NeoPixel RGB Color Mixer

Run the NeoPixel RGB Color Mixer MicroSim Fullscreen

About This MicroSim

Your robot's Maker Pi RP2040 board has two NeoPixel LEDs on GPIO 18. Each NeoPixel has three tiny lights inside it: red, green, and blue. You set each one to a number from 0 (off) to 255 (full). Mixing the three makes any color. This is how every phone and TV screen makes color too.

In MicroPython you set a color with a line like np[0] = (255, 80, 0), where the numbers are red, green, and blue. Then you call np.write() to send the colors to the LEDs, as shown in Chapter 9.

This MicroSim shows the two LEDs glowing on the board. The swatch shows the same color without the glow. The code box shows the exact lines to type. The Closest name line compares your mix with the color table in the chapter.

How to Use

1. Move the Red, Green, and Blue sliders, or type numbers into the boxes. Watch the LEDs and the code box change.
2. Choose which LED to edit: LED 0, LED 1, or Both. A dashed ring marks the LED you are editing.
3. Click a color button, such as Yellow, to load a row from the chapter's color table.
4. Click a Status button to load a traffic-light color: Clear (green), Caution (yellow), Stop (red), or Standby (blue).
5. Lower the Brightness. Each value is multiplied by the brightness and rounded down, and the code box shows the new numbers.
6. Try to make a color without the presets, then check the closest name.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://dmccreary.github.io/stem-robots/sims/neopixel-rgb-color-mixer/main.html"
        height="507px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

Grades 8–12

Duration

15 minutes

Learning Objective

Students will apply additive RGB color mixing to choose R, G, and B values from 0 to 255 that produce a target color, and will write the matching np[0] = (r, g, b) line, including brightness scaling.

Prerequisites

• Tuples and lists from Chapter 5: Data Structures, Modular Programming, and Version Control
• Integers and multiplication from Chapter 3: MicroPython and Development Environment Setup
• The Maker Pi RP2040 board layout from Chapter 2: Hardware Platform and Robot Assembly

Materials

• One robot per pair (optional, to test colors on the real NeoPixels)

Activities

1. Predict (2 min). Ask: "What color do you get when red and green are both at 255 and blue is 0?" Many students expect brown. Check it in the sim (yellow).
2. Match the table (4 min). Students hide the presets (no clicking) and try to make yellow, orange, and white from scratch, then check with the closest name line.
3. Two LEDs (3 min). Students choose LED 1 and give each LED a different status color. They copy the two np[...] lines and the np.write() line from the code box.
4. Brightness math (3 min). Students set yellow, then brightness 20%, and compute the new values by hand before reading the code box.
5. Hardware check (3 min). Pairs paste their lines into the REPL on the real robot and compare the LEDs with the sim.

Assessment

• Challenge: "Make a yellow that matches the chapter's table. What values do you use?" ((255, 200, 0).) "Lower the brightness to 20%. What does the code box show?" ((51, 40, 0).)
• Write the code: "Write the lines that make LED 0 red and LED 1 blue." (np[0] = (255, 0, 0), np[1] = (0, 0, 255), np.write().)
• Rubric (4-point): Exemplary — builds target colors without presets, explains additive mixing, and computes brightness-scaled values correctly. Proficient — builds target colors and writes correct np[...] lines. Developing — relies on presets and forgets np.write(). Beginning — confuses the channel order or expects values above 255.

Simplifications to Mention

• A screen can only suggest how bright a real LED looks. Real NeoPixels at full white are very bright, so many robot programs use low brightness.
• The MicroPython neopixel module has no brightness setting. You scale the numbers yourself, just like the code box does.

References

1. Chapter 9: Display Systems and Visual Output — NeoPixel LEDs — the color table and set_status_color() code.
2. MicroPython neopixel module — official documentation for NeoPixel() and write().
3. WS2812B datasheet (Adafruit) — the LED controller chip inside each NeoPixel.
4. Adafruit NeoPixel Überguide — wiring, power, and best practices for NeoPixels.
5. RGB color model (Wikipedia) — how red, green, and blue light mix to make other colors.
6. NeoPixel Color Mixer (learning-micropython) — the earlier MicroSim this one was adapted from.