CHAPTER 1 DTMF TECHNOLOGY1.1 DTMF SignalDual-tone multi-frequency (DTMF) signaling is used for telephone signaling over the line in thevoice frequency band to the call switching center. The version of DTMF used for telephone tonedialing is known by the trademarked term Touch-Tone, and is standardized by ITU-TRecommendation Q.23. A different version is used for signaling internal to the telephonenetwork. DTMF is an example of a multi-frequency shift keying (MFSK) system. Today DTMFis used for most call setup to the telephone exchange, at least in developed regions of the world.1.2 HistoryDTMF was developed at Bell Labs in order to allow dialing signals to dial long-distancenumbers, potentially over non wire links such as microwave links or satellites. Encoder/decoderswere added at the end offices that would convert the standard pulse signals into DTMF tones andplay them down the line to the remote end office. At the remote site another encoder/decoderwould decode the tones and perform pulse dialingDTMF tones were also used by some cable television networks to signal the local cable companyto insert a local advertisement. These tones were often heard during a station ID preceding alocal ad inserts. Terrestrial television stations also used DTMF tones to shut off and turn onremote transmitters.1.3 KeypadWhen you press the buttons on the keypad, a connection is made that generates two tones at thesame time. A "Row" tone and a "Column" tone. These two tones identify the key you pressed toany equipment you are controlling. If the keypad is on your phone, the telephone companys"Central Office" equipment knows what numbers you are dialing by these tones, and will switchyour call accordingly. If you are using a DTMF keypad to remotely control equipment, the tonescan identify what unit you want to control, as well as which unique function you want it toperform.1 2 3 697 Hz4 5 6 770 Hz7 8 9 852 Hz* 0 # 941 Hz1209 Hz 1336 Hz 1477 Hz
When you press the digit 1 on the keypad, you generate the tones 1209 Hz and 697 Hz. pressingthe digit 2 will generate the tones 1336 Hz and 697 Hz. Sure, the tone 697 is the same for bothdigits, but it take two tones to make a digit and the telephone companys equipment knows thedifference between the 1209 Hz that would complete the digit 1, and a 1336 Hz that completes adigit 2.1.4 DTMF Event FrequenciesEvent Low frequency High frequencyBusy signal 480 Hz 620 HzDial tone 350 Hz 440 HzRing back tone 440 Hz 480 HzThe tone frequencies, as defined by the Precise Tone Plan, are selected such that harmonics andInter modulation products will not cause an unreliable signal. No frequency is a multiple ofanother, the difference between any two frequencies does not equal any of the frequencies, andthe sum of any two frequencies does not equal any of the frequencies. The frequencies wereinitially designed with a ratio of 21/19, which is slightly less than a whole tone. The frequenciesmay not vary more than ±1.5% from their nominal frequency, or the switching center will ignorethe signal. The high frequencies may be the same volume or louder as the low frequencies whensent across the line. The loudness difference between the high and low frequencies can be aslarge as 3 decibels (dB) and is referred to as "twist".1.5 Why not computer signals instead of DTMFRadios 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 isthat DTMF passes transparently over normal two-way radio channels. It doesnt require specialchannel widths, or expensive equipment. In most instances you can simply attach a cable to thespeaker 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 themost flexible features for the lowest cost!
CHAPTER 2 EMBEDDED TECHNOLOGY2.1 Embedded systemA hardware system which is designed to perform a specific task in a particular time period e.g.mobile phones2.1.1 ComponentsComponents in an Embedded System are as:- Hardware Input & Output Software2.1.2 Input DevicesInput devices are as follow:- Sensors Keys Analog signals Pulses2.1.3 Output Devices LED’s LCD Motors Serial data
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, Motors2.1.5 CharacteristicsCharacteristics 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 systemBasis components are: Keys LCD Memory Backup Some control unit
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.
CHAPTER 3 MICROCONTROLLER3.1 Micro-ControllerA microcontroller (sometimes abbreviated µC, uC or MCU) is a small computer on a singleintegrated circuit containing a processor core, memory, and programmable input/outputperipherals. Microcontrollers are designed for embedded applications, in contrast to themicroprocessors 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 microcontroller220.127.116.11 4 – Bit Microcontrollers Most popular microcontroller made in terms of production numbers Economical Application: appliances and toys18.104.22.168 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 collection22.214.171.124 16 – Bit Microcontrollers Provide faster response and more sophisticated calculations Applications: control of servomechanism like robot arm
126.96.36.199 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
CHAPTER 4 A2Z Control System4.1 Hardware usedTo 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 mounted4.2 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