Design Your Own Smart LED Lighting System

This project follows the Engineering Design Process. Confirm with your teacher if this is acceptable for your project, and review the steps before you begin.

Designing Your Smart LED System

It might be tempting to dive right in and start building something, but part of the engineering design process is coming up with a design before you start building.

In this case, you need to figure out what the objective of your smart LED lighting system is. Do you want to build motion-activated lights that turn on automatically when someone enters a room? Do you want to make an auto-dimming "sunset" night light that gradually changes color and dims when it is time for bed? A warning light that changes from green to red when people get too close to your room? A dance party light system that reacts to music? There are endless possibilities, and it is up to you what you build.

For all of these cases, you need to think about what sensor(s) you need, where you will physically mount the LED strips, and how the LED strips will react to the sensors. Follow our guide for the engineering design process and move to the next section when you are ready for the prototyping step.

Using Your LED Strip

https://www.youtube.com/watch?v=WtP7sxWSF9c

When building a complex system, it is often easier to build and test it one part at a time instead of building it all at once. That way you can make sure that the individual parts of your system are working before you test the whole thing. This approach also makes it easier to isolate and troubleshoot issues when something does not work. For this project, that means connecting and testing your LED strip before you connect any sensors.

1. If needed, cut your LED strip to the length you want. Many LED strips have lines to help you cut them to length, usually spaced after every three LEDs. Make sure you read the instructions for your LED strip before cutting it.
2. If needed, solder wires to the tabs on your LED strip, then wrap them in heat shrink tubing (Figure 4). Make sure you color-code the wires so you know which one is which. If your LED strip came with wires attached, you can skip this step.

   Image Credit: Ben Finio, Science Buddies / Science Buddies

   Figure 4. Wires soldered to an LED strip.
3. Orient your Arduino and breadboard so they match the orientation in Figure 5.
4. Place the three MOSFETs in the breadboard with the writing on the black side facing to your right and the large metal tabs facing to your left. Each MOSFET has three pins, and each pin should go in its own row.
5. You will connect the three MOSFETs such that each one controls one color (red, green, or blue) on your strip. Decide which MOSFET will control which color. For each MOSFET:
   1. Connect the pin closest to the top of the breadboard (the MOSFET's "source") to the ground bus.
   2. Connect the pin closest to the bottom of the breadboard (the MOSFET's "gate") to an Arduino PWM pin (a pin with a "~" next to it). Our example code uses pins 3, 5, and 6 for red, green, and blue respectively.
   3. Connect the center pin (the MOSFET's "drain") to the corresponding wire from the LED strip.
6. Put the switch in the breadboard so that each of the three pins is in its own row.
   1. Connect the center pin to the power bus on the right side of the breadboard.
   2. Connect the top pin to the positive wire from your 12 V power supply. (Use an adapter if needed, but do not plug your power supply into the wall yet.)
7. Connect power to your circuit.
   1. Make sure the entire circuit has a common ground. The Arduino's GND pin, the negative wire from your 12 V power supply, and both breadboard ground buses should all be connected.
   2. Connect the 5 V pin from your Arduino to one of the breadboard's power buses (in Figure 5, this is the bus on the left). Make sure you do not connect the breadboard's two power buses to each other. This will short-circuit 12 V to 5 V and could damage your circuit.
   3. Connect the +12 V wire from your LED strip to the 12 V power bus on your breadboard (the right side in Figure 5).
   4. Plug your power supply into the wall but keep the power switch in the "off" (down) position for now.
   5. Plug your Arduino into your computer with a USB cable.
   6. If you see or smell smoke or if anything feels hot, immediately unplug both your power supply and the USB cable. You have a short circuit somewhere. Double check your entire circuit, paying particular attention to whether you have accidentally shorted 12 V to 5 V.
   Image Credit: Ben Finio, Science Buddies / Science Buddies

   Figure 5. A breadboard diagram for connecting an analog RGB LED strip to an Arduino.
8. Download the led_strip_fade.ino example code and upload it to your Arduino. This code uses the Arduino's analogWrite command to set the brightness of each LED color between a value of 0 (off) and 255 (maximum brightness).
9. Turn the power switch on the breadboard to the "on" (up) position. You should see your LED strip automatically fade through different colors! If your strip does not power on at all or does not change colors, double check all the connections on your breadboard, especially to the MOSFETs.
10. Open the serial monitor in the Arduino IDE (Tools → Serial monitor) and watch the red, green, and blue values as they change. How do they correspond to the color of the LED strip?
11. Try changing the fadeDelay variable in the code and see what happens.
12. At least one of the color values (red, green, or blue) is always zero in this example code. What happens if you activate all three colors at once?
13. Optional: How does the brightness of the LEDs correspond to the analogWrite value? If you set the brightness of a single color to 128 and leave it constant, does it appear half as bright as when it is set to 255?

Using a Sensor

After your LED strip is working, you should test your sensor separately. Remember that this makes it easier to find and identify any problems in your circuit.

1. Save your LED code and open a new file.
2. If you followed our circuit diagram in Figure 5, you should have plenty of space on the left side of your breadboard to connect one or more sensors. Connect your sensor to the Arduino and write a simple program to test its output—by controlling a single regular LED, for example, or by printing the sensor value to the serial monitor.
3. Follow along with the appropriate tutorial(s) to test your sensors. Tutorial videos for the five sensors shown in Figure 2 (PIR, ultrasonic, potentiometer, microphone, and photoresistor) are listed below. If you purchased a sensor that is not listed here, you can check our How to Use an Arduino page to see if your sensor is listed, or you can look up another tutorial online.

https://www.youtube.com/watch?v=3gj_68ywod4

https://www.youtube.com/watch?v=n-gJ00GTsNg

https://www.youtube.com/watch?v=Wa8CjGsOFzY

https://www.youtube.com/watch?v=bMs5J4bJOD0

https://www.youtube.com/watch?v=XwJQJnY6iUs

4. Think about how you will use your sensor in your project and where it needs to be positioned. For example, you might start testing an ultrasonic sensor just by waving your hand in front of it while it is sitting on a table. But if you want it to detect a person walking toward a room, it may need to be mounted on a wall. Depending on where you put your Arduino, you might need longer wires to connect the sensor to your breadboard. Make sure you test your sensor under these real-world conditions.

Making Your LED Strip React to a Sensor

So far you have one program that controls your LEDs and one program that takes a reading from your sensor. Now you need to combine them and make your LEDs react to your sensor. If you need help getting started, refer to these example programs for the five sensors we have discussed:

• PIR sensor
• Ultrasonic sensor (HC-SR04 and PING)
• Potentiometer
• Microphone
• Photoresistor

Note that the Arduino map function is very useful in some of these programs to convert the sensor's output from its original range (which can vary) to the range needed to control LED brightness (0 to 255).

You can change these programs as much as you want. If you are using multiple sensors, you may want to combine their programs. And if you are using a completely different sensor, you can write your own program! Remember that there is no right or wrong way to do this project—it all depends on the criteria you set for your design in the engineering design process.

After writing your program, make sure you test it. You may need to make changes to your code. For example, you might have to change a sensor threshold value or adjust the R, G, and B values to get the exact color(s) you want.

Once your design is finalized, you can impress your friends and family with your own smart RGB LED lighting system!