Half my LEDs don't light up. - Page 1
Forum section: electronics / beginners

author: JustTheTip
author_rank: Newbie
timestamp: April 19, 2025, 05:21:40 pm
content: Hello,The answer to this is going to be very simple but I have basically no experience with electronics so I won't work it out on my own.I purchased these LED fairy lights from Ebay...https://www.ebay.co.uk/itm/364043540168?var=633363858088They're powered by a USB type plug that has a small circuitboard which allows them to flash in about 8 different ways. However I just want them to be lit solidly without flashing and selecting the non-flashing option means pressinbg the button 8 times every time I turn them on.So I googled for a solution and found this video which I followed...I ordered one of the voltage regulators used in the video instructions from Amazon, linked below.https://www.amazon.co.uk/dp/B07DYP6L35/ref=cm_sw_r_as_gl_undefined?linkCode=ml1&tag=theurbanexplo-21I cut the USB flash controller plug off the LED string and attached the LED string to the voltage regulator (set to 4.7V) and it worked...the lights came on and no flashing...Only not all the lights are lit. Every other LED on the string is not lit...One lit, the next is unlit, the next one lit, and next one unlit, all the way down the string to the end...What's going on here then...? How come these LEDs don't all light up together...? I tested it by reataching them to the original USB flashing controller plug and they all lit up again, but not when I bypass it and just plug them stright into some power via my voltage regulator.As I said, the answer is going to be very easy for someone who knows about this stuff but I've really only just started doing electronics and I know morre or less nothing. My school boy memory remmebers something about bulbs being lit in poaralel and in series. Is it something to do with AC vs DC power...? I dunno...any ideas...?

author: themadhippy
author_rank: Super Contributor
timestamp: April 19, 2025, 05:26:14 pm
content: often these things work by reversing the polarity,so you have half the leds one way around and the other half the other way around.To acheive that youll need to build something toreverse the polarity at a fast enough rate not to notice the flicker.

author: JustTheTip
author_rank: Newbie
timestamp: April 19, 2025, 06:11:21 pm
content: I think it's got something to do with them needing to flash when connected to their original USB controller. If they were all wired up together then getting them to flash alternately wouldn't be possible. Having every other LED wired up to each other allows for them to appear to flash alternately rather than just flashing with them all on and then all off.But the last of the 8 settings had them all onconstantly, which is what I want...I just don't know how to achieve that now I'm powering them without the original controller...

author: themadhippy
author_rank: Super Contributor
timestamp: April 19, 2025, 10:31:13 pm
content: First thing to do is reverse the polarity and see if the leds that are on and off swap over.If thats the case as mentioned above you need to build something to do that,plenty of ways to skin the cat but id most probably go with a simple oscillator using 2 schmitt inverters and a third inverter to also get an inverted output,the good ole 7414 would do the job nicely. and use both outputs to control an H bridge