Source - http://www.engineersgarage.com Humidity and temperature monitoring systems are quite common in industries. These environment factors need constant supervision to maintain reliability and efficiency of the industrial devices. The monitoring systems used in industries are generally wired where sensor unit and the sensor monitoring system connects through a cable wire. The humidity and temperature monitoring systems can be made wireless using the 434 RF modules. With wireless connectivity, the sensor and the monitoring systems can be installed separately and industrial equipment can be remotely supervised. Plus, the cost for extensive cable installation is also saved.

1. Wireless Humidity and Temperature Monitoring
System
Humidity and temperature monitoring systems are quite common in industries.
These environment factors need constant supervision to maintain reliability
and efficiency of the industrial devices. The monitoring systems used in
industries are generally wired where sensor unit and the sensor monitoring
system connects through a cable wire. The humidity and temperature
monitoring systems can be made wireless using the 434 RF modules. With
wireless connectivity, the sensor and the monitoring systems can be installed
separately and industrial equipments can be remotely supervised. Plus, the
cost for extensive cable installation is also saved.
The 434 RF modules have an operational range of 50-60 metre and can be
extended to 300-350 metre using antenna and increasing the transmission
power. Therefore, RF modules attached to antenna can be easily installed
anywhere and can perform wireless data communication to an impressive
range. (Even a Wi-Fi router have range limited to 45 metre indoor and 92 metre
outdoor).
This project uses a DHT11 humidity and temperature sensor and is built on
Arduino Pro Mini. The RF modules are directly interfaced to Arduino boards for
wireless implementation. The sensor readings are displayed on a 16X2 LCD
screen.
Components Required -
Sr. no. Name of component Required qut
1 RF Tx module (434Mhz) 1
2 RF Rx module (434Mhz) 1
3 Arduino pro mini 2
4 DHT11 1
5 LCD 1
6 Battery – 9V 2
7 Bread board 2
8 connecting wires

2. Block Diagram -
Circuit Diagram -
Circuit Connections -
There are two circuits in the project - a) Temperature and humidity sensor
circuit and b) Sensor reading display circuit. In the sensor circuit, the data pin
(Pin 2) of DHT11 sensor is connected to A2 analog pin of the Arduino Pro Mini.
The pins VCC (Pin 1) and Ground (Pin 4) are connected to VCC and ground
respectively. An RF transmitter is interfaced to the Arduino board with its serial
input pin (Pin 2) connected to pin 12 of the Arduino board. An antenna is
connected at pin 4 of the transmitter for range extension.
On the display circuit, an RF receiver is connected to another Arduino Pro Mini
with serial out pin (Pin 2) of receiver connected to pin 11 of Arduino. An
antenna is connected to pin 8 of the receiver for range extension. An LCD is

3. interfaced to the Arduino board for displaying temperature and humidity
readings. . The 16X2 LCD display is connected to the Arduino board by
connecting its data pins to pins 7 to 4 of the Arduino board. The RS and RW pin
of LCD is connected to pins 3 and 2 of the Arduino Pro Mini respectively. The E
pin of the LCD is grounded.
LCD Arduino UNO
RS 3
RW 2
E GRND
D7,D6,D5,D4 7,6,5,4 respectively
The standard code library for interfacing Arduino UNO and Arduino Pro Mini
are used in the project to program LCD with the board.

4. How the Circuit Works -
DHT11 Temperature and Humidity Sensor is a digital sensor with inbuilt
capacitive humidity sensor and Thermistor. It relays a real-time temperature
and humidity reading every 2 seconds. The sensor operates on 3.5 to 5.5 V
supply and can read temperature reading between 0° C and 50° C and relative
humidity between 20% and 95%.
The sensor cannot be directly interfaced to a digital pin of the board as it
operates on 1-wire protocol which must be implemented on the firmware. First
the data pin is configured to input and a start signal is sent to it. The start signal
comprises of a LOW for 18 milliseconds followed by a HIGH for 20 to 40
microseconds followed by a LOW again for 80 microseconds and a HIGH for 80
microseconds. After sending the start signal, the pin is configured to digital
output and 40-bit data comprising of the temperature and humidity reading is
latched out. Of the 5-byte data, the first two bytes are integer and decimal part
of reading for relative humidity respectively, third and fourth bytes are integer
and decimal part of reading for temperature and last one is checksum byte.
When interfacing DHT11 with Arduino, already a code library is available and
the sensor data can be read by read11() function of the DHT class.
On the sensor circuit, the temperature and relative humidity readings are first
fetched by the Arduino and their character representation are stored in
separate arrays. The character buffer is serially transmitted on the RF using the
VirtualWire library of the Arduino. Check out the transmitter side Arduino
program code to learn how Arduino gets the sensor value and store them to
arrays for RF transmission.
On the display circuit, character representation of sensor readings is detected
by the RF receiver and serially passed to receiver side Arduino board. The
program code on receiver side Arduino board reads the character buffer and
convert it to integer form for displaying on LCD. The standard functions of lcd
library are used to display readings on LCD. Check out the receiver side Arduino
code to learn how sensor values are read from the buffer and converted to
proper format for display on LCD screen.

5. Programming Guide -
On the transmitter side Arduino, first the program code imports the required
standard libraries. The VirtualWire library is required to connect with RF
module and DHT library is needed to interface DHT11 sensor. A "DHT" object is
instantiated. Global variables ledPin and Sensor1Pin are declared and mapped
to Pin 13 where transmission progress indicator LED is connected and Pin A2
where data pin of DHT11 temperature and humidity sensor is connected
respectively. A variable Sensor1Data is declared to stored sensor reading and
character type arrays Sensor1CharMsg and Sensor1CharMsg1 are declared to
store decimal representation of the relative humidity and temperature reading.
#include <VirtualWire.h>
#include <dht.h>
#define dht_dpin A0 //no ; here. Set equal to channel sensor is on
dht DHT;
// LED's
const int ledPin = 13;
// Sensors
const int Sensor1Pin = A2;
int Sensor1Data;
char Sensor1CharMsg[4];
char Sensor1CharMsg1[4];
A setup() function is called where indicator LED pin is set to output while
sensor connected pin is set to input mode using pinMode() function. The baud
rate of the Arduino is set to 9600 bits per second using the serial.begin()
function. The initial messages are flashed to the buffer using Serial.Println()
function. The baud rate for serial output is set to 2000 bits per second using
the vw_setup() function of the VirtualWire library.
void setup() {
// PinModes
// LED
pinMode(ledPin,OUTPUT);
// Sensor(s)
pinMode(Sensor1Pin,INPUT);

6. Serial.begin(9600);
delay(300);//Let system settle
Serial.println("Humidity and temperaturenn");
delay(700);
// VirtualWire setup
vw_setup(2000); // Bits per sec
}
A loop function is called where reading from DHT11 sensor are read using the
read11() function on DHT object and the character representation of decimal
base of the humidity reading is stored in Sensor1CharMsg array and the
character representation of decimal base of the temperature reading is stored
in Sensor1CharMsg1 array.
void loop() {
// Read and store Sensor 1 data
// Sensor1Data = analogRead(Sensor1Pin);
DHT.read11(dht_dpin);
// Convert integer data to Char array directly
itoa(DHT.humidity,Sensor1CharMsg,10);
itoa(DHT.temperature,Sensor1CharMsg1,10);
The sensor readings are serially out as human-readable ASCII text using the
Serial.print() and Serial.println() function.
// DEBUG
Serial.print("Current humidity = ");
Serial.print(DHT.humidity);
Serial.print("% ");
Serial.print("temperature = ");
Serial.print(DHT.temperature);
Serial.println("C ");
delay(800);
// END DEBUG

7. The transmission progress indicator LED is switched on by passing a HIGH to pin
13. The character message containing the temperature and humidity reading is
sent serially using the vw_send() function and vw_wait_tx() is used to block
transmission until new message is available for transmission. The LED at pin 13
is switched OFF by passing a LOW to indicate successful transmission of
message.
digitalWrite(13, true); // Turn on a light to show transmitting
vw_send((uint8_t *)Sensor1CharMsg, strlen(Sensor1CharMsg));
vw_wait_tx(); // Wait until the whole message is gone
delay(200);
vw_send((uint8_t *)Sensor1CharMsg1, strlen(Sensor1CharMsg1));
vw_wait_tx(); // Wait until the whole message is gone
digitalWrite(13, false); // Turn off a light after transmission
delay(200);
} // END void loop...
This ends the transmitter side Arduino code.
On the receiver side Arduino, the program code first imports the required
standard libraries. LiquidCrystal.h is imported to interface the LCD and
VirtualWire library is imported to read serial input from the RF receiver. The
pins 2 to 7 are mapped to Liquid Crystal object lcd.
#include <LiquidCrystal.h>
#include <VirtualWire.h>
LiquidCrystal lcd(2, 3, 4, 5, 6, 7);
The pin 13 where transmission progress indicator LED is connected is assigned
to ledpin variable and two variables - "Sensor1Data" and "Sensor2Data" to
capture reading of DHT11 in integer form and arrays "Sensor1CharMsg1" and
"Sensor1CharMsg2" to store character representation of the readings are
declared. There are counter variables "i" and "j" also declared.
// LED's
int ledPin = 13;
// Sensors
int Sensor1Data;
int Sensor2Data;
// RF Transmission container

8. char SensorCharMsg1[4];
char rxAray[8];
char SensorCharMsg2[4];
int j,k;
A setup() function is called where baud rate of the Arduino is set to 9600 bits
per second using Serial.begin() function. The lcd object is initialized to 16X2
mode. The led connected pin and pin connected to RS and RW are set to
output mode using the pinMode() function.
void setup() {
Serial.begin(9600);
lcd.begin(16, 2);
// sets the digital pin as output
pinMode(ledPin, OUTPUT);
pinMode(9, OUTPUT);
pinMode(8, OUTPUT);
The RF transmitter and receiver module does not have Push To Talk pin. They
go inactive when no data is present to transmit or receive respectively.
Therefore vw_set_ptt_inverted(true) is used to configure push to talk polarity
and prompt the receiver to continue receiving data after fetching the first
character. The baud rate for serial input is set to 2000 bits per second using
vw_setup() function. The reception of the data is initiated using vw_rx_start().
// VirtualWire
// Initialise the IO and ISR
// Required for DR3100
vw_set_ptt_inverted(true);
// Bits per sec
vw_setup(2000);
// Start the receiver PLL running
vw_rx_start();
} // END void setup
A loop() function is called inside which, array "buf[]" to read serial buffer and
"buflen" variable to store buffer length are declared. The counter variables are
initialized to zero.
void loop(){
uint8_t buf[VW_MAX_MESSAGE_LEN];

9. uint8_t buflen = VW_MAX_MESSAGE_LEN;
j = 0;
k = 0;
The character buffer is detected using the vw_get_message() function, if it is
present, a counter "i" is initialized. The buffer readings are first stored to
RxAray array using the for loop with the initialized counter and after detecting
the null character, the temperature and humidity sensor readings clubbed in
RxAray are separately stored to "SensorCharMsg1" and " SensorCharMsg2"
arrays.
// Non-blocking
if (vw_get_message(buf, &buflen))
{
int i;
// Message with a good checksum received, dump it.
for (i = 0; i < buflen; i++)
{
// Fill Sensor1CharMsg Char array with corresponding
// chars from buffer.
rxAray[i] = char(buf[i]);
}
rxAray[buflen] = '0';
while( j < 2)
{
SensorCharMsg1[j++] = rxAray[j++];
}
while( j < 4)

10. {
SensorCharMsg2[k++] = rxAray[j++];
}
The variable value along with relevant strings enclosed is passed to the
microcontroller's buffer and passed to the LCD for display in a presentable
format.
// DEBUG
Serial.print(" hum = ");
Serial.println(SensorCharMsg1);
Serial.print(" temp = ");
Serial.println(SensorCharMsg2);
lcd.setCursor(0,0);
lcd.print("Humidity = ");
lcd.print(SensorCharMsg1); // change the analog out value:
lcd.setCursor(0,1 );
lcd.print("Temparature = ");
lcd.print(SensorCharMsg2);
// END DEBUG
}
}
This ends the loop() function and the receiver side Arduino code.
PROGRAMMING CODE
#include <VirtualWire.h>
#include <dht.h>
#define dht_dpin A0 //no ; here. Set equal to channel sensor is on
dht DHT;
// LED's
const int ledPin = 13;

11. // Sensors
const int Sensor1Pin = A2;
int Sensor1Data;
char Sensor1CharMsg[4];
char Sensor1CharMsg1[4];
void setup() {
// PinModes
// LED
pinMode(ledPin,OUTPUT);
// Sensor(s)
pinMode(Sensor1Pin,INPUT);
Serial.begin(9600);
delay(300);//Let system settle
Serial.println("Humidity and temperaturenn");
delay(700);
// VirtualWire setup
vw_setup(2000); // Bits per sec
}
void loop() {
// Read and store Sensor 1 data
// Sensor1Data = analogRead(Sensor1Pin);
DHT.read11(dht_dpin);
// Convert integer data to Char array directly

12. itoa(DHT.humidity,Sensor1CharMsg,10);
itoa(DHT.temperature,Sensor1CharMsg1,10);
// DEBUG
Serial.print("Current humidity = ");
Serial.print(DHT.humidity);
Serial.print("% ");
Serial.print("temperature = ");
Serial.print(DHT.temperature);
Serial.println("C ");
delay(800);
// END DEBUG
digitalWrite(13, true); // Turn on a light to show transmitting
vw_send((uint8_t *)Sensor1CharMsg, strlen(Sensor1CharMsg));
vw_wait_tx(); // Wait until the whole message is gone
delay(200);
vw_send((uint8_t *)Sensor1CharMsg1, strlen(Sensor1CharMsg1));
vw_wait_tx(); // Wait until the whole message is gone
digitalWrite(13, false); // Turn off a light after transmission
delay(200);
} // END void loop...
#include <LiquidCrystal.h>
#include <VirtualWire.h>
LiquidCrystal lcd(2, 3, 4, 5, 6, 7);

13. // LED's
int ledPin = 13;
// Sensors
int Sensor1Data;
int Sensor2Data;
// RF Transmission container
char SensorCharMsg1[4];
char rxAray[8];
char SensorCharMsg2[4];
int j,k;
void setup() {
Serial.begin(9600);
lcd.begin(16, 2);
// sets the digital pin as output
pinMode(ledPin, OUTPUT);
pinMode(9, OUTPUT);
pinMode(8, OUTPUT);
// VirtualWire
// Initialise the IO and ISR
// Required for DR3100
vw_set_ptt_inverted(true);
// Bits per sec
vw_setup(2000);

14. // Start the receiver PLL running
vw_rx_start();
} // END void setup
void loop(){
uint8_t buf[VW_MAX_MESSAGE_LEN];
uint8_t buflen = VW_MAX_MESSAGE_LEN;
j = 0;
k = 0;
// Non-blocking
if (vw_get_message(buf, &buflen))
{
int i;
// Message with a good checksum received, dump it.
for (i = 0; i < buflen; i++)
{
// Fill Sensor1CharMsg Char array with corresponding
// chars from buffer.
rxAray[i] = char(buf[i]);
}
rxAray[buflen] = '0';
while( j < 2)
{

15. SensorCharMsg1[j++] = rxAray[j++];
}
while( j < 4)
{
SensorCharMsg2[k++] = rxAray[j++];
}
// DEBUG
Serial.print(" hum = ");
Serial.println(SensorCharMsg1);
Serial.print(" temp = ");
Serial.println(SensorCharMsg2);
lcd.setCursor(0,0);
lcd.print("Humidity = ");
lcd.print(SensorCharMsg1); // change the analog out value:
lcd.setCursor(0,1 );
lcd.print("Temparature = ");
lcd.print(SensorCharMsg2);
// END DEBUG
}
}