Removing Cycle function - Page 1
Forum section: electronics / projects

author: havok44
author_rank: Newbie
timestamp: July 15, 2021, 09:16:18 am
content: Hi all, I have a kmart led string light that has 7 different modes. Soon as you turn it on it runs through all 7 modes and is very annoying.I have to press the mode button 7 times to get to always on as its the last setting.I want to connect it to a Wifi power adaptor to turn it on with Google home.Can anyone tell me which points to solder to get it to just be always on.AUS 220V mains

author: ajb
author_rank: Super Contributor
timestamp: July 15, 2021, 04:00:17 pm
content: It's going to depend on what kind of LED string this drives. What sorts of patterns does it do and how is the string constructed?It sort of looks like there's an H-bridge driving the output, which suggests it's the style of string where all of the LEDs are in parallel but with alternating polarity. When the string is powered with one polarity half of the LEDs light up, and with the opposite polarity the other half light up. By alternating back and forth you can have different patterns or make them both light up. So if that's what you've got you can't just apply constant power to the string and have the whole thing light up. You need to drive the H bridge so that it's alternating polarity. The easiest way to do that is probably to remove the 8-pin IC from the output side of the board and bodge in a new MCU or Arduino to drive the bridge.

author: havok44
author_rank: Newbie
timestamp: July 15, 2021, 11:23:54 pm
content: Thank you for replying! Yes I think you are right in the light function. There are more modes too like fading too.Thought it was just soldering a couple points to make it constant. I didnt think I'd have to buy an arduino for this.Is there a power adaptor I can buy to replace this? Its outputing 24v 3.6WDo they sell variable ones?

author: Zero999
author_rank: Super Contributor
timestamp: July 16, 2021, 01:21:23 pm
content: It's not that straightforward.It's a two wire LED string H-bridge controller. The output is 24VAC PWM. The LED string consists of two LED strings wired in reverse parallel. To keep the voltage the same, the LEDs are all be blue or violet dies, with a phosphor to convert the light to other colours. To switch between the strings, the polarity is changed by the H-bridge. The brightness is controlled by varing the PWM duty cycle. To make both strings light continiously, the each string is lit alternately with a duty cycle of 50%, but a such a high frequency, it appears to be continiously on.Q1, Q2, Q3 & Q4 form the H-bridge. U2 is a microcontroller. To light both LED strings continiously, U2 will need to be replaced with another microcontroller, with the same power supply pin-out, which is programmed to quickly turn Q1 and Q2. Going from your photograph of the PCB, pins 6 & 7 control Q1 & Q2. R8 & ZD form a shunt regulator, which powers U2. Pin 1 of U2 is +V (3V or 5V) and pin 8 appears to go to 0V. Check using a multimeter, before looking for a suitable replacement for U2. It's highly unlikely you'll be able to reprogram 2, as it's most likely locked, or one time programmable.See the website below for a schematic of the output stage.https://www.da-share.com/circuits/2-wire-led-strings/

author: havok44
author_rank: Newbie
timestamp: July 21, 2021, 03:17:16 am
content: ok I guess I will just leave it alone and get used to it.Thank you for taking the time to explain to me