IoT Balut Candling System, a ESP32 project

This IoT balut candling system automates egg viability assessment using light transmission analysis. The ESP32 controls a high-intensity LED that shines through each egg while an LDR photoresistor measures light penetration, classifying eggs as fertile, infertile, or spoiled based on opacity readings.

The guide provides a complete wiring diagram, parts list, and step-by-step assembly instructions for building the candling enclosure. Firmware is included with WiFi connectivity for remote monitoring via a web interface, plus a push-button trigger for manual scans and real-time classification results.

Wiring diagram

Gather all the parts

Qty	Component
1	LDR photoresistor module with AO output 3.3 V AO module The small light sensor module that turns light passing through the egg into an analog reading.
1	High-intensity white candling LED White LED The bright white lamp that shines through the egg during a scan.
1	Resistor 220 Ω Through-hole resistor (current-limiting in series with an LED)
1	Push Button Tactile switch Momentary push button switch

Assemble it in 5 steps

1. Place the parts in the candling enclosure

Mount the white candling LED below the egg opening and point the LDR module at the opposite side, so light has to pass through the egg before it reaches the sensor. Paint or line the inside of the enclosure black and keep outside light away from the sensor.

Test the fit with an egg before making permanent holes. A soft dark ring around the opening helps block room light.
Do not look directly into the bright LED at close range, and do not let the LED touch wood or plastic if it becomes hot.

2. Wire the light sensor

Connect the LDR module VCC pin to ESP32 3V3 (power), its GND pin to ESP32 GND (ground), and its AO pin to GPIO34 (light-reading signal).

Use the pin labelled AO, not DO. The AO wire carries a changing light level to the ESP32.
Do not connect the LDR module VCC to 5V: its AO output could then rise above the ESP32's safe 3.3 V input level.

3. Wire the candling light

Connect GPIO25 to one end of the 220 Ω resistor (LED current protection). Connect the resistor's other end to the LED anode, which is normally the longer leg (light control). Connect the LED cathode, normally the shorter leg and flat-edged side of the LED body, to ESP32 GND (ground).

The resistor can go on either side of the LED as long as it remains in series. Keep the LED and sensor facing each other through the egg position.
Make sure the LED long and short legs are not swapped — reversed polarity prevents it lighting, and leaving out the resistor can damage the LED or ESP32 pin.

4. Wire the Scan button

On the tactile button, use one leg from each opposite side. Connect one side to GPIO27 (scan signal) and the opposite side to ESP32 GND (ground).

A four-leg tactile switch has two legs already joined on each side. Put it across the breadboard center gap, then use legs from opposite sides.
Do not use two legs on the same side of the tactile switch; that makes the button appear permanently pressed.

5. Power and use the candler

Check that every GND wire meets an ESP32 GND pin, then power the ESP32 from its USB port. Place one egg over the light opening, block stray room light, and press Scan once. On a phone or computer, join Wi-Fi named Balut-Candler using password candling123, then open http://192.168.4.1 to see the latest reading and classification.

The board measures a reference reading briefly at startup. Keep the enclosure in its normal dark, empty condition while power is first connected.
USB power is only for the ESP32 and this small indicator-style LED. If you replace it with a high-power lamp, use a suitable transistor or MOSFET driver and separate rated power supply instead of connecting it directly to GPIO25.

Review all connections

1. Connections between "ldr_module_1" and "ESP32"

Function	ldr_module_1	ESP32
`power`	VCC	3V3
`ground`	GND	GND
`analog`	AO	GPIO 34

2. Connections between "led_resistor_1" and "ESP32"

Function	led_resistor_1	ESP32
`digital`	P1	GPIO 25
`digital`	P2 → High-intensity white candling LED ANODE	EXT

3. Connections between "candling_led_1" and "ESP32"

Function	candling_led_1	ESP32
`ground`	CATHODE	GND

4. Connections between "scan_button_1" and "ESP32"

Function	scan_button_1	ESP32
`digital`	SIGNAL	GPIO 27
`ground`	GND	GND

Deploy the firmware

main.cppOpen in Schematik

#include <Arduino.h>
#include <WiFi.h>
#include <WebServer.h>


// Forward declarations
String classifyEgg(int reading);
void takeScan();
String pageHtml();

constexpr int LDR_PIN = 34;
constexpr int CANDLING_LED_PIN = 25;
constexpr int BUTTON_PIN = 27;
constexpr float INFERTILE_THRESHOLD = 0.85f;
constexpr float FERTILE_THRESHOLD = 0.55f;
constexpr unsigned long LIGHT_STABILIZE_MS = 300;
constexpr unsigned long DEBOUNCE_MS = 300;

const char *AP_NAME = "Balut-Candler";
const char *AP_PASSWORD = "candling123";

WebServer server(80);
int baseline = 1;
int lastReading = 0;
String lastResult = "Waiting for a scan";
unsigned long lastPressMs = 0;

String classifyEgg(int reading) {
  float ratio = static_cast<float>(reading) / static_cast<float>(baseline);
  if (ratio >= INFERTILE_THRESHOLD) {
    return "Infertile";
  }
  if (ratio <= FERTILE_THRESHOLD) {
    return "Dead / Spoiled";
  }
  return "Fertile / Developing";
}

void takeScan() {
  digitalWrite(CANDLING_LED_PIN, HIGH);
  delay(LIGHT_STABILIZE_MS);
  lastReading = analogRead(LDR_PIN);
  lastResult = classifyEgg(lastReading);
  digitalWrite(CANDLING_LED_PIN, LOW);

  Serial.print("Reading: ");
  Serial.print(lastReading);
  Serial.print(" -> ");
  Serial.println(lastResult);
}

String pageHtml() {
  float ratio = static_cast<float>(lastReading) / static_cast<float>(baseline);
  String html = "<!doctype html><html><head><meta name='viewport' content='width=device-width,initial-scale=1'>";
  html += "<meta http-equiv='refresh' content='3'><style>body{font-family:Arial;background:#fff7e6;color:#3b2a1b;text-align:center;margin:30px}.card{max-width:460px;margin:auto;padding:24px;border-radius:16px;background:white;box-shadow:0 2px 12px #d8c8af}h1{color:#b45f06}.result{font-size:1.7em;font-weight:bold;color:#7f6000}p{font-size:1.05em}</style></head><body><div class='card'>";
  html += "<h1>Balut Candling System</h1><p>Latest result</p><p class='result'>" + lastResult + "</p>";
  html += "<p>Light reading: " + String(lastReading) + "</p><p>Reference reading: " + String(baseline) + "</p>";
  html += "<p>Reading ratio: " + String(ratio, 2) + "</p><p>Press the physical Scan button with one egg over the light.</p></div></body></html>";
  return html;
}

void setup() {
  Serial.begin(115200);
  pinMode(CANDLING_LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  digitalWrite(CANDLING_LED_PIN, HIGH);
  delay(500);
  baseline = analogRead(LDR_PIN);
  if (baseline < 1) baseline = 1;
  digitalWrite(CANDLING_LED_PIN, LOW);

  Serial.print("Reference reading: ");
  Serial.println(baseline);

  WiFi.mode(WIFI_AP);
  WiFi.softAP(AP_NAME, AP_PASSWORD);
  Serial.print("Wi-Fi page: http://");
  Serial.println(WiFi.softAPIP());
  server.on("/", HTTP_GET, []() { server.send(200, "text/html", pageHtml()); });
  server.begin();
}

void loop() {
  server.handleClient();
  if (digitalRead(BUTTON_PIN) == LOW && millis() - lastPressMs >= DEBOUNCE_MS) {
    lastPressMs = millis();
    takeScan();
    while (digitalRead(BUTTON_PIN) == LOW) {
      server.handleClient();
      delay(5);
    }
  }
}