Some questions regarding a Christmas light circuit board

MillenniumFalsehood · Mon Dec 01, 2008 12:17 pm

Okay, here's two pics of the boards I managed to salvage when our family switched to LED lights this year:

http://i60.photobucket.com/albums/h4/Mi ... rds001.jpg

http://i60.photobucket.com/albums/h4/Mi ... rds002.jpg

Can someone tell me:

a) if it's possible to hook up these boards to DC current?

b) if it's possible to mod them for DC?

c) if they'll accept low (i.e., 12v) voltage?

Scott Hasty · Post by **Scott Hasty** » Mon Dec 01, 2008 5:29 pm

Those traces look a little fried...

I see what looks like a full wave bridge rectifier (will convert an AC sine wave to DC), but I don't see a transformer. You'd need this to step down the 120VAC to a usable voltage before being converted to DC.

I tried to search for a datasheet on those chips, no dice...

Was there anything soldered to the "starburst" or was that a rotary switch assembly?

Sparky · Post by **Sparky** » Mon Dec 01, 2008 5:37 pm

I'm guessing that it runs off 120 v rectified, was there a wall wort with it? It's probably pretty dirty but there's a cap in there to filter it. It is also possible that the custom chip in there has a regulator build into it.

There is a plus on the board, if you check from there to ground (or the neutral on the house wiring side) you should see the rectified and filtered voltage (its kind of DC at this point).

Scott Hasty · Post by **Scott Hasty** » Mon Dec 01, 2008 5:40 pm

Sparky wrote:I'm guessing that it runs off 120 v rectified, was there a wall wort with it? It's probably pretty dirty but there's a cap in there to filter it. It is also possible that the custom chip in there has a regulator build into it.

There is a plus on the board, if you check from there to ground (or the neutral on the house wiring side) you should see the rectified and filtered voltage (its kind of DC at this point).

That means they're running the LED's in series. If that's the case, I'd be careful. Probably not enough current to kill you, but 120V will knock you for a loop.

What do these boards do anyway?

Sparky · Post by **Sparky** » Mon Dec 01, 2008 11:40 pm

If there's a wall wort it could be anything like 9 V. Lucent brand answering machines (the one I had and my parents had) had 9 VAC wall worts. all rectification and regulation was done in the unit.

MillenniumFalsehood · Post by **MillenniumFalsehood** » Tue Dec 02, 2008 1:42 am

Scott Hasty wrote:Those traces look a little fried...

I see what looks like a full wave bridge rectifier (will convert an AC sine wave to DC), but I don't see a transformer. You'd need this to step down the 120VAC to a usable voltage before being converted to DC.

I tried to search for a datasheet on those chips, no dice...

Was there anything soldered to the "starburst" or was that a rotary switch assembly?

The traces are covered in a grease of some sort to lubricate the switch; they're not burnt. The starburst is the switch mechanism; it clicks into place due to the spring loaded metal strip.

There was no wall wart or anything like that, but it did come with a fuse assembly in the plug; is there some off chance they provide a lot of resistance?

The boards do several things, all selected by the rotary switch: chaser, flasher, burst, steady on, etc.

I should also mention that the two in the second pic are identical and that they ran bulbs, not LEDs.

Sparky · Post by **Sparky** » Tue Dec 02, 2008 11:50 am

runs off of >120 volts. That is after rectification and a little filtering you'll not get a the peak 120 volts. you probably get around 110 VAC anyways so after processing that it will be even lower. Either way it'll need a lot of battery to get the same effect.

Pat Amaral · Post by **Pat Amaral** » Tue Dec 02, 2008 12:43 pm

My guess it those boards weren't meant to drive LEDs. I doubt that chip is anything more than a custom brute force sequencer and the transisters are there to provide isolation for the four series strings. Since the chip is probably built to run off 110v rectified, it probably wont function on anything lower than that. I agree that, with just that simple filter on the output of the rectumfrier, the signal is going to be pretty dirty. I'd bet it needs a pretty substantial load too (100 lights or more). In my opinion, it wouldn't be very practical to use a DC source to drive these things.