Circuit Documentation

Summary

This circuit is designed to monitor temperature, humidity, and battery level using an ESP8266 NodeMCU microcontroller. The circuit includes a DHT11 sensor for temperature and humidity measurements, a 16x2 LCD display for visual output, and a 9V battery for power supply. The ESP8266 NodeMCU is programmed to send data to a Blynk IoT platform and display information on an OLED screen.

Component List

1. Rocker Switch

   • Description: A simple on/off switch to control the power supply.
   • Pins: output, input

2. DHT11

   • Description: A digital temperature and humidity sensor.
   • Pins: DATA, GND, VCC

3. LCM1602 IIC

   • Description: An I2C interface for 16x2 LCD displays.
   • Pins: GND, VCC, SDA, SCL, D6, D7, A, K, VSS, VDD, V0, RS, D2, D3, D4, D5, RW, E, D0, D1, LED_A, LED_B

4. 16x2 LCD

   • Description: A 16x2 character LCD display.
   • Pins: VSS, VDD, V0, RS, RW, E, D1, D0, D2, D3, D4, D6, D5, D7, A, K

5. ESP8266 NodeMCU

   • Description: A Wi-Fi enabled microcontroller.
   • Pins: D0, D1, D2, D3, D4, 3V3, GND, D5, D6, D7, D8, RX, TX, A0, RSV, SD3, SD2, SD1, CMD, SD0, CLK, EN, RST, VIN

6. 9V Battery

   • Description: A 9V battery for power supply.
   • Pins: -, +

Wiring Details

Rocker Switch

• output connected to VIN of ESP8266 NodeMCU
• input connected to + of 9V Battery

DHT11

• DATA connected to D2 of ESP8266 NodeMCU
• VCC connected to 3V3 of ESP8266 NodeMCU
• GND connected to GND of ESP8266 NodeMCU

LCM1602 IIC

• SDA connected to A0 of ESP8266 NodeMCU
• SCL connected to CLK of ESP8266 NodeMCU
• GND connected to GND of ESP8266 NodeMCU
• VCC connected to 3V3 of ESP8266 NodeMCU

16x2 LCD

• VSS connected to VSS of LCM1602 IIC
• VDD connected to VDD of LCM1602 IIC
• V0 connected to V0 of LCM1602 IIC
• RS connected to RS of LCM1602 IIC
• RW connected to RW of LCM1602 IIC
• E connected to E of LCM1602 IIC
• D1 connected to D1 of LCM1602 IIC
• D0 connected to D0 of LCM1602 IIC
• D2 connected to D2 of LCM1602 IIC
• D3 connected to D3 of LCM1602 IIC
• D4 connected to D4 of LCM1602 IIC
• D6 connected to D6 of LCM1602 IIC
• D5 connected to D5 of LCM1602 IIC
• D7 connected to D7 of LCM1602 IIC
• A connected to A of LCM1602 IIC
• K connected to K of LCM1602 IIC

ESP8266 NodeMCU

• GND connected to - of 9V Battery

Code Documentation

ESP8266 NodeMCU Code

/*
  -----------------------
  ESP8266 Monitor its Own Battery Level using IoT
  -----------------------
  Website: https://iotprojectsideas.com/
  -----------------------
*/

// Fill-in information from your Blynk Template here
#define BLYNK_TEMPLATE_ID "TMPxxx-xxx-xxx"
#define BLYNK_DEVICE_NAME "Smart IoT"

#define BLYNK_FIRMWARE_VERSION        "0.1.0"

#define BLYNK_PRINT Serial
//#define BLYNK_DEBUG

#define APP_DEBUG

// Uncomment your board, or configure a custom board in Settings.h
//#define USE_SPARKFUN_BLYNK_BOARD
#define USE_NODE_MCU_BOARD
//#define USE_WITTY_CLOUD_BOARD
//#define USE_WEMOS_D1_MINI

#include "BlynkEdgent.h"
#include <DHT.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128    // OLED display width, in pixels
#define SCREEN_HEIGHT 64    // OLED display height, in pixels
#define OLED_RESET -1       // Reset pin # (or -1 if sharing Arduino reset pin)

#define DHTTYPE DHT22     // DHT 22
#define DHTPIN D4 //DHT22 Pin D4(GPIO 2)

DHT dht(DHTPIN, DHTTYPE);
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

float voltage;
int bat_percentage;
int analogInPin  = A0;    // Analog input pin
int sensorValue;
float calibration = 0.40; // Check Battery voltage using multimeter & add/subtract the value

void setup()
{
  Serial.begin(115200);
  delay(100);

  BlynkEdgent.begin();

  dht.begin();
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C); //initialize with the I2C addr 0x3C (128x64)
  display.clearDisplay();
  display.setTextColor(WHITE);

  delay(100);
}

void loop() {
  BlynkEdgent.run();
  float t = dht.readTemperature();
  float h = dht.readHumidity();

  sensorValue = analogRead(analogInPin);
  voltage = (((sensorValue * 3.3) / 1024) * 2 + calibration); //multiply by two as voltage divider network is 100K & 100K Resistor

  bat_percentage = mapfloat(voltage, 2.8, 4.2, 0, 100); //2.8V as Battery Cut off Voltage & 4.2V as Maximum Voltage

  if (bat_percentage >= 100)
  {
    bat_percentage = 100;
  }
  if (bat_percentage <= 0)
  {
    bat_percentage = 1;
  }
  
  //send data to blynk
  Blynk.virtualWrite(V1, t); //for Temperature
  Blynk.virtualWrite(V2, h); //for Humidity
  Blynk.virtualWrite(V3, voltage);  // for battery voltage
  Blynk.virtualWrite(V4, bat_percentage);  // for battery percentage
  
  //Print data on serial monitor
  Serial.print("Temperature: ");
  Serial.print(t);
  Serial.println(" *C");

  Serial.print("Humidity: ");
  Serial.print(h);
  Serial.println(" %");

  Serial.print("Analog Value = ");
  Serial.println(sensorValue);
  Serial.print("Output Voltage = ");
  Serial.println(voltage);
  Serial.print("Battery Percentage = ");
  Serial.println(bat_percentage);

  Serial.println();
  Serial.println("****************************");
  Serial.println();
  delay(1000);
 
  if (bat_percentage <=30)
  {
    Serial.println("Battery level below 30%, Charge battery on time");
    //send notification
    Blynk.logEvent("battery_low", "Battery is getting low.... Plugin to charge") ;
    delay(500);
  }

  // display temperature on OLED
  display.clearDisplay();
  display.setTextColor(WHITE);
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.print("Temperature: ");
  display.setTextSize(2);
  display.setCursor(0, 10);
  display.print(t);
  display.print(" ");
  display.setTextSize(1);
  display.cp