OpenRov 2.8 auxiliary wires specs, adding external lights


I just finished building OpenRov 2.8 #2501. I would like to add auxiliary lights, however I couldn’t find specs for the 6 auxiliary wires, what is what. I am looking for information on what auxiliary wires to connect the lights? What is the nominal voltage output for the lights and what is maximum current recommended?


Hmm. Thanks for the reminder. I need to get the controller board schematic for 2.8 up on the GitHub site. I’m also slowly working on an application note for the 2.8 Controller Board that will help guide one in making custom mods to the ROV.

The short answer to your question: The external lights are powered by the PWM3 channel, which delivers battery voltage, in this case ~9V, to the lights. Maximum recommended current draw is 2 amperes. The signal from the lights can be modulated (PWM) for dimming purposes. The six auxiliary wires are color-coded for identification purposes. I don’t have a 2.8 in front of me now, but I think the two wires for lights are something like purple with a red stripe and purple with a black stripe.

Software support for external lights is built into SW 30.0.2.

Hope this helps. I’ll try to get the 2.8 info onto GitHub today.




For 2.7 I presume everything is the same except the wires are all grey and they need to be connected internally. I know there was another post on the connections, which I have saved off.

That said, 9V and 2A is a lot of light. I think the onboard lights draw about half an amp and produce 180 lumens max as I remember.

Has anyone tried specific external lights or potted up some LEDs? I just put in a mouser order for some LEDs to try. I have not decided yet how I am going to pot them. So thoughts welcome.



Hi Chris:

On the 2.7 ROV, you have to pick a couple of the spare wires to use for external lights ( on 2.8 we use TP20 for external lights (+) and TP21 for external lights (-) ). Then, internal to the ROV, you need to run wires from the TP20 and TP21 test pads back to PWM3+ and PWM3- on the prototyping headers. Then finally, to activate the PWM3 channel, you need to solder a 0-ohm resistor or a short piece of wire in the slot for R32, which will place battery voltage (~9V) onto PWM3.

As I mentioned in this thread, we’ve tried a bunch of different light combinations, both immersed in mineral oil and potted. You can wire up a simple circuit with LEDs and a dropping resistor, but it’s not that efficient, and throws off a lot of heat. Better designs use a switching circuit to drive the LED with a constant current. The little light cubes that we’re currently readying for production are potted, have a metal case for thermal dissipation, and not only have a switching regulator, but also have a thermal regulator, so they don’t melt if you turn them on while out of the water. The LED we’re using on these is a Cree XHP50A, throwing off about 750 lumens of light. We should probably get some photos of the prototypes up on the forum for people to see.



The files from Walt are up on the Electronics GitHub Page.

I will work on getting these pictures up next week once the wire comes in.

External Lights Take 2

Thanks for all of the information Walt. The external lights sound great, but it looks like they will not be available until next season. So I have created a first prototype light here to see if I can improve things for my next dive.

I built the light into some scrap pieces of battery tube that I had. I don’t think I need 750 lumens of light, so I used LEDs that throw out about 45 lumens with 120mA of current. Here it is with the epoxy curing. I filled it so that the electronics are covered but the LED light surface is exposed. I don’t know if that is a good idea or not…

It seems to work in the water, although a small jar is not much of a test

To keep the light stable in the battery environment I used a two transistor current source. If we want 120mA through the two LEDs, then we want 120mA through R2. When the voltage across R2 approaches 0.6V then Q1 turns on and turns off Q2. So we get an equilibrium. You can not easily calculate the value of R2 (even though it seems like ohms law should make that easy) and it is best found experimentally. I used a 2.2 ohm 1/4 watt resistor.

So I get 90 lumens from this light. The plan is to have two of them for 180 lumens total. The light does not get hot, even when out of the water because very little power is wasted in the current source.

I also tested this with the ROV in a dark room, having modified my 2.7 electronics to feed voltage to the external wires. It worked well. Alt-I turned the light on/off and there is a definite improvement in video quality when there are no reflections inside the main tube.

As I said. This is prototype 1. It seems larger than needed. Perhaps epoxy is not good for electronics that get warm. Maybe the current source should be in the main electronics tube and not in the light (which could then be smaller). Perhaps a different housing would be easier to mount (I will have to 3D print a bracket). Perhaps there is a better (simple) circuit because two LEDs (at 3.5V drop each) plus 0.6V for each transistor is very close to our total voltage budget. But that is also why we have little heat, so it’s a trade off.

There are probably a hundred other ways to make this better, so comments welcome.



Thanks for all information! I connected external lights to purple/black and purple/red -wires and it works nicely.


Hi Walt,

I’m planning to make my own external lights for my OpenRov (2.8). You said you’re using the Cree XHP50A LED, looks like a good choice. But what other electronics are you using? Driver? There are a lot of drivers with PWM available, but the ones I have been looking at needs to be placed inside the electronic tube, and need both +9v, and PWM signal (typical max 6v). Would appreciate some help with choosing the electronic parts, so it can be built into the lamp, and use only the 2 wires from the board, meant for external lights. Is the PWM3 ports set up with 9v as default? Can it be set to 5v?




Hi Rune:

We’ll have the schematics for the Light Cubes available when we start selling them in the store, which I’m hoping will be in a month or so. The prototypes are all working well in the lab, and the first production order for the aluminum bodies has been placed.

We’re using an Infineon ILD4001 as the driver.

The Power-PWM ports on the ROV can be set up with your choice of battery voltage (~9V), 5V, or 3.3V. On the 2.8 Controller Board, the PWM3 channel (typically used for external LED lights) is set at the factory for battery voltage. You can change it to 5V by removing R32 and placing a jumper at R31. See sheet 6 of the controller board schematic, available on our GitHub site.