Automatic Smart Lighting Based on Ambient Light and Schedule

1. Introduction

This project turns a 12V/5V LED strip into a "smart" light: the ESP32 reads ambient light through an LDR photoresistor, while syncing real time via NTP to know the current time of day. Using a 12V/5V LED strip as the standard load keeps this build completely safe, with no risk of electric shock.

The light only turns ON automatically when it's dark out and within the configured schedule window (e.g. 6:00 PM–11:00 PM), avoiding a false trigger on an overcast day and preventing the light from staying on all night outside the intended hours.

2. Components Needed

3. Wiring Diagram

Note: the relay module only needs 5V/GND/IN connected to the ESP32 — its NO/COM terminals wire directly into the LED strip's power line (an external supply); never connect AC mains to an ESP32 GPIO pin. The DARK_THRESHOLD value should be calibrated in the real environment for your specific LDR voltage-divider circuit.

4. Example #1 — Reading the LDR Light Sensor (ADC)

void setup() {
  Serial.begin(115200);
  pinMode(PIN_LDR_AO, INPUT);
}

void loop() {
  int ldrValue = analogRead(PIN_LDR_AO); // 0-4095, lower = darker
  bool isDark = ldrValue < DARK_THRESHOLD;
  Serial.printf("ldr=%d dark=%s\n", ldrValue, isDark ? "true" : "false");
  delay(500);
}

5. Example #2 — Controlling the Relay Based on Light + NTP Schedule

void setRelay(bool on) {
  // Relay active-low: IN=LOW => kích hoạt (đóng NO, bật đèn)
  digitalWrite(PIN_RELAY_IN, on ? LOW : HIGH);
  relayState = on;
}

bool inSchedule(struct tm &timeinfo) {
  int hour = timeinfo.tm_hour;
  return (hour >= SCHEDULE_START_HOUR && hour < SCHEDULE_END_HOUR);
}

// Trong loop(): bật đèn khi VỪA tối VỪA trong khung giờ lịch
bool shouldTurnOn = isDark && inSchedule(timeinfo);
if (shouldTurnOn != relayState) setRelay(shouldTurnOn);

6. Example #3 — The Complete Application: WiFi + NTP + LDR + Relay

/*
  Đèn chiếu sáng thông minh tự động theo ánh sáng và lịch giờ
  Board: ESP32 DevKit V4 (board_esp32_devkitc)
  - LDR (mod_ldr_analog)  AO -> GPIO34
  - Relay 1 kênh (mod_relay_1ch) IN -> GPIO26 (điều khiển dải LED 12V/5V qua tải DC)

  Đèn sẽ bật khi: trời tối (LDR đọc dưới ngưỡng) VÀ đang trong khung giờ lịch (vd 18:00-23:00).
  Ngoài khung giờ hoặc trời đủ sáng -> tắt.
*/

#include <WiFi.h>
#include <time.h>

const char *WIFI_SSID = "YOUR_WIFI_SSID";
const char *WIFI_PASSWORD = "YOUR_WIFI_PASSWORD";

const int PIN_LDR_AO = 34;
const int PIN_RELAY_IN = 26;

const int DARK_THRESHOLD = 1800;
const int SCHEDULE_START_HOUR = 18;
const int SCHEDULE_END_HOUR = 23;

const char *NTP_SERVER = "pool.ntp.org";
const long GMT_OFFSET_SEC = 7 * 3600;
const int DAYLIGHT_OFFSET_SEC = 0;

const unsigned long WIFI_RETRY_INTERVAL_MS = 5000;
const unsigned long WIFI_CONNECT_TIMEOUT_MS = 10000;
const unsigned long TELEMETRY_INTERVAL_MS = 5000;

unsigned long lastWifiAttemptMs = 0;
unsigned long lastTelemetryMs = 0;
bool relayState = false;
bool ntpSynced = false;

void connectWiFiNonBlocking() {
  if (WiFi.status() == WL_CONNECTED) return;
  unsigned long now = millis();
  if (now - lastWifiAttemptMs < WIFI_RETRY_INTERVAL_MS) return;
  lastWifiAttemptMs = now;

  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);

  unsigned long start = millis();
  while (WiFi.status() != WL_CONNECTED && millis() - start < WIFI_CONNECT_TIMEOUT_MS) {
    delay(200);
  }

  if (WiFi.status() == WL_CONNECTED) {
    if (!ntpSynced) {
      configTime(GMT_OFFSET_SEC, DAYLIGHT_OFFSET_SEC, NTP_SERVER);
      struct tm timeinfo;
      if (getLocalTime(&timeinfo, 5000)) {
        ntpSynced = true;
      }
    }
  }
}

void setRelay(bool on) {
  digitalWrite(PIN_RELAY_IN, on ? LOW : HIGH);
  relayState = on;
}

void setup() {
  Serial.begin(115200);
  delay(300);
  pinMode(PIN_LDR_AO, INPUT);
  pinMode(PIN_RELAY_IN, OUTPUT);
  setRelay(false);
  connectWiFiNonBlocking();
}

void loop() {
  connectWiFiNonBlocking();

  int ldrValue = analogRead(PIN_LDR_AO);
  bool isDark = ldrValue < DARK_THRESHOLD;

  bool inSchedule = false;
  struct tm timeinfo;
  bool haveTime = ntpSynced && getLocalTime(&timeinfo, 10);
  if (haveTime) {
    int hour = timeinfo.tm_hour;
    inSchedule = (hour >= SCHEDULE_START_HOUR && hour < SCHEDULE_END_HOUR);
  }

  bool shouldTurnOn = isDark && inSchedule;
  if (shouldTurnOn != relayState) {
    setRelay(shouldTurnOn);
  }

  delay(200);
}

7. Common Issues

8. Summary

You now have a light that turns on automatically based on both real light conditions and a desired schedule, using two common modules (LDR + Relay) with a safe 12V/5V LED strip as the standard load, and the ESP32's built-in NTP support.

Possible extensions: multiple schedule windows, app/MQTT control, or PWM+MOSFET dimming instead of a hard on/off switch.