- Insert the positive (long) leg of the LED into any hole of the blue row.
- Insert the negative (short) leg of the LED into any hole of the black row.
Warning: If the LED is plugged into the red row (5V) and black row (GND) the LED will break.
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.
LED did not light up
- 1. Make sure the LED is in correctly (long in blue, short in black)
- 2. Flip the LED
- Check that the resistor in the red and blue row of the breadboard.
- Check that the red wire connects from 5V to the red row.
- Check that the black wire connects from GND to the black row.
- Double check the wires are in the correct pins on the Arduino.
- Sometimes it’s just one pin hole off on the Arduino (for example, did they plug into 3.3V or maybe it’s not in GND)
- Replace LED (Sometimes the wires cross and they break, sometimes kids put the LED directly on red and black and it can break)
LED legs are bent
- It’s ok for the legs of the LED to be bent or reshaped.
Can’t find the long/short leg of LED
- If the legs of the LED have been reshaped too much, it can be difficult to figure out which leg is short or long.
- Placing the LED in backwards won’t have a negative effect on the LED, it just won’t turn on, so try it one way and if that doesn’t work, try flipping it around.
LED is on, but the resistor and LED are in each other's spots
- 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. As long as the positive and negative side of the LED are "pointing" towards the positive and negative sides of the power source, respectively, and a resistor in its pathway, then it should work.
1. This is an opportunity to gauge the students understanding of translating a schematic to an actual circuit by asking “ Where does the positive and negative sides of the LED plug into the breadboard”
- Hopefully they answer: positive goes into blue and negative goes into black
2. If they don’t answer correctly, try retracing how the schematic translates to the circuit.
3. This is also an opportunity to describe a complete circuit. Place your finger at 5V and remind them how this is the positive side of power,… then go through each step:
• Can electricity travel through the red wire?
o Yes, travel through the red wire go to the red row of breadboard.
• Can electricity travel through the red row?
o Yes, move your finger across the red row until you hit the resistor.
• Can electricity travel through the resistor?
o Yes, travel 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?
o Yes, travel along the blue row until you hit the LED.
• Can electricity travel through the LED?
o Yes, travel through up and over the LED into the black row.
• Can electricity travel through the black row?
o Yes, travel along the black row until you hit the black wire.
• Can electricityI travel through the black wire?
o Yes, travel back to GND.
• Do you see how this is a complete circuit from a positive and negative source of power?
4. If you have a 3- volt coin cell battery, this works as a great 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 you know it is burnt out. It is also good to reinforce that the coin cell battery does not need a resistor since it is only 3 volts, which is exactly what our LED needs.
Thinkabit Companion Notebook: have students fill in the blank on page 4 after “LED” with “long leg (+) in blue row, short leg (-) in black row.”