Download MIT Edgerton Center: Build Your Own Flashlight

MIT Edgerton Center: Build Your Own Flashlight - Teacher’s Guide
Preparation 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, helping 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 switchsized 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 long
Per 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
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, 2013
Page 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).
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 connection 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.
Box A
Box B
Please write down your observations of how you think the flashlight works (think about
the circuit – which pieces are connected?):
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 directions the electrons
travel: negative
to positive. The
current flows in the
opposite direction:
positive to negative.
____________________________________________________________________________________________________
Now you are ready to see what materials you will use to BUILD Your Own Flashlight!
 MIT Edgerton Center 2012
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© MIT Edgerton Center, 2013
3. Look at the list of electrical components below. Then, following the directions,
build the circuit.
Ask students to read each part. Have them find the part and
discuss.
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!
 MIT Edgerton Center 2012
© MIT Edgerton Center, 2013
Student Worksheet p. 2
Allow 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 stranded 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 differentsized 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 explain how to safely use a soldering iron.
2
Page 3
FLASHLIGHT CIRCUIT INSTRUCTIONS
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.
You are now ready to begin showing
students how to build their flashlight.
Step 1:
longest wire
Push the LED wires through the hole in the
Use the longer teacher version (left) to
plastic cap.
Step 6:
Feed the red wire through the small hole in ONE prong of switch. Bend
remind yourself of the steps. See also
Leaving the longest of the 4 wires straight,
the exposed wire in half, into a hook. Twist the loose tail of the wire back
bend the other wires away from each other
around the other half; connect metal to metal as many times as possible.
the completed circuit photo “Flashlights
and flat against the plastic cap.
Step 7:
Instructions” on the next page. DependStep 2:
Feed the yellow wire through the small
Bend the longest LED wire into a hook. Bend one end of the resistor wire
hole in the remaining prong of the
ing on your students’ age and prior
into a hook; splice this to the LED wire hook. Twist each.
switch. Bend the exposed wire in half,
into a hook. Twist the loose tail of the
knowledge of electronics, you may wish
wire back around the other half of the
wire as many times as possible.
to go step by step, or you may encourage them to place all their components
Step 8:
Put electrical tape over each of the
on the table to show how they would
connections to the switch. Be sure to
cover not just the wire, but the prongs
put them together to form a circuit
as well.
Step 3:
Wire stripping - using the 22ga size
(without making actual connections unon the wire strippers, remove one
inch of insulation from both the red
til you show them how to strip the wires,
and black wires from battery snap.
Step 9:
andFlashlight
give the go-ahead).
You could
CirCuit CARD
(student)
Attach a battery and touch the free
end of the yellow wire to each LED
print
out
the
“Flashlights
Instructions”
wire. Notice which colors appear and
choose which one you like; make a
Step 4:
wire
photolongest
(shown
on
next page) and allow
hook on that wire and connect to the
Wire stripping - using the 22ga size on the wire strippers, remove about one
1.
2a.
free end of the yellow wire.
inch of insulation off of each end of the yellow wire.
students to check their own work.
Solder remaining connections and tape
over the solder with electrical tape.
If you choose to go step by step, then
2b.
get out your model LED, resistor and
wire to show how the hooks and coniMagEs 2a
and 2b the
- Create a hook on
nections are made. Hand
out
one end of resistor wire, and another
iMagE 1 - With longest wire still upright,
hook on black battery snap wire. Constudent half sheet card of Flashlight Circuit Instructions (below). During instruction, askbendstudents
to
refer to
their card for
all other LED wires flat
against
nect hooks, and then twist wires back
plastic cap. (Make sure they don’t
on themselves to “lock” into place.
touch each other.)
diagrams and photos of how to attach certain components.
Flashlight CirCuit CARD (student)
3a.
Notes: 1) For the circuit to work, stu4.
dents must attach the resistor to the
longest wire
Which
1.
color?
2a.
LED’s long negative lead, and then
time to
choose!
attach the other end of the resistor
iMagEs 3a and 3b - Connect the red wire
through one prong of the switch, twisting the
bare wire back around itself. repeat with the
2b.
to the black, negative wire from the
yellow wire. Cover both connections with
electrical tape, as in
battery snap. 2) If the other LED leads
3b.
image 3b. (Be sure
to cover the prongs,
too!)
touch each other, then the color
iMagEs 2a and 2b - Create a hook on
image 4 - to complete circuit, create a
one end of resistor wire, and another
may change. Some students are enhook on yellow wire and a hook on your
iMagE 1 - With longest wire still upright,
hook on black battery snap wire. Conchoice of lED wire; twist wires to “lock”
bend all other LED wires flat against
nect hooks, and then twist wires back
into place.
plastic
cap.
(Make
sure
they
don’t
thralled by a “blue-green” light which
on themselves to “lock” into place.
touch each other.)
can be created by twisting the blue
Follow these instructions to build your flashlight circuit. (Teacher version)
© MIT Edgerton Center 2012
© MIT Edgerton Center 2012
MIT Edgerton Center
MIT Edgerton Center
© MIT Edgerton Center 2012
Page 4
3a.
MIT Edgerton Center
© MIT Edgerton Center, 2013
4.
Which
color?
4. Draw a picture of the circuit for your flashlight. Label each component after you
have drawn it below.
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 bypassing the switch.
4) Be sure students 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. 3
Ask 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. Students 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.
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.
 MIT Edgerton Center 2012
3
As students finish their drawings, instruct them to collect the tubes, caps, tape, and markers. They may begin to decorate. 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.
© MIT Edgerton Center, 2013
Page 5
Name: Answer Key
TRAFFIC LIGHT ACTIVITY Blue- student answers
Red-instructional notes
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
Bread Board
What it Does
Schematic Symbol
Schematic
Symbols:
A flat base
that allows us to The Language of Electronics!
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.
Wire:
Note: there is no schematic
symbol for a breadboard
Battery:
Supplies electrical energy to the
Battery
Switch:
Wire
(+) (-­) circuit. This battery has 9 Volts of
power, and a positive (+) and
negative (-) end.
Note: parentheses indicate
direction, but are not part of the
schematic; instructional
reference only.
Carries current around the circuit
and connects the different parts
of the circuit together.
LED:
(-­) (+) The Light Emitting Diode is an
(-­) Answer (+) Name:
Key
electrical component that lights
up when
current
flows
through inBlue- student answers
TRAFFIC
LIGHT
ACTIVITY
one direction, but not the other.
Red-instructional notes
Long you
leg (wire)
is electrical
positive. Short
+
Today,
we’re_ going to make
into an
engineer! With the tools of an
(wire)
is negative.
electrical engineer, you can leg
make
almost
anything, from microwave ovens to
Resistor
computer monitors. We’re going to start by making a traffic light that can show
Reduces
thecomponents.
voltage going
us the basics of electrical circuits
and
through the electrical
components.
protects
them
Part 1: Electrical Components and their
SchematicThis
Symbols,
Basic
Circuits
from harm. Resistance is
measured
in ohms (Ω). We have
Electrical Component
What it Does
Schematic Symbol
many different powers of resistors
Bread Board
depending on the number of
A flat base that allows us to
ohms.
connect all our components. The
holes are connected in a special
Note: there is no schematic
way as shown in the picture. All
symbol for a breadboard
the holes in the picture that are
joined in a line are electrically
connected with all the other
©Edgerton Center, MIT 2013
1
holes on that line.
Battery
(+) Supplies electrical energy to the
(-­) circuit. This battery has 9 Volts of
power, and a positive (+) and
negative (-) end.
Note: parentheses indicate
LED
Resistor:
MY CIRCUIT WRITTEN IN SCHEMATICS
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.
direction, but are not part of the
schematic; instructional
reference only.
(+) (-­) 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.
(-­) (+) ©Edgerton Center, MIT 2013
Note: The
(+) and
(-) are not
actually
part of the
schematic, they
are shown
here to
indicate
directionality.
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. Everything 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. 4
When all students have soldered and put their flashlights together, gather them for this basic introduction
to schematics. First discuss the way we use picture symbols 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 schematic 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!
1
Time to go camping!!!
 MIT Edgerton Center 2012
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© MIT Edgerton Center, 2013
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 soldering 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 safety 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, 2013
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