Dr. Janet K. Lumpp, jklumpp@uky.edu
KEEP - Kentucky Electronics Education Project
Flashing LED Circuit Assembly Activity
Project: Each student will build a flashing LED circuit to take home.
Skills:
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Safety first
Listening to directions
Following directions and diagrams
Learning to solder
Working with a partner
Safety:
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Safety goggles - during soldering and cutting wires
Long hair pulled back
Proper use of soldering irons
Top and bottom of the circuit board:
The shiny copper pattern is the bottom of the circuit board. The top of the circuit board is blank.
Components are placed on the top side of the board with the wire leads sticking through on the
bottom side of the board. The component leads will be soldered to the copper wires to complete
the circuit. Set the board on the table with the copper side facing the table and the words at the
bottom.
Bottom
Top
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Placing Components:
Empty out the envelope of components and sort them. It is extremely important to place the
components in the right locations on the board and in the right directions. We will go through
the placement as a group, please do not go ahead because you may put something in backwards.
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Dr. Janet K. Lumpp, jklumpp@uky.edu
KEEP - Kentucky Electronics Education Project
LED = light emitting diode, “light bulb”
1 green, 1 yellow - either location, in the right direction
Two ways to determine the direction of the LED:
Long lead and short lead
Flat side on the colored plastic
On the circuit board - four holes along right side
“long leg - short leg - long leg - short leg”
Push LEDs all the way down through the board until the colored plastic is at the surface of the
board. Bend the legs apart in a V to keep the LEDs from falling back out of the holes.
Long lead
Short lead = flat side
Long lead
Short lead = flat side
Resistors - “peanuts with colored stripes”
Two resistors with orange-orange-orange-gold stripes = 33,000 ohms
Resistors do not have a required direction. Since we
are using two of the same value, they can go in either
location.
Hold the resistor “peanut” and bend the leads into a U
shape. Insert one resistor through each pair of holes. Pull on
the leads with the needle nose pliers to get the resistor down
to the surface of the board.
Bend the leads into a V or X to keep the resistors from falling out of the holes.
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Dr. Janet K. Lumpp, jklumpp@uky.edu
KEEP - Kentucky Electronics Education Project
Notch
IC = integrated circuit = chip, “spider”
One 555 timer chip, must be placed in the right direction.
Determining the right direction:
Spot
Notch at one end of black body
Round spot near one corner of the black body
Stand the chip on its leads, “spider on its legs” and find the notch or spot.
Notch at the top
Spot in the upper left, away from the LEDs
Carefully, insert the four leads on one side and then work on the other side.
Notch
Spot
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Dr. Janet K. Lumpp, jklumpp@uky.edu
KEEP - Kentucky Electronics Education Project
Capacitor - cylinder, “pop can, soda can”
One black cylinder with a white stripe, leads stick
out of the top and bottom of the can.
Finding the right direction:
Indentation
White stripe
V arrows
Indentation in can
White stripe with V arrows
Bend the leads, insert in the right direction, and use pliers to pull the capacitor down to
the surface of the board.
Bend the leads into a V or X to keep the capacitor from falling out of the holes.
Indentation
V arrows
Battery connector - red and black wires with 9V battery snap
Red = + (Red Cross), positive side of battery voltage
Black = - , negative side of battery voltage
Insert the black and red wires into the +/- holes on the left side of the board.
Tape the wires to the top side with black electrical tape.
+ Red
+ Red
- Black
- Black
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Dr. Janet K. Lumpp, jklumpp@uky.edu
KEEP - Kentucky Electronics Education Project
Double check the orientation of each component
LEDs – long/short/long/short leads
Resistors – no required direction
IC – spot away from the LEDs, notch at the top
Capacitor – indentation at top, arrows pointing down
Battery wires – red+, blackClosing the loop, completing the circuit:
If we connected a battery now, nothing would happen because we have open circuit connections
between the circuit board wires and the component leads. We close the circuit by soldering.
Soldering melts a small amount of metal at each open circuit and makes the metal to metal
conductor between the circuit board wires and the components.
How to solder:
Soldering iron – the soldering iron is our heat source. The metal pointed end gets hot.
The brown plastic part is the handle. When you are soldering, you hold the iron like a pencil –
right or left handed – with the tip pointing down. When you are not soldering, the iron goes in
the stand. The coil part of the stand keeps us from bumping into the hot part. The sponge on the
stand is for wiping off the tip.
DO NOT – hand the soldering iron to someone else.
DO NOT – lay the soldering iron down on the table.
DO NOT – poke or sword fight with the soldering iron.
DO NOT – melt or burn anything other than the solder and circuit board.
In order to solder, we need to heat three things: 1.) the copper “donut” on the circuit
board, 2.) the component wire sticking through the hole, and 3.) the solder.
Component lead wire
Copper donuts
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Dr. Janet K. Lumpp, jklumpp@uky.edu
KEEP - Kentucky Electronics Education Project
1. Heat the donut and
component lead with the
soldering iron. Press the tip
of the iron on the donut and
wire, count to 5.
2. Bring the solder wire near
the tip of the iron and watch
for the solder to melt.
Continue to add solder until
it flows all of the way
around the donut and part
way up the wire lead.
3. Take the solder away.
4. Take the soldering iron away.
Remember to – keep the soldering iron in place while the solder melts, and take the solder away
before removing the iron.
If the solder gets stuck to the board – melt it again with the soldering iron.
The right amount of solder:
Not enough – solder only covers part of the donut
Too much – solder forms a ball shape or crosses over to another donut (short circuit)
Just right – solder covers entire donut and forms a cone or “kiss” around the wire
Solder joints can be reheated to add or remove solder.
Suggestions:
Start with larger donuts spaced farther apart.
Hold the board still for your partner while they solder, take turns.
Trim long wires AFTER soldering at the top of the solder cone.
Solder IC leads last, do not trim.
Review soldering safety
Wear safety goggles, pull back long hair
Which part of the soldering gets hot?
Which part do you hold on to?
How do you hold it?
What do you do with the soldering iron when you are not soldering?
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Dr. Janet K. Lumpp, jklumpp@uky.edu
KEEP - Kentucky Electronics Education Project
Start soldering:
Let the students solder.
Circulate to help them get started.
Remove excess solder with solder wick, as needed.
Before connecting a battery:
Look for excessive solder and short circuits around the LED and IC leads.
Drag a hot soldering iron tip between the leads.
Use solder wick to remove excess solder.
Look for joints with too little solder.
Ask the student to add solder.
Hook up a battery!
If it works – LEDS flash alternately - Congratulations!
If it does not work:
Look for short circuits and open circuits in the soldering.
Look for components incorrectly placed.
Re-melt each solder joint to improve the connections.
Turning the circuit off:
Disconnect the battery snap from the battery.
Students may keep their circuit and battery.
Use a permanent marker to mark their name or initials on the circuit board.
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