RF based Home Automation using 8051

Radio Frequency or RF based Home Automation using 8051 is a simple application oriented project, where you can control different home electrical and electronic appliances using RF Communication.

With the advancement of technology, number of equipment and modern household appliances are increasing to make life easier and comfortable. Operating them manually is a tedious job and hectic sometimes.

Life will become simpler if we can control devices like TV, fan, light or a music system with a remote from a distance just by pressing the button.

This project deals with an interesting manner of automating the home appliances with the help of RF Communication Technology.

Construction and Output Video

Principle behind the project

The principle behind the RF based Home Automation circuit is based on the RF Communication between the RF modules.

RF Communication between the Transmitter and Receiver modules works on the principle of Serial Communication, which means the RF transmitter will send the data serially to the RF Receiver which is paired to it.

When any key is pressed in the transmitter section, a 4-bit data is read by the Encoder IC. This 4-bit parallel data is converted to serial data by the Encoder IC and this serial data is sent to the RF Transmitter.

The RF transmitter transmits this serial data using radio signals.

At the receiver side, the RF receiver receives the serial data using RF Communication. This serial data is sent to HT12D decoder IC. The Decoder IC converts the serial data into 4-bit parallel data and transmits it to the microcontroller.

The microcontroller will turn ON or OFF the loads according to the button pressed.

Also see How to interface RF Transmitter and Receiver Modules

RF based Home Automation Circuit and Components

Circuit of Receiver Part


RF based Home Automation Receiver Circuit

Components for Receiving Circuit

Microcontroller Part

  • AT89C51 Microcontroller
  • 8051 programming board
  • Electrolytic capacitor – 10µF, 16V
  • 10KΩ Resistor x 2
  • Push button
  • 11.0592 MHz crystal
  • 22pF capacitors x 2
  • 1KΩ x 8 Resistor Pack
  • Pot – 10KΩ

RF Receiver Part

  • 434 MHz RF Receiver Module
  • HT-12D Decoder IC
  • 33KΩ Resistor
  • LED
  • Connecting wires

Load Part

  • 1N4007 Diode
  • 2N2222 NPN Transistor
  • 1KΩ Resistor
  • 12V Relay

Circuit of Transmitter Part

RF based Home Automation Transmitter Circuit

Components for Transmitting Circuit

  • 434 MHz RF Transmitter Module
  • HT-12E Encoder IC
  • 750KΩ Resistor
  • Push Buttons x 4

Step-by-Step Project Guide with CODE: RF Based Home Automation using 8051

RF Module (RF Transmitter and Receiver) Description

The main component of the RF based Home Automation is the RF Module. An RF Module is a small electronic circuit which is used to transmit or receive data wirelessly.

RF Modules are often used in consumer applications where you need to remotely control some machines or appliances without making any physical contact with them.

Some of the common applications are wireless alarm systems, garage door openers, industrial remote controls, wireless home automation systems and smart sensor applications.

RF modules do not require line-of-sight operation. Hence, they are often used instead of infrared remote controls.
Depending upon the type of application, the RF module is chosen.

For example, in case of short range wireless control applications, we can use ASK modulated RF Module of frequency 315 MHz or 433 MHz.

RF module generally comprises of an RF Transmitter and an RF Receiver. RF Transmitter is used to transmit the data while the RF Receiver is used to receive the data.

Here is the Pin Configuration of the RF Transmitter and Receiver Modules.

RF Pin configuration

RF Communication between the Transmitter and Receiver modules works on the principle of Serial Communication. In order to transmit or receive the data serially through RF module, we need to interface two ICs named HT-12E and HT-12D.


The HT-12E is an encoder IC which is used with the RF transmitter for encoding the conventional n-bit data i.e. 4-bit, 8-bit or 16-bit data in to serial data for data transmission.

Here is the pin configuration of this IC.

HT12E encoder

This encoder IC has 2^12 series encoders integrated in it. This IC is mainly used in RF communication. This IC converts 12-bit parallel data to serial data. Out of the 12 bits, 8 bits are the address bits and 4 bits are data bits.


The HT-12D is a serial decoder IC which is used with RF receiver for decoding the received serial data back to original parallel data.

Here is the pin configuration of this IC.

HT12D decoder

Similar to the encoder IC, the HT-12D Decoder IC has 2^12 series decoders integrated in it. It can decode 12-bit serial data of which 8 bits are the address and 4 bits are the data bits.

Read this interesting Post on: RF Controlled Robot without Microcontroller

How to Design RF based Home Automation Circuit?

The main components of the project are 8051 based microcontroller, 16×2 LCD, and RF Transmitter and receiver modules.

Receiver Circuit

First we’ll see the connections with respect to the microcontroller. In that, first is the clock. To use the on-chip oscillator, an 11.0592MHz quartz crystal is connected to XTAL1 and XTAL2 pins. Two 22pF ceramic capacitors are used with the crystal.

The reset circuit consist of a resistor, a capacitor and a push button. A 10KΩ resistor is connected from the RST (Pin 9) of the microcontroller to ground. A 10µF electrolytic capacitor is connected between the positive supply and RST pin.

A push button is connected across the capacitor. Upon pushing the button i.e. applying a high pulse to RST pin, the microcontroller will reset.

The External Access pin (Pin 31) is pulled high using a 10KΩ resistor. This completes the basic connections with respect to microcontroller.

Now we’ll see the connections with respect to other devices. In that, first is the LCD display. A 10KΩ pot is connected to contrast adjust pin (Pin 3) of the LCD to adjust the contrast of the display.

The three control pins RS, RW and E (Pins 4, 5 and 6) are connected to the first three pins of Port1 i.e. P1.0 to P1.2. The 8 data pins of the LCD display (Pins 7 to 14) are connected to PORT2 pins of the microcontroller.

The next component we are going to connect is the RF Receiver module. The data pin of the RF Receiver is connected to Din pin of the HT-12D Decoder IC.

An LED is connected to VT pin of the decoder IC to indicate valid transmission of data.

A 33KΩ resistor is connected between the OSC1 and OSC2 pins of the Decoder IC in order to complete the internal oscillator.

The 4 data pins of the decoder are connected to Port0 of the microcontroller. But in order to use Port 0 as I/O port, it must be connected to a pull-up resistor.

Finally, we’ll see the connections to a single load. A 2N2222 NPN Transistor is used to control the relay. A 1KΩ resistor is connected to the base of the transistor. And the input to the transistor (base) is connected to Port 0 pin.

Transmitter Circuit

The transmitter part of the circuit consists of RF Transmitter Module, a Series encoder and 4 push buttons. The data pin of the RF Transmitter module is connected to the Dout pin of the Encoder IC.

A 750KΩ resistor is connected between the OSC1 and OSC2 pins of the encoder IC to complete the internal oscillator.

In order to control the loads, we are using 4 buttons. These 4 push buttons are connected to the 4 data pins of the encoder and the other ends of the buttons are connected to ground.

In order to transmit the data, the transmission enable pin (Pin 14) of the Encoder IC must be connected to ground.

Related Post: RF based Home Automation without Microcontroller

How RF based Home Automation System Works?

The aim of this project is to design an RF based Home Automation system using 8051 microcontroller, in which different home appliances are remotely controlled using RF technology. Now we’ll see the detailed working of the project.

For the proper working of this project, the RF transmitter and receiver modules are switched ON before turning on the microcontroller. This is to avoid the junk data , received by the receiver module , when it is pairing with the transmitter.

Once the modules are successfully paired, the LED attached to VT pin of the receiver module will glow. From now onwards , the data out pins of the decoder will continuously give logic high as there is no button pressed in the transmitter.

Once we turn on the microcontroller, all the loads connected to it are switched OFF as it receives logic high continuously from the receiver. The status of the loads is displayed on the LCD.

If any of the button is pressed in the transmitter, the corresponding pin in receiver will become low. This transition will help the microcontroller to understand that a key is pressed and will turn ON the corresponding load as mentioned in the program.

If the same button is pressed once again, the microcontroller will turn OFF the load.


Applications and Advantages

  1. This circuit can be used to wirelessly control different home appliances.
  2. As it is an RF Communication based system, there is no need for any line of sight communication as in case of IR Communication.
  3. The RF Transmitter and RF Receiver can work up to 100 meters even when there is an obstruction between them.

Limitations of the Circuit

  1. The RF Transmitter, Receiver and the microcontroller unit must be separately powered for better operation.
  2. It has limited life time due to use of battery for powering the circuit.

One Response

  1. The code link is inaccessible… can you please fix this problem or give the code in response to this

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