Introduction: The Book of Light
Since the ancient times, light has been associated with wisdom and understanding. There are many Latin expressions referencing the light, and many philosophers have used it in metaphors and analogies.
I thought it would be cool to combine light, and all what it represents, with a book, which is also very symbolic by itself.
This "book of light" is basically a book which has been hollowed in some places to hold some LEDs and a battery, it has a push switch, which turns on the light when the book is open, and vice versa. It's a neat project to do on a weekend, or during just an afternoon, as I did. It can be used to complement a costume or cosplay, impress your friends or just to keep it in the shelf in case a power shortage occurs.
This book is also inspired in the briefcase that appears in Pulp Fiction, which emits a yellow glow from the inside when it's open, making it quite mysterious, specially since the content of such briefcase was never shown in the film and not even Tarantino gave a clue about what it contained.
Step 1: Materials:
You will need the following materials:
- A book
- 2x 1W LEDs (you can use 0.5W if you want)
- 2x Resistors (I'll show how to calculate the values)
- Some copper wire cable (I prefer stranded over solid for this project)
- A battery (I used a 3.7 volts Li-Po from a laptop battery pack)
- Micro door switch (Or pushbutton)
- Utility knife, x-acto knife... (anything with a very sharp edge)
- Small brush
- Food wrap (or another kind of plastic)
- Wood or paper glue
- A weight
NOTES: You might want to use warm LEDs, since they emit a gold-like light that in my opinion produces a better effect than a white light.
You can also use normal AA batteries combined to some kind of boost converter (aka. joule thief), just make sure it can output the amount of current you'll need. The batteries won't last as long as a Li-Po battery.
DANGER:You'll be using very sharp tools, you can cut yourself easily. You'll need to use some force to cut through the paper, if the knife slides it can make some serious cuts. Always keep your fingers behind the path of the knife.
Step 2: Choosing a Book
We begin by choosing a book, it must be the correct size for the LEDs and battery to fit in, it's preferable to choose one with a nice rigid cover. If the cover isn't rigid you'll have many problems, and the circuit could be damaged over the time.
Step 3: Page Division:
The next thing we want to do is to separate the pages of the book in two, to do this, we count the pages and leave half of them to one side, and the other half to the other side, we place food wrap in between, so the two parts don't stick together when we apply the glue. Next we cover the cover of the book with the food wrap, this will avoid getting glue on it.
We then apply glue to the sides of the book with a brush, covering all the borders of the pages. You may want to wrap the food film tightly so it doesn't gets in the way during this step. Make sure the glue is evenly distributed, brush during 1 or 2 minutes to make sure the sides are soaked with glue, then with a paper towel, remove the excess, this will avoid leaving the sides shiny.
Place a weight on top of the book and let the glue dry. Use a weight heavy enough so the borders of the pages are compressed together, I used a big transformer which weights around 4kg.
Step 4: Design the Internal Layout
Once the glue is dry you can remove the food wrap, it should peel off very easily. Now you can start designing the internal layout. To do that, we choose the zones were the components will be fit, for the LEDs I draw a square of 3x3 cm at the center of the book, and for the battery and the switch I draw a rectangle big enough for them to fit, leaving some extra margin just in case. The hollow spaces will be joined by grooves to pass the wires though. All must sit below the level of the page, or the book won't close correctly.
You can also add your own features, like a small zone to keep some money, red LEDs to give it a "cursed" appearance...
Step 5: Start Cutting
Once the layout is complete you can start cutting, this is quite tedious, and it can take you some time.
To cut the holes properly, make sure your utility knife is as sharp as it can be, grab it as vertical as you can and start cutting following the lines, stop after some cuts and remove the paper. You can go out of the lines at the edges to avoid leaving chunks of paper that can't be removed afterwards. Those cuts won't affect the final look or the structural integrity of the hole.
Again, keep your fingers behind the path of the knife.
If you want more info about hollowing a book you can visit this webpage, I learned how to do it there.
Step 6: Reinforcing the Holes
The pages are just hold by the glue at the sides, so every time you finish a hole you should apply glue to the sides of the hole, as we did with the sides of the book, let the glue soak a bit, then put food wrap over the hole, close the book and put a heavy weight on it.
After the holes are finished you can make the groves for the cables, to do this you just need to make two parallel cuts joining the holes.
Step 7: Wiring It Up
After wiring up the micro door switch, attach it to the book close to the hinge, you can do this with screws as I did, or use glue instead, just make sure the switch won't move.
For the wiring I strongly advice to use stranded cable, since it allows to be bent easily and won't snap if you bend it too many times, just make sure the connections are sturdy, using glue or shrink tube to reinforce them and protect them against vibrations. I used solid cable and it snapped at the hinge. Before rewiring with stranded cables I made a hole so the cables could be hidden between the spine and the pages, that way the cables don't bent that much and it's less probable they snap again.
Remember to wire the switch in a way that the circuit is closed (active) when the switch is not pressed. You can check this with the continuity setting of your multimeter of looking for the NC pin (normally closed or connected).
Step 8: Resistance Calculation
Once the switch is installed we should install the LED and the resistance in its place. But first we need to calculate the resistance. This can be done easily knowing this basic formulas :
- Power = Voltage * Current
- Voltage = Resistance * Current
We know the forward drop voltage of the LED is 3.3V (this voltage can vary depending on the LED color and can be lower than the manufacture value), we also know the voltage of the battery we'll be using is 3.7.
To obtain the current that should flow through out LED we use the first formula, since we know the power is 1Watt and the voltage is 3.3 we can calculate the current, which will be around 0.3 Amps.
If I wanted to run the LEDs at full power I could use the second formula and find the resistance value, but in this case I've decided to use half of the power (0.15 Amps), not only because the LEDs won't be properly heatsinked, but also because I want the battery to last longer, and 1 Watt of light is enough for me.
Now I've got the desired current value I use the second formula to obtain the resistance, to do this I subtract the forward drop voltage of the LED to the voltage of the battery and divide it by the current. In my case I obtain 2.6 Ohms, but this is not a standard resistor, and for the sake of energy consumption I choose 3.3.
If you're not sure about how to do this you can go to this website , after entering the data, the wizard will calculate everything you need, giving you the standard value and even the power rating of the resistors. I used 1watt resistors just in case, you can use the "common resistors" as long as the power emitted by them doesn't exceeds 250mW.
I've made an screencap of the page so you can compare your data, if you need further help feel free to ask in the comments.
Step 9: Wiring the LEDs
To wire the LEDs I attached one of the cables coming out of the switch to the resistor and then to the positive part of the LED, I repeat the operation in the other hole, I've bent the leads of the resistor it in such a way so they fit into the 3x3 cm square I made before. I pass the cables through the grooves and hold them with some sellotape for now.
I've glued the LED and the resistor to the bottom of the hole. Since paper is not a good heat conductor you might want to stick the LED to a copper board and then to the hole.
You might be wondering why I'm using two resistors when I could use one. If just a single resistor is used, the current flowing through the LEDs would probably be uneven, and they could get damaged.
Step 10: Final Details
To finish, I glued a paper sheet over the pages to cover the circuit and keep the cables from moving. I also used some sandpaper to sand the sides of the book to remove any superficial traces of glue.
I'm quite impressed with the brightness, even though I'm running the LEDs at half of their power.
Thanks for watching.
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