Before New Year I've searched for a multicolor LED strings to decorate my home. But there was a problem. All strings at our stores must be powered from mains 220VAC. But there are some places at home without mains power outlets due to safety and 12VDC only. And the other reason is poor quality of most these products. Some of them are really dangerous and can burn without any visible reason.
So I decided to make some rework of a cheap LED string.
Click on any photo for full size. |
| 60+60 series LED's work with 12VDC supply |
I've bought simple 12 meter 4 color 120 LED string. Here are photos of native PCB without LED wires.
Source:
Here we can see a rectifier bridge, two SCR's and a board with IC. No fuse, no protection. AC wires soldered badly and can produce short-circuit. So this board go to my junk box.
LED's in a string connected in a series with 2 branches: Red-Yellow and Green-Blue with some small 0.125W resistors (not at all LED's, only 3-4 at beginning of branch) with common positive. I need about 160-190VDC to lit a branch of 60 LED's.
Rework:
High voltage is not a problem - we can use boost converter. I'm using 34063 with IRF840 MOSFET. Lights controlled by Attiny13A with MPSA42 BJT's at low side. HV capacitor may be 4.7-10 uF >250V. |
| Schematics |
 |
| DC-DC test run to check output voltage ripple, FET and coil heat |
MOSFET tab was cut to fit small enclosure height.
Firmware was written in C at Atmel Studio 6. Used ~720 bytes (7 programs, without button support).
Of course code can be optimized.
Please note: button support was not tested, maybe some bugs there. Firmware is built without button support.
Files:
- Schematics (DipTrace 3)
- My PCB Layout version (DipTrace 3)
- Firmware & Source Code (Atmel Studio 6.1)
And some macro photos of LED's (just for fun)
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