10. Output Devices

Group assignment:
- Measure the power consumption of an output device.
- Document your work on the group work page and reflect on your individual page what you learned.

Individual assignment:
Add an output device to a microcontroller board you’ve designed and program it to do something.

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Group assignment

1. Output Devices in Embedded Systems

1.1 Neopixels WS2812

WS2812 is a smart lamp bead with integrated control circuit and RGB three-color LED,
which supports single-wire serial communication (only 1 data pin can control multiple lamp beads).
Each LED can be independently programmed to achieve rich lighting effects (such as gradients,
running water lights, etc.), and is widely used in decoration, display screens, DIY projects and other scenarios.

• core characteristic Single-wire control: multiple lamp beads are connected in series,
  and only 1 data line is required for control.

• 24-bit color: Each LED can display 160,000 colors (8 bits each of red, green, and blue).

• Cascade function: The data is automatically transmitted downwards,
  and the number of lamp beads can be theoretically expanded infinitely (limited by refresh rate and power supply).

• Voltage range: Usually 5V powered (some models support 3.5 V-5.3 V).

Precautions

1. Power Supply Issues

2. Current Requirements: A single WS2812 LED draws approximately 60mA when displaying full white.
   For 10 LEDs, ensure a power supply with at least 600mA capacity.

3. Power Source Selection: Avoid powering LEDs directly from a microcontroller (insufficient current).
   Use an external independent power supply and verify its total power rating.

4. Voltage Matching: 5V LEDs require a 5V power source. For 3.3V microcontrollers (e.g., ESP32),
   consider adding a logic level converter for signal compatibility.

5. Signal Interference

6. Data Line Length: Excessively long data lines (>0.5 meters) may cause signal distortion.

7. Wiring Sequence: Data flows from DI (Data Input) → DO (Data Output).
   Reversing the order will disable the entire LED strip.

8. Coding & Libraries

9. Timing Sensitivity: WS2812 requires precise timing control.
   Always use dedicated libraries like FastLED or NeoPixel (for Arduino).

10. Avoid Blocking Code: Replace delay() with non-blocking methods (e.g., millis()) for smooth animations.

11. Static & Heat Management

12. Heat Dissipation: Prolonged high-brightness use may cause overheating.
    Add heat sinks or reduce brightness.

13. Soldering & Wiring

14. Soldering Temperature: For surface-mount WS2812 LEDs, keep soldering temperature ≤300°C
    and duration ≤3 seconds to avoid damage.

15. Parallel Power Supply: For long LED strips, power both ends to minimize voltage drop.

16. Debugging Tips

17. Segment Testing: Start with a small group (3–5 LEDs) to verify code/hardware before expanding.

18. Common Ground: Connect the microcontroller and LED strip to the same GND to prevent voltage mismatches.

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1.2 4Ω 3W Speaker

The speaker converts varying electrical current signals into mechanical vibrations through the principle
of electromagnetic induction, ultimately generating sound.

Microcontroller + Amplifier Driving Speaker Precautions

1. No Direct Connection:

2. Arduino pins have insufficient current; amplifier modules (e.g., LM386, MAX98357) are required to amplify signals.
   A 3W speaker with 4Ω impedance requires a current .I = √(P/R) = √(3/4) ≈ 0.87A.

3. Independent Power Supply:

4. For speakers ≥1W, use an external 5V 1A+ power supply (with shared ground to Arduino).

5. Signal Processing:

6. Simple tones: Use tone() to output PWM (requires RC filter).

7. Music/voice: Use I2S modules (e.g., MAX98357) or DAC.

8. Speaker Matching:

9. Power: ≤ Amplifier’s max output (e.g., MAX98357 supports 3.2W).

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2. Measure Power Consumption

The first time I used XIAO-to control the WS2812 RGB light, I was surprised that the light was not on at all.
I tried many times and finally updated the latest FastLED library to solve this problem.
I was devastated by the process, but I was happy because I learned how to eliminate other distractions.

• Check WS2812D wiring, V-5v, GND-GND, DIN-D7, and light orientation is correct (not from out to in).

• Programming the WS2812 using microbit, the light displays normally, so there is no problem with the light.

• Use the D7 of the xiao expansion board to control the LED to turn on and off, and the light can flash.
  Therefore, xiao, expansion board, D7, and data cable are all normal.

Finally my tutor gave me some reference,
deleted the old Fastled library and added the new one, and solved the problem smoothly.

Test program

#include <FastLED.h>
#define NUM_LEDS 10   
#define DATA_PIN 9     
CRGB leds[NUM_LEDS];

void setup() {
  FastLED.addLeds<NEOPIXEL, DATA_PIN>(leds, NUM_LEDS);

  for(int i = 0; i < NUM_LEDS; i++) {
    leds[i] = CRGB::White;  // 使用预定义白色
  }
  FastLED.show();
}

void loop() {
}

Current measurement preparation

• Multimeter Setup Pen:
• red → mA jack, black → COM Gear:
• DC current gear A-, range 200mA

• Wiring optimization (ensure current series connection)
  (This is a common mistake)

• XIAO 5V → Red Watch Pen → Black Watch Pen → WS2812 VCC

• WS2812 GND → XIAO GND;
• WS2812 DIN → XIAO D7;

• Measuring step
• Power off → follow the above wiring → upload the code.
• Power on → directly read the value of the multimeter, normal value: single WS2812 all white ≈ 50-60mA.

Voltage measurement preparation

• Multimeter settings
• Probes: Red → VΩmA jack, Black → COM

• Position: DC voltage range V⎓, range 20V (covering 5V range)

• Wiring method (parallel measurement)
  (This is a common mistake)

• WS2812 VCC → XIAO 5V

• WS2812 GND → XIAO GND
• WS2812 DIN → XIAO D7
• Multimeter red probe → WS2812 VCC

• Multimeter black probe → WS2812 GND

• Measurement steps

• Power off → Connect as above → Upload code.
• Power on → Read the multimeter value directly. Normal value: WS2812 VCC-GND voltage ≈ 4.8-5.2V.

Measurement results:
When 1 lamp beads light up white at the same time
I=32mA， U=4.9 V

When 10 lamp beads light up white at the same time
I=32mA， U=4.4 V

When 30 lamp beads light up white at the same time
I=32mA， U=2.9 V

When 60 lamp beads light up white at the same time
I=32mA， U=2.4 V

Conclusion

The data provided is invalid due to incorrect measurement methods or power supply configuration.
In actual situations, the current of WS2812 should increase linearly with the number of lamp beads,
and the voltage should remain stable when the power supply is sufficient.

Make sure the multimeter is connected in series to the positive line of the main power input of the lamp bead,
not the power supply line of the Arduino:

Correct Wiring Diagram
Power Supply (5V)
│
├────[Multimeter Red Probe]→[Black Probe]───────→ WS2812 LED VCC
│
└───────GND─────────────────────→ WS2812 LED GND
│
└───────────────→ Arduino GND (Common Ground)

Arduino DIN Pin → WS2812 LED Data Input (DIN)

Measurement point location:
- Directly measure the external input current of the 2812RGB bead VCC.
- It is recommended to use an independent high-power power supply (such as 5V/5A) to directly power the lamp bead
and share the ground with the Arduino.
- If the number of lamp beads is large (such as 60 all white), the current may exceed 3A,
and the 10A range of the multimeter must be used to avoid burning the fuse.

Latest measurement results:
.....

Individual assignment:

Add an output device to a microcontroller board you’ve designed and program it to do something.