Lego Mindstorms EV3: Color Sensor In Detail

The Lego Mindstorms EV3 Color sensor can measure a color or the intensity of a light source and convert either measurement into a numeric value. It can measure up to seven different colors and will also detect the absence of color.

Within the EV3 Programming software, the Color Sensor block belongs to the Yellow group and it assumes that the color sensor is connected to port 3 on the EV3 Brick by default. This is not necessarily set in stone and can be changed by updating the port number on the top right of the brick:

How does the EV3 Color Sensor Work?

When looking at the color sensor you may notice that there are 2 lenses on the front. The larger lens is a LED lamp that is used to send out light and the smaller lens is the color sensor . The LED lamp emits different colored light depending on the mode the Color Sensor is running in and these modes are set within the Color Sensor programming block.

Reflected Light Intensity Mode

In Reflected Light Intensity mode, the EV3 Color Sensor will emit a red light from the LED lamp and measure the intensity of light reflected back into the color sensor. Using a scale from 0 (very dark) to 100 (very light), the sensor will assign a number to the intensity reading.

Ambient Light Intensity Mode

In Ambient Light Intensity mode the color sensor will measure the strength of light that hits the color sensor. It will output a numeric value based on the intensity of the light between 0 (very dark) and 100 (very light).

Color Mode

In color mode the LED lamp emits red, green and blue light and uses the color sensor to determine any one of seven colors (black, blue, green, yellow, red, white, brown), it will also detect no color.

EV3 Color Sensor Code Values

The EV3 Color Sensor assigns a numeric value to each color it recognises, the table below lists all these values (or color IDs):

Color	Value
No Color	0
Black	1
Blue	2
Green	3
Yellow	4
Red	5
White	6
Brown	7

EV3 Color Sensor Modes

There are three main modes within the color sensor programming block:

• Color Mode: Reads up to seven colors (plus it can detect the absence of color)
• Ambient Light Intensity Mode: measures the light being emitted from an external source (e.g. sunlight or a flashlight)
• Reflected Light Intensity Mode: measures the light intensity reflected off the surface of an object.

The details of how each of these modes work have been outlined within the How does the EV3 Color Sensor Work? section of this post.

Outside of these modes there are two different options you can use to run them in:

• Measure
• Compare

Each of the combination of these modes and options are outlined below:

Color Mode

Compare

In Compare Color Mode you are able to select one or more colors for the sensor to detect, once any one of the selected colors is found, the programming block will output True.

Measure

Measure Color Mode will out put the numeric value for the color that the sensor detects. This color value can then be wired into your program to activate other logic based on the output.

For more information on the color codes see the table within the EV3 Color Sensor Code Values section of this post.

Reflective Light Intensity Mode

Measure

In Measure Reflective Light Intensity mode the color sensor will detect the intensity of light reflected off a source and output the measurement as a numeric value between 0 (very dark) to 100 (very light).

Compare

In Compare Reflective Intensity mode the EV3 color sensor will compare the intensity of the reflected light to the configured threshold value and compare type. In this mode, the Color Sensor programming block will output either True or False.

Ambient Light Intensity Mode

Measure

In Measure Ambient Light Intensity mode the color sensor will detect the intensity of an external light source and output the measurement as a numeric value between 0 (very dark) to 100 (very light).

Compare

In Compare Ambient Light Intensity mode the color sensor will detect the intensity of an external light source and compare it to the threshold and compare type. When in this mode, the Color Sensor programming block will output either True or False.

Can I purchase an Additional Color Sensor?

Yes, you can purchase an additional color sensor. They retail for about $45 USD and can be purchased from Amazon here.

Why would I need an additional Color Sensor?

The most common use of an additional EV3 color sensor if for programming an EV3 Robot to follow a line, each sensor can be placed either side of the line and can be used to steer the EV3 Robot by reading the output of each sensor to determin where the line is.

Calibrating the EV3 Color Sensor

When running the EV3 Color sensor in Reflected Light Intensity mode then it’s recommended the sensor is calibrated, especially if lighting (or table) conditions change.

Calibrating will reteach the sensor what is black (0) and what is white (100).

How to Calibrate the Color Sensor

To calibrate the EV3 Color Sensor we’ll utilise the Calibrate Mode on the yellow Color Sensor programming block.

I’ll take you through creating this program step by step and we’ll create a program which execute the following logic:

1. Reset the Color Sensor Calibration
2. Show an onscreen prompt asking you to place the sensor on a black object
3. Wait for the center button on the EV3 Brick to be pressed
4. Calibrate the Black within the sensor and show the value on the screen for 2 seconds
5. Show an onscreen prompt asking you to place the sensor on a White object
6. Wait for the center button on the EV3 Brick to be pressed
7. Calibrate the White within the sensor and show the value on the screen for 2 seconds

Note: if you’d prefer to download the program,  I’ve put this EV3 Color calibration program together for a download in the next section.

Lets get started!

1. Reset Calibration: Drag and drop a Yellow Color Sensor block up to the Start button and set its mode to  Calibrate | Reflected Light Intensity | Reset

2. Add a prompt to place Sensor on Black line: Drag and drop a Green Display block next to the color sensor reset block.
   • Set the following attributes:
     • X = 3
     • Y = 50
     • aA (Text size)= 1
   • Set its mode to Text | Pixels and type the following text into the Text paramiter (top right):

Place Sensor on Black Line

3. Add Wait for the center button push: Next drag and drop a Orange Wait block next to the display block and set its mode to Brick Buttons | Compare| Brick Buttons
   • Leave its brick button input set to #2 (center)
   • Change the State value to 2

4. Calibrate Black within the sensor: Drag an drop a Yellow Color sensor block next to the wait block. 
   • Set its mode to Measure | Reflected Light Intensity
5. Store the calibrated value: Drag an drop a Yellow Color sensor block next to the other color sensor block.
   • Set its mode to Calibrate | Reflected Light Intensity | Minimum
   • Wire the value from the Measure (the first color sensor) into the second color sensor:

6. Show the calibrated value on the screen for 2 seconds: Drag and drop a green Display block after the color sensor.
   • Set its mode to Text | Pixels
   • Set the text field (top right) to Wired
   • X = 0
     
   • Y = 50
   • aA (size) = 2
   • Wire the output from the first Color Sensor block (measure mode) to the Text input on the display block:

7. Add the timer for the calibration display: Drag and drop an orange Wait block next to the display.
   • Set the time to 2

8. Add a prompt to place Sensor on White line: Drag and drop a Green Display block next to the wait block.
   • Set the following attributes:
     • X = 3
     • Y = 50
     • aA (Text size)= 1
   • Set its mode to Text | Pixels and type the following text into the Text parameter (top right):

Place Sensor on White Line

9. Add Wait for the center button push: Next drag and drop a Orange Wait block next to the display block and set its mode to Brick Buttons | Compare| Brick Buttons
   • Leave its brick button input set to #2 (center)
   • Change the State value to 2

10. Calibrate White within the sensor: Drag an drop a Yellow Color sensor block next to the wait block. 
    • Set its mode to Measure | Reflected Light Intensity
11. Store the calibrated value: Drag an drop a Yellow Color sensor block next to the other color sensor block.
    • Set its mode to Calibrate | Reflected Light Intensity | Maximum
    • Wire the value from the Measure (the color sensor from the previous step) into the second color sensor:

12. Show the calibrated White value on the screen for 2 seconds: Drag and drop a green Display block after the color sensor.
    • Set its mode to Text | Pixels
    • Set the text field (top right) to Wired
    • X = 0
      
    • Y = 50
    • aA (size) = 2
    • Wire the output from the first Color Sensor block (measure mode) to the Text input on the display block

13. Add the timer for the calibration display: Drag and drop an orange Wait block next to the display.
    • Set the time to 2

That’s it, you’re done! The final program should look like this:

Hit the Download and Play button and follow the prompts.

EV3 Color Sensor Calibration Program Download

If you don’t want to spend time following the instructions above, you can download a copy of EV3 Color Sensor calibration program here.

How to get Good, Reliable Readings from the EV3 Color Sensor

The color sensor works best when it’s about 8-12mm (or 1/2 inch) away from the object it needs to read. When using it in either Color Mode or Relfected Light Intensity Mode it’s recommended that the sensor is held at a right angle to the object it’s examaining.

It’s also more reliable when the object it’s reading is flat.

In regards to the size of the object, as long as the object is big enough to be full contained within the light the LED lamp emits then it should be good. Anything smaller will give mixed results.

Example Color Sensor Program

How to: EV3 “Say Color” Program

This program does not require a build, just the EV3 Brick and the color sensor attached to port 3. The program will enable you to place the sensor onto a color, press the center button when ready and the EV3 brick will say the color that it detects.

The steps below outline the logic that the program will follow:

1. Wait for the center button to be pushed
2. Using the Color Sensor from within the Switch block, measure the color value
3. Assess the numeric color value and using a sound block, say the name of the detected color
4. Loop back to step one

Let’s get started:

1. Place an orange Loop block to the right of the Start block
   • Leave its loop condition as infinite.

2. Place an orange Wait block inside the Loop block
   • Change the mode to Brick Buttons | Compare | Brick Buttons
   • Brick Button ID(s) = 2
   • State Input = 2

3. Drag and drop an orange Switch block next to the Wait block.
   • Set its mode to Color Sensor | Measure | Color
   • When dealing with a few cases within the switch I find it easiest to switch it to Tab view (top left of the block).

4. Click the rightmost plus button on the Switch block to add a new tab, click the red question mark on the new tab and select Blue. 

5. Continue the process above until a tab exists for each color (up to brown – 7). once that’s complete, you should now have 8 tabs:

6. Now it’s time to add the speech to the program. Select the Black color tab and drag and drop a green Sound block into it. Select the Black color sound file by clicking the top right of the block and selecting Lego Sound Files | Colors | Black

7. Repeat step 6 for each color
8. For the “No Color” tab we want it to play the words “No Color”: drag and drop 2 green Sound blocks. Set the first to play file: Lego Sound Files |Communication | No and the second Sound block to play file: Lego Sound Files |Information | Color. 
9. Click Download and Play to test out the program.

If you would like to try out another color sensor program, take a look at our post on moving EV3 robots. In this post we cover moving the robot until a color is detected. Click here to view the post.

Feel free to leave a comment if you have any questions.