I started out this project by thinking about some possibilities for the shape of the lantern. I decided to use a plastic water bottle to hold the circuit, because it would be easy to hold, and then the bottom of the bottle could function to disperse the light. After several sketches, I realized that it would be better to have a reflective surface between the LED and circuit, so that the light would reflect and there would be twice as much light. After a few days of searching for good materials, I still had not found the reflective surface (a CD) that I wanted, so I adjusted the design of the lantern.
I started out by building a simple circuit, consisting of a 9V battery, tin foil slivers for wires, a 3.2V LED, and a 270 Ohm resistor (a 290 Ohm resistor would have been ideal, but that was not available, so I chose the resistor that was a size smaller. I figured that a 300 Ohm resistor would not work as well as the 270 Ohm one, because it would take more energy away from the circuit and cause the light to dim). The circuit worked, so I then started building the lantern, using a water bottle I found in the trash, a plastic cup, and the shiny wrapper of a sleeve of cookies, which acts as a reflective surface for the LED to rest inside.
The most difficult part by far was designing a switch, because at first I had no idea what would be a reliable and quick way to close the circuit. My initial design concept was to have the wires suspended in the bottle, and a piece of cardboard covered in tin foil that could be pushed into the bottle and touch both of the wires. To turn the light off, the tin foil strip would be pulled slightly out of reach of the wires. I also considered having a tin foil covered wire-like element which would spin between the on and off positions. But while building the prototype, this was all much trickier than I had envisioned. So I made one of the wires longer, and taped a piece of electrical tape to it, with the ends of the tape forming a pull tab outside the bottle. When the tab is pulled, the circuit connects, and when it is pushed into the bottle, the circuit is open and the light is off.
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| One of the first conceptual sketches |
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| detailed sketch of what I had envisioned for the model |
| The final prototype! |
| The light is on and it works! |
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| and when the switch is in the off position |
battery = 8.99~9 V
LED = 3.2 V
current = 20mA
V=IR
(9-3.2 V) = 20mA (R)
5.8 V = .02A (R)
290 Ohms = R
I really liked your string concept for your lantern's switch. Although I saw it in class, I was wondering if you were able to keep the switch turned-hands free.
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