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.

3 thoughts on “Christmas tube lights

  1. My electronics is pretty rusty, however your main questions is answered in one of the pdfs you link to. The IC that went up in smoke is a rectifier. So it converts an AC-input voltage to a DC-voltage. I don’t see immediately what the output voltage would be.Unfortunately the rest of your writing is difficult to follow without a schematic drawing. If I remember correctly the IN4007 would be a diode, these are often used to reduce the voltage to the desired voltage range, just because these diodes give you a 0.7V voltage drop accross it.ps) The main text-book on electronics is probably The art of electronics by Horowitz, although heavily dated nowadays.

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  2. If you just want to make the tubes light up, you can connect a non-polarized capacitor in series to the lamps. The capacitance would need to be chosen according to the power rating of the lamps.If the lamps are actually LEDs, you will need to connect a diode and resistor in parallel to them, to allow the capacitor to be discharged.Concerning the IN4007: if they are not arranged like a rectifier, it might also be that not the 0.7V forward voltage drop but the 110V reverse drop is used.

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