Monitor Plant Health with a Color Sensor

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.

Build Your Circuit

Assemble your circuit as shown in Figures 3 and 4. Important: depending on where you bought your breadboard, the left-right orientation of the power and ground buses may be reversed. 

1. Connect red, yellow, and green LEDs to Arduino pins 8, 9, and 10 respectively. Use 220Ω current-limiting resistors for the Arduino UNO R3 and 470Ω resistors for the UNO R4. 
2. Connect the color sensor pins as follows. Use male-female jumper wires to connect the color sensor pins to your breadboard. Important: depending on where you bought your sensor, the physical order of the pins on your sensor board might not match Figures 3 and 4. Make sure you read the labels on your sensor and connect the pins accordingly.
   1. VCC pin to 5V (your sensor may have more than one VCC pin).
   2. GND pin to GND (your sensor may have more than one GND pin).
   3. S0 to Arduino pin 2
   4. S1 to Arduino pin 3
   5. S2 to Arduino pin 4
   6. S3 to Arduino pin 5
   7. LED to 5V
   8. OUT to Arduino pin 6

Image Credit: Ben Finio / Science Buddies

Figure 3. Breadboard diagram for connecting the color sensor and LEDs. Note that the pins on your color sensor may be in a different order, and the left/right orientation of the power (+) and ground (-) buses on your breadboard may be reversed.

Image Credit: Ben Finio / Science Buddies

Figure 4. Pinout diagram for the TCS3200 color sensor. Remember that the pins on your sensor may be in a different order, so make sure you read the pin labels. 

Test the Code

1. Download color_sensor_LEDs.ino.
2. Read through the commented code so you understand how it works.
3. Upload the code to your Arduino.
4. Open the serial monitor (Tools→Serial monitor).
5. Look at the red, green, and blue (RGB) values printed out on the serial monitor.
6. If you have not already, make sure you watch the tutorial video about the color sensor in the introduction. Remember that a smaller number (the pulse width measured by the pulseIn function) means more of that color light. If you find this confusing, you can uncomment the lines of code that use the Arduino map function. You can use this function to convert the light readings to a range where a bigger number means more light. 
7. Experiment with holding the color sensor over different color surfaces and at different distances and watch how the RGB values change. 

Calibrate Your Sensor

1. Gather the leaves that you plan to use for your experiment. Make sure you have several samples each of at least two different colors (healthy and unhealthy). 
2. Using the resources in the Bibliography, or other resources that you find online, try to figure out what the discoloration means for your specific plant species. What are some possible underlying causes? How are they treated?
3. Make a data table like Table 1. Add rows as needed.
4. For each leaf, fill in the actual color that you see with your eyes in the data table (green, yellow, brown, etc.).
5. Hold the color sensor directly over the leaf at a constant distance, and watch the RGB values in the serial monitor. They will fluctuate slightly even if you hold the sensor perfectly still. Write down typical or average values for the red, green, and blue readings. 
6. Repeat this process for each one of your leaves. If your leaves are large enough, you can even take readings at different locations on each leaf. 

6. Based on the values you recorded in Table 1, now you will need to add conditions to the if statements in the code to detect certain colors. For example, the condition (red > 40 && green < 20 && blue > 30) will be true if the red value is greater than 40, the green value is less than 20, and the blue value is greater than 30. This means that there is more green light and less red or blue light (assuming you are not using the map function to change the values so that a bigger number means more light, in which case you would need to reverse the greater than and less than signs). You can read more about if statements, logical operators, and comparison operators in the Structure section of the Arduino language reference.
7. Enter conditions you developed in the previous step in the code where it says "FILL IN YOUR CONDITIONS HERE" and uncomment the if/else statements. Re-upload the code to your Arduino and try holding the sensor over different leaves. Do the red, yellow, or green LEDs light up appropriately? If not, watch the RGB values in the serial monitor. How do they compare to the values you entered in your if statement conditions? You may need to leave a slight buffer or margin for error in your values. For example, if you typically read a green value of 20 on a green leaf, you could set the condition for green<25.
8. Continue iteratively testing your leaves and adjusting the conditions for your if statements. Document your conditions for each iteration in your lab notebook. Can you adjust your code so you avoid false positives (detecting a healthy leaf as unhealthy) or false negatives (detecting an unhealthy leaf as healthy)?
9. What other changes or improvements could you make to your code? See the Variations section for more ideas. 
10. Going forward, how could you use your color sensor to monitor plant health? What would your treatment plan be when you detect unhealthy leaves?