Schematic & Working of the project
The main objective of the project is to
control the functioning of the industrial/
agricultural load using wireless technology.
One cell phone will send digitized commands
to another cell phone which is in auto
answering mode at the receiving end.
The receiving cell phone codes are fed to the
microcontroller which is programmed to
recognize those codes for operating any kind
of load duly interfaced through relays and
relay drivers as per the sent commands from
the senders mobile
The receiving cell phone codes are DTMF
(dual tone multi frequency) decoded.
DTMF Decoder will identify the key
frequency and convert that frequency to
digital codes which are then fed to the
The 230V AC supply is first stepped down to
12V AC using a step down transformer.
This is then converted to DC using bridge
The AC ripples is filtered out by using a
capacitor and given to the input pin of
voltage regulator 7805.
At output pin of this regulator we get a
constant 5V DC which is used for MC and
other ICs in this project.
It is a smaller computer
Has on-chip RAM, ROM, I/O ports...
A single chip
4 I/O Ports
TxD RxDP0 P1 P2 P3
8K Bytes of In-System Programmable (ISP)
4.0V to 5.5V Operating Range
Fully Static Operation: 0 Hz to 33 MHz
256 x 8-bit Internal RAM
32 Programmable I/O Lines
Three 16-bit Timer/Counters
Eight Interrupt Sources
Full Duplex UART Serial Channel
This circuit detects the dial tone from a
telephone line and decodes the keypad
pressed on the remote telephone.
Two distinct frequency tones make up the
DTMF(dual tome multiple frequency), and
hence the name.
The dialer and the telephone exchange
communicate one way through the DTMF
The tone generator and the tone decoder
consist of a complete communication setup.
In this project, IC MT8870DE is used to decode
the input dial tone to the dialed numbers.
These digital bits are interfaced to a
microcontroller for any application.
Pulse/dial tone method is used in the modern
There is a dial tone generator on the caller side
and a unique tone consisting of two audible tone
frequency is generated when the user presses a
As an example, 697hz & 1209hz will be
generated when key '1' is being pressed on the
a decoder circuit is present on the receiver
side, which decodes the tone to a digital code.
A relay is an electrically operated switch.
Current flowing through the coil of the relay
creates a magnetic field which attracts a
lever and changes the switch contacts.
The coil current can be on or off so relays
have two switch positions and have double
throw (changeover) switch contacts as
shown in the diagram.
Relays allow one circuit to switch a second
circuit which can be completely separate
from the first.
For example a low voltage battery circuit can
use a relay to switch a 230V AC mains circuit.
There is no electrical connection inside the
relay between the two circuits, the link is
magnetic and mechanical.
To drive relay through MC ULN2003 relay
driver IC is used
ULN is Relay driver application
The ULN2003 is a monolithic high voltage and
high current Darlington transistor arrays.
It consists of seven NPN Darlington pairs that
features high-voltage outputs with common-
cathode clamp diode for switching inductive
The collector-current rating of a single
Darlington pair is 500mA.
The Darlington pairs may be paralleled for
higher current capability.
The ULN functions as
If the logic at input
1B is high then the
output at its
corresponding pin 1C
will be low.
Keil an ARM Company makes C compilers, macro
kernels, debuggers, simulators, integrated
environments, evaluation boards, and emulators for
ARM7/ARM9/Cortex-M3, XC16x/C16x/ST10, 251, and
8051 MCU families.
Compilers are programs used to convert a High Level
Language to object code. Desktop compilers produce
an output object code for the underlying
microprocessor, but not for other microprocessors.
i.e the programs written in one of the HLL like ‘C’ will
compile the code to run on the system for a particular
processor like x86 (underlying microprocessor in the
For example compilers for Dos platform is different from the
Compilers for Unix platform So if one wants to define a
compiler then compiler is a program that translates source
code into object code.
The mobile is connected to the DTMF
decoder IC and a call is made to data mobile
from another mobile.
When the network path is formed, any
mobile key is pressed.
If 1 is pressed then this tone is decoded to 4
digit data and given to MC by inverting the
MC compares this data and at output port
which is connected to ULN gets logic high
and the output of ULN is low which makes
the relay ON. Hence, load 1 will be ON.
Using DTMF technology the loads can be
operated from any where.
This project is used to control the loads in
Thus by using DTMF technology and
microcontroller the loads can be operated
from any place.