Arduino Project
Light Sensing
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.
1.1 Install Arduino IDE(Important)
1.2 Introduction of Arduino IDE
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 the 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
// -------- 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;
}