Light Sensing

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🎁 Looking for parts?Check out our all-in-one kits below — packed with components, beginner-friendly guides, and tons of fun.

Name	Includes Arduino board	PURCHASE LINK
Ultimate Sensor Kit	Arduino Uno R4 Minima	BUY
Elite Explorer Kit	Arduino Uno R4 WiFi	BUY
3 in 1 Ultimate Starter Kit	Arduino Uno R4 Minima	BUY

Course Introduction

In this lesson, you’ll build a light detection system using an Arduino UNO R4, an LDR, and a TM1637 display.

The display shows a 0–100 value that increases with light intensity, allowing real-time brightness monitoring.

Note

If this is your first time working with an Arduino project, we recommend downloading and reviewing the basic materials first.

Required Components

In this project, we need the following components:

SN	COMPONENT INTRODUCTION	QUANTITY	PURCHASE LINK
1	Arduino UNO R4 Minima/Arduino UNO R4 WIFI	1	BUY
2	USB Type-C cable	1
3	Breadboard	1	BUY
4	Wires	Several	BUY
5	4-Digit Segment Display Module	1	BUY
6	Photoresistor	1	BUY
7	10kΩ resistor	1	BUY

Wiring

Common Connections:

Photoresistor
- Connect to A0 on the Arduino. Then connect a 10k resistor to the negative power bus of the breadboard
- Connect to breadboard’s red power bus.
4-Digit Segment Display Module
- CLK: Connect to 3 on the Arduino.
- DIO: Connect to 2 on the Arduino.
- GND: Connect to breadboard’s negative power bus.
- VCC: Connect to breadboard’s red power bus.

Writing the Code

Note

You can copy this code into Arduino IDE.
To install the library, use the Arduino Library Manager and search for TM1637Display and install it.
Don’t forget to select the board(Arduino UNO R4 Minima/WIFI) and the correct port before clicking the Upload button.

#include <TM1637Display.h>

// -------- TM1637 pins (UNO R4) --------
#define CLK_PIN 3     // TM1637 CLK
#define DIO_PIN 2     // TM1637 DIO
TM1637Display display(CLK_PIN, DIO_PIN);

// -------- LDR analog pin --------
const int LDR_PIN = A0;

// -------- timing --------
const unsigned long SAMPLE_MS = 50;    // sample period
const unsigned long CALIB_MS  = 3000;  // auto-calibration duration

// auto-calibration range (updated during first CALIB_MS)
int adcMinSeen = 1023;
int adcMaxSeen = 0;

// simple low-pass filter (EMA)
float ema = 0.0f;
const float ALPHA = 0.25f; // 0~1, higher = more responsive

unsigned long t0;

void setup() {
  display.setBrightness(7);
  display.clear();

  // UNO R4 analogRead default is 0~1023 (10-bit), keep default
  // For higher resolution, you can enable: analogReadResolution(12); // 0~4095

  // Show "CAL " during calibration
  display.showNumberDecEx(0, 0, true, 4, 0); // clear
  display.setSegments((const uint8_t[]){0x39, 0x77, 0x38, 0x00}); // display "CAL "
  // If your library version doesn't support this, you can comment these two lines

  t0 = millis();
}

void loop() {
  static unsigned long last = 0;
  unsigned long now = millis();
  if (now - last < SAMPLE_MS) return;
  last = now;

  int adc = analogRead(LDR_PIN);   // 0(dark)~1023(bright) or reversed depending on wiring

  // 1) Auto-calibration during the first 3 seconds
  if (now - t0 < CALIB_MS) {
    if (adc < adcMinSeen) adcMinSeen = adc;
    if (adc > adcMaxSeen) adcMaxSeen = adc;
    return; // During calibration, do not update display
  }

  // If calibration range is too narrow, set default values
  if (adcMaxSeen - adcMinSeen < 50) {
    adcMinSeen = 100;
    adcMaxSeen = 900;
  }

  // 2) Map ADC to 0~100 (based on calibration range)
  // Regardless of wiring direction, map so that brighter = larger value
  int span = adcMaxSeen - adcMinSeen;
  long mapped = (long)(adc - adcMinSeen) * 100 / (span <= 0 ? 1 : span);
  if (mapped < 0)   mapped = 0;
  if (mapped > 100) mapped = 100;

  // 3) EMA smoothing
  ema = (1.0f - ALPHA) * ema + ALPHA * mapped;
  int value = (int)(ema + 0.5f);

  // 4) Display on TM1637 (0~100)
  // Right aligned: e.g. “  85”, “ 100”
  display.showNumberDec(value, true, 3, 1); // use last 3 digits for better centering
  // If you want right alignment using all 4 digits: display.showNumberDec(value, true);

  // (Optional) Update min/max boundaries slowly over time to adapt to environment:
  // if (value < 5)  adcMinSeen = (adcMinSeen*3 + adc)/4;
  // if (value > 95) adcMaxSeen = (adcMaxSeen*3 + adc)/4;
}