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!
Step 2: Create the stars
To solder the stars together, I used bluetack as a base to keep things in place. I pushed the negative legs of each of the 5 LEDs into the bluetack, and then carefully pulled, bent, and pushed the positive legs together into a point, and soldered. It wasn't the neatest piece of soldering I've ever done for the first one, but it got easier!
Give the star a second or two to cool down, then flip it over, using the bluetack again to hold it in place, and repeated the process for th negative legs, pushing them together and soldering into place.
The process was repeated with the other coloured stars.