2. What had been thought impossible at one time was achieved by man.
As technology advanced man was able to control everything from one place.
Controlling electrical appliances with mobile is one of the examples.
This makes the use of DTMF(Dual Tone Multi Frequency) technique.
The DTMF Decoder circuit is made using M8870 Decoder IC.
Just connect your cell phone headset (headphone) jack to the mobile phone and
then mobile control electrical appliances and electrical equipment via DTMF key
pad of your cell phone.
3. 1. Transformer 9-0-9, 750MA
2. Voltage Regulator 7805,7812
3. Resistors (1k Ω; 10kΩ; 100kΩ; 330kΩ)
4. Paper Capacitors (0.1µFx 2)
5. Electrolytic Capacitor i)10uf,63v ii)1000uf ,35v
6. Crystal Oscillator (3.579545MHz, 12MHz )
7. BC548 Transistor
8. Diode1N4007
9. 12 V DC Relay
10. 89S52 MicroController
11. DTMF Decoder IC (M-8870)
12. Headphone Jack
13. Continuous Vero Board
14. Leds
4. WORKINGThe project uses M-8870 DTMF decoder IC which decodes tone generated by the keypad
of cell phone.
When we press keys in our cell Phone when call is in progress, the other person will hear
some tones with respect to keys pressed. These tones are based on the DTMF
technology.
Data is transmitted in terms of pair of tones. The receiver detects the valid frequency pair
and gives the appropriate BCD code as the output of the DTMF decoder IC.
DTMF signal can be tapped directly from the microphone pin of cell phone device.
Cut the microphone wire and we will see 4 wires. Among these wires we need only 2
wires Ground and Right.
Take the right wire and connect it as input to the decoder circuit. Ground of jack should be
connected to common ground of our circuit.
The signals from the microphone wire are processed by the DTMF decoder IC which
generates the equivalent binary sequence as a parallel output as Q1, Q2, Q3, and Q4.
6. A varying current in the transformer's primary winding creates a
varying magnetic flux in the core and a varying magnetic field
impinging on the secondary winding. This varying magnetic
field at the secondary induces a varying electromotive
force (EMF) or voltage in the secondary winding. The primary
and secondary windings are wrapped around a core of infinitely
high magnetic permeability[d] so that all of the magnetic flux
passes through both the primary and secondary windings. With
a voltage sourceconnected to the primary winding and
load impedance connected to the secondary winding, the
transformer currents flow in the indicated directions
A transformer is a static machine used for transforming power
from one circuit to another without changing frequency. This is a
very basic definition of transformer
TRANSFORMER
7. A voltage regulator is designed to automatically maintain
a constant voltage level. A voltage regulator may be a simple
"feed-forward" design or may include negative
feedback control loops. It may use an
electromechanical mechanism, or electronic components.
Depending on the design, it may be used to regulate one or
more AC or DC voltages.
Electronic voltage regulators are found in devices such as
computer power supplies where they stabilize the DC voltages
used by the processor and other elements. In
automobile alternators and central power station generator
plants, voltage regulators control the output of the plant. In
an electric power distribution system, voltage regulators may
be installed at a substation or along distribution lines so that all
customers receive steady voltage independent of how much
power is drawn from the line.
VOLTAGE REGULATOR
8. The 89S52 has 4 different ports, each one having 8 Input/output
lines providing a total of 32 I/O lines. Those ports can be used to
output DATA and orders do other devices, or to read the state of a
sensor, or a switch. Most of the ports of the 89S52 have 'dual
function' meaning that they can be used for two different function
8051 Microcontrollers
AT89S52
8051 is the name of a big family of
microcontrollers. The device which we used
in our project was the 'AT89S52' which is a
typical 8051 microcontroller manufactured
by Atmel™. The block diagram provided by
Atmel™ in their datasheet that showed the
architecture of 89S52 device seemed a bit
complicated.
Pin Diagram
9. This circuit detects the dial tone from a telephone line and
decodes the keypad pressed on the remote telephone. The
dial tone we heard when we pick up the phone set is call
Dual Tone Multi-Frequency, DTMF in short. The name was
given because the tone that we heard over the phone is
actually make up of two distinct frequency tone, hence the
name dual tone. The DTMF tone is a form of one way
communication between the dialer and the telephone
exchange. A complete communication consist of the tone
generator and the tone decoder. In this article, we are use
the IC MT8870DE, the main component to decode the
input dial tone to 5 digital output. These digital bits can be
interface to a computer or microcontroller for further
application eg. remote control, phone line transfer
operation, LEDs, etc...
DTMF Decoder IC (M-8870)
10. 1209 H
z1209
1336 H
z
1477 H
z
1633 H
z
697 Hz 1 2 3 A
770 Hz 4 5 6 B
852 Hz 7 8 9 C
941 Hz * 0 # D
DTMF keypad frequencies (with sound clips)
11. The output Q4 from the DTMF decoder IC is fed to the clock input of
IC 7474 d flip flop which acts as a buffer to the output from M8870
DTMF decoder IC.
IC7474 is configured as Toggling mode that is if it gets a clock pulse
the output of this IC (Pin 5) sets to high and further clock pulse reset
back the IC. (The outputs toggle whenever a key is pressed).
When we press and release any of the keys among 1, 3, 5, 7, 9 and *
keys, the DTMF decoder IC generates a high pulse which acts as a
clock to our flip flop and sets the output flip lop to high.
The output of flip flop is connected to the relay driver circuit via 100Ω
resistor; this output energizes the relay coil through BC547 transistor
and turns ON the bulb that connected at the normally open terminal
of relay circuit
12. A relay is an electrically operated switch. Many
relays use an electromagnet to mechanically
operate a switch, but other operating principles
are also used, such as solid-state relays. Relays
are used where it is necessary to control a circuit
by a low-power signal (with complete electrical
isolation between control and controlled circuits),
or where several circuits must be controlled by
one signal. The first relays were used in long
distance telegraph circuits as amplifiers: they
repeated the signal coming in from one circuit and
re-transmitted it on another circuit. Relays were
used extensively in telephone exchanges and
early computers to perform logical operations.
RELAY
14. APPLICATIONS
This system can be used in industrial applications.
This system can be employed in houses ,where people often forget
to switch off electrical appliances
This system can be used to control AC’s to set the room
temperaturewhen we are outside
We can extend this circuit to control many electrical devices with
some modifications using 4 x16 decoder IC.
15. ADVANTAGES
Quick response is achieved.
Construction is easy.
Easy to maintain and repair.
Comparatively the operation cost is less.
Design is efficient and low cost.
Power consumption is low.
Controlling electrical devices wirelessly
Saves electricity (when we forget to switch off and go out).
We can control appliances from any place round the globe.
16. This system is not capable of displaying the feed back status of
the devices being operated.
This system needs a cell phone to be placed in circuit.
Any one who knows the phone number and code can control our
electrical appliances
Number of electrical appliances that can be controlled by this circit
is limited
17. FUTURE SCOPE
This project can be further enhanced to the High voltage A.C Applications by changing the ratings of the Relay.
In this project in future we can add a multimedia camera to see what is going inside the home by sitting in
office or somewhere
We can also add some security features in the circuit. One of the way is password protection.
We can control and monitor the high speed induction motors as well as synchronous motors. This can be done
in an economical way
Through this only selected people can access this control over the home appliances.
