Cascade LED tube investigation

Today I decided to see if could figure out how those cascade LED tubes I mentioned recently actually work. Here’s one:

IMG_20140125_135428

 

They’re simple to take apart (I’ll leave re-assembly as an exercise for the reader πŸ™‚ ) – just remove the clear plastic heatshrink from the top and it all falls to bits:

IMG_20140125_135634

 

Here’s a closeup of one of the LEDs:

Nothing special then

Nothing special then

The first test I did was with the voltmeter. Connecting to “-” at the top of the board and then to each pin of the LED in turn I expected to find one that read 0V at all times. Nope. Both of the LED pins have a fluctuating voltage relative to the incoming “-” pin with one bigger than the other. Not sure what that means but we’ll try to find out. Incidentally the 5V incoming also has a fluctuating voltage relative to “-” πŸ™‚ – the PSU really is a piece of shit by the look of things.

Right, now for some more investigation…

Look at one LED

Look at one LED

I connected the end LED up to a couple of probes on the Open Logic Sniffer (and the GND probe to the “-” connection). That was as clear as mud. It looks like there’s some kind of PWM going on but that’s about all I can see really. I wasn’t able to relate it to what the lights were doing and there’s definitely a signal on both pins. Weird.

Taking a closer look at the chip…

mystery_ic

Hmmm….

Well that was useful. So it’s some kind of “no name” chip with 8 pins and a ground/heat dissipation pad underneath.Β Time to dig a little deeper…

Looking at circuit board traces

Looking at circuit board traces

As you can see, it’s not possible to see where the tracks go to try and associate pins with traces since they appear to duck under the chip. Not sure what good that would have done anyway, since I don’t know what the pins do but, whatever.

I wondered if sampling 4 LEDs at once would shed any more light on things…

4 LEDs, 8 pins to measure

4 LEDs, 8 pins to measure

This time, the answer was conclusive…

As clear as mud...

As clear as mud…

That’s a “No” then πŸ™

Time to put this away and not worry about how it works. I think I’ll just appreciate them for what they are πŸ™‚

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