Question about modifying the PCB in the USB plug of an LED fairy light string

Thread Starter

LaimaB

Joined Mar 9, 2024
2
Hi - apologies for another question about fairy lights, but I'm wondering if someone can help me figure out what I can do to bypass this really horrible 8 options of blinking patterns (with no memory on what was set), so I can just have solid(ish) lights on.
These lights are reversing polarity to manage the blinking patterns, so I can't just replace the plug, but I'm wondering if there are bits that I might be able to solder to make the pattern appear solid (which is the eighth button press).
I've taken the plug apart and took pictures of the controller, but I'm new at this hobby and can't figure out what is driving the patterns and polarity switching. The first picture shows the ?FET? bent over the little controller, then I noticed it was covering something so I lifted it up and got a better picture of the controller underneath.2024-03-10 17.56.07.jpg2024-03-10 17.56.13.jpg2024-03-11 00.42.17.jpg
I've tried to search through the other posts asking similar questions about these controllers, but this PCB is different from the ones I saw in the older questions.
Would anyone have suggestions about what I could try to make these stop blinking?
Thank you!
 

Ya’akov

Joined Jan 27, 2019
9,264
Welcome to AAC.

Unfortunately, what you have to modify is not on the board and accessible to a soldering iron, it is in the rectangular 8 lead IC, specifically in the non-volatile memory of that little custom microcontroller.

You could build an alternative of your own relatively easily, at least couple of ways. Keep in mind, choosing either one, you would find a lot f help here to make it work. People tend to be very generous with time and expertise, and while this project may appear to be a steep climb, they are already at the top with long lines they can drop to pull you up—so don’t let the learning stop you.

1. A (kind of slick) substitution of an MCU you can program (pretty easily, using the Arduino ecosystem) that uses the same size package. You might have to perform a little surgery on the PCB, but with some luck, the power and ground pins on the MCUs will match up.

1.1 Alternatively, still using a small MCU (Like the ATTiny13A or 95) and Arduino ecosystem, just on your own board—designed and manufactured (cheap, easy) or using a protoboard, “manhattan”, ”dead bug”, or some other style fabrication.​

2. Make your own circuit using the cheap, ubiquitous, and versatile 555 IC. You’d need a few components in addition but the circuit would be simple and it could be constructed using the ideas from 1.1 above. The 555 is amazingly popular and a lot of folks here enjoy designing application circuits for it.

Both methods will get the job done, both will teach you new skills—but I think 1.x offers a way to enter an entirely new world of possibilities. The ease of use and incredible capacity of the Arduino ecosystem is very compelling. Once you build one thing, and see how easily you can interface a tiny computer to sensors and actuators and make your program’s code change the physical world you‘ll see all sorts of reasons to do it.

Either way, or if you choose, no way—good luck in the future.
 

Thread Starter

LaimaB

Joined Mar 9, 2024
2
Thank you for your very supportive answer Ya'akov! My kids have asked me to keep lights up for holidays, and these are the Easter lights that have "smarter" switches on the decorations, which don't fit with my Hubitat automation and themes.
I want to investigate the suggestions that you gave me, but it won't be in time for this Easter!! For the ones that don't have the reverse polarity, I was able to replace the plugs with regular USB, working out voltage and milliamps and resistors. I'm early on in learning all the pieces, and have the "Make: Electronics book to work through, which has been helpful. I have an Arduino learning kit for the next steps, so eventually, I'll see what that can do!
Thanks again for the suggestions!

Laima
 

Ya’akov

Joined Jan 27, 2019
9,264
Thank you for your very supportive answer Ya'akov! My kids have asked me to keep lights up for holidays, and these are the Easter lights that have "smarter" switches on the decorations, which don't fit with my Hubitat automation and themes.
I want to investigate the suggestions that you gave me, but it won't be in time for this Easter!! For the ones that don't have the reverse polarity, I was able to replace the plugs with regular USB, working out voltage and milliamps and resistors. I'm early on in learning all the pieces, and have the "Make: Electronics book to work through, which has been helpful. I have an Arduino learning kit for the next steps, so eventually, I'll see what that can do!
Thanks again for the suggestions!

Laima
Well—quick and dirty answer is: run the strips from AC. Use a transformer that drops the mains to the appropriate voltage. Half the time one polarity will be on, half the other. There may be a bit of flicker, but if it is really troublesome you might be able to clear it up with a pair of capacitors.
 
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