ESP8266: DHT22 temperature sensor

Temperature and humidity reading from RHT03 (also known as DHT22) using ESP8266 WeMos D1 mini board.

As many other examples available on the internet, it was inevitably to post myself a temperature and humidity reading application.

The values from sensors are displayed on the mobile phone, using Blynk IoT framework.

Ingredients:

ESP8266 WeMos D1 mini board

RHT03 temperature and humidity sensor

Sensor specifications:

• 3.3-6V Input
• Humidity from 0-100% RH, ±2% RH accuracy
• -40 – 80 degrees C temperature range,±0.5 degrees C

source: http://cdn.sparkfun.com/datasheets/Sensors/Weather/RHT03.pdf

Details here: https://learn.adafruit.com/dht

Download and install DHT22 arduino library into your Arduino IDE. The library is available here: https://github.com/adafruit/DHT-sensor-library

Blynk knowledge and blynk app installed on your android or iphone.

Breadboard and wires

Ok, let’s put this ingredients into one “bowl”, like this

Connect the data pin of the sensor to GPIO2 (marked as D4) which already has an internal 10k pull-up resistor.

#define BLYNK_PRINT Serial // Comment this out to disable prints and save space
#include <ESP8266WiFi.h>
#include <BlynkSimpleEsp8266.h>
#include <SimpleTimer.h>
#include <DHT.h>

#define DHTPIN D4 //pin gpio 2 in sensor
#define DHTTYPE DHT22 // DHT 22 Change this if you have a DHT11

DHT dht(DHTPIN, DHTTYPE);
//static const uint8_t SDA = 4;
//static const uint8_t SCL = 5;
//
//static const uint8_t LED_BUILTIN = 2;
//static const uint8_t BUILTIN_LED = 2;
//
//static const uint8_t D0 = 16;
//static const uint8_t D1 = 5;
//static const uint8_t D2 = 4;
//static const uint8_t D3 = 0;
//static const uint8_t D4 = 2;
//static const uint8_t D5 = 14;
//static const uint8_t D6 = 12;
//static const uint8_t D7 = 13;
//static const uint8_t D8 = 15;
//static const uint8_t RX = 3;
//static const uint8_t TX = 1;

////////////////////
// Blynk Settings //
////////////////////
char BlynkAuth[] = "142da76c91af47b192d396xxxxxxxxx";
char WiFiNetwork[] = "xxxxxxWlan";
char WiFiPassword[] = "xxx_xxx_xxx_xxx";
SimpleTimer timer;

float t,h;
unsigned long previousMillis = 0; // will store last temp was read
const long interval = 2000; // interval at which to read sensor

void setup() {
    Serial.begin(115200); // Serial
    // put your setup code here, to run once:
    pinMode(BUILTIN_LED, OUTPUT); // initialize onboard LED as output
    dht.begin();
    // Initialize Blynk
    Blynk.begin(BlynkAuth, WiFiNetwork, WiFiPassword);
    // Setup a function to be called 30 second
    timer.setInterval(30000L, sendUptime);
}

void loop() {
    // put your main code here, to run repeatedly:
    //digitalWrite(BUILTIN_LED, HIGH); // turn on LED with voltage HIGH
    //delay(1000); // wait one second
    //digitalWrite(BUILTIN_LED, LOW); // turn off LED with voltage LOW
    //delay(1000); // wait one second
    Blynk.run();
    timer.run();
}

void sendUptime()
{
    // You can send any value at any time.
    // Please don't send more that 10 values per second.
    //Read the Temp and Humidity from DHT

    gettemperature();
    Serial.print("temp:");
    Serial.println(t);
    Serial.print("humi:");
    Serial.println(h);
    Blynk.virtualWrite(10, t); // virtual pin
    Blynk.virtualWrite(11, h); // virtual pin
}

void gettemperature() {
    // Wait at least 2 seconds seconds between measurements.
    // if the difference between the current time and last time you read
    // the sensor is bigger than the interval you set, read the sensor
    // Works better than delay for things happening elsewhere also
    unsigned long currentMillis = millis();

    if(currentMillis - previousMillis >= interval) {
        // save the last time you read the sensor
        previousMillis = currentMillis;

        // Reading temperature for humidity takes about 250 milliseconds!
        // Sensor readings may also be up to 2 seconds 'old' (it's a very slow sensor)
        h = dht.readHumidity(); // Read humidity (percent)
        t = dht.readTemperature(); // Read temperature as C
        // Check if any reads failed and exit early (to try again).
        if (isnan(h) || isnan(t)) {
            Serial.println("Failed to read from DHT sensor!");
            return;
        }
    }
}

Change your BlynkAuth, WiFiNetwork, WiFiPassword to your settings.

This program generate a serial output like this:

The blynk app has a gauge, a value display and a history graph item

updated 2020.07.23

BOM used in this article:

• Blynk app for android
• ESP8266 Wemos D1 mini (Amazon, Aliexpress)
• DHT22/AM2302/RHT03   temperature sensor (Amazon, Aliexpress)
• Breadboard Solderless Prototype with 4 power rails (Amazon, Aliexpress)