Electronics for external lights


#1

Hi all. I would love to get some tried and tested cube lights from the store but $70 shipping to the UK isn’t an option and there’s aways a nasty sting in the tail with the import duty.
I can get all kinds of different CREE LEDs from RS Components and i already have some optically clear epoxy for potting. I’m a digital engineer but I’m afraid my analogue knowledge is very poor so I wonder if I could get some answer to the following:

  1. Is the OpenROV 2.8 plug 'n play with the 2 PWM channels, i.e. just connect and they will work? Will they dim like the internal lights and can they be used independently of the internal lights?
  2. I believe the current limit is 700mA to avoid damage. What would be the best way to limit the current draw of the LEDs?
  3. What colour works best in salt water? Warm white, cool white? They are available in everything from 6000K to 2700K

Sorry, so many questions. It seems a bit cheeky when you guys have put so much research time in. I don’t suppose you’ve published the cube light circuits :blush:


#2

Hi Andi,

I have connected a 10w LED directly to the Board without any Electronic in between And it works very Good . The Maximum Output is 2000ma . I can also dimm the LED as the internal ones. I think the Could white light is more eficient. The only disadvantage if you don’t use a constant current Source is that the light will be sometimes aliitle but darker if you Need a lot of current for the motors.


#3

Hey, thanks. Can I ask, what LED did you use?
Do you have to map keys on the keyboard?
Andrew


#4

Hey, i’m using this ones . I have bought it from eBay . To Switch on and dimm the external light press alt+ i

Dominique


#5

Thanks Dominique, very helpful.
Andrew


#6

Hi Andrew:

The circuit for the light cubes is open source- you can find it on our GitHub site. Go to the main OpenROV web page, and pull down the tab Open Source / Electronics. You’ll find a folder there for the External Light Cube Data Package.

The 2.8 controller board is pre-wired for one set of external lights, on the PWM3 channel. If you have up-to-date software this is already mapped to the keyboard, using the same keys as the internal lights, but using (IIRC) the Alt-key as well. So Alt-I to toggle the external lights.

The PWM3 channel can handle 2A of output current.

If you want a second set of external lights, you’ll have to hook up the PWM4 channel and map it to the keyboard yourself. It is also rated for 2A, but note that if you pull 2A from both PWM3 and PWM4 you will start to overheat the current sense resistor that measures the non-ESC current flow. Anyway, you can get the schematics for the controller board from the same GitHub site and play to your heart’s content.

If you’re not that concerned about efficiency, I’d just wire two 3V white LEDs in series, and then put in a resistor to limit the current flow to whatever you want, but less than 2A. A number of people have made forum posts doing just that- if you search around a bit you’ll find them.

There is no “best” color in saltwater- it all depends upon what you’re trying to do. Colder light (i.e. higher color temperatures) will give better LED efficiency and better penetration, but worse color recognition. Low color temperatures (warmer light) give good color rendition but shorter range. The best color for range in seawater is green light, which LEDs don’t really generate very well.

For reference, the internal LED lights are 3500K and the light cubes are 4000K.

Hope that helps.

-W


#7

Hey Walt. What a fantastic, comprehensive answer. Thanks very much for that. I think I’ll stick with one pair for the time being, I want to spend all my time exploring, not repairing the controller board :grin:
That is, of course, if it ever stops raining here in Scotland! Our boat’s going back in the water around middle of March and we’ve got two fantastic wrecks within 5 miles.
Thanks again.
Andrew


#8

Hi I also used the cheap LEDs from ebay. here is how i did mine.

But first a quick tip. if you want to put some lights that draw higher than 2 amps they sell 10 amp RC switches that will use your servo output to toggle the switch on and off. I think they are around $12 on places like hobby king.

To start do be aware that the LEDs off ebay are crap for efficiency (the individual leds are all random as far as when they turn on, use a variable DC power supply and see for yourself) they are probably throw a ways or B grade. but I’m going to run a large Lipo so im not too concerned about battery life.

But this does equate to heat. I originally got these for my quadcopter so had to mount them to a heat sink using some thermal compound on their backs and put them under the props. This shouldn’t be an issue with them in the water.

I used two 10watt LEDs rated for 12V in parallel. They draw around 2.4 amps at 12v but I like them better at 10v around 1 amp and the light seems to be of the same intensity. These babies GET HOT even with the heat sink but in the water they will be fine.

I used a piece of Lexan for the front and used painters tape to seal around it creating a small trough. Poured in the epoxy and then gently worked in the LEDs mounted to the aluminum.

This is my first attempt. There are a number of things i will do different now that i know it works pretty well. better wire, different epoxy that is more viscous (hope for less bubbles) and smaller heat sink. that size heat sink is not needed in water just in the air with the quad. Open to any comments about how I could make them better.


My ROV for college project
#9

Hi there. I have shamelessly used the open source BOM and PCB Gerber files, which is still less than half the cost of shipping from the U.S. to UK. I’m not sure yet what I’m going to pot them in, but a good choice for epoxy might be Opti-Tec 5013 which is an optically clear epoxy. I’ve used it before for terminating fibre optic connectors and it is fantastic stuff.
I might try and rig up a small vacuum pump to evacuate the air bubbles once mixed, before potting.
Andrew


#10

Andrew,

Good ideas. I would also like to try the vacuum approach but can’t justify the cost for how little it would get used by me. Not sure if the pictures show it very well but i used a piece of lexan for the front and pushed the LEDs up to it so there is almost no loss of light or clarity though epoxy (because there isn’t any). The piece I used was just what i had laying around and was about .25" thick, next one i make I will use a thinner piece which should help even more. I’m going to look up the epoxy you mentioned. The one thing I noticed about mine is they shine light in all directions. It really needs some type of reflector around the edges. I’m thinking that in the water it will light up areas you don’t want or cause a glare on the camera. I could be wrong here.