As an electronics teacher, I spend a lot of my time teaching repetitive products from kits - mostly, that I've had little input with and am really just making sure they understand the components. I decided it was about time I challenged myself, so designed my own project, found the components, and did the maths.... Luckily, being in school, I also have a whole load of unwanted projects, which I rip apart to reuse - all the components in this project are recycled.
For a chain of 3 StarLights, you will need:
1 2xAA battery case
Battery Clip (PP3 clip)
15 3mm LEDs - 5 yellow, 5 red, 5 green
3 10ohm resistors
2.5m red wire
2.5m black wire
Step 1: Do the Math, Test the Circuit...
I started out by testing my circuit using breadboard - you don't need to do this step. I used R = V/I to work out the resistor values for LEDs in parallel, like this:
V = 3 (supplied by battery) - 2.2 (forward voltage of LED) = 0.8
I = Combined current required by the LEDs = 0.02 x 5 = 0.1
0.8 / 0.1 = 8ohms of resistance
I tested the maths on the breadboard, and thankfully, it worked!