Generate A Clean High-resolution Technical Engin, a ESP32 project

This project builds a wearable gas detection and environmental monitoring system using an ESP32 microcontroller. It combines temperature and humidity sensing with gas detection to create a personal safety device that alerts the wearer to hazardous conditions through both visual and audio feedback.

The guide provides a complete wiring diagram, parts list, and step-by-step assembly instructions for integrating the 16x2 LCD display, DHT11 climate sensor, MQ-2 gas sensor, piezo buzzer alarm, push button, and HC-05 Bluetooth module. The included firmware handles sensor reading, alarm triggering, display management, and wireless communication, allowing real-time monitoring and remote data access from a paired mobile device.

Wiring diagram

Gather all the parts

Qty	Component
1	16x2 I2C LCD, 3.3 V compatible 16x2 I2C, 3.3 V A two-line, sixteen-character display module that shows the vest sensor readings.
1	DHT11 DHT11 Digital temperature and humidity sensor (lower accuracy than DHT22)
1	Piezo Buzzer 3.3 V piezo Passive piezo buzzer element driven by a 3–30 V peak-to-peak square wave; loudest around 4 kHz, usable from 2–10 kHz. Differential drive (swapping which pin is high/low each half-cycle) doubles the volume.
1	Hc 05 Bluetooth Module HC-05 Serial Bluetooth module for wireless communication using UART interface. Operates at 9600 baud (Data Mode) or 38400 baud (AT Command Mode). Supports two-way full-duplex wireless functionality with range up to 100m.
1	MQ-2 Gas Sensor MQ-2 module Analog combustible-gas and smoke sensor module. Detects LPG, propane, methane, hydrogen, alcohol, and smoke using a heated tin-dioxide (SnO2) sensing element whose resistance falls as gas concentration rises. The breakout board provides an analog output (AO) proportional to concentration plus a digital output (DO) that trips when concentration crosses an onboard potentiometer threshold. Requires a 5 V supply for the internal heater and a 20-30 s warm-up before readings stabilise; the AO voltage is relative, so the sensor needs a clean-air baseline calibration rather than reporting an absolute ppm value.
1	Push Button Momentary Momentary push button switch
1	10 kΩ Resistor 10 kΩ The upper resistor in the MQ-2 output divider that lowers the sensor voltage before it reaches A0.
1	10 kΩ Resistor 10 kΩ The lower resistor in the MQ-2 output divider that keeps the ESP8266 analog input safely below its limit.

Assemble it in 5 steps

1. Place the controller and make power rails

Place the NodeMCU ESP8266 in the middle of the breadboard. Run one red wire from its 3V3 pin to a positive rail and one black wire from GND to a ground rail. Run a second red wire from VIN (5 V while USB powered) to a separate 5 V rail; do not join the 5 V and 3.3 V rails.

Keeping 3.3 V and 5 V on different breadboard rails prevents accidental damage to the ESP8266 inputs.
Do not connect the 5 V rail to any NodeMCU signal pin — ESP8266 pins can be damaged by 5 V.

2. Wire the LCD and climate sensor

Connect lcd_16x2 VCC to 3V3 (power), lcd_16x2 GND to GND (ground), lcd_16x2 SDA to NodeMCU D2 / GPIO4 (data), and lcd_16x2 SCL to NodeMCU D1 / GPIO5 (clock). Connect dht11_1 VCC to 3V3 (power), dht11_1 GND to GND (ground), and dht11_1 DATA to D3 / GPIO0 (signal).

If the DHT11 is a bare four-pin sensor rather than a small three-pin module, add a 10 kΩ pull-up resistor from DATA to 3V3.
The display may use address 0x27; if it stays blank after deployment, its board may instead use 0x3F.
Make sure VCC and GND are not swapped on either module — swapped power can damage the parts.

3. Wire the alarm, button, and Bluetooth module

Connect piezo_1 Lead 1 to D5 / GPIO14 (alarm signal) and Lead 2 to GND (ground). Connect button_1 SIGNAL to D0 / GPIO16 (signal) and button_1 GND to GND (ground). Connect hc05_1 Vcc to VIN / 5 V (power), hc05_1 GND to GND (ground), hc05_1 TX to D6 / GPIO12 (Bluetooth data into the board), and hc05_1 RX to D7 / GPIO13 (Bluetooth data out of the board).

The button uses the board's built-in pull-up, so it should read as a press only when it connects D0 to ground.
Follow the labels printed on the HC-05 breakout board; TX and RX cross between the module and controller.
Do not use an unregulated battery or supply on the HC-05 Vcc pin; use the board's USB-powered 5 V rail for this version.

4. Add the protected gas-sensor connection

Connect mq2_1 VCC to VIN / 5 V (heater power) and mq2_1 GND to GND (ground). Connect mq2_1 AO to one end of r_mq2_top. Join the other end of r_mq2_top to one end of r_mq2_bottom and to NodeMCU A0 (gas-level signal). Connect the remaining end of r_mq2_bottom to GND (ground). Use the two 10 kΩ resistors exactly as this divider.

The joined resistor ends and A0 are one shared row on a breadboard.
Let the MQ-2 warm up for several minutes before treating its reading as meaningful.
Never connect MQ-2 AO straight to A0 — its 5 V output can damage the ESP8266 analog input.

5. Fit the electronics into the vest

After checking every wire, mount the board and modules inside a non-conductive pouch on the vest. Keep the MQ-2 sensor exposed to air and away from fabric, and route wires so they cannot pull loose when the wearer moves. Power the NodeMCU from USB for this design.

Use strain relief such as tape or small cable ties near each module so a tug does not bend its pins.
Place the buzzer opening and LCD where they can be heard and read.
The MQ-2 heater gets warm during use; keep it away from skin, loose fabric, and anything flammable.

Review all connections

1. Connections between "lcd_16x2" and "ESP32"

Function	lcd_16x2	ESP32
`power`	VCC	3V3
`ground`	GND	GND
`i2c`	SDA	GPIO 4
`i2c`	SCL	GPIO 5

2. Connections between "dht11_1" and "ESP32"

Function	dht11_1	ESP32
`power`	VCC	3V3
`ground`	GND	GND
`data`	DATA	GPIO 0

3. Connections between "piezo_1" and "ESP32"

Function	piezo_1	ESP32
`digital`	Lead 1	GPIO 14
`ground`	Lead 2	GND

4. Connections between "hc05_1" and "ESP32"

Function	hc05_1	ESP32
`power`	Vcc	VIN
`ground`	GND	GND
`data`	TX	GPIO 12
`data`	RX	GPIO 13

5. Connections between "mq2_1" and "ESP32"

Function	mq2_1	ESP32
`power`	VCC	VIN
`ground`	GND	GND
`analog`	AO → 10 kΩ Resistor End 1	EXT

6. Connections between "r_mq2_top" and "ESP32"

Function	r_mq2_top	ESP32
`analog`	End 2	GPIO 17

7. Connections between "r_mq2_bottom" and "ESP32"

Function	r_mq2_bottom	ESP32
`ground`	End 2	GND
`analog`	End 1 → 10 kΩ Resistor End 2	EXT

8. Connections between "button_1" and "ESP32"

Function	button_1	ESP32
`ground`	GND	GND
`digital`	SIGNAL	GPIO 16

Deploy the firmware

main.cppOpen in Schematik

#include <HardwareSerial.h>
#include <Arduino.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <DHT.h>

// Forward declarations
String fit16(String text);
void showStatus(const String &line1, const String &line2);
bool readAcknowledgePress();

constexpr uint8_t LCD_SDA_PIN = 4;   // NodeMCU D2
constexpr uint8_t LCD_SCL_PIN = 5;   // NodeMCU D1
constexpr uint8_t DHT_PIN = 0;       // NodeMCU D3
constexpr uint8_t BUZZER_PIN = 14;   // NodeMCU D5
constexpr uint8_t BT_RX_PIN = 12;    // NodeMCU D6, receives HC-05 TX
constexpr uint8_t BT_TX_PIN = 13;    // NodeMCU D7, sends HC-05 RX
constexpr uint8_t MQ2_PIN = A0;
constexpr uint8_t BUTTON_PIN = 16;   // NodeMCU D0

constexpr int GAS_ALARM_LEVEL = 650;
constexpr unsigned long SAMPLE_INTERVAL_MS = 2000;
constexpr unsigned long DEBOUNCE_MS = 40;

LiquidCrystal_I2C lcd(0x27, 16, 2);
DHT dht(DHT_PIN, DHT11);
HardwareSerial bluetooth(2);

bool alarmAcknowledged = false;
bool previousButtonReading = HIGH;
bool stableButtonState = HIGH;
unsigned long lastButtonChangeMs = 0;
unsigned long lastSampleMs = 0;
String lastLine1;
String lastLine2;

String fit16(String text) {
  if (text.length() > 16) return text.substring(0, 16);
  while (text.length() < 16) text += ' ';
  return text;
}

void showStatus(const String &line1, const String &line2) {
  if (line1 != lastLine1) {
    lcd.setCursor(0, 0);
    lcd.print(fit16(line1));
    lastLine1 = line1;
  }
  if (line2 != lastLine2) {
    lcd.setCursor(0, 1);
    lcd.print(fit16(line2));
    lastLine2 = line2;
  }
}

bool readAcknowledgePress() {
  bool reading = digitalRead(BUTTON_PIN);
  if (reading != previousButtonReading) lastButtonChangeMs = millis();

  if ((millis() - lastButtonChangeMs) > DEBOUNCE_MS && reading != stableButtonState) {
    stableButtonState = reading;
    if (stableButtonState == LOW) {
      previousButtonReading = reading;
      return true;
    }
  }
  previousButtonReading = reading;
  return false;
}

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  digitalWrite(BUZZER_PIN, LOW);

  Wire.begin(LCD_SDA_PIN, LCD_SCL_PIN);
  lcd.init();
  lcd.backlight();
  dht.begin();
  bluetooth.begin(9600, SERIAL_8N1, BT_RX_PIN, BT_TX_PIN);

  showStatus("Safety Vest", "Starting sensor");
  delay(1200);
}

void loop() {
  if (readAcknowledgePress()) {
    alarmAcknowledged = true;
  }

  if (millis() - lastSampleMs < SAMPLE_INTERVAL_MS) return;
  lastSampleMs = millis();

  float humidity = dht.readHumidity();
  float temperatureC = dht.readTemperature();
  int gasRaw = analogRead(MQ2_PIN);
  bool gasAlarm = gasRaw >= GAS_ALARM_LEVEL;
  bool dhtValid = !isnan(humidity) && !isnan(temperatureC);

  if (!gasAlarm) alarmAcknowledged = false;
  bool soundAlarm = gasAlarm && !alarmAcknowledged;
  digitalWrite(BUZZER_PIN, soundAlarm ? HIGH : LOW);

  String line1;
  if (dhtValid) {
    line1 = "T:" + String(temperatureC, 1) + "C H:" + String((int)humidity) + "%";
  } else {
    line1 = "DHT11 check";
  }

  String line2 = "Gas:" + String(gasRaw);
  if (gasAlarm) line2 += alarmAcknowledged ? " ACK" : " ALERT";
  showStatus(line1, line2);

  bluetooth.print("TEMP=");
  if (dhtValid) bluetooth.print(temperatureC, 1); else bluetooth.print("NA");
  bluetooth.print(",HUM=");
  if (dhtValid) bluetooth.print(humidity, 0); else bluetooth.print("NA");
  bluetooth.print(",MQ2=");
  bluetooth.print(gasRaw);
  bluetooth.print(",ALARM=");
  bluetooth.println(gasAlarm ? "1" : "0");
}