Project Presentation on
DTMF Based Remote Controlling of Home
Appliances Using Mobile Phone
Aim of the project is to use a mobile phone to control home
With this project a caller can remotely control home
appliances by pressing different keypad buttons which
generates identical DTMF signal.
To get desired controlling output using Microcontroller.
Control of home appliances involves 3 different phases
First part is the decoding of DTMF tone generated by
pressing a key in calling phone.
Audio signal output from receiving phone is fed to DTMF
Decoder chip converts DTMF tone into binary codes to be
fed to Microcontroller.
After perception stage, microcontroller processes the binary
codes it receives
Microcontroller is pre-programmed in ”C” to perform specific
task according to input bits.
Program is written in AVR Studio and Simulated in Proteus7.7
Final stage is to switching ON/OFF the home appliances
connected across the main power line of 220 V 50 Hz
For switching purpose electromagnetic Relays were
BASIC BLOCK DIAGRAM OF THE PROJECT
Figure 1. Basic block diagram of the project (ref.p-4 )
DTMF- Dual Tone Multi Frequency.
• DTMF is the signal that generates upon pressing an ordinary
telephone’s any keypad button.
• Signal generated by the superposition of two pure sinusoidal
• One is high frequency & another is low frequency tone signal.
1 2 3 697
4 5 6 770
7 8 9 852
* 0 # 941
1209 1336 1477 Frequency(Hz)
Each button lies at the intersection of the two tones
Table 1- Row and column frequency correspondence
Structure of 8870 DTMF decoder
Figure 2- Structure of 8870 DTMF decoder (ref. p-6 )
ATmega 16 Microcontroller Features
High performance, Low power 8 bit Microcontroller.
16 KB Flash Memory with read and write capabilities.
512 Bytes EEPROM.
1 KB Internal RAM.
32*8 General purpose working Registers.
Internal/ External Interrupts.
The operation is initiated by calling the second mobile phone at
Mobile at receiving end receives the DTMF signals, which is
generated by pressing the keypad of caller mobile phone.
DTMF signal is passed to the DTMF decoder IC 8870 and
decodes binary outputs.
Binary output is inverted using IC 7404.
The inverted output is fed to the input PORT A of the
The Microcontroller then gives desired output as it was
When any output pin of PORT D becomes high then connected
corresponding Relay become active and it makes the circuit close
to switch ON any circuit or Device.
Output of DTMF
Both relays off
One relay on
Another relay on
Both relays on
Table 3-Actions performed corresponding to the key pressed
• Microcontroller program was written in C language on AVR Studio.
• Program was converted into desired Hex file using AVR Studio.
• Circuit was simulated in Proteus 7.7 Software
Simulation circuit is given in Figure 3
MAIN CIRCUIT DIAGRAM
Figure 4- Main circuit diagram (ref. p-15)
Relay is an electromagnetic switch.
It consists of a control coil and a load circuit.
Control coil controls the operation and load circuit is a
Current flowing through the control coil creates a small
magnetic field causes the load circuit switch to close and
relay is then active.
Microcontroller output pin PD0 and PD1 are connected with
relays through BC 547 transistor.
When transistor becomes ON then relay also be active.
A relay used as a switch of the home appliance which is
connected across the main power supply 220 V- 50 Hz AC.
Here two 220V – 10 W bulbs are used as home appliances.
The system can be used in controlling home appliances.
Can be used in office, lab ,class and factory etc.
This setup with a little modification can be adapted to the following applications
1) Combination Lock
2) Home Security System
3) Mobile / Wireless Robot control
4) Wireless Radio Control
5) Continuous monitoring of system status