XMAS tree for 3mm (fading) leds

thingiverse

In contrast to most Thingiverse Christmas trees, this one is specifically designed for 3mm LEDs. Red LEDs have a voltage drop of 2 volts, which means that when we connect three in series with a 9-volt battery cell and 5mA LED current, a 560 Ohm resistor can be used (as shown in the illustration). Blue and green LEDs, on the other hand, require the same resistor but only two LEDs in series. Using slow-fade LEDs adds an interesting twist when they're installed. The price for 50 of these LEDs is remarkably low, as one of the illustrations clearly shows. This XMAS tree is designed to be positioned near a wall and features only half a tree. For a complete tree, simply print it twice and glue the two halves together after installing the LEDs.