Add the LED

Warning: Do not connect the LED into the red row and black row.  If the LED is plugged into the red row (5V) and black row (GND) the LED will break.

1. Insert the positive (long) leg of the LED into any hole of the blue row.

2. Insert the negative (short) leg of the LED into any hole of the black row.

STEM Connections

When you plug the negative leg of the LED into any hole in the black row, it completes the electrical circuit. This allows electric current to flow in a circle from the positive terminal of the power source through the Arduino board, then through the red wire, the red row of the breadboard, the resistor, the blue row of the breadboard, the LED, the black row of the breadboard, the black wire, and finally back through the Arduino board and into the power source.

At the Thinkabit Lab, we gauge students' understanding of translating a schematic to an actual circuit and provide them with an opportunity to describe a complete circuit. We engage students in the following discussion:

1. Ask students: “Where does the positive and negative side of the LED plug into the breadboard?”

2. Students should respond: positive goes into blue and negative goes into black.

3. Ask students to place their finger at 5V and remind them that this is the positive side of power, and then go through each of the following steps:

   • Can electricity travel through wire?
              Yes, Electricity travels through the red wire going to the red row of the breadboard.
      
   • Can electricity travel through the 5 holes of the red row of the breadboard?
              Yes, Move your finger across the red row until your finger touches the resistor.
      
   • Can electricity travel through the resistor?
              Yes, Electricity travels up through one leg of the resistor, through the resistor and down to the blue row of the breadboard.
      
   • Can electricity travel through the blue row?
              Yes, Use your finger to travel along the blue row until your finger touches the LED.
      
   • Can electricity travel through the negative leg of the LED?
              Yes, Electricity travels through the LED into the black row.
      
   • Can electricity travel through the black row?
              Yes, Electricity travels along the black row until you hit the black wire.
      
   • Can electricity travel through the black wire?
              Yes, Electricity travels back to GND.
      
4. Confirm that students understand that this is a complete circuit from a positive and negative source of power.
    
5. Ask students: “Is a battery a source of power?"
   • Yes! It has both positive and negative ends and it contains stored energy.  We can use a 3-volt coin cell battery as an LED tester. Simply place the long leg against the positive side of the battery and the short side against the negative side of the battery. If the LED does not turn on, then it is burnt out.
      

If you are using the Thinkabit Lab Notebook:

Have students fill in the blank on page 13 after “LED” with “long leg (+) in blue row, short leg (-) in black row.”

LED:    long leg (+) in blue row    
             short leg (-) in black row   

LED did not light up

1. Make sure the LED is placed correctly by placing the long leg/ positive side in the blue row of the breadboard and the short leg/ negative side in the black row of the breadboard.

2. Flip the LED.

3. Check that the resistor is in the red and blue row of the breadboard.

4. Check that the red wire is connected from 5V to the red row.

5. Check that the black wire is connected from GND to the black row.

6. Double-check the wires are in the correct pins on the Arduino.

7. Sometimes it is just one pin hole off on the Arduino (for example, did students plug the red wire into 3.3V or maybe the black is not in GND).

8. Replace LED (Sometimes the wires cross and they break, sometimes students put the LED directly on red and black and it breaks).

LED legs are bent

1. Bend and reshape the legs of the LED, as necessary.

2. Replace the LED if it breaks. It is normal for LEDs to break after repeated reshaping of the legs.

Can’t find the long/short leg of LED

1. If the legs of the LED have been reshaped too much, it can be difficult to figure out which leg is short or long.

2. Placing the LED in backward won't have a negative effect on the LED, it just won't turn on, so you can try it one way and if it doesn't work, flip it around.

3. You can also identify the short leg of the LED by doing the following:

   • If you trace your finger along one of the legs up to the plastic bulb, you should see a flat edge. That flat edge of the bulb is also an indicator that it is the negative side/short leg.

   • If you look inside the bulb, you’ll notice two different metal pieces, a big one and a little one. The big one is on the side of the short leg/ negative side.

LED is on, but the resistor and LED are in each other's spot

1. There are different ways to get an LED to turn on as there are different ways to build a circuit and still have the same effect. If the positive and negative side of the LED is " pointing" towards the positive and negative sides of the power source, respectively, and a resistor is in its pathway, then it should work.