Build an led christmas star
This is a how-to as to build a lighting christmas star that is controllable through the internet. We use WS2812B RGB ledstrips. The leds of these strips are individually addressable with a microprocessor, in this case an ESP8266-12E. This means there is minimal hardware needed. We can give each of the leds a different color and brightness, which gives the opportunity to program spectacular licht effects. I programmed a nice webpage for the ESP that alows us to set a color or run two different animation programs. Moreover the ESP knows the time and i can configure a timer via its webpage so that it switches on and off automaticly.
So what do you need for a start.
* a sheet of mdf 4 mm thick.
* Two ledstrips of 1 meter and 60 led each.
* An ESP8266-12E
* A 5v 4A dc wallpug powersupply.
* 2 components PU resin.
* Paint and decoration material.
The general idea was to have a star with the led tops peeping out of the surface. The only way to accomplish this is to sink the strip in a gutter along the edges of the star. And then fill the gutter with pu resin so that only the leds are visible. I started with drawing the star. This is difficult enough without instruments. So i cut 10 strips of 1cm wide and the length of a 10 length ledstrip an layed this out on the mdf sheet. This way you can also decide on the most conveniant and advantageous way to saw the star. Now i could draw the star along the inside of the strips an saw it out of the sheet. We also need 10 mdf-strips of 20mm wide and 40mm longer than the led-strips. And for the sides another 10 strips of 25mm wide to be sure that the case will be deep enough to house the arduino. See the drawing below.
Some notes as to the power supply: When 105 pixesl are white at full brightness, the current would be 105 pixels * three colors * 20mA = 6.3A!
In the programm we can set any color by mixing the red, green and blue in a certain ratio. When we want red then we would set red to pwm 255 and the other two colors to 0. However when we want white and we would set all three colors to 255, the brightness would be three times stronger. In this case we can give each led a pwm of 80. Now the brightness is less strong and the power consumption about one third lower .
So by playing with these pwm values we can equalize the brightness of the mixed colors and limit the power consumption.
WARNING: the voltage of the powerplug tends to be higher than 5V. This wil damage your leds. In my case i had to put a power diode in series to get a voltage drop of 0,6V An example programm for the ESP can be downloaded
Because of the resistance in the strip i connected the power at three spots. To ensure that the leds are equally powered. See the electrical scheme.
The star has 5 peaks so there are 10 strips needed. I used strips of 10 leds with an extra led in the peak. This means a total of 105 leds. Soldering the strips can be tricky so i was happy i had some spare leds.
When cutting and soldering the strips you should see to it that the smd component (i think its a resistor) always points in the same direction. When fitting the strips on the star you will need an underlaying strip of 3mm thick to get the ledstrip on the desired hight. I used cardboard but this has a large disadvantage. Its hollow so a lot of resin will dissapear in it. And the escaping air can cause bubbles and holes in the surface of the resin. So for this underlayment you should find another solid material of 3mm thick.
I first programmed a testprogam in a arduino nano that i had laying around. The connection with the strip is simple, two powere wires and one data wire connected to pin6 of the nano. Next i connected one strip en perform a test. Then soldered the next one and then test again if it works. After each soldered connection i tested again. I managed to brick a couple of them so be careful! Before casting the resin, be sure everything works fine!
To see some pictures click