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General FAQ for the Pine Cone Christmas Tree
The ideal battery for this project would be around 3 volts so why use a 9 volt battery?
We use a 9 volt battery for a number of reasons. First off the 9 volt battery connectors are cheap. It's difficult to find a battery holder that is readily available and inexpensive. The other reason is we can take advantage of the internal resistance of the battery to cause much more random blinking. When you first turn on the 'tree' all the LEDs come on at the same time. For a moment they start to blink at the same rate and color. When they are all on, it is near the capacity of a 9 volt battery and the internal resistance became a big factor. When they blink off, they momentarily stop drawing current and allow the battery voltage to return to 9 volts. This causes some LEDs to see a full 9 volts when they start and the others that were on at that time were running at less voltage. Depending on the color, LEDs draw different current/voltage. Red LEDs require the least amount of voltage so are more inclined to blink red when the voltage is low (Other are on, drawing the voltage down). As the blinking rate continues the battery voltage is all over the place and causes the blink rate and colors to be much more random. If we had a unlimited 3 volts, the LEDs would more or less keep blinking at the same rate/color because they would have much less affect on the internal resistance of the battery. Over time the battery starts to drain down and the internal resistance is more of a factor. The first thing you will notice is you will see a lot less Blue colors and the White LED will start to blink and then go out. The White LED and Blue end of the spectrum draw more current and require more voltage. As the battery continues to drain on down, you will then start to loose the green and finely before it actually dies you will just have blinking Red. A fresh 9 volt battery will last about 24 hours before it is obviously dying.
The resistors are way beyond what they should be, so what's the deal?
Using Ohms law the resistors should be around 330 - 350 Ohms. This would limit the current to around 20 MA and drop the 7 volts you would expect. In our case we break all the rules and use 470 Ohm resistors. First off I do this to keep the brightness under control. These LEDs are bright as it is. Also running the recommended current would kill off the battery in nothing flat. 9 volt batteries are designed to provide much less current then what we would be drawing. Also, having more resistance helps with the randomness factor.
I want the top white LED to blink, but if don't!
The white LED is a super bright LED and is not intended to blink. But you can put it in series with one of the color LEDs and that would cause it to blink at the same rate as that color LED. Actually, considering each LED drops around 2-2.5 volts, 4 LEDs in series would allow the maximum life out of the battery because there would be no resistance loss. But that also means that those 4 LED's would blink at the same rate and color. I tried it that way, but it's really not as 'cool' as all the LEDs blinking at random rates.