Group Assignment on Output devices

🖨️ Week 10 - Output devices (Group Work)

In this week's group assignment, our task was to measure the power consumption of an output device.

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🟢 Neopixel testing

The current consumption of a Neopixel light strip was tested using two USB power meters and driver code from Wokwi.com. The line #define LED_PIN D3 below was updated to include the 'D' prefix, which was required to correctly reference digital pin D3 on the board.

#include <Adafruit_NeoPixel.h>

// Which pin on the Arduino is connected to the NeoPixels?
#define LED_PIN   D3    // D prefix added

// How many NeoPixels are attached to the Arduino?
#define LED_COUNT 60   // this was adjusted

// Declare our NeoPixel strip object:
Adafruit_NeoPixel strip(LED_COUNT, LED_PIN, NEO_GRB + NEO_KHZ800);
// Argument 1 = Number of pixels in NeoPixel strip
// Argument 2 = Arduino pin number (most are valid)
// Argument 3 = Pixel type flags, add together as needed:
//   NEO_KHZ800  800 KHz bitstream (most NeoPixel products w/WS2812 LEDs)
//   NEO_KHZ400  400 KHz (classic 'v1' (not v2) FLORA pixels, WS2811 drivers)
//   NEO_GRB     Pixels are wired for GRB bitstream (most NeoPixel products)
//   NEO_RGB     Pixels are wired for RGB bitstream (v1 FLORA pixels, not v2)
//   NEO_RGBW    Pixels are wired for RGBW bitstream (NeoPixel RGBW products)

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  Serial.println("Hello, ESP32!");
  strip.begin();           // INITIALIZE NeoPixel strip object (REQUIRED)
  strip.show();            // Turn OFF all pixels ASAP
  strip.setBrightness(250); // this was adjusted, (max = 255, 50 recommended for normal use)

  // Fill along the length of the strip in various colors...
  colorWipe(strip.Color(  255,  255, 255), 00); // White
}

void loop() {
  // put your main code here, to run repeatedly:
  delay(10); // this speeds up the simulation
}

void colorWipe(uint32_t color, int wait) {
  for (int i = 0; i < strip.numPixels(); i++) { // For each pixel in strip...
    strip.setPixelColor(i, color);         //  Set pixel's color (in RAM)
    strip.show();                          //  Update strip to match
    delay(wait);                           //  Pause for a moment
  }
}

To run the code, the Adafruit Neopixel library was first installed in the Arduino IDE:

The color of the LEDs can be changed with the following line of code: colorWipe(strip.Color(255, 255, 255), 00); // White

The brightness can be adjusted with: strip.setBrightness(250); // this was adjusted, (max = 255, 50 recommended for normal use)

The number of LEDs is set with: #define LED_COUNT 60 // this was adjusted

⚡ Power Measurement

Initially, a single white LED was tested at a brightness level of 250, using a 'Color TFT USB Tester' power meter. The meter was connected between the computer's USB output and the ESP32-C3, which was used to drive the LED strip. The measured values were:

1 white LED, brightness: 250 → voltage: 5.13 V, current: 0.096 A

With the LEDs disconnected (only the ESP32-C3 connected), the power consumption was measured at 5.14 V, 0.018 A. Thus, power consumed by the LED alone was: 5.14 V * (0.096 A – 0.018 A) = 400 mW.

Current consumption at different brightness levels were tested using 10 white LEDs:

10 white LEDs, brightness 25 → 5.12 V, 0.096 A

10 white LEDs, brightness 250 → 5.08 V, 0.418 A

Next, the power consumption was measured using a different USB power meter ('Keweisi'). At lower current levels, this meter showed a noticeable difference compared to the 'Color TFT USB Tester':

10 white LEDs, brightness 25 → 5.14 V, 0.130 A

10 white LEDs, brightness 250 → 5.09 V, 0.430 A

⚠️ USB Current Limits

When using a USB port to supply voltage to external output devices, it's important not to exceed the USB's current limits. According to Wikipedia, USB Power Delivery 3.0 (Standard Power Range) can provide 5–20 V at up to 3 A, with even higher currents and voltages possible when using special USB cables.

In this group work, power was supplied via a standard USB-A port, which typically supports lower current (up to 500–900 mA) compared to the higher capacity of USB-C with Power Delivery.

🎯 Summary

• Multiple LEDs at high brightness can easily exceed USB power limits.
• Power meter accuracy can be low especially at low current levels.

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