Does anyone have any experience with RGB LED strip/ribbon lights? I have a curious case of a lighting controller that's designed to work with these types of lights but seems to be implemented completely incorrectly.

The lights are the variety that come on a reel and are often sold in a kit with a 12v power supply and a remote-controlled RGB controller to change colors and turn the strip on and off. The controller I'm having the issue with is a separate product that provides some of the same features but can also automatically change the lighting in reaction to sound.

The light strip has 4 wires, RGB and a BLACK wire. Going by the functionality of the working controller and manual connection to a power supply, the black wire is a common ground and each of the R,G and B wires are supplied with varying voltage (+12 to 0) which determines the intensity of each light component and creates the varying colors.

The issue with the music/sound controller is that it doesn't have a common ground. It has common voltage, and each terminal for RG and B are then tied to ground, first passing through some bits on the circuit board (1 transistor each, plus some resistors, then tied to a small IC) to reduce the voltage on input from the remote. This means that the voltage is passing in reverse polarity through the LED strip, -12v instead of +12v. And of course the LED strip will not light up this way.

Which leaves me with a giant WTF!?

Reversing polarity on the power supply doesn't work to remedy the problem - no voltage can be measured on the board this way. Might this be a matter of flipping around a few components to get this to work? I only see 3 diodes on the entire board, one big through-hole and two smt.

I purchased this stuff from two sellers on Amazon, but I notice that the seller I bought the strip from also has the exact same controller on their web site. Arrgh.

Ask him for details on how it's meant to work?

Already wrote to both, but no reply. I'm expecting to get back messages from each telling me that they can't help because both sets of parts didn't come from them.

I just don't know how this controller would work for anything.

Lovely. So that controller, as-is, is useless with those LED strips.

One way to salvage the situation would be to add three more power transistors (PNP), one in series with each of the existing R-G-B trio on the controller board, except selected and wired to reverse the voltage output. Those will likely need a pair of resistors each to scale down the ouput of the existing transistors to levels that can be used to control the add-on ones.

Cheers

..assuming, of course, that the existing drivers are transistors, as opposed to SCRs or something like that.

Or.. perhaps rewire the emitter/collector paths of the existing drivers to get the correct ouput polarities. That might not be too bad, actually. Probably the best approach, depending on the exact details.

Edit: I wonder if the board layout has optional traces already to accomplish just that ?

Oh.. say, I've never seen an RGB LED strip in person, but.. aren't they the kind you just "cut to length" ?

In which case, the OTHER end of your cut strip might be opposite polarity..

Digging around some more, it appears there are also LED strips wired to match your controller, with a common (+) wire. Eg. This one from DX.

The LED strip's black wire is actually marked +12v, so it might be one of the strips you would think are wired for that controller. But it most definitely does not work if you apply +12v to that wire and then ground any of the color wires.

And the controller it comes with also definitely supplies (up to) +12 on the RGB and ground on the black.

The LEDs are all wired in parallel and connecting the wires to the other end doesn't have a different effect. It's the same from either end.

It would also not be possible to make this work only be changing around some components - the polarity at the supply would also need to flip, otherwise the black wire would still continue to receive +12 since that terminal on the outputs is connected directly to the corresponding VCC terminal on the supply side.

I'm going to take some photos of the strip and controller PCB and post them up.

In the meantime, found the same controller on Alibaba:
http://okled.en.alibaba.com/product/5212..._spotlight.html

Here are some images. Hope the traces and labels are easy enough to see.

What's the number on those transistor-like drivers? I cannot make out the part between the first "K" and the "A".

Thanks

Sounds like the factory messed up and accidentally printed up a common-cathode strip as though it was common-anode (which presumably they also make), then supplied it to your supplier as common-anode. You should take it up with your strip supplier, maybe they got a whole batch which were mislabelled...

Peter

The "missing" letter is an "I", so the part number is KIA50N06, a MOSFET transistor.

Here is a marked up image showing how to reverse the polarity to your LED strips. The black lines are where to CUT the existing traces (seven places in total), and the coloured lines show where to add new wires, with little black ticks indicating solder points.

Note that you can actually do the soldering at any existing blobs within the same strips, rather than having to scrape away a lot of green stuff to do them exactly where shown.

Cheers

Mark, it's an "I" (capital i)

Peter, I did write to the supplier, Hitlights.com (still waiting for reply), but even though the labeling may be incorrect, they are shipping them with small controllers that are wired correctly for the strips.

Since they also sell what looks like the exact same music controller, I asked about that too, so we'll see what they come back with.

Just saw the diagram Mark. I see you've made enough mods to rewire the polarity on all the terminals. I'm going to give this a shot - I think my soldering skill should be good enough with these large targets.

Any recommendations on how to best cut the traces on the board? Scrape them with a nail? Cut them with utility/x-acto knife?

Actually, the part I'm most worried about is soldering wire to points on the board where there aren't any existing pads (marked in green). Should I just scrape up a small area for the wire?

Here is a second version, same circuit as above, but showing one possible way to run the wires to existing solder blobs.

Great, mostly what I was thinking as well. I just hadn't taken the time to look for pads to use for the areas marked in green (the ground).

THANKS! It's early enough that I will probably try this today after a bite to eat.

Xacto knife: two cuts, slightly apart, angled toward each other, almost making a mini V-groove. Then just peel the copper away from between the two cuts. A gap of a millimetre (or more) is the minimum needed.



You can do it without any scraping, but for the red wires I personally would scrape away the green stuff to make room for new pads. That way I wouldn't be soldering too close to any components I might damage.

Cheers

If you do the red wires directly to the existing blobs, then use three individual wires, one for each transistor. That will be easier than trying to daisy chain a single wire like I drew above.

Cheers

When you finish rewiring, dig out an ohmmeter and measure resistance between the new RED and GREEN traces -- it should must NOT be zero!!

Cheers

Ok, just finished cutting the traces - before I saw your tip. I did something similar, but scraped the copper off between the two lines. Don't have an X-Acto handy (can't find it) so I'm using my trusty Stanley FatMax utility knife. Yeah, the same one I use for carpets, flooring, etc.

I tested for continuity before and after every cut to make sure that I was making a clean break. So far so good.

I'm not sure I can scrape the green stuff off of a flat area well enough to leave a surface suitable for soldering... I'll try.

A Dremel tool with a small grinding head might work for scraping.

When you get to soldering, USE FLUX. Even if the solder has a flux core. USE FLUX.

Cheers

Don't have any flux right now, but the flux-core solder worked well enough. Pre-tinned all the wires and didn't have any issues. I did three red wires as suggested and the point where all three attach is the ugliest part of the whole re-work

Everything seems to check out, but it's not working. The top two blue wires measure 4v and the bottom 2.5v

Can the wiring work the way it's illustrated above, with the constant voltage applied to the FET's drain instead of source? In other words, backwards from how the FET would normally work.

The current flow is from Drain to Source in the original circuit, and it remains that way in the modified circuit (unless I've goofed).

So it should work. But you did say earlier than you'd tried it with the power supply polarity reversed, and perhaps that damaged the controller?

I'll look at it again and think about it some more.

I'm unable to locate a datasheet for the transistors, so I don't know what the turn on voltage/current ratings are and so forth.

But a place to start is disconnect the LED strips, and then tell the controller to "turn everything on". Then measure the Drain Gate voltage at each transistor, the three readings should be identical.

The controller didn't get damaged - I checked voltage was working remote operated before doing the rework.

I'll check the gate voltage next. The info I browsed for FETS indicated current coming in on source, leaving on drain, controlled/modulated by gate.

It was all wired in this fashion except that instead of + it was all wired to ground instead. So the gate is wired to an IC whose PIN 1 is wired to the ground plane.

These devices can be made in either polarity. Some conduct from Drain to Source, and others go the other way round.

Given the way this one was wired originally, (+) connects to the Drain pin, and (-) goes from the Source pin. The modified circuit doesn't change that (in theory).

It should all still have exactly the same voltage drop between Source and Drain as it had before, but now there is going to be a different voltage between Gate and Drain than what was there before. I don't know if/how that changes anything.

GATE of each FET in orientation of photo (gate is the top leg of each FET) with color set to white (each FET getting constant voltage) and brightness set to maximum.

Top FET: 4.73v
Middle FET: 4.0v
Bottom FET: 2.75v

The Source leg measures exactly the same for each FET. And ON/OFF (with the remote) of the controller doesn't make a difference.

Ahh.. this might be it: on the copper side of the board, there are tiny little resistors near each MOSFET. One side of each resistor connects to the Gate, but I cannot see where the other side connects.

Have a look and figure that out for us, will ya?

If they connect to what used to be the big fat ground trace, then that's the problem. You'll need to somehow restore a true ground to that side of each of the resistors.