14 November 2019

Bipolar Christmas LED lights memory hack

LED controller with missing memory chip

After I moved to a house, I wanted to have LED lights around the roof for Christmas. I bought some cheap leds in the local store and mounted them around the house. Everything was great except one thing - after you power off the leds and power them on again the next day, you will need to press the controller button 6+ times to have the leds always-on without them flashing crazy all the time. Since I was manually unplugging/plugging the led lights in the socket that was not a big issue, however I decided to add Sonoff wifi relay and set the lights to switch on after sunset and switch off at midnight. But I still needed to manually press the controller to activate the non-flashing state of the lights. That's when I decided to take apart the controller and see if I can make the steady lights permanent.

To my surprise I found that only two wires are being used to flash the lights. That means that the controller outputs AC-like current but with higher frequency. The power adapter is rated 31v so if the lights are bipolar then we get somewhat around -15v to 15v switching at 240hz (tested that with osciloscope).

At this point I had two choices - either I create my own controller based on 555 IC timer chip or I make the current controller do what I need. After I took the chinese controller apart, I found out that there is missing a chip on it. I could not read the model number of the controller chip (it looks like XHH1410B but nothing comes up on google) so I searched around if someone had a similar issue... And I found this youtube video which was exactly what I was looking for. The controller in the video was different, but the idea was the same.

24C02N chip

The video author recommends using 24C02B chip but ended up ordering 24C02N. I ordered N version and also M version because in my local store M version was SOP8 but N version was DIP8 (meant for plugging in a socket). It looks like aliexpress have N version as SOP8 as well. You can order 24C02 by searching "24c04 sop-8"

I soldered the chip on the controller and now was the moment of truth - I powered on the unit... as expected the lights were blinking. Then I changed the programm to always-on and unplugged the leds from power. After plugging the power adapter back in the leds were not flashing. Complete success, the chip worked. Now I have my always-on Christmas lights come up on sunset and I don't need to change the controller program anymore...