Remote Temperature Monitoring System

The temperature regulator or monitoring system is one of the most requested systems in almost all processing and manufacturing industries. Here, the given application demonstrates a completely new type of temperature control and control system. This one monitors the temperature, displays it, sends wireless signal to the remote monitoring node and give this node a remote alarm when the temperature exceeds the critical value limit. Performs the following tasks

  • Continually senses the current temperature using the temperature sensor
  • Display the current temperature on the LCD screen
  • Transmit the signal to the remote monitoring node if the temperature is continuous
  • rising or falling
  • Transmit signal to trigger alarm on remote monitoring node when
  • the temperature exceeds the critical limit
  • the remote monitoring node continuously indicates that the temperature drops /
  • increasing with the LED GREEN / RED
  • It activates the alarm through the relay when it receives the alarm triggering signal
  • transmitter

The advantage of this system is to remotely monitor the temperature and you get the idea if the temperature is constant / rising / falling. Another and the most important advantage is when the temperature exceeds the specified limit the signal is available on the remote terminal. This can help anyone take it right away or automatic action.

System block diagram

As shown in the figure, there are two nodes, one is the monitor-monitor-transmitter sensor and another is the remote receiver node.

Sensor monitor transmitter node

It consists of temperature sensor, micro-controller, LCD panel, RF encoder and RF ASK transmitter.

Temperature sensor: Feels the temperature. He is a translator. Gives change tooutput voltage as the temperature changes.

Micro-controller: Performs the following tasks

  • Analog voltage input from sensor is required. Turn it into a digital equivalent using built-in ADC. Then convert it to decimal to display it
  • Displays this temperature value on the LCD to monitor the local temperature
  • Send signal to the remote monitoring node if the temperature is not constant ,it means either rising or falling. If the temperature is constant, it does not transmit
  • When the temperature exceeds the specified limit, it send the signal to trigger the alarm on the remote monitoring node

RF encoder: encodes parallel data on 4-bit micro-controller data in serial bits current.

RF Transmitter ASK: Transmits the serial bit stream given by the RF encoder over 434 MHz conveyor. Uses ASK modulation.

Remote monitoring node

Includes RF ASK receiver, RF decoder, LEDs and relays

RF ASK receiver: receives the bit stream transmitted by the RF ASK transmitter demodulates it and gives it to the RF decoder

RF decoder: decodes the serial bit stream and offers 4-bit parallel data output

LEDs: The red LED indicates that the temperature is rising and the GREEN LED indicates temperature drops

Relay: Used as an actuator. It can trigger any kind of alarm such as audio signal (horn,bell or bell) visual signal (flashing lamp) etc.

Circuit diagram

Sensor monitoring transmitter node circuit

As shown in the figure the circuit consists of temperature sensor LM35, AVR micro-ATMega32 controller, HT12E RF encoder, 16×2 LCD and RF transmitter.

  • The LM35 output is connected to the ADC input of the ATMega32
  • The data pins D0 – D7 on the LCD are connected to the PORTC
  • Two RS (4) and En (6) LCD control pins are connected to the PORTD PD0 pins respectively PD1. The RW pin (5) is grounded
  • Data input pins D0 – D3 of HT12E are connected to the PORTB PB0 – PB3 pins.The Enable (TE) transmission is connected to PB4. Also, a blue LED is connected to this pin to indicate transmission
  • The serial output of HT12E is connected to the data input From RF RF Tx
  • 16 MHz crystal and two 22 pf capacitors are connected with crystal input pins as shown

Remote monitor node circuit

It consists of HT12D RF decoder, RF receiver, few LEDs and transistors and one C/O (change over) type relay

  • Data output The RF receiver socket is connected to the serial input of the HT12D
  • Data output D0 of the units HT12D relay RL1 through two transistors Q1 and Q2 connected in the Darlington configuration
  • D1 data output drives RED LEDs, D2 drives GREEN LEDs and D3 BLUE drives LED as shown
  • The valid transmission pin (VT) drives a RED LED through the Q3 NPN transistor to indicate that the receiver is active

Circuit operation

  • The micro-controller reads the temperature sensed by the temperature sensor and display this on the LCD screen
  • Each time, check if the value of the new temperature is the same as the previous one
  • temperature value. If the value of the last read temperature is within ± 2 o. Then it does not transmit signal to the remote monitoring node every time. It will only transmit signal once to indicate the temperature is constant on the BLUE LED
  • If the new read temperature value is higher than the previous temperature value then the 4-bit data (D0 – D3) is transmitted so that on remote monitoring the RED LED node will glow
  • Similarly, if the new temperature read value is lower than the previous temperature the value then the 4-bit data is transmitted so that on the remote monitoring GREEN LED node will glow
  • If the temperature exceeds 150 o, then 4-bit data is sent which will start the relay to give an alarm signal. Then, when the temperature drops to 140 o, the data is transmitted to stop the relay
  • On the transmitter side, the BLUE LED blinks when the data is transmitted and the RED LED
  • on the receiver side flashes to indicate that the data is received


The software program incorporated in the AVR microcontroller is responsible complete operation of the circuit. Performs the following tasks

1. Initialize the LCD and embed it in the ADC

2. Reads the analog voltage values ​​of the sensor and converts it into digital equivalent using built-in ADC

3. Convert this digital value to equivalent decimal value and display it LCD

4. Compare the recent value with the previous value to make data decisions transmission

5. Send the appropriate data to the remote monitor node to indicate the temperature rising or falling

6. Send the data to activate the alarm when the temperature exceeds the limit The program is written in C language. It is compiled using the GCC AVR compiler and simulated using the AVR simulator for the ATMega32 microcontroller. Both AVR GCC AVR compiler and simulator are available embedded in the AVR studio software tool (V4). When the program is successfully compiled, it generates a HEX file. This file can be uploaded on the ATMege32 target device using any suitable programmer (such as ponyprog). Here is full program code with the required comments.

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