Fullscreen HTML5Med Res (??MB)HTML4

• HOW I E • BUSY HONE Build the Interphone: a 10-station exchange for your home Do you have a lot of phones in your home? Would you like to have all the features of an automatic switchboard like a Telecom Commander system? The system presented here provides many of the features of a Commander system but at only a fraction of the cost. By JEFF MONEGAL 68 SILICON CHIP These days, few people are content to have just one or two telephones in their home. They want one in each bedroom, one in the kitchen, one in the garage and, in fact, they probably would like one in most rooms of the house. This may be desirable but four or five phones is probably the limit as far as a normal installation is concerned otherwise reliability may be prejudiced. And with all those phones in the household, wouldn't it be nice to use them as a multi-station intercom? With the Interphone you can have this feature and quite a lot more besides. The main features of the unit are listed in an accompanying panel. If you were to have a Commander system installed in your home, it would cost you many thousands of dollars. You can have an Interphone system with all the features listed in the panel for around $300 to $400 in kit form. Before we proceed any further, we should clarify a couple of terms which often cause confusion in articles about telephones. The terms are "off hook" and "on hook". When a phone is "off hook" it is actually connected to the phone lines. Similarly, when a phone is "on hook" it is disconnected from the phone lines. Now let's talk about how the Interphone is used. You can have as many as 10 extensions or remote stations. Each of these stations has its own identification number, from 0-9. To use the intercom feature, simply pick up the phone and the busy LED will start to flash on all stations. You then press the number of the wanted extension for at least one second. The ringer of the wanted extension will then sound and will continue to sound for as long as you hold down the relevant button on your handset or until the extension is answered. You then have 2-way communication. Unlike standard intercoms, both parties can talk at the same time. This is full duplex communication and is great if two people want to yell insults at each other at the same time. To make an outside call, you pick up any of the extensions and press' the # button. The switching unit detects the tone associated with this button and connects the outside line to the system. You hear a dial tone and use the phone as normal. To answer an incoming call, just pick up the phone and press the# button again. You will be connected to the line and the incoming caller. Transferring calls If, after answering an incoming call, the caller wants to talk to someone else you can place them on hold by pressing the* button on your handset. You then use the system as an intercom to call another extension and tell them that a call is waiting. You then hang up your phone. Yo_u r spouse (son, daughter, etc) then presses the# button to talk to the outside caller. A caller can only remain on hold The Interphone is built into a large plastic case, with rows of sockets for the various extensions mounted on the rear panel. The base station board is on the left, while two remote station boards are stacked to the right. Each remote 'station board services three extensions. for about 30 seconds before a signal is sent to all stations which sounds the ringer. That way, you cannot accidentally forget about a caller on hold. You must then take the caller off hold and if you wish place them back on hold. Ring tones The "ringer" associated with this project indicates three different conditions. With an incoming call, the ringer has the familiar telephone ring cadence. Features • Up to 10 tone phones can be connected. • Make calls from any station. • Answer calls from any station . • Transfer an answered call to any other station. • All stations can talk to each other (intercom mode). • An outside caller can be put on hold while you talk to another station on the intercom. • Phone off hook indication at all stations. • Full isolation from phone lines using a Telecom-approved isolation transformer. If a caller has been on hold for 30 seconds, then the ringer will sound for one long ring until the caller is taken off hold. If someone is paging an extension, then the ringer will sound for as long as the calling station has their button pressed. Any standard tone phone can be connected to the Interphone but your local telephone exchange must have DTMF tone dialling. Most exchanges in Australia now have tone dialling available even though a lot of modern phones may still be using pulse dialling. How do you know if your exchange has DTMF (stands for dual tone, multi frequency) dialling available? The first way to tell is to lift up your phone. If the dial tone is a tone and not the old familiar "brrr" of pulse exchanges, you have no problems. Second, even if you're presently not using tone dialling it is highly likely that your local exchange has it. To get your phone changed over, all you do ·is ring your local Telecom office and ask to have it changed over. You then have to switch your phone from pulse to tone dialling (via a switch under the handset). As a bonus, you will then have much faster dialling and connection of called numbers. All wiring from the Interphone to AUGUST 1992 69 You can build as many remote station boards as you like & stack them one above the other to give the required number of extensions (10 maximum). The remote stations decode the intercom control tones & provide the ringer facilities. extensions involves running standard 4-core telephone cable around the home. A standard tone phone must be connected at all times to the incoming phone lines and the Interphone is connected in parallel with it. All the extensions are then connected to the Interphone. By having a phone directly connected to the incoming lines, you will always have a telephone service during blackouts - the Interphone needs a mains power supply to work. However, the directly connected telephone will not have the ability to talk to the extensions, put calls on hold or transfer calls. How it works The circuit ,for the Interphone is broken into two sections - base station and remote station. There can be as many as 10 remote stations although they will all be built into the same case as the base station board. Now let's look at the circuit of the base station which is shown in Fig.1. This circuit provides isolation for the incoming phone lines, power supplies, internal exchange facilities and so on. At the top lefthand corner of the circuit you can see the incoming phone line pair. This is connected to a bridge rectifier and also to IC5 (at bottom of circuit). IC5 is used as a ring voltage detector. When the ring voltage of around 90VAC appears across the incoming 70 · SILICON CHIP line it feeds the internal LED of IC5 via a 100kQ resistor and O. lµF capacitor. Diode Dl 1 ensures that the LED is not reverse biased by the ring voltage. Thus, when ring voltage is present, the output at pin 4 of IC5 is a square wave at the frequency of the ring voltage. This is filtered to produce a DC signal at pin 13 ofIC4d and when this signal is present, pin 11 goes high and this sounds the ringer on all extensions. More on this later. Whenever a button on any extension phone is pressed, a DTMF tone appears on the internal line (adjacent to transformer Tl on Fig.1). This is clipped to an amplitude of ±0.6V by diodes D5 and D6 and fed to pin 7 of ICl which is DTMF tone decoder chip. It produces a BCD code at its outputs which are fed to IC2 , a 4028 1-of-10 decoder. a Unconventional decoding The outputs from ICl are not connected to IC2 in the conventional sequence, however. This has been done to allow IC2, which will normally only decode states 0-9, to give an output when BCD codes outside the normal 0-9 are present. The decoded output from ICl for the # button on a standard tone phone would be seen by IC2 as 1010 (decimal 12) which IC2 cannot decode. The same occurs for the * button. Its BCD code from ICl is 1011 (decimal 11) which again is outside the limit of IC2. Connecting IC2 and ICl with one of the BCD lines out of sequence allows the circuit to decode the * button and # button codes. Other codes are ignored by ICl and IC2. When IC2 is fed the BCD code for the # button, its Q9 output, pin 5, goes high. This sets flipflop IC3b, taking its pin 13 high. Q3 now turns on, energising relay RLY2 which connects the incoming phone line to the primary of isolating transformer Tl. Line current is now drawn from the phone line and the telephone exchange will interpret that as a phone off hook. A dial tone will now be heard from the handset and calls can be made in the normal manner. When any phone extension is lifted off hook the OFF HOOK line goes high. This causes pin 11 of IC6d to go low. This prevents anything from happening in the circuit until the phone is placed back on the hook. The OFF HOOK line goes low again and about one second later pin 11 of IC6d goes high. This results in a short positive pulse being fed to the reset pin of flipflop IC3b. Q3 then turns off, releasing relay RLY2 and disconnecting the phone line. What this means is that by placing the extension phone back on the hook you effectively hang up the phone in the normal manner. Line on hold If an outside call is in progress and the * button is pressed, another tone is placed on the internal line which is also decoded by ICl and IC2. This time, pin 4 of IC2 will go high. This sets flipflop IC3a, turning on transistor Q2 and relay RLYl This connects transistor Ql and its associated components across the incoming phone line and disconnects transformer Tl. Transistor Ql draws current from the phone line and maintains the "off hook" condition. The Interphone is now in intercom Fig.1 (right): the base station circuitry provides isolation for the incoming phone lines and includes the power supplies and logic circuitry for the internal exchange facilities & so on. IC1 and IC2 decode the # and buttons which control the hold, transfer & intercom facilities. * -..i ... N co co ..... -J (/) C: 0 > C: PHONE LI NE ~K uu 10k • • IGO 47k ECB ·-w. + 10 ..:- ; +5V -- INTERNAL LINE +5V B EOc -:- .,. *) 05l • VIEWED FROM BELOW ,rr;.::r··1 I 01 -,I XTALJc, INTERPHONE BASE STATION 011 1N914 012 1N914 ~ I T1 .,,,h 10 01 BC548 ., 06\. I / : . +5V + 14 1 113 0 D7 1N4004 I • _ 2 09 15 03 15 02 oo~14 01 1000 T '""°f 0.1 f .,. IN[ V+ !.- . 100k +5v--4F .,. IC2 4028 100t 11 O 12 C ~ (f) A 13 B J..!! OFF HOOK LINE OUT RING SIGNAL 12VAC FROM PLUG-PACK -:- IC1 MC145436 47! :I 101 16 10 ◄ -:- 0.1 100k 08 1N4004 V+ .,. 1 ~ +5 V J 10..: 7 I J: +5V 470 35VWJ +5V 013~ 1N914':t' RLY1 ~. ------rt +5V -:- I 01j POWER~ LED3 K A. 470il TO ALL BUSY LEDS K A + 470'2 LINE SEIZED LED2 I ----~ 03 BC548 "~t 470il +5V--- 010 1N4004 1 -----------------<11------- - -----------, + S V 0 - - - - - - - -...... 16 10 IC9 MC145436 +50V 0.1 INTERNAL LINE IC10 ,4028 + 2.2k 1W 10k 220pFJ . .4 021 020 .,. PHONE 12 10k .,. 100k -r .,. 10k .,. 022 1N914 .,. STATION SET OFF HOOK 1k 120k +50V 22k RING 82k 10k 023 1N914 .,. 0.1! INTERPHONE REMOTE STATION Fig.2: this remote station circuitry must be duplicated for each extension phone. IC9 & IC10 decode the control tones but note that only one of the 10 outputs from IC10 is used on each remote station board. mode and you can page any of the other extensions simply by pressing the corresponding numeric button on the phone you are using. This will cause their ringer to sound. They pick up the phone and talk to you. If they now press their # button, ICl and ICZ will again decode this and take the caller off hold and connect the new extension to the outside line. Whenever a caller is placed on hold, pin 2 offlipflop IC3a is low. Diode D9 is now forward biased which prevents flipflop IC3b from being reset if all phones are placed on hook. This means that if a caller is on hold, then you cannot disconnect the caller simply by replacing all phones. When pin 2 of IC3a goes low (incoming caller placed on hold), diode D12 is reverse biased which allows the lO0µF capacitor associated with IC6b to discharge. This takes about 30 seconds after which pin 4 of IC6b goes high. The Schmitt trigger oscilla72 SILICON CHIP tor built around IC6a now runs at a frequency of about lHz. This is fed through IC6c and IC4d and causes the ringer on all extensions to sound in 1second bursts, indicating that a caller is still on hold. Any extensions can then take the caller off hold by press- ing the # button and talking to the caller. IC4b, IC4a and diode D9 reset flip flops IC3a and IC3b when power is first applied. This is highly desirable since without this feature, the circuit could either pick up the outside line or ring all extensions when power was first applied and this could be in the middle ,Q_f the night, after a blackout! DC rails WARNING! In order to comply with the Telecommunications Act, we draw the reader's attention to the following: "This customer equipment has no AUSTEL permit and may be dangerous or damage a telecommunications network. Connection to a telecommunications network is an offence under section 253 of the Telecommunications Act 1991 and may attract a maximum fine of $12,000". Power for the circuit comes from a 12V plugpack transformer. This feeds halfwave rectifiers D7 and Dl 7, and their associated filter capacitors. Both of these rectifiers produce about 18V DC unregulated and the supply associated with D17 then feeds a 7805 regulator to produce 5V DC. The 5V rail powers all the CMOS circuitry while the unregulated supply feeds the relays. Diodes Dl4, D15 & D16, in conjunction with two 470µF capacitors and one lO00µF capacitor, form a voltage tripler. This produces a little over SONY. SONY. LNK LQQK PARENTS ILLUSTRATED • D ENCYCLOPEDIA PARENTS · 11 n LANGUAGES OF . liil THE WORLD Why pay $1000's for books? Buy an entire educational centre plus so much more tor $1140. NATIONAL GEOGRAPHIC M SOCIETY'S MAMMALS* Not only is this Software Educational - It's fun too! ~ ~ Not only can this fantastic software package educate you and your children, it also can provide hours of entertainment. Learning can be difficult_for many people, but with Interactive Educational Software, you interact with the computer, ask questions and watch the answers. Info on 200 animals, photos, range maps, motion clips essays and 155 animal vocalizations. P11 1M MIXED-UP MOTHER GOOSE* 1 ages. The World Atlas brings the entire globe to your computer screen . This atlas, almanac and world fact book in one, gives you instant access to over 240 fully detailed, EGNVGA colour maps and a huge database of international information . n u ~ ~ An interactive game designed to stimulate your child's imagination with full colour graphics and digitized sound , voices and music. What CDRoms are available? WORLDATLAS* The perfect reference tool for travellers, educators, business people, librarians and students of all A program which translates to and from Chinese, Danish, English, Finnish, French, German , Italian, Japanese, Norwegian , Spanish & Swedish. Allows retrieval of translations, dictionary entries and synonyms & then export to WP packages(Chinese and Japanese display only) . Includes the full text of 18 dictionaries in 12 languages. Compton's Encyclopedia (from Brittanica) contains full text of 26 volumes, 9 million words, 32,000 articles, 1500 illustrations including SO\Jnd and speech recording. Forget flipping through volumes, instead, follow key pathways on words and subjects - access information in the blink of an eye. n l'J ,. MICROSOFT ~ REFERENCE LIBRARY~ - GREAT FOR STUDENTS- This indispensable collection of reference materials includes the American Heritage Dictionary, Roget's II Electronic Thesaurus, the World Almanac and Book of Facts, Bartlett's Familiar Quotations, and more-all on a single CD-ROM disc. For added efficiency, all reference volumes interface directly with more popular word processing programs. Over 1000 Rom products are available including SUBJECT ACCOUNTANTS AEROSPACE AGRICULTURE ART BIBLE STUDY BIOLOGY BIOMEDICINE CARDIOLOGY CHEMISTS CHESS CINEM A CIVIL ENG COMPUTER S DESKTOP PUBLISHING ELECTRICAL ENG , ENVIRONMENT GEOGRAPHY GEOLOGY HISTORY HORTI CULTURE TITLE - Oi skro m Tax Law Database - Ae rospace Database - Agricola - Coafe's Art Review Imp ressionism - CD Word/The Bible Lllrary SUBJECT LAW LIBRARY - MUSIC NURSING OCEANOGRAPHY PATENTS PEOPLE SCIENCE SPAC E TRAVEL VETERINARY WI LDLIFE GENERAL Biolog ical Abstracts Bibllomed Bibliomed Cardiology Se ries Excerpta Medica - Drugs & Pharmacology - Chess Datarom -Cinescan - Citis C D-ROM - Caro usel/C-CD ROM.Com puter Se lect - Clip Art (Various) - FT Bu si ness Graphics - lnspec On Disc. - Envi ronm ental Li brary - Count ries of The Workj - Geovision Wi ndows on the World - The Midd le East Diary - The Plant Doctor MEDICI NE TITLE - Case Law, NSW, SA, TAS & VIC - Books in Print Pl usfBNB on CD Rom Busin ess Pe riodicals Cancer on DisctConsult Medical Posindex Music Library Sound Recordi ngs Nurses Med ical Partne r Aq uatic Scie nce Automated Patent Searc h (US' Biography Index · Applied Science Library Nasa Space En cyclopedi a Great Cities Of The World The Merck Veterinary Man ual Wildlife & Fis h Worldwide Australi a On a Disk Best Encyclopedia --Grolier Business Pe riodicals on Disk Facts on File 1980-90 G uinness Book of Records Jane's All The World's Aircraft Oxford Eng lish Dictionary ~----"-------------~ COMPUTER REQUIREMENTS XT/AT Compatible, 512 Ram. DOS 3.1 or above hard disk drive. Recommended VGA Monitor-& VGA adapter Mouse *Requires VGA (For PS2 MCA 1/F card add $320) PACKAGE CONTENTS Sony external drive model CDU 7205U (which supports CD Rom mode 1 & 2 & Audio combined CD) Sony bus.interface card (half card value $180) Software Collection (as detailed) PELHAM PTY LTD 1st Floor, 100 Yarrara Road , Pennant Hills 2120 Ph (02) 980 6988 Fax (02) 980 6991 AMATEUR RADIO EQUIPMENT KENWOOD ELECTRONICS AUSTRALIA PTY. LTD. P.O. BOX 504, 8 FIGTREE DIVE, AUSTRALIA CENTRE, HOMEBUSH, N.S.W. 2140, AUSTRALIA. (A.C .N . 00 1 499 074) . 50V DC which is used to run all the extension phones in the system. By this means, all the extension phones are powered by the plugpack supply and not by the incoming phone lines. Remote stations Let us now discuss the remote station circuitry which is shown in Fig.2. One remote station is needed for each extension phone and you can have as many as 10 extensions. The limit of 10 is set by the 4028 1-of-10 decoder used in each remote station .board. Our prototype, by the way, is built with six remote stations, three to a PC board. Each remote station board has the job of decoding intercom tones , sending control tones and providing the ringing facilities (via a buzzer). IC9 and IClO decode any tones found on the line but only one of the 10 outputs of ICl0 is used on each remote station board. This is the nominated number for that extensi_on. For example, if button 5 is pressed on any extension phone, then pin 6 of ICl0 ·on every remote station board will go high. However, only one remote station is designated as station number . 5, via a linking option on the board. When a remote station detects its number, the lOµF capacitor associated with diode D22 charges up via a 120kQ resistor (from the decoded output of IClO). After about one second, pin 10 of IC8c will go high. This enables a Schmitt trigger oscillator based on ICl la which gates oscillator ICl lc on and off via IG11b. The output of ICl lc is buffered by ICl ld which then drives Q6 and Q7 and thence the buzzer. This provides the ringer for each extension. We should note that standard tone phones do have their own ringer but this requires a high AC voltage which the Interphone circuitry does not provide - hence the need for separate ringer circuitry. Q7 is supplied from the 50V DC rail, in order to provide a high drive voltage to the buzzer. Before we leave this part of the circuit, we should explain the reason for the one second delay provided by the lOµF capacitor at pin 13 of IC8d. This delay is necessary because if it was not there , then when the digits of a phone number were being pressed to dial out, the ringer would sound on each extension, corresponding to the digits being pressed. PARTS LIST Base station 1 large instrument case, Altronics Cat. H-0490 1 PO board, 130mm x 80mm 1 12VAC 500mA plugpack transformer 1 600Q isolation transformer (T1 ); Altronics Cat. M-1000 or equiv. 2 12V miniature relays 4 100kQ 1 82kQ 2 47kQ 610kQ 31kQ 3 470Q 2100Q Miscellaneous Hookup wire, phone sockets, solder, screws, nuts. Remote station Semiconductors 1 MC145436 DTMF decoder (IC1) 1 4028 BCD to decimal decoder (IC2) 1 4013 D flipflop (IC3) 1 4001 quad NOR gate (IC4) 1 4N28 optocoupler (IC5) 2 4093 quad NANO Schmitt trigger (IC6,IC7) 1 7805 3-terminal 5V regulator 3 BC548 transistors (01 ,02,03) 1 BD140 transistor (04) 5 1N914, 1N4148 signal diodes (D5, D6, D9, D11-D13) 11 1N4004 power diodes (D1 -D4, D7, D8, 'D10, D14-D17) 1 5mm orange LED (LED1) 2 5mm green LED (LED2,4) 1 5mm red LED (LED3) 1 3.58MHz crystal ,(Xtal1) Capacitors 2 1000µF 16VW electrolytic 1 1000µF 63VW electrolytic 2 470µF 35VW electrolytic 1 100µF 16VW electrolytic 4 10µF 16VW electrolytic 1 4.7µF 16VW electrolytic 2 1µF 16VW electrolytic 1 1µF 250VAC metallised polycarbonate 7 0.1 µF monolithic 1 220pF ceramic Resistors (0.25W, 5%) 3 1MQ 1 2.2kQ IC8a and IC8b detect when the extension phone is off the hook. When the phone is on hook, the voltage at pins 1 & 2 of IC8 is clamped at about +5.6V. When the phone is taken off hook, the voltage at the junction of the 2.2kQ and l00kQ resistors will fall to a low value and so pin 3 of IC8a will go high, which causes pin 4 of IC8b to go low and turn on transistor 1 PC board, 115 x 77mm 1 DTMF phone (tone phone) 1 100kQ trim pot Semiconductors 1 4001 quad NOR gate (IC8) 1 MC145436 DTMF decoder (IC9) 1 4028 BCD to decimal decoder (IC10) 1 4093 quad Schmitt trigger (IC11) 1 3.58MHz crystal (Xtal2) 6 1N914, 1N4148 diodes (D18,D19,D20,D21,D22,D23) 1 BC558 transistor (05) 1 BC548 transistor (06) 1 BD140 transistor (07) 1 red or green LED (Busy LED) Capacitors 1 10µF 16VW electrolytic 1 4.7µF 16VW electrolytic 2 1µF 16VW electrolytic 2 0.1 µF monolithic 1 220pF ceramic Resistors (0.25W 5%) 1 1MQ 410kQ 1 120kQ 1 6.8kQ 2 100kQ 1 4.7kQ 1 82kQ 1 2.2kQ 1W 1 47kQ 1 1kQ 2 22kQ Miscellaneous Phone sockets, hook up wire, screws, nuts, solder, etc. Q5. This causes the OFF HOOK voltage line to go high. This line is fed back to the Base Station board (Fig.1) where it is detected, as discussed earlier. This causes the Busy LED at all extensions to light. Next month, we will complete the description of the Interphone with the assembly and installation procedures. SC A UGUST 1992 75