[Mon Apr 5] New Project

At the beginning of the class, Oscar showed us "the most useless machine" that is based on boxes that we just learned to make. Apparently you can do all sort of cool things with boxes...

Anyways, today we officially started our new project - a lantern! We are going to work in groups this time and my partner is Essie. We are going to use AA/AAA batteries (two or three), LEDs and resistors, and we will make battery holder and switches to make the circuit workable. We could also add more complicated designs such as potentiometers, but Oscar said those were too complex to do with the time and knowledge we have.

First we learned the basics of LEDs. They have two legs.
The longer end is positive while the shorter end is negative. In order for the LEDs to function as light sources, there are two things that we need to pay attention to: LEDs' colors and the current going through them. Human eyes' ability to perceive lights of different colors differ, and the ranking  of the our eyes' detection of light color is (from high to low): red, green, yellow, blue, and white. Essie thinks that red LED is not very pretty, so we selected yellow and green.


Then we have to think about the current in the circuit. LED has a negligible resistance itself. Therefore, we need some resistance in the circuit to adjust the appropriate current going through the circuit. The most basic design is:

We can calculate the resistance needed in the circuit to have a certain amount of current going through the LED.

We can always think of different designs to make the circuits do different things:

(1) We can have one LED on at each time or two on at the same time by controlling which part of the circuit is connected using the switches.
(2) We can have one LED on at each time by controlling which part of the circuit is connected.
(3) We can change the brightness of the LED by controlling the resistor being connected in the circuit.
(4) We can change the brightness of the LED by controlling the resistance in the circuit.

Essie and I decided that we want to use design (1) because it's simple and we are more familiar with the set up. We could have designed something original, but we thought that would probably come out to be too complex to build.

Then we talked about the battery holder. Oscar offered a couple designs:

But Essie and I decide to build something similar to an actual battery holder like this:

http://www.google.com/products/catalog?hl=en&q=battery+holder&bav=on.2,or.r_gc.r_pw.r_cp.,cf.osb&biw=1366&bih=643&um=1&ie=UTF-8&tbm=shop&cid=5183386961189604477&sa=X&ei=eqiNT9HePMWs0AHH5_28Dw&ved=0CKUBEPICMAM

Although it looks very complex and I don't know whether we would stick with it in the end.

Lastly we talked about switches. Oscar offered us some ideas, but someone found switches in the lab, so we are just going to use those:

(Taken by Essie)

Lecture ended there. We broke into groups to start our design process. Essie and I searched on the Internet and got some idea. It is going to have a box at the bottom. The LEDs will come out of the box, and the circuit will be in the middle layer inside the box. There will be a light-bulb shaped arch going over the LEDs. We will also make a slide opening at the bottom of the box so we can switch batteries from the bottom. It is going to be made out of wood because it's prettier. Then we started to select materials:

(1) Yellow LED with a 270 Ohms resistor (we put the LED in the circuit and change resistors to find the one that gives the LED the most brightness).

(Taken by Essie)

(2) Green LED with a 330 Ohms resistor (chosen with the same method above).

(3) AAA batteries (because they are smaller than AA)

(Taken by Essie)

Here are the materials we are using for the circuit:

(Taken by Essie)

That was all we had time for during class. Essie worked outside the class to draw the design for the box. I helped her cut out part of the design and assembled it. Here is what we got so far:

(Taken by Essie)

We also realized that we wouldn't be able to make our lantern out of wood because there is only one piece of fine wood... We compromised to use clear acrylic.