Birthday Cake with Color-Changing LED Candles

thingiverse

This is a further development of my other birthday cake: https://www.thingiverse.com/thing:4754407 This one has six independent, slowly color-changing LEDs. They start with red, then synchronously change to green, blue etc. After a few minutes they become desynchronized and show a bouquet of changing colors. ==================================================================== Update 24 June 2021: I added a gift box with integrated snap in place compartment for a spare battery and with a cover. ==================================================================== For building you need: - A specific (see picture) 30 mm diameter LED candle light to be modified as a battery holder and on/off switch only, available e.g. on aliexpress.com at KITOSUN Retail Store. - Six slowly color-changing 3 mm LEDs, available e.g. on aliexpress.com at CHANZON Official Store. There is another flavor of these LEDs with fast-changing colors. Personaly I prefer the slow ones. - Six small (1/4 Watt, 2.5 mm diameter, 7 mm long) resistors of 470 Ohm. The Ohm value is not very critical and can be chosen between 270 and 1'000 Ohm, but it will determine brightness and battery usage. - Some wires and soldering skills. Prepare the LED candle light as follows: - Remove both CR2032 batteries and the battery seal. - Remove the O-ring from the battery holder bottom. - Grind the LED dome of the battery holder top until you can pushout the LED together with the PCB (printed circuit board). - Saw the remaining LED dome from the battery holder top. - Unsolder the spring, the tiny black SMD resistor (marked "R1") and the 5 mm LED from the PCB. - Drill the LED PCB holes to a suitable diameter (e.g. 1 mm). - Solder two short (ca. 7.5 cm / 3 in) isolated wires to the LED PCB holes. The flat side of the LED symbol indicates the hole for (-). - Solder the spring to its former place. - Solder a short circuit wire across the SMD resistor (R1) contacts on the PCB. - Insert the so prepared PCB back into the battery holder cap. - Assemble the battery holder top and bottom with only one (only one!) CR2032 battery, keeping the second CR2032 battery as a spare. Do not fully tighten the battery holder bottom to the top (= no voltage across the wires yet). - 3D print the cake base. - Insert the prepared battery holder into the cake base from below. Push it firmly to the stop. No glueing should be necessary. Install the blinking 3 mm LEDs as follows: - 3D print the cake top and the flames (the flames preferably with transparent PLA). - Glue the flames to the top of the candles (I use Revell Contact PROFESSIONAL). Let dry. - Turn the printed cake top upside-down. There is a wiring rig on the underside. - Insert the LEDs fully, with each long leg (+) oriented towards the center and the short leg to the outside. Drill the holes to a diameter of 4 mm if you feel resistance while inserting the LEDs. - Click the resistors (470 Ohm, 1/4 Watt, 2.5 mm diameter, 7 mm long) radially into the rig and shorten the resistor wire in the center. - Solder the resistors to the long (innermost, see above) LED legs and cut the resistor wire to size. - Solder all resistors together in the center. - Solder a single circular wire connecting all short (outer) legs of the LEDs (-). - Solder the wires from the PCB (+) to the resistors' center, fropm the PCB (-) to the circular wire. - Check for short circuits. A short will drain the battery quickly and it being a Litium battery it may even start burning or explode. - Fully screw the battery holder bottom upwards until the LEDs light. If they don't light there may be a short circuit. - Assemble cake top and cake base. It is a tight fit, rendering glueing unnecessary. - Check again whether the LEDs will light (i.e. no short circuit). If they don't light unscrew the battery holder bottom, remove the battery, push the cake top out via the four slots in the cake base's bottom and check your wiring. Enjoy! I include the OpenSCAD source file. It is still a bit of a mess, sorry. Caution: This is not a toy for small children. They may bite off a flame and swallow it.