Some news about my christmas lights

So today I was able to ask to a couple of friends who knows electronic way better than I do, and they confirmed what I was already thinking. The IN4007 are actually 1N4007 diodes, simple 1000V-rated diodes, and the way they are used is just a standard Graetz bridge (a rectifier bridge).

For those who want to see what I’m talking about, I uploaded the photos on Flickr, see the set here .

After passing through the diodes, the 220V AC wave is replaced by a (very bad) approximation of (about) a 220V DC supply. I wonder if it was the unstable supply (there is no capacitor to smooth the wave) that blew up the SCR.

The 180KΩ resistor is part of the CR/RC net (not sure what it is yet, I haven’t dug that up, as I don’t much care), together with the capacitor; they are used as a timered trigger for one port of the actual controller, so I’m counting them off, as I need to replace the thing anyway.

The 240KΩ resistor is used to reduce the voltage that powers the controller, not knowing the current absorbed by the controller, it’s difficult for me to guess which voltage was given to the controller. I could probably just plug the thing in and take a look with a voltmetre. It’s anyway superfluous, as the controller is, once again, something I want to get rid of.

Now what I know is that the lights are powered by DC, there’s no resistor, so the direct output of the bridge is used, they probably don’t need the supply to be stable at all.

So now I know something more about the thing I’m working on, which is an interesting thing. Now I just need two ideas to complete the basic design of the thing, so that I can move to a proper design with microcontroller and code.

The first idea is how to reduce 220V DC to something usable for the microcontroller supply; for smaller voltages I usually used LM7805, but the LM78 series does not support voltages higher than 40V; a quick search around suggested that the LM78S series could actually support 220V voltage, but I can’t find any datasheet of that series, nor I can find the ICs anywhere around.

The second idea is how to dim the lights; what I was thinking of was using a digital potentiometer, I know I seen some of those around, but I’m not sure if they work well with a 220V passing voltage, and how easy are to actually program.

I’m also wondering if it’s easier to get an IC for the diode bridge or just using the four diodes as the current PCB does (adding a capacitor to smooth the output); I seen Texas Instruments have DIP packages with two or four Schottky diodes, but those are rated only up to 50V, I need at least 240V.

Any suggestion is welcome :)

Christmas tube lights

So, my mother is preparing the house for Christmas, yes it’s tremendously late, but this year we had some problems, somehow related to my health condition.

One recurring problem with Christmas time, is when the lights break. In most cases the lights lasts for enough years to let us just throw off the broken ones, and get new ones. This year, though, a tube of light broke down, this was bad because I bought it just four years ago, and they aren’t as cheap as standard lights.

So I opened the controller box on the cable to check it out, and indeed, one of the ICs was burnt down. The IC is a PCR406J, produced by UTC. For what I gather on Google, this IC is used in mass production of Christmas light controllers, it works directly on the 230V alternate current, although I’m still not sure *what the IC does*… (the best I could find is that it’s a Silicon Controlled Rectifier I can’t seem to be able to order that IC anywhere on my usual webshops, and also for what I read it’s also hard to find in standard shops; also, the lights controller might as well be fried, if something was able to fry this IC.

So what are my current options? The first and probably easiest is to throw away the tube, and buy a new one. But it’s not funny to do.
The funny thing to do is… design a new controller! :)

I certainly won’t be able to design it before this Christmas, or before the end of the holiday season, but I can try for next year’s at least. It will be a nice project to distract me from other more complex stuff, and might finally give me the time to refresh my electronic skills, as I don’t want to die knowing to do just one thing (developing).

Right now, I need to find how the thing works: it’s entirely AC-powered, no transformer or converter of sorts. There are the two PCR406J, a 50V 10µF capacitor, two resistors (one 180KΩ, one 240KΩ, neither seems to be ready for high power dissipation), and four things that are probably diodes, they seem to be IN4007 from DC Components (they are Rectifiers, but I admit I don’t know what they are or what they actually do). The board is certainly handmade, and the only two components I could track down to a producer, are Chinese, so I suppose the whole thing is Chinese.

The lights themselves look like a lot of LEDs, but I somehow doubt they are actually LEDs, probably some gas lights or something like that. The lights are connected through three wires, one red and two black wires. I know there are two series of lights, so one is the common (probably the red one), and the other ones are returns for the two sets. Also, as one of the programmed modes had the lights fading in and out, I’m sure that they work at different voltages, and they decrease their luminosity depending on the voltage they are given.

I start to doubt they actually use 220V and even less that they work on AC, as the red wire is connected to two rectifiers, each of one connected to one of the two mains’ wires. I suppose this could be the part of the circuit that straighten AC into DC, although I’m by no mean expert of that. The 220V idea was mostly killed by the 50V capacitor, and the size of the two resistors.

This is the time when I’d like to have a controllable power supply like I had in the lab at school, to check out which voltage do the lights take correctly.

Actually, I think the capacitor and the 180KΩ resistor could actually be an RC net, which makes sense, as the controller changes the program after a few seconds. So I should probably ignore those two, as they are part of the controller. There is also a button used to change the current program, but that just concerns the controller circuit which I don’t care about.

The controller is connected to the two SCRs (PCR406J) by two lines, which are, as far as I can see, connected the gates of the ICs. Which makes sense, as the controller decides when to turn on either of the lines.

I have doubts right now on how the thing the fade in/out thing, as that was a pretty nice effect.

Now, I suppose it shouldn’t be too difficult to design a new controller, maybe with some extras like music (this one does not support it), through a programmable (versus hardwired) microcontroller. It might not be convenient (as in it could probably cost more than a new tube of lights) but it would be interesting.

My main problem now is how to control the lights, do they work in DC or AC? Which voltage do they support? If they work in DC, I suppose I could get the fade in/out effect by using a potentiometer, a digitally controlled one for instance, or by using two properly sized capacitors.

If I need DC, I can use that to power up the microcontroller, otherwise I can simplify things by using batteries to power it.

Anyway, this is the start of a new project for me. If someone can help me by providing information I might be lacking in all this, it’s certainly welcome. As it would be welcome a configurable power supply, or at least some idea on where to find a cheap one.

Oh by the way, there’s a good side to writing your own lights controller if one breaks, I think and hope: it should produce less waste to just create a new controller rather than throwing away the old lights and buy a new tube.