Blinking Christmas tree
by teachermakesthings, published
For about $1 worth of components, you can have a merry table decoration that you can show off your 3D printing and electronics prowess with this year.
The tree has 16 holes for 5mm LEDs, room for the circuit and battery inside, with a switch in the base
Circuit design is included.
edit: Fixed some overhang issues and made holes a little bit bigger to more easily accommoate 5mm LEDs
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I took the easy way out and purchased four each of red, blue, yellow and green LEDs which had a built in flashing circuit. Now sits on my desk at work. This was a good first print for my new Mendel90 printer - too tall for my Huxley! Well done.
I've only shown one of the blinking circuits and with only one pair of LEDs for each side for simplicity.
You can parallel as many of either as you like (I used 2 LED pairs per side and 2 blinking circuits to give a total of 4 pairs, on my PCB design there is provision for 8 pairs though)
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I use Green ABS for the tree top, and brown ABS for the base. 10% fill will work fine.
Either etch the PCB yourself, or get someone else to (alternatively, you could find another circuit and use that.) Included is a negative that you can make a transparency with whatever method you use.
Drill 3mm holes for the 2 mounting screws. Use 0.8mm holes for everything else.
Assemble and solder the resistors, transistors and capacitors to the PCB as per the "PCB placement" diagram (make sure polarity of the capacitors is correct).
Make 4 strings of LED's as per the "LED strings" diagram. I mix the colours up a bit to make it interesting. Give yourself a decent length of wire between LEDs (about 4cm works) and 10-15cm leads on each end. Solder to the PCB.
Solder a switch via short leads to the middle pair of pads. Note this should be soldered onto the solder side of the board so it can be mounted in the hole in the base for it.
Solder the battery clip to the other pair of pads (component side).
Screw switch into the base, then screw PCB onto base using M3 screws.
Insert the LEDs into the holes in the tree top. I try and spread them round a bit so the blinking is a bit more distributed.
Plug in battery, put the rest together and enjoy the show.
Note: There are two blinking circuits in parallel which will get out of sync (depending on the variability in your components) which adds a nice 'random' blinking effect. You can change the rate of blinking by using different values for either the 1M resistors, or the capacitors (larger = slower). Try avoid using resistors over 1M if using BC547/8 transistors.
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