Here is an idea for a nice string of Christmas lights.
It is made by bright ping pong balls slowly changing their color through the sequence RED, GREEN, BLUE, YELLOW, CYAN, PURPLE, WHITE and again ...
At first all balls change color at the same time, but due to the less than perfect LED chip internal clock, after some minutes each led has its color different from the others !
Step 1: Parts and Materials
- slow flash color LEDs (browse ebay with these keywords), I used 30 of 5mm type
- white plain ping pong balls (you can find the by dozen on ebay or just on your street stores)
- a simple pvc insulated bipolar copper cable (I used a white one, but choose every color you want)
- a wall wart power supply (I used a 12V/1000mA one, but every type from 7V upto 13V works)
- an LM317 regulator IC (a 7805 type can be used, but in other way, see next steps)
- a 2.2 ohm 1.5W resistor (or a parallel of higher value resistor group, see next steps)
- a 1000uF/16V electrolytic capacitor (470uF or 2200uF work as well)
- heat shrinking tubing (2-3 mm type)
- clear hot glue (with the relevant gun of course)
- moderate power soldering iron
- typical christmas plastic fake green festoons (optional)
Step 2: Prepare the Balls
Take care the hole be smaller than a led, it have to be pushed inside with some resistance.
Step 3: Prepare the LEDs
Take care the glue "blob" is smaller than led's diameter so it can fit the ball hole.
Step 4: LEDs Into the Balls (ouch!)
2) Cut short pieces of 3mm hot shrink tubing. The have to be 3-4mm shorter than the shorter led terminal (cathode "-") to allow soldering.
3) Insert hot shrink tubing pieces on both led's terminals, then bend with pliers the residual exposed lenght of both terminal at right angle, I suggest in opposite way.
4) Finally take care to pre-tin the bended part of terminals to easy the soldering on next steps. Tubing can start to shrink with solder heat but it is not a problem.
Maybe better insert the insulating tubing BEFORE hot gluing the led, so the glue can secure and seal the tubing itself. In some cases I did it this way, see next steps photo.
Step 5: Prepare the Wire
It is a good idea to mark the same side of bipolar wire on every step so you can know the polarity when you'll solder the leds (they are polarized, have a + and - terminals, invert them and led is "fried")
2) Using a cutter, cut away a small amount of insulating pvc on both side of the bipolar wire to expose a 2-3 mm of nude copper
3) using the solder iron and electronics tin solder wire, tin the exposed copper wire on both sides of the bipolar wire
Step 6: Solder LEDs to the Wire
You have to deal between fast action and good solder, since LEDs don't love too much heating their terminals and even PVC insulating tends to melt easily and retire from heated copper, you can make short circuits between the + and - wires !
All in all the major trouble is the PVC melting, since LEDs terminal are long enough to avoid excessive heating.
But push away your fear and let's go !
Face the bended part of LED's terminals to the tinned copper wire and solder them together.
Since you have pre-tinned both parts, it would be relatively easy and you don't need a third hand to get more tin solder wire there !
Repeat for each ball, examine every joint for short circuits or fake soldering, heat the tubing to shrink them to the minimum diameter (it would be 1 mm or so), then hot glue each joint to insulate them from environment. If necessary hot glue the ball side of tubing to seal them.
Finally solder the electrolytic capacitor at the wire ends, respecting polarity of course.
A hot glue touch over its soldered terminals helps to seal them from moisture or so.
Step 7: Make the Power Supply
The formulas from datasheet say current I (ampere) = 1.25 (volt) / R (ohm).
I supply 20mA (0.02 A) to each led, so total current has to be 30 x 20 = 600 mA (0.6 A).
This lead to a 2.083 ohm resistor. I used a 2.2 ohm standard value one.
This piece has to dissipate almost P (watt) = V x I = 1.25 * 0.6 = 0.75 watt, so I used a 1.5 watt resistor to avoid overheating.
You can also put on parallel a lot of higher value resistor to obtain the right value:
- 7 x 15 ohm resistors
- (9 or 10) x 22 ohm resistors
- 13 x 27 ohm resistors
- 16 x 33 ohm resistors ... and so on, but remember you have to enclose all these part in a small housing.
Thus these resistors can share the dissipation in equal parts, so they can be 1/4W type.
I soldered components each to other by their terminals, insulate where needed and put all inside a small plastic container I found in an easter egg. Two holes on the opposite sides allow wire from wall wart and to LEDs string to enter the small egg (a tight knot on both wires ensures circuit safety from external pulls). Please double check the circuit to avoid short circuits, otherwise all LEDs can be fried !
With a 12V wallwart all circuit doesn't overheat so much, even inside the plastic housing, but avoid to wrap all internal circuit in electric tape.
So this is a Constant Current power supply, but what if I would use a costant voltage one ?
I say that it would works as well, but until now I don't tried to use it with this circuit, so I can't assure there are no problems with it.
This CC type have been worked well from 2 years now, without any problem.
Maybe I decided to use it cause at that time I didn't know well these color changing led (eg. which voltage they need), or I thinked at first to make a standard led string and want to save a lot of resistors, I don't remember ...
If you want use a standard 7805 Voltage regulator, you can build a simple circuit just like the Candle Moodlight.
Step 8: Fire !
voil� you have your own CCCP (Color Changing Ping -pong) lights !
My light string was installed outdoor without problems, due to the tight seal of hot glue, but I suggest to use indoor if you are no sure about it.
Merry Christmas !
Step 9: Variations ...
Accurately wash bottles inside to avoid "mold" and definitely light dimming.
Punch caps with hot solder iron tip and enlarge hole if needed to allow LED
inserting (it must be TIGHT), then hot glue LED on top first, then on the
bottom (internal) pour hot glue to secure LED and have a diffusing layer.
After cooling a while, close caps on the bottles (well, indeed bottles are
screwed into the caps).
Remember the hot shrinking tubing for insulate and solder LEDs terminals as said before.
A 7805 voltage regulator with classic wiring was used successfully.