Telephone Controlled Switch
PROJECT TITLE TELEPHONE CONTROLLED SWITCH COMPOSED BY IOANNIS PLITSOS Abstract. The primary objective of the ¨Telephone Controlled Switch¨ is to control up to three relays via the worldwide telephone network. ... The receiver, the telephone part, the micro controllers’ part and the relays circuitry. ... All the above must be accomplished using the telephone lines or more specifically, to operate the relays not from being next to the unit, but miles away using the worldwide telephone network. ... After the accurate soldering and numerous tests, the ¨Telephone Controlled Switch¨ took form and life. ... 2: THE TELEPHONE NETWORK AND THE DTMF SIGNALS 7 1. ... 0: DESCRIPTION OF THE TELEPHONE CONTROLLE SWITCH 13 3. ... 1: THE TELEPHONE BOARD 14 3. ... 1: THE TELEPHONE BOARD 20 4. ... The following presentation concerns the research and design of a system that controls different relays and switches via the telephone lines. Man after the discovery of telephone and its worldwide rapid development managed to have instant communication via the telephone lines with other people. The telephone by any means established the audio connection, therefore the communication, between people that a significant distance was between them. ... This project deals with the ability of the worldwide telecommunications network to establish the control between man and machines and that’s why its name is Telephone Controlled Switch. ... Applications of the telephone controlled switch. The applications of the telephone-controlled switch are various. They begin from in house applications, like light control, watering system control, central heating, going to hospital and industrial applications, like heaters control, tarmac blenders, central heating, ending to more stylish systems, like direct banking from telephone etc. ... 2) The Telephone Network And The DTMF Signals. A pioneering solution is using the telephone lines, as part of the relays circuit, where the signals are transferred with a different transmitter and filter for every independent frequency. ... A first thought therefore, in order to built a system, like the telephone controlled switch was to use Flip-Flops systems in combination with RL, RC, RLC circuits. ... Now with simple connections between these four cards the system is easier to be controlled and tested as well as repaired. ... As it was described earlier in chapter 1 the dual tone multi frequency is a dual frequency that is transmitted from the DTMF transmitter or the telephone keypad. ... This kind of transmission is worldwide used, because is the safer way to transmit numbers throughout the global telephone network, knowing that the receiver to the other side received the tone without any acknowledgment needed. 2) The DTMF transmitter; is the device that generates the DTMF tones and takes place on a telephone device. ... The DTMF dialing matrix Detection frequency board Low Group f0 High Group f0 Row 0 = 697 Hz Column 0 = 1209 Hz Row 1 = 770 Hz Column 1 = 1336 Hz Row 2 = 852 Hz Column 2 = 1477 Hz Row 3 = 941 Hz Column 3 = 1633 Hz Figure 1 3) Backwards acoustic signals; These are the signals that are generated from the micro controller and travel along the telephone lines, back to the user in order to give an information bit about the relays condition. ... CHAPTER 3-Description Of The Telephone Controlled Switch. ... The system is designed to operate relays through the telephone lines. ... It can operate up to three relays, connect the device with the telephone network as well as disconnect it when is needed or when an illegal operation has taken place. ... C is used by the power relays and the telephone switch, which connects and disconnects the device from the telephone network respectively. ... The power relays can support from in house electrical devices such as television, VCR, coffee machine, blender, central heating, central lighting, alarms, to in plant power machines such as heaters, tar and cement blenders with the only difference on the telephone controlled switch device, the bigger power relays that the engineers are going to place. ... These four boards are 1) the telephone board, which contains the telephone line matching circuit and the ring detectors’ circuit, 2) The DTMF board, 3) The micro controllers’ board and 4) The relays board. ... 1) The telephone board. The telephone line matching circuit; is a crucial circuit because without it, it would be impossible for the unit (telephone controlled switch) to stay connected to the telephone mesh. This is because its function is to match the telephone networks impedance with the unit’s impedance. ... The ring detectors circuit; from the moment that the user connects the unit with the telephone lines (a, b) the ring detector is the only subsystem that communicates with the entire system and connects the telephone lattice with the micro controller. When the user calls from a telephone the unit, the ring detector senses the ringing. ... So when these 5 Volts is becoming 0 Volts because the phototransistor pulled the 5 Volts down to earth the micro controller is taking this as a telephone fact No 1. The micro controller is programmed to answer or in other words to connect the unit with the user after five telephone facts which is five ringing tones. After the five rings the microprocessor makes the telephone switch to function, or it switches it on. ... The option of an optocupler in the ring detectors circuit is highly recommended, for the reason that it isolates the telephone lines varying voltages from the entire system. The ring detectors circuit as well as the impedance matching circuit on the telephone board are shown in schematic figure. ... It is a suitable device connected with the telephone lines (a, b). ... Then these pulses are sending to a transistor arrangement in order to be amplified before they are sent back to the user through the telephone lines. ... 1 The telephone board. The matching circuit; consists of an arrestor in the entrance of the telephone line. ... Many times happened the telephone lines to carry high voltages because of the terrible design of some telephony local exchanges. ... Between the telephone lines entrance and the DTMF receiver is a 1:1, 600 Ohms audio transformer (see schematic figure). This is needed for the reason that the DTMF receiver must receive only acoustic tones through the speech channel the local exchange provides, and not any kind of current the telephone lines carry. The transformers impedance is 600 Ohms since the telephone lines impedance is the same. The telephone lines operating current limits could be anywhere between 20 to 120 mA. ... Capacitors C2, C3 are to cut any high frequencies passing through the telephone lines. ... The ring detectors circuit; it consists of the 4N35 integrated circuit which is the optocupler and is described in chapter 3, a capacitor C17 which does not allow the direct current of the telephone lines to harm the 4N35 chip. ... Figure 2 The applications of the receiver are variable, such as paging systems, credit card systems, remote control, PCs, telephone answering machines, etc. ... The transmitter is the telephone keypad in TONE mode. ... Every time a switch is activated the micro controller sees a high at its input port B where the user password applies. ... The circuitry is applied to pin 20 of the micro controllers port C and also to the audio transformers right end to pass the backward acoustic signals to the telephone lines back to the user.