CHAPTER-1 INTRODUCTION TO WIRELESS DEVICE CONTROL 1.1 INTRODUCTION Being able to achieve reliable long distance communication is an important open area of research. Today, everyone wants a comfortable lifestyle with everything controlled by just a press of some buttons. This project intends to make a device which can be used to control home Appliances by just pressing some buttons of a cell phone. It will use the existing infrastructure of cell phone networks for communication and device control. This will eliminate the need of a new infrastructure and detailed technical research. Currently, the primary mode for wireless communication uses RF (radio frequency). RF is an obvious choice for communication since it allows more information to be transferred at high speed and over long distance. However, creating RF network of long range for many simple applications is an impractical solution. Thus, by using existing RF Network of Cell Phones it minimizes the cost development and maintenance. It will help in conserving energy as with help of this device any appliance can be controlled from any distance. It also has application in Robotics and various other fields which require long distance communication. Here we designed a system which can be used to control Appliances (maximum of 8) from anywhere in the world just by pressing some buttons on a cell phone i.e. it is totally DTMF based. 1.2 HISTORY OF DTMF Before DTMF was created, telephone networks used a dialling system called Decadic (also known as Pulse Dial). The Decadic system was used extensively in modern telephone networks to dial numbers, which were entered by the telephone companies users. The Decadic (Pulse Dialling) system used a series of clicks (which could be heard through the speaker of the phone) to dial the numbers which were dialled via a keypad or rotary dial. The clicking sounds were actually the connection of the phone line being connected, disconnected, and reconnected again in a certain pattern. The Decadic (Pulse Dialling) system was very useful, but was limited to the local exchange connections, requiring an operator to connect long distance calls. 1 In the late years of 1950, DTMF was being developed at Bell Labs for the purpose of allowing tone signals to dial long distance numbers, which could be potentially be dialled not only via standard wire networks, but also via radio links and or satellites. DTMF was being developed for the future of electronic telecommunications switching systems, as opposed to the mechanical crossbar systems, which were currently in use at the time. After DTMF was created, Decadic dialling was made pointless to continue, it made no sense to continue using that particular dialling system in the equipment circuits which the telephone exchanges were using at the time. Plans were then made to begin the manufacture of DTMF controlled switching systems in the communications exchanges and later standard customer owned telephones were upgraded to using DTMF circuits rather than Decadic (Pulse Dial). After various tests were performed on the DTMF system throughout the 1960s (when DTMF became known as Touch-Tone), DTMF was made official, and was then used as the main telecommunications dialling and switching system, and remains that way to this day. 1.3 MOTIVATION ³Save Electricity´, this statement motivated us in designing this system. It has been noticed several times that people are not use to in switching off the lights and fans when they are leaving their respective places. And later, they realize that they have forgotten to switch off the lights and fans. In order to deal with this problem we have designed a system from which one can operate the lights and fans of his home from a little cell-phone only i.e a DTMF based device is been introduced which will help in controlling the electric appliances of one¶s place. In this way, this system saves energy as well as brings comfort in life. 1.4 OBJECTIVE The fundamental requirements for the cell phone based device control system remained fixed throughout the design process. The goal was to design a system which would allow the user automated and convenient access to their appliances through a telephone network. The fundamental objectives of the system include: y Correctly decode DTMF signals from the user2. Correctly decode caller identification information from the phone line. y Allow the user to automatically switch ON/OFF the devices. 2 1.5 PROJECT OVERVIEW In this project the system, is controlled by a mobile phone that makes call to the mobile phone attached to the system in the course of the call, if any button is pressed control corresponding to the button pressed is heard at the other end of the call. This tone is called dual tone multi frequency tone (DTMF) microcontroller receives this DTMF tone with the help of phone stacked in the decoder. The received tone is processed by the microcontroller with the help of DTMF decoder CM8870 the decoder decodes the DTMF tone in to its equivalent binary digit and this binary number is send to the microcontroller, the microcontroller is programmed to take a decision for any give input and outputs its decision to relay drivers in order to energize or de-energize the relay for switching purpose. The mobile that makes a call to the mobile phone stacked on the system acts as a remote. So this simple project does not require the construction of receiver and transmitter units. DTMF signalling is used for telephone signalling over the line in the voice frequency band to the call switching centre. The version of DTMF used for telephone dialling is known as touch tone. DTMF assigns a specific frequency (consisting of two separate tones) to each keys that it can easily be identified by the electronic circuit. The signal generated by the DTMF encoder is the direct algebraic submission, in real time of the amplitudes of two sine (cosine) waves of different frequencies, i.e., pressing 5 will send a tone made by adding 1336 Hz and 770 Hz to the other end of the mobile. The important components of this system are DTMF decoder, Microcontroller and relay driver & relay. A CM8870 series DTMF decoder is used here. All types of the MT8870 series use digital counting techniques to detect and decode all the sixteen DTMF tone pairs in to a four bit code output. The built -in dial tone rejection circuit eliminated the need for pre- filtering. When the input signal given at pin (IN-) single ended input configuration is recognized to be effective, the correct four bit decode signal of the DTMF tone is transferred to outputs. The microcontroller used here is a common 8 bit Atmel microcontroller AT89S52.It is a low power, high-performance CMOS 8-bit microcontroller with 8K bytes of In-System Programmable (ISP) Flash program memory and 256 bytes of RAM,. It has 32 programmable input output lines .The resulting architecture is more code efficient. Outputs from port pins of the microcontroller are fed to inputs IN1 through IN4 to relay. Switch S1 is used for manual reset. 3 CHAPTER-2 DTMF 2.1 DTMF BASICS DTMF is a generic communication term for touch tone (a Registered Trademark of AT&T). The tones produced when dialling on the keypad on the phone could be used to represent the digits, and a separate tone is used for each digit. However, there is always a chance that a random sound will be on the same frequency which will trip up the system. It was suggested that if two tones were used to represent a digit, the likelihood of a false signal occurring is ruled out. This is the basis of using dual tone in DTMF communication. DTMF dialling uses a keypad with 12/16 buttons. Each key pressed on the phone generates two tones of specific frequencies, so a voice or a random signal cannot imitate the tones. One tone is generated from a high frequency group of tones and the other from low frequency group. The DTMF (Dual Tone Multiple Frequency) application is associated with digital telephony, and provides two selected output frequencies (one high band, one low band) for a duration of 100 ms. The matrix for selecting the high and low band frequencies associated with each key is shown in Figure 1 . Figure2.1 DTMF keyboard matrix 4 Each key is uniquely referenced by selecting one of the four low band frequencies associated with the matrix rows, coupled with selecting one of the four high band frequencies associated with the matrix columns. The low band frequencies are 697,770, 852, and 941 Hz, while the high band frequencies are 1209, 1336, 1477, and 1633 Hz. The frequencies generated on pressing different phone keys are shown in the Table 1. Button Low Frequency(Hz) High Frequency(Hz) 1 697 1209 2 697 1336 3 697 1477 4 770 1209 5 770 1336 6 770 1477 7 852 1209 8 852 1336 9 852 1477 0 941 1209 * 941 1336 # 941 1477 Table 2.2 ± Frequencies generated on Key presses Each row and column of the keypad corresponds to a certain tone and creates a specific frequency. Each button lies at the intersection of the two tones as shown in Table2. 1 2 3 697 4 5 6 770 7 8 9 852 * 0 # 941 1209 1336 1477 Frequency (Hz) Table 2.3 ± Row and Column Frequency Correspondence 5 When a button is pressed, both the row and column tones are generated by the telephone instrument. These two tones will be unique and different from tones of other keys.