Extending lights which already have a controller?

[Cheater]

It seems like setups could be simplified significantly if you get LED strings which can already fade and do patterns.
Then you can unscrew the box, chop out the chip, attach your own PWM controller to the outputs and then your done since all the circuitry for handling the mains power is already there for you. :D

I'm just starting my collection this year, and I've got experience with microcontrollers (especially AVRs).
So I've bought 5x 10 meters of LED christmas lights which already do patterns off ebay and they are in the mail at the moment.

I've been skimming this forum and the wiki but I havent seen anyone mention doing this before?

[David_AVD]

Some of the controllers that come with typical strings are pretty dodgy to start with. They usually make them only just good enough to work with the string to keep costs down. Interfacing to them could be difficult and potentially dangerous IMO.

[wjohn]

Cheater,

The best option is to remove the controller (MFC) completely. I have seen a number of the MFCs, and the workmanship is fairly poor.

Trying to interface into the IC controller would be problematic, of the 6 builtin programs, it would be hard to know what one the unit will start in, and who to 'step' them thru to your selected sequence. I'd be more incline to watch the programs and get a feel for how you could replicate some of them in vixen (with better control).


The overall design is the same for 240 and 24 V versions. the Board is designed a single chip controller, and 2 to 5 SCRs to switch the load.

AC is rectified by a full wave bridge (normally 4 diodes), a Zener diode is used to provide a 5 Volt rail for the IC, and a sample of the AC is used by the IC to calculate ZC.

The Common is generally the positive rail (for 24 VAC, this will be unfiltered DC at over 30 V DC), and the SCRs are Sink switching to the negative rail.

Removing the controller, you will end up with a string that can be controlled by a AC SSR (single channel) or DC SSR (multiple channels).

There will be a need to measure and adjust current flows thru the LEDs. I have generally found that the LEDs are being drive at or over 20mA.

There were a lot of discussions on the BIG W string thread on ways to normalise the current on those strings, the concept is the same for MFC strings. Most will just need a low ohm value resistor added to the negative line to limit current flow thru the LEDs.

hope that helps.

[Cheater]

The best option is to remove the controller (MFC) completely.
Thats my intention. :)
Ditch the chip which has the preset patterns but keep the support electronics.

While the circuitry may be dodgy, I'm kinda lazy and it saves quite a bit of work. ;)
Hong Kong quality should do the trick....just.

I have to wait for them to arrive but that information should help me a lot. :)
If the IC runs on 5v then I'm thinking of simply using a optoisolator or similar to trigger the lights.
Less parts and simpler that way.

[David_AVD]

Part of the problem John & I are alluding to is you'll probably waste more time and money than it's worth trying to part of the original controllers.

If you're just keeping the switching section, then that's only four $0.50 TRIACs. You'd still need to add opto's etc.

[wjohn]

There is no optical isolation on the MFC, I would not recommend any galvanic connection of your PC to your lights, a small amount of induced voltage on the lights/controller/PC is a recipe for upset/tears/ broken PC...

Majority of the SSR designs have a 4000V isolation coupler as part of the design. MFCs dont include this part as they have no connection to any other device and are double insulated for user protection.

[Matt_Edwards]

Crapper triacs and PCBs are no excuse for dangerous installations.
I understand your desire to do as little work or conversely re-use as much as possible, but safety must come first. John rightly points out the isolation of Optos, they are used for you and your viewers protection.

Anyway welcome to the hobby of Blinky Flashy. More AVR types are always welcome to offset the evil PIC balance (just kidding!)

[Warlock]

Cheater I have tried something like this...With the simple diodes that are in most of these sets to control the patterns it is not worth it to use any of it at all.You can simply wire it all together (into one set) and control it allot better and safer then with that stuff left intact..Please understand this advice is coming from someone who has tried (with not listening to the advice of allot of members here) and had bad results..SO believe me when I say this..Try what is trusted and what these guys (who are doing this so seeing is believing) are saying as your best interest and less time and money in the long run...

[Cheater]

There is no optical isolation on the MFC
No no I'd be adding the isolation of course.
As far as I can tell the USB spec says 'release magic smoke when exposed to 240v' ;)

More AVR types are always welcome to offset the evil PIC balance
GCC makes them a winner for me. :)
Easier to get from where I am as well.

Please understand this advice is coming from someone who has tried (with not listening to the advice of allot of members here) and had bad results
I dont have them yet, but when I get them I will check the insides.
They may be the mythological type which uses quality components. :P
Then again I might have to scrap the circuitry completely.

[David_AVD]

I don't have them yet, but when I get them I will check the insides.
They may be the mythological type which uses quality components. :P
Then again I might have to scrap the circuitry completely.

I think you'll be under-whelmed! LOL

[Cheater]

Grabbed some from a store and yup, dirt cheap components. :p
I would tap the existing circuitry if I didnt have to turn the enclosure in to small chunks of plastic.
Damn IP44 waterproofing and the glue inside.

They use a 24VAC wall wart with 4 rectifier diodes on the board.
The chip magically makes 5v (well 4.2v) from what I assume are zener diodes.
There are two strings wired to a common positive rail, and each string is operated by two SCRs. No clue whats happening there except it looks like the board might have been designed for 4 channels.
Each string seems to register ~14v. No clue where that comes from.

Attached is a photo of the board with the traces overlaid.