2.4 Drag Strip
Countdown Light Activity
Embedded Files
What to expect
Today we will start building the components for a drag strip that we will use to test the micro:bit-powered dragster race car that you built in the last activity. In today’s activity, we will build a device with LED lights that counts down to the start of the race. In a real-world drag race track, the National Hot Rod Association (NHRA, https://www.nhra.com/nhra) calls these count-down lights a “Christmas tree.” These lights tell the race car driver when to start the race. See Figure 1 for a real-world example of what we are building today.
In the last activity, we built a micro:bit-powered dragster race car. Today we will build an LED light countdown circuit a.k.a. “Christmas tree.” In the next activity, we will build the race track itself.
Figure 1. Drag strip “Christmas tree”, used to indicate the countdown to the start of the race
Connections
Before the Chicago Bulls played in the United Center, they played their first season in 1966-1967 in the Chicago International Amphitheater. The Amphitheater was home to Livestock shows and sporting events from 1934 until it was demolished in 1999. It was also home to Indoor Drag Races in the 1960's. Before NASCAR came to Chicago and before illegal street races took hold during the pandemic, indoor drag racing was a thing. Can you imagine the smell??
Chicago International Amphitheater Indoor Drag Racing
March 17, 1963 Wayne Bryant Omega Photo
How would indoor drag racing of electric vehicles be different?
Materials
Materials to complete one countdown light circuit (work in teams of approximately four people):
micro:bit
USB cable to connect the micro:bit to a computer
Battery Pack for the micro:bit
1 strip of 5 LED lights
3 Alligator Clips (1 Red, 1 Green, 1 White)
Instructions
In groups of approximately four people, work together to create a countdown light. The countdown light is a simple circuit that uses the connection points on the bottom of the micro:bit. We will use this circuit in the following several weeks to count down to the start of the drag race!
To build the countdown lights, we will use a strip of RGB Light Emitting Diodes (LEDs). An RGB LED actually contains small individual red, green, and blue LEDs, and it uses different combinations of these colors to create more than 16 million different possible output colors.
Collect three alligator clip wires: 1 Red, 1 Green, and 1 White. Note: if you run out of wires of a particular color, you can substitute other colors.
Connect one side of the RED alligator clip wire to the red wire from the LED strip. Connect one side of the GREEN alligator clip wire to the green wire from the LED strip. Connect one side of the WHITE alligator clip wire to the white wire from the LED strip. **In the image, note the connection of the red alligator clip to the red LED strip wire (for 3V power), the green alligator clip to the green LED strip wire (for the signal telling the LED strip how to light up), and the white alligator clip to the white LED strip wire (for a return path a.k.a. ground)
2. Connect the other side of the RED alligator clip wire to P2 on the micro:bit. Connect the other side of the GREEN alligator clip wire to the 3V connection on the micro:bit. Connect the other side of the WHITE alligator clip wire to GND on the micro:bit. ** In the image, note that the green alligator clip (for signal) is connected to P2, the red alligator clip (for power) is connected to 3V, and the white alligator clip (for the return path a.k.a. ground) is connected to GND.
3. Don’t let the exposed metal parts of the alligator clips touch each other.
4. Countdown circuit code:
Go to the code for this circuit by clicking here: Countdown Light Circuit
Click “Edit” in the upper right corner of the screen
Inspect the code. Pause here, and take a moment to think about what this code will do.
5. In the simulator window on the left side of the screen, use your cursor to click on button A. What happens?
Connect your micro:bit to the computer with the USB cable and download the code to your micro:bit (instructions)
6. Test the circuit by pressing the “A” button on your micro:bit. If everything is working correctly, you should see the LEDs light up sequentially.
Disconnect the micro:bit from the computer and connect it to a battery pack so you are able to run the program on the micro:bit without being attached to the computer.
If you have extra time, you can use cardboard to make a housing stand for your lights.
Troubleshooting
If the countdown circuit is not working properly:
Check that the alligator clip wires are connected to the correct wires on the LED strip and the connections on the micro:bit.
Check that the exposed metal parts of the alligator clip wires are not touching each other.
Check that the micro:bit is powered on (either by the USB cable or a battery pack).
Think about it
How could you change the delay time between the blinking lights?
How could you change the order in which the lights blink?
How could you change the color that the lights blink?
Feedback Link
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Next Activity Congratulations on building your own drag strip countdown circuit! In the future, we will use this countdown circuit to automatically start the micro:bit drag race. In the next activity, you can place your countdown circuit next to the race track that you will build next time.
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