12v Chinese LED strings. Proper controller advice.

[Diabolical Artificer]

My daughter bought these and they weren't exactly cheap - £17. Unfortunately she can't remember which purveyor of cheap tat she got them off, I've looked so a refund is out of the question.

The device in question comprises of about 6m of LED tape with four wires out, these plug into a "controller" box, which has an infra red or similar LED flopping about on a length of 3 core, two 8 pin chips on a board, one has it's ID scratched off ( I expected a micro controller), 12v goes into this from a cheap ar*e power brick. Lastly there is a horrible remote, which is a thin matrix thingy, like on a calculator with a chip on board.

The fault is that the LEDs get stuck on one colour and won't flash. I had a quick look yesterday and scoped the infra red LED on the remote, all I got was a LF distorted sine wave, no pulse width change etc.

Rather then mess about trying to fix this pile of wombat doings and as the LED string doesn't look too bad, can anyone suggest a controller kit or similar. Searching on ebay etc just gives you pages and pages of similar s**t. I presume a controller works similar to a TV, IE mixing the red, green, blue LED's to get different colours, with maybe a pulse width modulated PSU. Would a 555 do the job here?

Attached pics, parental advisement warning - images of horrible electronics, Andy.

[brunel]

If the payment method was PayPal, the seller could be traced via the PP account.

[Herald1360]

TBH that electronics doesn't look at all rubbishy, though I can't comment on the wall wart bit.

Looks like three simple common anode chains, one for each colour. Probably a mix of series and parallel for each colour- presumably the RR, GR and BR resistors are limiters to keep things happy on 12V supply.

Try gently prodding the chains with a current limited variable supply to see if applying straight 12V seems reasonable in terms of current and brightness.

Controller would ideally involve clever stuff with a PIC or similar, but a few 555s and a bit of logic could give a range of interesting effects.

[Diabolical Artificer]

Payment was via card brunel, paperwork lost & have tried every mean possible. It's academic anyroad as I've trashed the case.

They've never worked Chris, the 12v brick is intermitant, the controller has splashes of solder on the board as well as atrocious hand soldering, so it's possible the chips have been shorted.

"Try gently prodding the chains with a current limited variable supply to see if applying straight 12V seems reasonable in terms of current and brightness." I've done that and 12v 3A seems about right although the SMPSU brick says it was rated at 5A however the thing is light as a feather compared to proper SMPSU's I have.

So a 555 might do the job, rather than use a remote I wonder if I can use a few momentary switches? I think flashing on/off to varying speeds and a bit of colour changing might do the job. I'll look online and see what I can find.

Andy.

[Herald1360]

Is that 3A 1A per colour or 3A each colour? Either way you'll need some reasonably watty switching devices. Logic level mosfets perhaps easiest to drive. For different colour mixes maybe reduce drive to R/G/B as required with added series resistors. Probably easier just to do a few different twinkly patterns with varispeed 555s plus an all on steady mode.

If you use unsmoothed DC for the LED supply you could use thyristors as the switches- the dead zone in the current from the LED drop should be adequate for commutation.

[SiriusHardware]

To get on with diagnosis of the original problem, try swapping the wire going to the LED string the unit gets stuck on - if that can be determined - with the wire going to another string. Does it get stuck on the same LED string, or on the same driver output?

If you are determined to make your own controller then off-the-shelf micro boards like the Arduino family have 'analogue' outputs which are actually digital PWM outputs - use as many of these as there are LED strings to drive MOSFETs or whatever switchers you prefer. You just use a line of code to tell the Arduino what 'value' to output to the 'analogue' pin and it will then maintain the appropriate PWM mark-space ratio on that output until you send it a different value.

A word of warning - high current PWM going through a long string of LEDs is just about the worst thing you could inflict on your own HF radio reception.