feedback I've gotten here and elsewhere, I'm going to start looking at clear plastic tubing, rather than PVC. This way, I can avoid any joints in the middle and any underwater wiring.

I've started a new thread asking about how to position/mount LED's inside the plastic tubing. Here is a link to that new thread:

http://forum.allaboutcircuits.com/showthread.php?p=313032#post313032

 

Wont be easy to snake everything through a tube or even sets of tubes but I suppose it's doable.

I now see why you want to put them in parallel such that you can have individual control but series would be easier in short sets of 5 and waterproof connectors can be found that will work well, simple marine grade silicone seal should seal up the tube ends.

 

What about the semi-flexible PVC clear tubing that people made LED Hula-Hoops from? Might not be the cheapest option though.

Another source would flourescent light bulb packing tubes, some come in a clear 1" plastic tube, others come in cardboard, but if you could find enough of the clear tubes, setting up the circuit wouldn't be a problem.

Come to think of it, the only place you would need the tubes would be where electrical connections occur and you want to "aim" the LEDs, in between could be standard "christmas light wire" in white. This would be a lot easier to store as well.


--ETA: One of the fitness centers here has a similar concept for the track (not sure if this is where you got your idea or not). There are panels with 3 different colored (Blue, Red, Green) lights around the outside of the track about 20 feet apart, each blinks at a different speed for a different lap time. Similar idea could be used with the swimming, use 3 colors for 3 different "pace speeds", or add a 4th color for a custom speed.