How do the trees breathe?
By Alan Killan
How does a tiny computer control hundreds of lights to make a breathing tree?
A SIMPLE EXPLAINATION
by Alan Kilian, who designed and built the voltage controllers for “Winterlights: A Circle of Peace.” (This is written for non-engineers, the details are a little bit more complex than this explanation.) The way we vary the brightness of the trees is by sending them different voltages. If we send a lower voltage, the tree is dim. If we send a higher voltage, the tree is bright. Our tiny computer can create different voltages so it seems that we could connect the small computer to the tree and have the computer send different voltages which would make the tree breathe, but it's not that easy.
TO MAKE A TREE BREATHE
Our tiny computer can only produce a small amount of power and the trees take a medium amount of power to light up. Our computer could send voltage to 10 lights just fine, but the trees have hundreds of lights and that required more power than our small computer can produce.
We need something in between the computer and the trees which can be told how much voltage to send and can send enough power to light up all the lights on a tree.
We use a variable voltage power supply to send the voltage to the tree. It can send enough power to light up all the lights on a tree. But we need to make it listen to the computer to send different voltages as the tree breathes.
Imagine our power supply is a person looking at a display that shows a voltage. We ask our person to turn a knob until the display say 12 Volts. If the display says 13 Volts, the person turns the knob down a little until the display says 12 Volts. If the display jumps down to 5 Volts, the person turns the knob up a lot until the display once again says 12 Volts. This is what our variable Voltage power supply is doing. We ask it to send 12 Volts out and it "turns a knob" inside itself to make the voltage match what we want it to be at 12 Volts.