mit edgerton center: build your own flashlight - teacher’s guide … · 2014-11-03 · build your...

MIT Edgerton Center: Build Your Own Flashlight - Teacher’s GuidePreparation and classroom materials:-Review your copy of the 2 page “Flashlight Circuit Instructions” for the teacher, and “Flashlights Instructions” showing a photo of the completed circuit. These are shown on p. 4 and 5 of this guide. -Gather art materials such as colored duct tape, and permanent markers. -Create a large model LED, Resistor, and black wire out of colored and silver pipe cleaners. Cut a hole in a paper plate to model the flashlight cap. - Cut the mailing tube into 4.5 inch pieces. Use a sturdy hole punch to punch through the cardboard tubes and a punch or 3/16th” drill bit for making the LED hole in the cap. Place 4.5 inch tubes, and caps on side table.For four children per table, modify as necessary:-Set up a protected table with 4 soldering irons, safety glasses, solder wire, help-ing hands and carbon-filter fan. Turn on soldering irons half way through the lesson. Groups of 4 will rotate through while others decorate. -Place four sets of handouts, laminated cards and four pencils on each table.-Place four wires strippers and one needle-nosed plier at the front of each table. -Place 7 one-inch pieces of electrical tape per child on the side of the table (or place scissors and a roll of tape)-Prep and place baggies with flashlight parts for 4 students on side table.-Have store-bought flashlights and strands of 18 guage wire available on side table.

Parts List Per student:- Pencil - Student Worksheet: “Build Your Own Flashlight”- Laminated 1/2 card: “Flashlight Circuit Card (student)”- wire stripper- cardboard mailing tube (1.5”diam) cut 4.5” long with switch-sized hole punched through- 2 (1.5”diam) caps for tube, one with LED-sized (3/16 “) hole punched through - 9V Battery (not handed out until end)- 7 one-inch pieces of electrical tape- Small baggie or container with: - 1/4 W, 680 Ω (ohms) resistor - 9V battery snap - stranded wire, 6” - Momentary switch, single pull single throw, normally open, black pushbutton - tri-color LED (RGB), cathode longPer group of 4:- store-bought flashlight- 18 ga solid wire, 12”, both ends stripped of 1” of insulation- batteries for the flashlight- 1 pair needle nosed pliers

© MIT Edgerton Center, 2013

Clockwise from left: 1) The parts that each student will need. 2) A soldering station for one student. 3) Pipe-cleaner and plate models of components. 4) The hole punch and drill bit for the tubes and caps. 5) The flashlight, batteries and wire for the initial investigation. 6) The final product.

MIT Edgerton Center 2012 1

Name:____________________ Date: ____________________

Build your Own Flashlight!

First, we’ll look at a “store-bought” Flashlight....

1. Pick up a flashlight from the table in front of you. With your partners, take apart the flashlight. Can you make the light bulb glow using just a battery, the bulb and a piece of wire? EXPERIMENT! Draw in Box A.

2. Now, try to draw the whole circuit that is in our flashlight, use Box B (Hint: Are all the parts touching? If not, you might be missing a piece).

Please write down your observations of how you think the flashlight works (think about the circuit – which pieces are connected?): ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Now you are ready to see what materials you will use to BUILD Your Own Flashlight!

Box A Box B

This instructional guide is set up to work alongside the student worksheet, so we’ve included the appropriate pages from the worksheet for easier flow. Blue text or drawings indicate what students will draw or write. Red indicates instructional notes.

Student Worksheet p. 1 Begin by asking a student to read the first paragraph. Hand out one flashlight and one 12”, 18 gauge wire to each group of 4 students. Allow students time to talk, try out solutions, and struggle a bit before offering hints. As groups become successful, ask them to draw their solution(s) in Box A. Box A shows 2 possible solutions. Help any remaining groups.

Ask students what parts they discovered when they took apart their flashlight. Draw a flashlight on the board. Show how the metal of the switch makes the connec-tion between spring and light bulb. Label the parts of the flashlight with arrows. Then instruct students to work on part 2, drawing in Box B.


The batteries connect to each other, and to the light bulb and spring. When closed, the metal piece in the switch com-pletes the circle or circuit.

This picture shows a drawing from the chalk board, showing the direc-tions the electrons travel: negative to positive. The current flows in the opposite direction: positive to nega-tive.

Student Worksheet p. 2Allow students to open their parts bag, and be sure that each person has all the parts. Read through each of the definitions on page 2 and ask students to find each part as you do so. A) Ask students to find an example of both stranded and solid wire among their parts. Explain that strand-ed wire is more flexible and less likely to break than solid wire. B) Explain how this switch only turns on the light when pressed, so that they can not leave their flashlight burning and wear down the battery. It’s called a “momentary” switch.C) Explain that students will receive their battery once their circuit is complete, to avoid short circuits. D) Note the red and black wires, and the different-sized snaps. Red is positive, black is negative.E) After examining the LEDs, and noting the different lengths of the leads, point out that though most LEDs have a longer positive end, with this special tri-color LED, the long lead is the negative one. F)You may relate the resistor to a funnel, only allowing the right amount of current through. Explain that we will use a 680 ohm resistor today to protect our LED.

Explain the tools briefly. You will explain them further as student use them. Show students an unplugged soldering iron, and ex-plain how to safely use a soldering iron.



3. Look at the list of electrical components below. Then, following the directions, build the circuit.

Parts for a Flashlight Circuit

A. Stranded or Solid Wire: We will use this flexible wire to connect the different parts of our circuits. B. Switch: Using this, we change the circuit from open to closed when we turn the flashlight on. C. Battery: We use this as a power source for our flashlights. It has 9 Volts of power. D. Battery Clip: When we attach this to our battery, we can connect our battery power into the circuit so that it connects to the rest of the flashlight. E. LED: LED stands for Light Emitting Diode, an electrical component that lights up when current flows through in one direction, but not the other. The longest of the 4 wires is negative. F. Resistor: We use this to reduce the electric current flowing through the circuit so it does not burn out the LED.

Tools for Building your Flashlight Circuit

A. Wire Strippers: We use the V-shaped notch in this tool to strip (or peel) the insulation off of wires. B. Needle-Nose Pliers: We use this tool to work with small electronic parts. C. Solder: We use this melted tin/lead alloy as a metal "glue" to hold the loose and less sturdy parts of the circuit together. D. Soldering Irons: We use these tools to melt the solder so it can make a good connection with the other metal parts of the circuit. It is 800 degrees, so wear safety glasses and BE CAREFUL!

Ask students to read each part. Have them find the part and discuss.

You are now ready to begin showing students how to build their flashlight. Use the longer teacher version (left) to remind yourself of the steps. See also the completed circuit photo “Flashlights Instructions” on the next page. Depend-ing on your students’ age and prior knowledge of electronics, you may wish to go step by step, or you may encour-age them to place all their components on the table to show how they would put them together to form a circuit (without making actual connections un-til you show them how to strip the wires, and give the go-ahead). You could print out the “Flashlights Instructions” photo (shown on next page) and allow students to check their own work. If you choose to go step by step, then get out your model LED, resistor and wire to show how the hooks and con-nections are made. Hand out the

student half sheet card of Flashlight Circuit Instructions (below). During instruction, ask students to refer to their card for diagrams and photos of how to at-tach certain components. Notes: 1) For the circuit to work, stu-dents must attach the resistor to the LED’s long negative lead, and then attach the other end of the resistor to the black, negative wire from the battery snap. 2) If the other LED leads touch each other, then the color may change. Some students are en-thralled by a “blue-green” light which can be created by twisting the blue

© MIT Edgerton Center 2012 MIT Edgerton Center

Flashlight CirCuit CARD (student)

longest wire

iMagE 1 - With longest wire still upright, bend all other LED wires flat against plastic cap. (Make sure they don’t touch each other.)

1.2a.

2b.

iMagEs 2a and 2b - Create a hook on one end of resistor wire, and another hook on black battery snap wire. Con-nect hooks, and then twist wires back on themselves to “lock” into place.

3a.

3b.

iMagEs 3a and 3b - Connect the red wire through one prong of the switch, twisting the bare wire back around itself. repeat with the yellow wire. Cover both connections with electrical tape, as in image 3b. (Be sure to cover the prongs, too!)

4.

image 4 - to complete circuit, create a hook on yellow wire and a hook on your choice of lED wire; twist wires to “lock” into place.

Which color? time to choose!


Flashlight CirCuit CARD (student)

longest wire

iMagE 1 - With longest wire still upright, bend all other LED wires flat against plastic cap. (Make sure they don’t touch each other.)

1.2a.

2b.

iMagEs 2a and 2b - Create a hook on one end of resistor wire, and another hook on black battery snap wire. Con-nect hooks, and then twist wires back on themselves to “lock” into place.

3a.

3b.

iMagEs 3a and 3b - Connect the red wire through one prong of the switch, twisting the bare wire back around itself. repeat with the yellow wire. Cover both connections with electrical tape, as in image 3b. (Be sure to cover the prongs, too!)

4.

image 4 - to complete circuit, create a hook on yellow wire and a hook on your choice of lED wire; twist wires to “lock” into place.

Which color? time to choose!



FLASHLIGHT CIRCUIT INSTRUCTIONSFollow these instructions to build your flashlight circuit. (Teacher version)

Step 1:Push the LED wires through the hole in the plastic cap.

Leaving the longest of the 4 wires straight, bend the other wires away from each other and flat against the plastic cap.

Step 2:Bend the longest LED wire into a hook. Bend one end of the resistor wire into a hook; splice this to the LED wire hook. Twist each.

Step 3: Wire stripping - using the 22ga size on the wire strippers, remove one inch of insulation from both the red and black wires from battery snap.

longest wire

Step 4: Wire stripping - using the 22ga size on the wire strippers, remove about one inch of insulation off of each end of the yellow wire.


Step 6: Feed the red wire through the small hole in ONE prong of switch. Bend the exposed wire in half, into a hook. Twist the loose tail of the wire back around the other half; connect metal to metal as many times as possible.

Step 7: Feed the yellow wire through the small hole in the remaining prong of the switch. Bend the exposed wire in half, into a hook. Twist the loose tail of the wire back around the other half of the wire as many times as possible.

Step 8: Put electrical tape over each of the connections to the switch. Be sure to cover not just the wire, but the prongs as well.

Step 9: Attach a battery and touch the free end of the yellow wire to each LED wire. Notice which colors appear and choose which one you like; make a hook on that wire and connect to the free end of the yellow wire.

Solder remaining connections and tape over the solder with electrical tape.

Step 5: Make a hook on the unattached end of the resistor wire; make a loose hook on the black wire of the battery snap; splice the resistor to the black wire.


and green leads together. If any lead touches the red, the red will “win”. 3) Do not solder the wire connections at the switch, as the heat may destroy the switch. You do want to cover all metal with tape to avoid bypass-ing the switch.4) Be sure stu-dents have taped down the other 2 wires of their LED to the cap. Bend the wires around on the flat part of the cap, so that the cap will eventually sit snugly in the tube.

Student Worksheet p. 3Ask students to begin drawing their completed circuit in the box. Encourage them to label all parts. As they do this, begin the soldering rotations of 4 students each. Stu-dents should solder the places where they attached the resistor to the negative LED lead and the black battery snap wire. See “A note on soldering” on p. 7 of this guide.

As students finish their drawings, instruct them to collect the tubes, caps, tape, and markers. They may begin to deco-rate. Remind them to avoid covering the switch’s hole on the tube with tape. Do not put the circuits inside the tubes until after students have soldered.


4. Draw a picture of the circuit for your flashlight. Label each component after you have drawn it below.

MY FLASHLIGHT CIRCUIT:

4. Now we move on to finishing your circuit. You may have to wait to solder your connections, so you can work on the body of your flashlight. You can use:

cardboard tubes scissors caps

markers colored tape

5. Re-attach the battery to the battery clip and try out your circuit. Once you have a working circuit, and you have soldered the connections, fit it all into your flashlight body tube. You’re done! 6. Draw a picture of your circuit in a DIFFERENT LANGUAGE: schematic symbolism. If you have time, compare your schematic picture with anyone else who is sitting around you. You can communicate with them using these schematics just like electricians and electrical engineers communicate with each other.

Once students return from soldering, have them cover their soldered joints with electrical tape. Then they may unscrew the nut and washer from their switch, place the switch inside the tube and push it out through the hole. Then replace the washer and nut to secure. Ev-erything else gets stuffed inside the tube. Placing the cap on top of the flashlight can be difficult. Students may flip over their flashlight and press it down hard on the table. Do the same for the bottom cap.

Student Worksheet p. 4When all students have soldered and put their flash-lights together, gather them for this basic introduction to schematics. First discuss the way we use picture sym-bols to represent ideas, such as a heart to indicate love or a pictogram of a woman or man on a bathroom sign. Ask if anyone knows or wants to guess what the sche-matic symbol is for a particular electronic component. When you have filled in the chart, draw the schematic for the flashlight, and ask students to copy it on their papers. Point out how much easier it is to draw than their earlier drawings of the flashlight circuit, and how much more clearly it communicates what parts are needed. Now they, too, can communicate with an electrical engineer!



Schematic Symbols: The Language of Electronics!

Wire:

Battery:

Switch:

LED:

Resistor:

MY CIRCUIT WRITTEN IN SCHEMATICS

Time to go camping!!!

Name: Answer Key

©Edgerton Center, MIT 2013 1

TRAFFIC LIGHT ACTIVITY Today, we’re going to make you into an electrical engineer! With the tools of an electrical engineer, you can make almost anything, from microwave ovens to computer monitors. We’re going to start by making a traffic light that can show us the basics of electrical circuits and components.

Part 1: Electrical Components and their Schematic Symbols, Basic Circuits

Electrical Component What it Does Schematic Symbol Bread Board

A flat base that allows us to

connect all our components. The holes are connected in a special way as shown in the picture. All the holes in the picture that are joined in a line are electrically connected with all the other

holes on that line.

Battery

Supplies electrical energy to the circuit. This battery has 9 Volts of power, and a positive (+) and

negative (-) end.

Wire

Carries current around the circuit and connects the different parts of the circuit together.

LED

+ _

The Light Emitting Diode is an electrical component that lights up when current flows through in one direction, but not the other. Long leg (wire) is positive. Short

leg (wire) is negative.

Resistor

Reduces the voltage going

through the electrical components. This protects them

from harm. Resistance is measured in ohms (Ω). We have many different powers of resistors

depending on the number of ohms.

Blue- student answers

(-) (+)

Note: parentheses indicate direction, but are not part of the schematic; instructional reference only.

Red-instructional notes

(-) (+)

Note: there is no schematic symbol for a breadboard

(-) (+)

Note: The (+) and (-) are not actually part of the schemat-ic, they are shown here to indicate direction-ality.

Name: Answer Key

©Edgerton Center, MIT 2013 1

TRAFFIC LIGHT ACTIVITY Today, we’re going to make you into an electrical engineer! With the tools of an electrical engineer, you can make almost anything, from microwave ovens to computer monitors. We’re going to start by making a traffic light that can show us the basics of electrical circuits and components.

Part 1: Electrical Components and their Schematic Symbols, Basic Circuits

Electrical Component What it Does Schematic Symbol Bread Board

A flat base that allows us to

connect all our components. The holes are connected in a special way as shown in the picture. All the holes in the picture that are joined in a line are electrically connected with all the other

holes on that line.

Battery

Supplies electrical energy to the circuit. This battery has 9 Volts of power, and a positive (+) and

negative (-) end.

Wire

Carries current around the circuit and connects the different parts of the circuit together.

LED

+ _

The Light Emitting Diode is an electrical component that lights up when current flows through in one direction, but not the other. Long leg (wire) is positive. Short

leg (wire) is negative.

Resistor

Reduces the voltage going

through the electrical components. This protects them

from harm. Resistance is measured in ohms (Ω). We have many different powers of resistors

depending on the number of ohms.

Blue- student answers

(-) (+)

Note: parentheses indicate direction, but are not part of the schematic; instructional reference only.

Red-instructional notes

(-) (+)

Note: there is no schematic symbol for a breadboard

(-) (+)

A note on soldering: We’ve found it best to teach soldering in groups of 4 in a separate room. It is possible with older students to have a sol-dering station on the side of the room or even to have soldering irons at tables. We use lead free solder, which takes a little longer to flow, but still works well. When you bring students to the location of the soldering table, instruct them not to touch anything except for their safe-ty glasses, which they should put on. They may lay their cicruit on the table.Start by showing students how to place their circuit in a “helping hand” clip, trying to hold the wire twists that need soldering in an easy-to-access configuration. Then explain how hot the irons can get (ours are 700 degrees F), so any silliness will not be tolerated, and will mean that they do not get to solder. Show students what parts of the iron get hot, including the metal rod, not just the tip, as some students may not realize they need to keep their fingers clear of that too. Show them how to hold the iron, in the hand they write with, like a pencil, with the cord over the back of their hand.They will hold the soldering wire in the other hand. Show them how to pick up the iron and place it back in the holder safely.Show them how to melt a tiny bit of solder on the tip, but then tell them they should try not to touch the tip with solder again, rather, they should heat up the places they wish to place solder (every part they twisted, except those attached to the switch), and then melt the solder on those parts. If the solder refuses to flow, they may touch the tip again briefly. Show them how to hold the tip of the soldering iron onto the wire twists that need soldering. Have students count to ten while holding the iron there firmly. Students often wiggle their hands or forget and remove the iron for a few moments, and wonder why the metal is not getting hot. When the wire connections are hot, show them how to bring in the solder wire and let it melt over the twists. Point out that since the end of the solder wire has melted, their fingers are now closer to the tip. Tell them to remind themselves over and over to move their fingers back from the end of the solder wire, keeping about 2 inches of wire in front of their fingers. Show students how “less is more” and encourage them to avoid making big globs. Show them how to quickly swipe off any excess on the sponge. Though it is tempting, ask students not to jam the solder tip on the sponge until it steams or burns. When they have finished each joint, they should replace the iron in its holder, wait a few seconds and then pull on the wires to be sure the joints are secure.


mit edgerton center: build your own flashlight - teacher’s guide … · 2014-11-03 · build your...

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