Friday, November 14, 2014

Science Party: Fiber Optic Lamp

What's a Science Party without Physics, right?

To balance out all those other Chemistry experiments, Emily and I decided it would be fun to do a little electric circuitry. We also wanted to stage a fake dissection as a token Biology offering, but fabric frog innards were too time-consuming to sew, so we filed away that idea into the Maybe Another Party category of my brain. 

Before we settled on classic from-scratch circuitry, we considered the more trendy electric playthings now circulating the internet. Like electric playdough, for instance. We made it, it worked for us, but we couldn't see 16 kids "playing" with it and taking home something concrete at the end of the day to show for it. Also, the resistance of the playdough was so high that we'd need 9V batteries (instead of the usual 1.5V variety) and all kinds of safety and theory lesson bytes in order for the kids to fully get what was going on.  So those were - again - filed into the Maybe Another Party category, and I returned to basics. 

Just for info, electric circuitry is not the same is electronics. "Electric" is literally electricity flowing through a circuit and making light or sound or whatever. It can be low-current (e.g. batteries) or high-current (e.g the wiring of a house connected to the 110 V/220 V mains). Electronics involves logic and the circuit actually doing something clever (e.g. a robot vacuuming your floor when the dirt level gets high enough to set off a sensor, or turning on a sprinkler system at certain times of the day or when the humidity is low, or frying someone's head if they walk across a intruder-alert laser beam). The current involved in the actual  circuit is usually very small because it involves semiconductors which operate at the electron level, but electronic circuits can also be relayed to the mains to control regular high-current appliances. 

I like both, but I like electric circuitry more because I can see what's happening in the circuit. Electronics is cool and magic and high-tech and everything, but I can't see what the circuit is doing because it's all at the nano-level. Also, with IC boards and programmable gizmos like Arduinos and computers and whatnot, the circuit itself becomes a black box - we can use it without really knowing how exactly it works, only that it "does XYZ if you plug the green wire into the yellow socket". 

Over the summer, Emily, with all that sunshiney time on her hands, started to dabble in electronics and simple computer programming. (Someday I will write a post on our electronic toys [we love Makey-Makey and Little Bits!] and how we like them, and how to start your own electric/electronic stash for your kids to play with. But not today.) It was just toe-dipping, but she loved it, and while she was messing about in my tub of electric and electronic knick-knacks, we decided to make optic fiber lamps for her party. 


Lamps are electric circuits, but optic fiber lamps are more fun than regular light-bulb lamps, and we could pick colors and do light shows in the dark and all kinds of other cool things. 

Fancy on the outside but, at heart, a simple, basic electric circuit with a battery, wires and a thing that lights up. 

Some shopping had to be done first since, pack rat though I am, I don't usually keep enough stock at home for 16 optic fiber lamps. In summary, this is what we used for each lamp:

  • Power Source
  • Wires
  • Light device (we used LEDs)
  • Optic fiber bundle
  • Switch
  • Lamp shell (we used paper cups and cardboard)


Let's deconstruct each of those.

1 Power Source and Wires
First, we bought batteries. From Costco, which is Bulk Heaven. We needed a 3V (explanation later) power source, so we taped two batteries + to - as shown, with masking tape.

This is how to make a home-made battery pack. You'll need the taped batteries, a short, thick rubber band, two connecting wires and electrician's tape.

First, loop the end of one of the wires.

Lay it on one end of the battery pack, and tape it down with electrician's tape, stretching the tape to ensure a tight seal. Repeat with the other wire and the other end.

Loop the rubber band around the battery pack as shown. This compresses the batteries together and makes a tight connection.

Never, never connect the two free ends of the battery pack wires to EACH OTHER. This short circuits the batteries, which heat up and die. You can, however, now connect devices (we call them "loads" for the function they perform in a circuit) between the ends of those two wires, like this LED.




To prevent accidental touching during storage, we taped the ends with scotch tape until the party day. 

2 Light Device
You can use light bulbs like the kind found in traditional flashlights. We used LEDs because they were a lot brighter and also more colorful. I bought our LEDs from Radioshack, along with limiting resistors. 

Do not be frightened, people. It's quite layman. If you've worked with LEDs, you will have heard all the dire warnings to "always use a limiting resistor!!!!!" so as not to kill your sensitive LED. That is a good principle. Here's how LEDs work: they have something called a forward voltage. Different LEDs have different forward voltages. This means that if the potential difference (which is what a power source provides) is bigger than this forward voltage, the LED will turn on because a current flows through it. All you need is a combined battery voltage that is just a little bigger than the LED's forward voltage to work it.

The problem is that many LEDs have forward voltages that are either bigger than regular single 1.5 V Duracells but much smaller than 9V batteries. And there aren't any in-between battery values unless you are willing to buy battery holder packs or invest in lead-acid accumulators. And if you ignored the rules and put a huge 9V voltage across an LED with a forward voltage of, say, only 3.8V, you could fry the LED. I've done it - sometimes I don't save the packages my LEDs come in and I forget their forward voltage and I accidentally kill them when I next fiddle with them. So most people buy 9V batteries (because 1.5V batteries are too weak) and limiting resistors, which make the overall current smaller so it's still safe. See?

Or you could look for LEDs whose forward voltages are just about 3V, and use two 1.5V Duracells and be done with it.

Here's what I mean in pictures. Behold: the forward voltage on the packs - 3.0V. Most 1.5V batteries when brand new are about 1.6 V. Which means two batteries are 3.2V, which is more than the 3.0V forward voltage, which works. Hurrah!

This red one has a lower forward voltage (2.6V) , so I added a low-value resistor (that little brown peanut with stripes on it, taped to one of the legs of the LED) to it, to be safe. You can calculate resistor values on your own or you can google a resistor calculator like this and just plug the values in.

So, long story short: I wired up all the 16-different colored LEDs. Some required limiting resistors and some didn't. The LED leads (those pointy leg things) work perfectly left as is, but I needed to color-code them for easier connecting during the party, so I twisted their ends to connecting wires in blue and red, and taped them with electrician's tape. All will be made clear later.

3 Optic Fiber Bundle
The next stop was the optic fiber store. I've heard that you can, in a pinch, use fishing line, but it's not as good, and real optic fiber is not as expensive as you might think. I bought about 200 feet of .75 mm fiber for about $25, enough for about 20 lamps.

Then we made bundles of optic fibers - mine were about 7" long, and tied in bundles of about 20.

I used those infernal rainbow loom rubber bands that are littered all over our house - they are the perfect smallness for an optic fiber bundle. Also, I cut the end of the bundle (regular scissors work well) so they were flat.

And then I taped them to the top of an LED lens so they were in actual contact,

winding the tape all around to hold them together in place.

When you power it up, most of the light is transmitted to the tips of the fibers. Some light might "leak out" around the tape at the connection points, which is okay.

Here they all are, awaiting their transformation into lamps.


4 Switch
Switches are optional. But they are nice to have because they offer the option of turning the lamp off if you aren't using it. I've made a swing switch with a paperclip before, here, and today's touch-switch is just another variation. You'll need a strip of cardstock, a craft knife for making slits, and two brass paper fasteners.

Fold the strip into quarters, bent as shown, and insert the brass fasteners,

so that, when folded tight, you get a spring-loaded touch-switch. When you press the two halves together, the brass fastener heads will touch.

Open it out again and connect the ends of two free wires to each pair of fastener legs.

Like so, taped securely with electrician's tape.

We decorated our switches with washi tape, because white was boring.


Ta-da! Homemade switch.


Lots of home-made switches.


And finally, we have all the parts of a simple circuit - the switch, the battery pack and the optic fiber light. 

To make it easy to give instructions at the party, I color-coded the wires so that all I needed to say was, "Connect blue to blue, black-to-black and red-to-red", and with three twists, 

the entire circuit is connected, taking care of LED polarity (LEDs have a +/- direction, like batteries).

And this circuit lights the optic fibers when the switch is pressed closed. Easy! Even kindergarteners could do it.

However, this circuit does not make a lamp, and for that, we need a little cardboard help.

5 Lamp Body

First, we need a small paper cup with a radial-slit hole 

for the optic fiber bundle to poke through.


Next, we need a cardboard circle with a collar that is glued to its center.

The battery pack gets inserted into this, so it stands up.

Then we need a larger upside down paper cup, with a hole in its base for the other end of the battery pack, plus a slit for the wires to nest in. The cardboard circle with the collar is glued to the cup's opening - you can see the collar below the hole.

The battery pack is now slid into the top hole

and into the collared base (which is detached from the rim of the cup to show you the battery fitting into it). The battery pack is now held upright and in place by this collar and the top hole of the bigger paper cup.

Observe:


To insulate the twisted-end connections and prevent them from accidentally touching each other (and shorting the circuit), we tape over them - either with electrician's tape or regular scotch tape.

Then we push the wires through that slit in the bigger paper cup, pop the smaller cup on top of the bigger, tape them together, and the lamp is finished.

Press the switch to turn it on, and release it to turn it off. 

This kind of switch turns the lamp on only as long as it is held closed. To leave the lamp on without holding the switch, either slide a rubber band around the paper cup, pressing the switch closed, or wedge the switch in the slit where the wires are nestled.

On the day itself, we provided stickers and markers for the kids to decorate their lamps after they'd made them.

Some shots of the instructional diagrams I drew to help explain the different steps of the circuit-assembly.


And with that, Emily's Science Party posts are finished! I'll update the main party post with links to the various individual activity posts. 

Next up is a return to drafting! See you soon!



15 comments:

  1. Y'know, you're pretty sneaky. You disguise all these lessons as a "birthday party"! Then the kids (and we) learn things without even realizing they were in "class". Pretty smart there, Mom! And I bet your own kids were the biggest beneficiaries of these lessons. Awesome! :)

    P.S. I loved the lamps!

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  2. I am completely in love. Totally. I'm gonna try this with my kids at home. Thanks a lot!

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  3. That is amazing. It made my non-science brain go "huh" quite a few times, but I think I could figure out your instructions. I think this would be great fun to do with my girls.

    Do you have any suggestions where would be a good place to buy supplies in Singapore? Sim Lim Square seems an obvious choice, but is there somewhere better?

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    1. Katie: Sim Lim is your best bet. And go to Sim Lim TOWER, not SL Square. Be prepared for crazy-disorganized shops within, though. If you need anything, just ask the store people. I usually know what I'm looking for and I still ask them all kinds of stuff. Occasionally, the odd neighborhood HDB shops have electronic stuff, too, but it depends on the shop. At Sim Lim, however, you're sure to be able to buy what you need. They may even have fiber optic stuff. I don't know; I never shopped for that there.

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  4. You are one amazing mom with such super cool ideas!! I learned circuitry way back in my engineering days but never thought one could use it for a birthday party!! Now just waiting for my 2.5 year old to grow to enjoy these kind of things!! Thank you so much for such awesome ideas and taking efforts to share it on your blog!

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  5. I'm totally in love with this party. I mean I'm allways impressed by the birthday parties you organize, but having only boys some themes don't offer that much inspiration. Plus I'm a scientist and spend most of my day in a lab.

    Just an idea: if you'd use metallic snaps instead of the office brads you could change the touch switch into an on-off switch.

    Thank you so much for sharing all the amazing ideas.

    SilkyBee

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    1. Silky Bee: Snaps are brilliant! Thank you!

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  6. Amazing! I'm going to have to try this at home with my kids now. And I'love the idea of using snaps for switches.

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  7. very interesting to make it for my son, please visit my blog and follow back , thank you

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  8. A brilliant idea! Your tutorial and is just perfect, I love your instructions,for the children, on how to build their lamp. You will be responsible for a few Engineers in the future. I have just discovered your blog and have been spending hours(days) catching up. I am enjoying your posts and tutorials immensely. I am so fortunate to have found your site. Thank-you!

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  9. I loved this birthday party theme. We are planning on doing many of your activities for a January birthday. But first making a couple fiber optic lamps as Christmas gifts from my son.
    Thank you for the instructions. And SilkyBee for the snap addition.

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  10. That's really a very cool idea... I appreciate it... Will be getting some Solid Quality Fibres and will surely try out... Thanks.

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  11. That's really awesome one ................... thnq for helping me by showing ur idea

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