Christmas light mod

martinsvi

this topic really has nothing to do with radio, but since I didn't find any DIY electronics forum and I suppose a lot of the forum members here are somewhat familiar with some DIY electronics anyway - I'll post my question here:

I bought these lights from argos - http://www.argos.ie/static/Product/partNumber/2427447/Trail/searchtext%3ECHRISTMAS+LIGHT.htm

and I'm using them with a timer. The problem is that every time they come on they have no "memory" of the setting that was chosen and they turn on in one of those epileptic-seizure causing randomly blinking modes that is super annoying. One of the other light sets (different type) actually "remembers" the chosen setting even after spending whole year in the box in the attic

now my question is

a) can I do some modification to the schema itself to make it remember the setting
b) can I just cut off the schema box all together and simply connect the lead to the power supply directly to give me a steady light? There seems to be no power converters in the box, just the PCB and a button for changing modes.

GekkePrutser

Yes it would be nice if there was a diy electronics forum. But every radio ham should indeed be very familiar with electronics as we have to pass an electronics exam to become one.

The easiest thing you could do is measure the input voltage into the controller box and the output of it in 'steady' mode. If it's the same you should be good. Of course you'll need a multimeter.

Please note though that it might be doing PWM (rapid flashing to reduce brightness) even in steady-on mode. If so it might mean the lights will be brighter if you do this, and worse, the transformer might not be rated for continuous power draw of all lights.

So I'd check the current the output side when you have all the lights on and see if it matches the rating of the power supply. It should be written on it.

Also note that your multimeter will have to have a high-amp mode if you want to measure the power draw. If you don't have this or don't know how to measure all this it'd be better to ask someone you know that's into electronics a bit Saving a few button presses is not worth the risk of burning your house down no matter how small the risk.

martinsvi

ok so here's where I am - there was no way to measure anything in the controller - there was glue everywhere. I took my chances and cut of the box and wired it direct - now every second light doesn't light up. After loads of googling I was surprised how many like-minded people are out there facing the same issue. Anyway, most articles suggest that for the lights to be used without the controller it has to be replaced by a diode bridge (rectifier). So I had a couple of 1N4002S lying around and decided to make one.. unfortunately without any joy, lights didn't came up and I can't figure out why? the power supply is rated for 38V, some good few amps (it was either 5 or 8, can't remember, it's in the shed now and I'm not going back out there. looking at the specs of 1N4002S, it appears that it's rated for voltages from 50 to 1000V, but then the current is just 1A.. is it the current or the voltage that was a showstopper for me I wonder?

Anyway what I'll do is I'll have a dig through my companies warehouse, I think there were few server PSU's that are written off, I'm sure I can take one apart and hopefully find my rectifier there...

martinsvi

having thought about it, you are probably right about the rapid flashing, nothing to do with AC/Rectifiers, the PCB alternates the current direction making both circuits seemingly light up while they're actually flickering in high frequency, not visible by a naked eye. That explains why half of the leds light up while connected directly and the other half goes up when the polarity is reversed. Ugh, now what do I do now...

GekkePrutser

Yes if that's how it works then a rectifier won't work. What you need is an inverter (which is much more involved than a simple passive component).

It makes sense actually, because LEDs only emit light with the voltage in one direction (and allow no current to pass in the other), they are probably mounted in a 'back and forth' fashion. That keeps the construction of the cable simple with no extra components and still using only 2 wires, while still allowing 2 separate groups of LEDs to be controlled. Smart idea actually

If it's indeed wired like this then you'll never be able to let all the LEDs glow at the same time so pulsing it with AC is the only option. Perhaps getting an AC transformer would do the job but what you really need is a square wave, not a sine wave.

The control box will contain an inverter circuit suitable for the job that you might be able to isolate on the PCB but if it's covered in glue that's probably not feasible.

What I'd do is look at the output of the control box with an oscilloscope, to see what it's really doing. But that's a hard thing to come by if you're not into electronics.

PauloMN

Have learned a bit on this thread, and also seen that I'm not the only one with the Christmas lights problem!!

When you cut out the box Martin, did you leave enough wire on it to put it back in?

martinsvi

PauloMN wrote: »

When you cut out the box Martin, did you leave enough wire on it to put it back in?

I wanted to but my clumsy hands failed to deliver...


anyone got any simple inverter circuit diagrams? I found the one below but I don't need the transformer piece and my tired brain can't quite figure out how to get rid of it - http://www.electronics-microcontroller.com/electronicsfile/circuit/POWER-INVERTER.GIF

95% of inverter diagrams contain tranformers or ic555.. don't have 555, have some similar ones but really the saddest thing is I was building these things at school million years ago and now can't remember a thing...

GekkePrutser

martinsvi wrote: »

anyone got any simple inverter circuit diagrams? I found the one below but I don't need the transformer piece and my tired brain can't quite figure out how to get rid of it - http://www.electronics-microcontroller.com/electronicsfile/circuit/POWER-INVERTER.GIF

95% of inverter diagrams contain tranformers or ic555.. don't have 555, have some similar ones but really the saddest thing is I was building these things at school million years ago and now can't remember a thing...

Too bad you can't attach the original module

Oh yes the ne555! Or other versions. Those are often used in timers, should work fine yes. Maplin sells them for 1 pound (probably 2 euro here). The datasheet contains some reference implementations. I also found this link that looks like what you're looking for. In this case you'll need to switch some serious current though (based on the rating of the PSU) so you'll need some power transistors.

I've never built an inverter, I've built some simple timers with NE555's in the 90s, though nowadays for that sort of thing I would just take a PIC/Arduino (e.g. adafruit trinket, that sort of thing), they cost half nothing and are nicely upgradable (so you can recreate the hated flashy modes ). I wouldn't be suprised if the original box worked this way.

That would work for the timing, and then something to switch the power. It will have to be solid-state, perhaps two solid-state relays would do! I'm not that good on power electronics myself but I assume it wouldn't be too hard to do with sufficient cooling. Perhaps you could even salvage some components from the controller box if you can get the glue off somehow.