2. CHAPTER 1
DTMF TECHNOLOGY
1.1 DTMF Signal
Dual-tone multi-frequency (DTMF) signaling is used for telephone signaling over the line in the
voice frequency band to the call switching center. The version of DTMF used for telephone tone
dialing is known by the trademarked term Touch-Tone, and is standardized by ITU-T
Recommendation Q.23. A different version is used for signaling internal to the telephone
network. DTMF is an example of a multi-frequency shift keying (MFSK) system. Today DTMF
is used for most call setup to the telephone exchange, at least in developed regions of the world.
1.2 History
DTMF was developed at Bell Labs in order to allow dialing signals to dial long-distance
numbers, potentially over non wire links such as microwave links or satellites. Encoder/decoders
were added at the end offices that would convert the standard pulse signals into DTMF tones and
play them down the line to the remote end office. At the remote site another encoder/decoder
would decode the tones and perform pulse dialing
DTMF tones were also used by some cable television networks to signal the local cable company
to insert a local advertisement. These tones were often heard during a station ID preceding a
local ad inserts. Terrestrial television stations also used DTMF tones to shut off and turn on
remote transmitters.
1.3 Keypad
When you press the buttons on the keypad, a connection is made that generates two tones at the
same time. A "Row" tone and a "Column" tone. These two tones identify the key you pressed to
any equipment you are controlling. If the keypad is on your phone, the telephone company's
"Central Office" equipment knows what numbers you are dialing by these tones, and will switch
your call accordingly. If you are using a DTMF keypad to remotely control equipment, the tones
can identify what unit you want to control, as well as which unique function you want it to
perform.
1 2 3 697 Hz
4 5 6 770 Hz
7 8 9 852 Hz
* 0 # 941 Hz
1209 Hz 1336 Hz 1477 Hz
3. When you press the digit 1 on the keypad, you generate the tones 1209 Hz and 697 Hz. pressing
the digit 2 will generate the tones 1336 Hz and 697 Hz. Sure, the tone 697 is the same for both
digits, but it take two tones to make a digit and the telephone company's equipment knows the
difference between the 1209 Hz that would complete the digit 1, and a 1336 Hz that completes a
digit 2.
1.4 DTMF Event Frequencies
Event Low frequency High frequency
Busy signal 480 Hz 620 Hz
Dial tone 350 Hz 440 Hz
Ring back tone 440 Hz 480 Hz
The tone frequencies, as defined by the Precise Tone Plan, are selected such that harmonics and
Inter modulation products will not cause an unreliable signal. No frequency is a multiple of
another, the difference between any two frequencies does not equal any of the frequencies, and
the sum of any two frequencies does not equal any of the frequencies. The frequencies were
initially designed with a ratio of 21/19, which is slightly less than a whole tone. The frequencies
may not vary more than ±1.5% from their nominal frequency, or the switching center will ignore
the signal. The high frequencies may be the same volume or louder as the low frequencies when
sent across the line. The loudness difference between the high and low frequencies can be as
large as 3 decibels (dB) and is referred to as "twist".
1.5 Why not computer signals instead of DTMF
Radios are a particular animal. They are mostly analog and they are optimized for voice signals.
DTMF was designed by the engineers to be in the normal human voice range. What this means is
that DTMF passes transparently over normal two-way radio channels. It doesn't require special
channel widths, or expensive equipment. In most instances you can simply attach a cable to the
speaker output of your two-way radio to a decoder, and it will be ready to go.
It’s straightforward, fast, and easy to understand, works on most any type of radio, and gives the
most flexible features for the lowest cost!
4. CHAPTER 2
EMBEDDED TECHNOLOGY
2.1 Embedded system
A hardware system which is designed to perform a specific task in a particular time period e.g.
mobile phones
2.1.1 Components
Components in an Embedded System are as:-
Hardware
Input & Output
Software
2.1.2 Input Devices
Input devices are as follow:-
Sensors
Keys
Analog signals
Pulses
2.1.3 Output Devices
LED’s
LCD
Motors
Serial data
5. 2.1.4 Software’s Hardware’s
Machine language Digital IC’s (driver, decoder, MUX)
Assembly language Linear IC’s (op amp, ADC, DAC)
High level language Passive components (L, C, R’s)
C, C++, Java, VB PCB, Relays, Motors
2.1.5 Characteristics
Characteristics of Embedded System are:-
Perform a single set of functions.
It works in a time constraint environment.
Most of the embedded system avoids mechanical moving parts because of friction & due
to friction losses are their & hence probability of accuracy decreases.
Embedded systems have low cost due to mars production.
2.1.6 Cell-phone: very common example of embedded system
Basis components are:
Keys
LCD
Memory Backup
Some control unit
6. 2.1.7 Applications of Embedded Systems
Consumer electronics, e.g., cameras, camcorders,
Consumer products, e.g., washers, microwave ovens, ...
Automobiles (anti-lock braking, engine control...)
Industrial process controllers & avionics/defense
Computer/Communication products, e.g. printers, FAX Machine
Emerging multimedia applications e.g. cell phones, personal digital assistants…
2.1.8 Difference between Embedded System & General Computing Platform
An embedded system will have very few resources compared to general purpose
computing systems like a desktop computer.
The memory capacity and processing power in an embedded system is limited where as it
is more challenging to develop an application in embedded system due to its constricted
environment as compared to developing the same for a desktop system.
7. CHAPTER 3
MICROCONTROLLER
3.1 Micro-Controller
A microcontroller (sometimes abbreviated µC, uC or MCU) is a small computer on a single
integrated circuit containing a processor core, memory, and programmable input/output
peripherals. Microcontrollers are designed for embedded applications, in contrast to the
microprocessors used in personal computers or other general purpose applications.
3.1.1 Types of Micro-controllers
4 – Bit microcontroller
8 – Bit microcontroller
16 – Bit microcontroller
32 – Bit microcontroller
3.1.1.1 4 – Bit Microcontrollers
Most popular microcontroller made in terms of production numbers
Economical
Application: appliances and toys
3.1.1.2 8 – Bit Microcontrollers
Represent a transition zone between dedicated, high-volume, 4-bit micro-controllers and
the high performance 16 bit microcontroller
8 – Bit word size adequate for many computing tasks and control or monitoring
applications.
Application: simple appliance control, high-speed machine control, data collection
3.1.1.3 16 – Bit Microcontrollers
Provide faster response and more sophisticated calculations
Applications: control of servomechanism like robot arm
8. 3.1.1.4 32 – Bit Microcontrollers
Design emphasis is more on high speed computation features and not on chip features
like RAM, ROM, Timers, etc
Applications: robotics, highly intelligent instrumentation, avionics, image processing.
Processing, telecommunications, automobiles, etc
9. CHAPTER 4
A2Z Control System
4.1 Hardware used
To design the specified project I require the following main hardware components.
DTMF encoder IC (91214b/91215b)
DTMF decoder IC (8870/9170)
One AT89S52 microcontroller
ULN 2004A IC
Nine keys for making a 3x3 key pad Matrix
LCD display
Two 12V Relays
9-0-9 V transformer for power supply
A PCB on which all the hardware is mounted
4.2 Brief overview of peripherals attached
DTMF Encoder (91214B) is used to generate a DTMF tone when a key is pressed.
DTMF Decoder (8870) is used to produce the BCD code for each key tone.
LCD is used to the display the no. of pressed key.
ULN2004A IC is used to operate relays.
Relays are used to control any electrical appliance except D.C. motor.
4.3 Block diagram
