8051 microcontroller based Intelligent Home Automation System

By | April 12, 2014


Here is a circuit through which a fan can be linearly controlled automatically, depending on the room temperature along with that it controls two light sources like CFL / Fluorescent Lamp using light intensity and motion sensing. The circuit is highly efficient as it uses a digital temperature sensor temperature measurement, a PIR sensor for motion detection and a LDR for light sensing. Alternatively, the same circuit can be used for automatic temperature controlled AC power control. In this circuit, the temperature sensor used is a DS1820 having precision of 0.5ºC. The light intensity threshold can be set by turning the preset attached to the system. The motion is detected by PIR (Passive Infra-Red) Sensor, which is a pyroelectric device that detects motion by measuring changes in the infrared levels emitted by surrounding objects. This motion can be detected by checking for a high signal on a single I/O pin.

The microcontroller does the above job. It receives the signals from all sensors, and this signal is operated under the control of software which is stored in ROM. Microcontroller AT89c2051 continuously monitor the temperature sensor, light intensity sensor and motion sensor When these sensors give more than threshold values(temperature and light) and logic high output(motion), micro controller turns on respective light/fan.



Intelligent Home Automation System (IHAS) is a micro controller based home automation system that uses multiple sensors for sensing the environment, enabling users to control physical devices automatically. IHAS is developed as a low cost alternative in home automation using inexpensive components. The aim of this project is to reduce the cost associate to home automation, which will encourage more people to install home automation technology in their home.

The reason that motivates us to develop such system is that there is a need for cheap and easy to implement home automation system. By using simple sensor network, we could save license fee for proprietary and close protocol.

Home automation system existed for decades but due to its high cost, it remains as a niche product for the high end consumers. With energy crisis looming in the horizon, home automation devices’ popularity has seen an uptake to reduce unnecessary electricity consumption. However, mass adoption of home automation technology is not possible unless there is a significant cost reduction in installation of home automation system. Therefore, we have to identify and implement ways to reduce the installation cost of home automation systems. Automation system appeals to us as we could cut down wiring cost in conventional home automation system.

In this project, IHAS will offer lighting control as a proof of concept. Also, IHAS also provides sensing methods in lighting control such as motion detection, light intensity sensor and temperature sensor. It is hoped that our project will spark the interest of home automation manufacturer in low cost home automation technology that is affordable to mass market.

Therefore, the objectives in this project are:

  • · Build a robust and scalable home automation system that is suitable for multiple devices such as lights, fans etc. 
  • · Design a complete automatic system, with an option to allow manual control too.


Block Diagram:



Major Components:

  1. Micro Controller : We have decided to use P89V51RD2 from NXP semiconductor which is compatible with 8051 core and has following features


The P89V51RD2 is 80C51 microcontrollers with 16/32/64 kB flash and 1024 B of data RAM.

A key feature of the P89V51RB2/RC2/RD2 is its X2 mode option. The design engineer can choose to run the application with the conventional 80C51 clock rate (12 clocks per machine cycle) or select the X2 mode (six clocks per machine cycle) to achieve twice the throughput at the same clock frequency. Another way to benefit from this feature is to keep the same performance by reducing the clock frequency by half, thus dramatically reducing the EMI. The flash program memory supports both parallel programming and in serial ISP.

Parallel Programming mode offers gang-programming at high speed, reducing programming costs and time to market. ISP allows a device to be reprogrammed in the end product under software control. The capability to field/update the application firmware makes a wide range of applications possible. The P89V51RB2/RC2/RD2 is also capable of IAP, allowing the flash program memory to be reconfigured even while the application is running.


  • 80C51 CPU
  • 5 V operating voltage from 0 MHz to 40 MHz
  • 16/32/64 kB of on-chip flash user code memory with ISP and IAP
  • Supports 12-clock (default) or 6-clock mode selection via software or ISP
  • SPI and enhanced UART
  • PCA with PWM and capture/compare functions
  • Four 8-bit I/O ports with three high-current port 1 pins (16 mA each)
  • Three 16-bit timers/counters
  • Programmable watchdog timer
  • Eight interrupt sources with four priority levels
  • Second DPTR register
  • Low EMI mode (ALE inhibit)
  • TTL- and CMOS-compatible logic levels


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