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ESP32-Based Environmental Monitoring System with Multiple Sensors and OLED Display

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Circuit Documentation

Summary

This document provides a detailed overview of a circuit that includes various sensors, a display, and an ESP32 microcontroller. The circuit is designed to collect environmental data such as temperature, humidity, VOC, and NOx levels, and display the information on an OLED screen. The ESP32 microcontroller is also equipped with Bluetooth capabilities for remote data transmission.

Component List

  1. MQ-136

    • Description: Gas sensor for detecting hydrogen sulfide (H2S).
    • Pins: GND, OUT1, OUT2, VCC

  2. DHT11 Humidity and Temperature Sensor

    • Description: Sensor for measuring humidity and temperature.
    • Pins: VDD, DATA, NULL, GND

  3. SGP41 VOC and NOx Sensor

    • Description: Sensor for detecting volatile organic compounds (VOC) and nitrogen oxides (NOx).
    • Pins: VIN, GND, SCL, SDA

  4. OLED Display 128x32

    • Description: 128x32 pixel OLED display.
    • Pins: SDA, SCL, VCC, GND

  5. ESP32 (30 pin)

    • Description: Microcontroller with built-in Wi-Fi and Bluetooth capabilities.
    • Pins: EN, VP, VN, D34, D35, D32, D33, D25, D26, D27, D14, D12, D13, GND, Vin, D23, D22, TX0, RX0, D21, D19, D18, D5, TX2, RX2, D4, D2, D15, 3V3

  6. 5V Battery

    • Description: Power source for the circuit.
    • Pins: Positive, Negative

  7. MQ135

    • Description: Gas sensor for detecting air quality.
    • Pins: VCC, GND, A0, D0

  8. pH Module

    • Description: Module for measuring pH levels.
    • Pins: GND, VCC

  9. TCS230

    • Description: Color sensor.
    • Pins: GND, OE, S1, S0, VCC, OUT, S2, S3

Wiring Details

MQ-136

DHT11 Humidity and Temperature Sensor

SGP41 VOC and NOx Sensor

OLED Display 128x32

ESP32 (30 pin)

5V Battery

MQ135

pH Module

TCS230

Code Documentation

// The script is written by Slavko Zdravevski
// If you want to support my work, you can subscribe to my youtube channel: https://bit.ly/3FG9hpK
// I do a lot of interesting things in my free time, so you might find something of your interest or we can exchange ideas and knowledge

// Libraries, I also put them on github
#include "BluetoothSerial.h"
#include <RCSwitch.h>

// Pinout declaration
int ledPin = 13;
int rfReceiverPin = 2;
int rfTransmitterPin = 4; 

// Additional variables needed through the code
unsigned long currentSecounds, previousSecoundsRecord;
String receivedCommand;
String commandToSend;

unsigned long receivedCodes[100];
int receivedProtocols[100];
int receiverCounter = 0;
bool canStoreCurrentCode = true;
unsigned long previousMillisLed = 0;
bool blinkLed = false;
int ledCounter = 0;

BluetoothSerial SerialBT;
RCSwitch mySwitch = RCSwitch();

void setup() {
  Serial.begin(115200);
  SerialBT.begin("ESP32"); // If you want to use my app, leave this line as it is, otherwise, it won't work
  mySwitch.enableReceive(rfReceiverPin);
  mySwitch.enableTransmit(rfTransmitterPin);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  currentSecounds = millis() / 1000;
  receiveBtData();
  decodeRfSignals();
  checkLedState();
  
  if ((currentSecounds - previousSecoundsRecord) >= 4) {
    previousSecoundsRecord = currentSecounds;
    SerialBT.println("Good connection");
  }
}

// Method declarations
void receiveBtData() { // Receives Bluetooth data sent from the Android device and acts accordingly
  if (SerialBT.available()) {
    receivedCommand += String((char)SerialBT.read());
  } else {
    receivedCommand.toLowerCase();
    if (receivedCommand != "") {
      Serial.println(receivedCommand);
      if (receivedCommand == "refresh data") {
        sendCurrentRfData();
      } else {
        int codeForSend = receivedCommand.substring(0,receivedCommand.indexOf("|")).toInt();
        int protocolForSend = receivedCommand.substring(receivedCommand.indexOf("|")+1, receivedCommand.length()).toInt();
        Serial.println(codeForSend);
        Serial.println(protocolForSend);
        sendCodeOverRfModule(codeForSend, protocolForSend);
      }
      receivedCommand = "";
    }
  }
}

void sendCurrentRfData() { // Sends the currently stored data in the microcontroller's memory to the phone over Bluetooth
  if (receiverCounter != 0) {
    for (int i=0; i<receiverCounter; i++) {
      commandToSend = String(receivedCodes[i])+"|"+String(receivedProtocols[i]);
      SerialBT.println(commandToSend);
      delay(200);
    }
  } else {
    SerialBT.println("empty memory");
  }
}

void sendCodeOverRfModule(int code, int protocol) { // Sends the code got from the parameter over the radio module
  blinkLed = true;
  // Optional set protocol (default is 1, will work for most outlets)
  mySwitch.setProtocol(protocol);
  mySwitch.send(code, 24);
}

void decodeRfSignals() { // Decodes the 433/315 signals received by the module, and stores them into local arrays
  if (mySwitch.available()) {
    blinkLed = true;
    for (int i=0