Introduction

DHT11 sensor measures and provides humidity and temperature values serially over a single wire.

It can measure the relative humidity in percentage (20 to 90% RH) and temperature in degree Celsius in the range of 0 to 50°C.

It has 4 pins; one of which is used for data communication in serial form.

Pulses of different TON and TOFF are decoded as logic 1 or logic 0 or start pulse or end of the frame.

Interfacing Diagram

NodeMCU LUA based functions for DHT module

Let’s see the LUA based functions of NodeMCU that can be used for DHT modules to read the Temperature and Humidity.

dht.read()

This function is used to read data from all kinds of DHT sensors, including DHT11, 21, 22, 33, 44 humidity temperature sensors.

Syntax: dht.read(pin)

Parameters:

pin: pin number from which output of the DHT sensor is to be read. 0 pin number (D0) is not supported.

Returns:

status: it returns one status out of dht.OK, dht.ERROR_CHECKSUM, dht.ERROR_TIMEOUT.

temp: temperature

humi: humidity

temp_dec: temperature decimal

humi_dec: humidity decimal

Note: the data type of return variables depends on firmware supported data types. i.e. if firmware supports floating then it will return float values otherwise it will return integer.

Also, we can use dht11.read() function to read output from only dht11 or dht.readxx() function to read output from dht modules other than dht11 i.e. xx will be 22, 33 etc. These functions have same syntax, parameters and return values.

Let’s write Lua script to read temperature and humidity from dht11

Lua Script for DHT11

pin = 1

status, temp, humi, temp_dec, humi_dec = dht.read(pin)--read dht11 from pin

if status == dht.OK then --check status is ok and print temperature and humidity
print(string.format("DHT Temperature:%d.%03d;Humidity:%d.%03d",
math.floor(temp),
temp_dec,
math.floor(humi),
humi_dec
))
elseif status == dht.ERROR_CHECKSUM then --else print either status
print( "DHT Checksum error." )
elseif status == dht.ERROR_TIMEOUT then
print( "DHT timed out." )
end



ESPlorer Serial Output Window

ESPlorer Serial monitor output window for DHT11 temperature & humidity measure

Arduino Sketch for DHT11

Here, we will be using DHT11 library by Mark Ruys from GitHub.

Download this library from here.

Extract the library and add the folder to the libraries folder path of Arduino IDE.

Once the library has been added to the Arduino IDE, open the IDE and open the example sketch named DHT_Test from the library added.

Change the DHT11 pin in the sketch. You can refer to the sketch given below for the change to be made.

Sketch For Reading Temperature And Humidity From DHT11

DHT dht;

void setup()
{
Serial.begin(9600);
Serial.println();
Serial.println("Status\tHumidity (%)\tTemperature (C)\t(F)");
dht.setup(D1); /* D1 is used for data communication */
}

void loop()
{
delay(dht.getMinimumSamplingPeriod()); /* Delay of amount equal to sampling period */
float humidity = dht.getHumidity();/* Get humidity value */
float temperature = dht.getTemperature();/* Get temperature value */
Serial.print(dht.getStatusString());/* Print status of communication */
Serial.print("\t");
Serial.print(humidity, 1);
Serial.print("\t\t");
Serial.print(temperature, 1);
Serial.print("\t\t");
Serial.println(dht.toFahrenheit(temperature), 1);/* Convert temperature to Fahrenheit units */
}

Arduino Serial Output Window

Arduino Serial monitor output window DHT11 temperature & humidity measure