Minimalist Xmas light controller

I've taken a few off in the past to see if there's text underneath, but none of them had text so far.

Big Clive

Might be worth breaking out the heat gun and checking the underside of that IC if you want to find a part number. I found some of the far-East microcontrollers and flash ICs seem to have their part numbers marked on the underside. Some of the Sonix SOIC parts are like this, not sure what other brands do it.

They are, but sometimes it's hard to tell what you're going to get.

Big Clive

I still have one or two sets of lights that plugged into the mains with no transformer. For eg each bulb in a 20 bulb set had a 12V filament, connected in series. But if one failed and you managed to touch any metal in the socket, you'd get a mains voltage zap! When cold, filaments have a much lower resistance than when hot. I haven't plugged them in for years, they're in the Old Format Museum. But hey, mains voltages plus cheap lights plus a flammable tree, what could go wrong?

Nigel Walker

I wonder if the phosphor based red and yellow LEDs are available on their own through the likes of AliExpress or eBay.

Seán Byrne

It sounds like an invisible broken track. Try gently probing with a continuity tester to validate all the connections.

Big Clive

I didn't realise the PICs could sink and source such a high current. Unless that's the chip total. The crystal is for the 6 hours on and 18 hours off timer. I tried implementing it on a PIC12F629 using the internal oscillator and it drifted wildly with battery voltage.

Big Clive

The pinout looks like the 12C508, whose datasheet says port pin current is 100mA max. If so, I don't understand why they've added a crystal. The 508 has good enough internal timing for Christmas lights.

Mike Page

I've got one of these that failed! It seems to briefly come back to life by flexing the circuit board, but will not stay running no matter what. I was hoping I could repair it since the LEDs are a nice purple color. I've looked under a microscope at the joints and all seems fine with the exception of a small dent on the crystal housing... I'd appreciate any thoughts!

I have a couple sets from last year with this exact feature set. "Slow fade" is the only setting that is tolerable IMO. And yes, it's also a bit shit.

I wonder if a small bridge-tied-load audio amplifier chip could be abused for this. Should be easy to build an oscillator around one. Something like TDA2822 or MAX9716 ?

David Reader

I miss the old ones that you plugged into the mains. Saved all the bother of changing the batteries when you leave them on all night. Disability and Christmas lights don't go together Clive.

Jeremy Travis

Sequential "not that exciting", slow glow "terrible", Chasing flash "alright, a classic", Slow fade "also a bit shit" ! Clive's Analysis? Brilliant! - The Big Clive guide to lighting effects! Each set should come with a Big Clive guidebook. Great insight into the circuitry and the reason that powering these with a USB power pack will be somewhat underwhelming.