'/ THE INTERNATIONAL MAGAZINE FOR ELECTRONICS ENTHUSIASTS ~ ee cect Lia ey er" The QTC loop antenna Toca ane me UOLmeLe ESC scree OTe eres ea eT UMC acl tet ee Timecode interface - Part 1 06 129) llDiesmieg Eeesined CONTENTS June 1991 Volume 17 Number 190 Apologies: We regret that owing to cecum: tans beyond our conta the “Timecode interlace for side controle had to be postponed after his moots ron cover had already been pte Innext month's issue + As usual in our July issue, ‘more than 0 small but interesting articles presenting new and practical ideas, concepts, ‘and developments on al aspects of electronies PLUS + Timecode itertace for side ‘contol - Part + Mit 0 for BK + Blackand.wfite video gies: Paci data systems Modern LED cock Logie analyser - Par Measurement techniques ~ Pans + Laser -Part’3 + One-sholsotstate relay timer + B68 singl-board computer Front cover ‘This month's project in four measurement series features a digital phase ‘meter. This is a rare Instrument, even in the laboratory or workshop of audio and hi-fi engineers, Many engineers and technicians measure phase shift with the aid of an oscilloscope (Lissajous figures). That is not & Yery accurate method: the phase meter presented is Accurate 10 within 0.5° ‘over the frequency range 10 Hato 20 kHz. Copyright© 1981 Elektuur BV 13 Main results of the 1991 Young Electronic Designer Awards L a 11 Telecommunications and safety of human lite Eye heam i 58 UHF audio/video modulator TDASO64X. Siemens Components Ure meee) 60 PROJECT: Real-time clock for Atari ST by F. Dossche a 30 PROJECT: Laser~Purt2 an BLV design $4 PROJECT: Light switch with TV remote control bby J. Ruffell from an idea by M. Dupessey 63 PROJECT: Stepper motor board ~ Part | by N. Kolter 43° Light wansmitter-receiver by T. Giffard LAN Ee Oe nc 14 PROJECT: Universal NiCd battery charger by A.Righy 46 PROJECT: Variable wc, power supply by L. Lemon RADIO, TELEVISION & COMMUNICATIONS) 27 PROJECT: Video A-D and D-A converter - Part 2 by P. Goon (Philips Components, Paris) 40 PROJECT: The QTC loop antenna by Richard Q. Marris, G2BZQ ‘TEST & MEASUREMENT 20 PROJECT: Logie analyser— Part 4 by K. Nischalke and HJ. Schulz 32 PROJECT: Digital phase meter by R. Lucassen, Eee EAU b React Events 13; Corrections 49; Switchbosrd 68: Terms of business 68: Readers services 69; Index of advertisers 74, ‘picture to restore or increase your {aith in youth and electronics: this young lady, Polyanna Robinson, who is only 4, won first prize in the Junior Category ofthe YEDA awards seepage 19, QTC loop antenna -p. 40 WAHHOws - 4, Variable ac. power supply p. 46 PLERTOR ELECTRONICS JUNE 199TELECOMMUNICATIONS AND SAFETY OF HUMAN LIFE HE DAY afer this issue of Elekror Blec tromies reaches the newsstands. Friday 17 May, is World Telecommunication Day, celebrated every year by member countries fof the International Telecommunication Union—ITU, It is the date of signature in Paris, in 1865, ofthe First International Tele~ graph Convention which set up the Interna- tional Telegraph Union, the forerunner of to- day's ITU, This year, World Telecommunication Day js celebrated as part ofthe Natural Dis- aster Prevention Decade proclaimed by the United Nations General Assembly. Other in= femational organizations, whose activities re significantly dependent on telecommu- nications, have therefore been associated to the celebrations: the International Civil Avi sation Organization (ICAO). the International Maritime Organization (IMO), the World Meteorological Organization (WMO). the Office of the United Nations Disaster Reliet Co-ordinator (UNDRO). and the League of Red Cross and Red Crescent Societies. The topic chosen for this yeur by the Ad rminstrative Council of the Intemational Telecommusication Union is Telecontunt cations and safery of human life Radio was first sed to save file at sea in Maref 1899, when it was used by a Lightship {fo report that the steamer Efhe had run aground. [0 was also in 1899 thai the first slip Was filled with radio, Since thal time radiogommunications has proved to be of Paramount importance to safety at sea [m1 1912. some three months after the pas- senger ship Tirunie disaster occurred with the Joss of more than 1500 lives, an international radio conference met in London to review sandamend the 1906 International Radiotele graph Convention which prescribed the dis- tress and calling frequencies, classes of ship service [waichkeeping). ship's radio equip- ment. and requirements for certification of ‘operators for shiop stations, Later, in January 1914, also in London, an intemational ma itime conference adopted the first Interna tional Convention for the Safety of Lite at Sea (SOLAS), which required cenain ships fo carry an MF radiotelegraph installation The existing distress system ‘The subsequent 1929, 1948, 1960 and 1974 SOLAS Conventions all required passenger ships and cargo ships of 16(K) tons gross and upwards to carry a radiotelegraph station. ‘was not until 1948 that requirements for MF radiotelephone stations were included in the convention and then only for ships «f be- ‘nveen 300and 1600 tons grossnot fitted with, an MF radiotelegraph station, Limited {quirements fora VHE radiotelephone station lor safety jon were included in SOLAS in 1974, but it way not until 1981 thal requirements for all SOLAS ships to he capable of communicating with each other by VHF and MF radiotelephone were achieved. Subsequent World Administrative Con- ferences (WARC) convened by the ITU pro- Vided the radiotelephone distress all, rie diotelephone distress and calling frequen- cies, and reduced the distress bands a5 radi technology and equipment improved, Until 1960, when IMO came into bein the ITU was solely responsible forall specs ‘of maritime radiocommunications, includ- ing distress and safety radiocommunics tions. The 1960s saw great changey and im provements in radiocommunication sys- tems, e.g. satellite communications. selec live calling, direct-printing telegeaphy. Both ITU and IMO recognized the advan- ages oFthese systems for improving all mar- itime radiocommunications, The existing morse radiotelegraphy and radiotelephone system, with a required ME communication range of 100-150 nautical miles, provided « distress system based. if time permitted onalerting ships in the vicin- ity of the distress and coust stations within range. The system therefore did not cover ships that sank suddenly’ or ships in distress that were too Far away from those who could assist Improvement of mari In February 1966. IMO decided to study the operational requirements tor a manitime satellite communication systern and in 1967 the ITU WARC invited IMO tocontinue this work. In the early 1970s. IMO. in close co-op- ration with ITU’s Intemational Radio Con- sultative Committee (CCIR}, started active preparations for the establishment of » ma itime satellite communication system 10 servethe maritime community. This workre sulted in 1979 in the establishment of the In- ternational Maritime ation INMARSAT. 1n 1973, IMO adopted a policy document ton the development of the maritime distress system, whieh outlined the steps that should be taken to gradually improve the existing systemmaind ultimately achieve what was then the distant future system arid is now known as she Global Maritime Distress and Safety ‘System (GMDSS), IMO also sought to improve search and rescue (SAR) world-wide for those in dis tress at Sea and, concurrent with the devel ‘opment of the INMARSAT Convention. pre: pared the SAR. Convention, whieh was adopted in 1979. Underthe convention, SAR is based upon co-ordination of all SAR op erations. wherever they occur in the world by responsible authorities ashore (rescue co- ‘onination centres RCCs)), As MF und VHF communications have limited range, tn order to enable RCCs wo meet their respansibilities under the SAR Convention, ships operating ‘outside the MF range need a long-range HF bor satellite communication capability. 3 Prac poi Wy ELERTOR ——FICEURST INS HE versa eit entnbee: 4 avrtan ELHCTRONICS ting) “eles (S80)2057 (aver) FRANCK. NETHERLANDS out 0.201857 ner) Bera Bieta BV torpor: Len Syrnar ‘eee: 8 200616 Naa {es Tos Tiles eer Teckel 3-4 cima aor | urine pred 0218 4 sirmca) 39 sons) SEPPE ‘LVR BEEK ator ee Editors DRS, MeyerGCP Racdcelt itor PEL. 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Gis Ree Pa Printed ie Netbeans NOM, POs 00% PETERNOROUGH NiFasistas7% te ed tener WL AVIV ain Pabiaer: son Del ELEKTOR ELECTRONICS JUNE 1991Continued froma page I Development of the GMDSS ‘The advent of INMARSAT enabled the velopmentof the GMDSS through carefully considered integration of satelite and mod: cern terrestrial radiocommunication tech niques and procedures. Development of the GMDSS required very close co-operation be- tween ITU and IMO. tn general. IMO are developing the operational requirements, while the ITU through CCIR recommend the technical specifications of the equip. ment and procedures for its use. I the fate 1970s, several countries, par arly the United States and the USSR begunexperiments with satellites that resulted in the COSPAS-SARSAT system bei tablished well before implementation oF the GMDSS, Since that time, the system has provided x significant coniribution to SAR ‘operations and has assisted in saving hun- dreds of lives, Inthe later 1970s, IMO, in co-operation with IHO, established the world-wide navi gation warning service (WWNWS) for the ‘ordination and broadcast of navigational ‘warnings 0 ships. Since 1929, Contracting Governments tathe SOLAS Conventionhave ‘undertaken to broadcast meteorological wart ings and forecasts to ships and to make ar rangements for the reception of da ings and meteorological reports,co-ordinated tie by WMO through its world weather watch (WWW), rom ships, These matters, together with broadcasts of SAR and other urgent in- formation, provide the maritime safety in- formation (MSI) element of the GDMSS, ‘The GDMSS will be fully implemented in 1999 when, except possibly fora few re- maining stations, use of morse radiotelew phy byshipswillceasesfter 100 yearsof ded- teated and faithful service. The concept of the GDMSS is based on the use of the most up-to-date radiocommu- nication technologies to provide a compre~ hensive distress and salety system of com- ‘munication between shipsand between ships and the shore and vice vers wherever inthe ‘world the ships may be situated, The fune~ tional requirements of the GMDSS include transmitting and receiving ship-to-shore and shore-to-ship distress alerts, ship-to-ship distress alerts, SAR co-ordinating commu ‘nications, on-scene communications, signals for locating, maritime safety information «MSI, general radiocommunieations. and bridge-to-bridge (navigational) communica- ions. Implementation of the GMDSS Implementation of the GMDSS willbe phased To allow for equipment redundancy 1. all ships to be fated with a NAVTEX re ceiver anid sarellite EPIRB by | August 1993: all ships constructed before! February 1992 to be fitted with a radar trunspon: der and two-way radiotelephone appara lus for survival eralt by 1 Rebruary 1995; 3. all ships constructed afler | February 1995 to comply with all appropriate re {quirements for the GMDSS: 4 all ships vo be fitted with at least one radar capable of operating in the 9 GHz band by 1 February 1995: 5. all ships to comply with the appropriate requirements for the GMDSSby I February 1999, Emergency distress alerting capability Adistressalert capability incasethe ship sinks suddenly of the radio station is destroyed is provided by a satellite emergency position indicating radio beacon (EPIRB) that is ca pable of floating free from the sinking ship and being automatically actuated and trans rmitting the ship's identity and either its po- sition INMARSAT) or a signal that pro- vides the ship’sposition (COSPAS-SARSAT). ‘The satellite EPIRB is portable and can be cartied into survival craft. which will also he equipped with portable VHF transceivers, ‘on-scene communications and search and res- ccug radar transponders (SARTS) For final To cation by SAR units arriving at the distress position Maritime Safety Informtion (61) Navigational sarnnes peaorolegical | SAR Information| Senin General concept of the GMOSS ELEKTOR ELECTRONICS JUNE 1991HRH The Duchess of York presentedthe 1991 Young Electronic Designer Awards on 3 April atthe Science Museum, London. The Senior Category was won by Stephen Brown of the Royal Naval Engineering College, Plymouth; the Intermediate Category was won by Jonathan Saville othe Queen Elizabeth Grammar School, Wakefield; and the Junior Category was won by Polyanna Robinson of The Godolphin School, Salisbury ‘The Texas Instruments Prize of £2,500for the most commercially viable project was awarded to Polyanna Robinson, ‘The Mercury Communications “Planet Award, also worth £2,500, for the most en: vironmental and socially aware technology ‘went to Fonathan Saville ‘The Duchess praised the work of all 21 HRH The Duchess of York and Professor John Eggleston, Charman o the YEDA Board of Trustees, sisuss Pollyanna Robinson's Quizmaster. This ‘device, which indicates the first contestant 10 respondtoa question nagame, earned olyanna (14) fist place in the Junior Category. IEE AND IFEIE PROGRAMME 3 June—Inspection and testing of electrical installations. 4 June—Loud and clear obtaining inteli- ible public address at stations, 5 Jne—Transparent optical networks in Europe. 5 June—High frequency resonant power supplies, 10 June—Testing tomorrow's technology today 10-12 June—Reliability ‘91. International ‘conference at the Royal Lancaster Hotel, London, Details from R. Matthews, AEA Technology, Wigshaw Lane, Culcheth, ‘Warrington WA3 ANE, (0925) 31244. 1 June—Broadcasting traffic information 12 June—Practical methods for robust con- nol system design, 12June—Satelliteantenna technology forthe 2st century. 14 June—Sofiware in ait tra tems, 14 June—National Library of Scotland phase 1: eleciical system and lighting. 17 June—Electtonie CADMAT in teaching, 17 June—t6th Edition — IEE wiring regula: tions. 20-22June—Television measurements Fourth International Conference, Montreux). ELEKTOR ELECTRONICS JUNE 1991 how much she admired their wgenuity and their understanding of the sci- ence of electronics. The 21 young design- ers, whose ages ranged from 12 10 24. came from 15 differenteducational establishments, in ll parts of the UK. YEDA is sponsored jointly by Texas Instruments Lid and Mercury Communications Lid, Ken Sanders, managing director of TI said: "A venture like YEDA requires a com- ‘mitment of years. rather than days, Sponsorship is more than just signing cheques. Sponsors should also try to provide ia Jonathan Saville (16) discusses his project, an electronic automated self-contained river water pollution monitor, with HAH The Duchess of York. aA 21 June—Embedded sofware control sys- tems. 24 June—Measurement uncertainties for Europe ~is there a common approach? 27 June—Electromagnetic compatibility for project engineers. Information on these. and many other, events, ‘may be obtained from the IEE, Savoy Place, London WC2R OBL, Telephone 071 240 1871 orthe LEEIE, Savoy Hill House, Savoy Hill, London WC2R OBS, Telephone (71836 3357. generator, cable ‘communal systems, an in-line recording con- sole and a newsroom autocue are among, ‘many new products that will Feature on the stands of more than 40 Britishcompanies ak- ingpar inthe TV Symposiumand Exhibition in Montreux from 13 to 18 June. The group. is being organized by the Electronic and Business Equipment Association in co-op- eration with the Depariment of Trade and ‘namism which will contribute to the Hife of the venture. This is why we are finding way's in which completed YEDA projects can be given a much wider audience among the general public” Peter van Cuylenburg, Mercury'schief ex: ecutive, added: “Mercury's co-sponsorship of the YEDA awards and the introduction of the Planet Award underline our deter nation to encourage new talent and our con- ‘cem for the well-being of our planet. By do- hating this award, we hope to encourage the development of safer and environmentally sympathetic technology’ Firstplacein the Senior Category wentto Stephen Brown (24), who developed a system that inte. actively displays images from the AutoCad de- sign package, Industry. In addition, the Association will mount an information stand where any en- quiries about the exhibits or the industry ‘may be directed, Details from the Department of Trade and Industry, 1-19 Victoria Street London SWIH OET: telephone 071 215 5000, This month, Frost & Sullivan will conduet seminarson ISDN Protocolsand implemen- tation: An introduction to telecommuni cations: the OSI reference model: X. and packet swi . 's new in IBM's INA2; and Advanced packet switching. Details fom Frost & Sullivan, Sullivan House, 4Grosvenor Gardens. London SW1W ODH, ‘Telephone 071 730 3438,UNIVERSAL Ni-Cd BATTERY CHARGER by A. Rigby Ni-Cd batteries are now used in so much everyday equipment that most households need at least one suitable charger. The one presented here can be used to charge virtually all current Ni-Cd batteries. HE charger is based on the Telefunken ‘Type U2400B processor. which has been specially developed forthis application. This device contains mastofthelogic circuits nec~ essary for automatically controlling the charg ing of Ni-Ca batieries. Tnitially, charging takesplace during a pre- determined periodof time,alter which tickle charging takes over. The trickle cha ‘which may continue for long periods of time, ensures that the battery capacity does not degrade during the life ofthe battery "The charger has s number of safety fe lures. Far instance, if the temperature of the batiery becomes too high or when the emf of the battery rises above a certain (prede- fermined) value. the charging eycle 1s dis continued immediately. The processor then assumes its stand-by mode and remains there Until the temperature or the em... drops below its fimiting value. A flow diagram of the charging process isgiven in Fig. 2. After the battery has been connected and the star reset aperated, the processor first arranges for the battery to be Uischarged. During the discharge cycle, the temperature of the battery (Tfjgh and the e.m.f ‘with the maximum preset) voltage (U>U pax) Furthermore. the content of the discharge res: ister and the battery temperature are moni- tored constantly. Attheendof the preset charg ing time (1>fyyac) the charging eycle is ter- ‘minared andthe processoractuatesthe trickle charging mode ‘As already mentioned, if during charg: ing one ofthe preset pararneters is exceeded, charging is discontinued. At ihe same time, the status of the error register is increased by 1 anal reread, Ifno error occurred previ ‘ously, the status of the counter after the pre~ sent error will be smaller than 2Z<2). the ‘counter status is smaller than 2, the en. and temperature of the battery are checl ‘once again; if these are all right, the ch ing process is continued. If the content of the error register iy greater than, or equal to 2. charging is continued or stopped. de- pending on the position of a switch as ex- plained later ‘As is scen in Fig. 1, the processor needs ‘only a few extemal components to perform the funectionsdiscussed so far: During the dis charge eyele. thee.m.f.of the battery ismon= itored via Ug (pin 6). In this, use fs made of a switchable vollage divider. Rag-Ras- Ry-P2, which attenuates the battery volt- age. During the discharge cycle, output bisichiarze} (pin 10) is ative and high. The discharging js assumed conpleie when the vollage level al pin 6 drops bs 40.53 V) of the internal reference voltage. During charging, ouiput Lon (pin 12) becomes active and high: the battery voli~ age is then applied to pint (yaa) Via potential divider ow the level quency-determining network Monitoring ofthe battery temperature is accomplished by Rp. which has & negative lemperature coefficient. The potential at Junetion Re-Re is monitored via input Ujensp (pin 5}. The charging process is stopped when the battery temperature reaches 40 °C: the resistance of Ry, is then about 4400. “The position of switch S; determines the selection made by the processor when two ‘or more errors in the charging process have been signalled. If the switeh is connected to the reference voltage, is continued even when two (but no more) errors have occurred; iF itis connected fo earth. how- cover. full charging is discontinued and rickle charging commenced The changing time is preset via the Tie Input, pin 13. When the internal 200 Hz os- cillauor is used, a high level at pin 13 sets me 0 | hour. When the pin is connected 1o earth (Now level) the charging. time 1s 30) minutes The timer may also be driven by an ex Rig-Rys-RoP), I'he volt- age at pin 4 is higher than the internal reference po: tential. the processor switches to the stand-by mode. Since itis important for the user to know in whieh State the processor is. (Wo LEDs are driven via sta- Tus output pin 9. Table T showsthe operation of these iodesintthe various modes, A reference voltage of 3.V (nominal) 1sapplied to Bite PWM ints series-vonnected LEDs. SeriescombinationRy-C at the input of the internal oscillator, pin 3, is a fre~ Fig. 1. Basic circu for the U24008 processor. ELERTOR ELECTRONICS JUNE 1991UNIVERSAL NICD BATTERY CHARGER ternal clock, connected to pin 16; pin 13 ‘must then be earthed, The internal 200 Hz oscillator then provides the clock signals for the remaining functions of the proces: sor. A frequency of 0.5 Hz at pin 16 sets the no battery connected; battery faulty or charging time to 1 hour; halving that frequency battery flat doubles the time. An external clock based discharge eycle on a 4060 IC as shown in Fig. 8 ean provide charging cycle frequencies down to 0.125 He, which would trickle charge mode give a charging time of 4 hours ‘charging continues after two errors trickle charging after two errors Charging In a practical charger, the processor does not drive a simple transistor, but a fairly complex current source, contralled as shown in Fig. 3. Thecharging current flowsthrough Roa. resulting in a potential drop aeross this resistor that is directly proportional to the charging curren Up22 = HooaR This voltage is used for controlling thecharg- ing current. Note that the negative battery voltage, Uys is in reality more positive than the supply voltage. Uy. beeause the positive terminal of the battery is connected toa sec: ‘ond, higher supply voltage Since transistor Ts isconnectedasa diode the emitter of To is connected to Uy at all times. Therefore. the potential drop across the emitter resistor, R., which is the quiva lent of Roy-Riy-Py in Fig. 8, is exactly the same as that across Ro Une = Upar = taeRe Asan example, assume that Ras =0.1 Q. 1 A,and that a current of I'ma is re- guited through the transistor. The dropacross Ravis 100 mY, so that 100x10-3/10-3 = 100.0, Since the emitter current is now known, the voltage drop seross the collector resistor Ugg = L2x10%109 = |.2V, ing current results i voltage at Fy. That volta Fig. 3. Part of the Fig. 2. Flow diagram of the battery charger. ing current, ircuit controlling the charg- ELEKTOR ELECTRONICS JUNE 1991Switch-mode power supply A switch-mode power supply is used (0 en- able the charger to cater for the simultane ‘ous charging of. say. uptotenatteries; acon- ventional mains supply could be used, but the dissipation in this Will be quite Targe when only a few batteries are being charged. 1 1 : Fig. 4. Concept of a switch-mode power supply The basic operation of such a supply is shown in Fig. 4. Electronic switch $ is switched on and off by electrical circuits. When itis closed. a current (; flows from the supply terminal lo earth via inductor across the emilter resistance, R, RS ‘The non-inverting input of the comparator in the collector eireuit of Ts is held at 27 V by zener diode Ds, The value of Rj, 1 determined by the collector current (1 mA) and the reference voltage: Ry 227/103 = 2.7 KO. ‘Theconnected batteriewaredischarged via Rosand Ts, which, with T,formsadarlington a the output of the comparator. Voltage monitoring The processor continually monitors the bat: {ery voltage via its pins 4 and 6, Since these inputs measure the voltage with respect 10 cearth and the negative terminal of the bat tery is connected 10 the © supply rail. a sim ple cireuit Hike that in Fig. [ean not be sed. This means that the battery vollage must be converted so that it cam be measured with respeet to earth. “To this end. « network as shown in Fig. 7 is used, The entire battery voltage is dropped consisting of resistors Rag-Rys—see Fig.8.Since Rhas avalucof | kO perconnected battery. the col lector current, through Tis 1 net JaxRe= UR where U, is the zener vollage When the batteries are charged, the col: eetor current is 145/108 = 1.45 mA and the voltage drop across Ry and potential di viders R>-P) and R3~Ps is 1-74 V. This voli has the correct polarity with respect to earth. The correct operating point is se with the two potentiometers: how many batteries are connected tothe chargeristhen no longer ‘of importance. The complete circuit Large parts of the diagram in Fig. 8 have al~ ready heen discussed, Note tha the switeh- ‘mode power supply operates only ifpin f of the LT 1070isconnectedtoeanh visthe LOAD ‘output of the processor and Ty, Since the resistors at like positions of Sy and S44 have the same value, the discharge and charging currents of batteries are iden: L. resulting in a magnetic field around the inductor. Diode D ts switched off and ca- pacitor C. therefore, has no influence on the circuit, although it can discharge via load resistance R (representing the balteries to be charged). ‘When S is opened, the self-inductance of L causes a current i2 in the opposite ditee- tion from i: and this charges C via the diode. The level of output voltage U3 depends ‘on the properties ofthe inductor. the switch- ing logtes and the on-off ratio of the switch. Inthe present charger, a commercial indui lor is used: it is not advisable 19 wind this yourselt The circuit of the supply used is shown in Fig. 5 I is based on Linear Technology's ‘Type LT 1070, A 40 kHz oscillator provides ‘train of rectangular pulses that are used 10 switch transistor viaa driver stage. The duty factor is determined primarily by the output voltage of the (dlfferential) cor amplitier. o— The collector voltage of Tyis 1.2 V when. theregulatoris ins stablecondition. Because dof its internal reference vollage of 1,24 V. the error amplifier then has no effect on the switching behaviour of the output transis tor. When the charging current increases 10 too high a level, Ug rises, and the output of the error amplifier goes low. This results in aan alleration of the on-off ratio of he tran= sistor, which lowery the charging current. Zener diode Dg limits the vollage to L8 V. Discharging Thedischargecireuitshownin Fig. bhassome points in common with the circuit in Fig, 3 Again, use ismdeo the voltage dropacross emitter resistor Rs» The supply vollaze and the battery volage have. of course, changed places, sce the discharge current flows {nto a different direction from the charg current Fig.6. cuit for contolling the discharge current, The Dis Fig. 7, Circuit for measuring the bat- ‘output of the U24008 provides the reference voltage for IC3. ‘ery voltage with respect to earth. ELEKTOR ELECTRONICS JUNE 1991aa) Fig, 8. Complete circuit diagram of the Ni-Cd battery charger. tical Teis,of course, essential that switch Sx {s sotto the correct number of connected batteries (maximum 10), Switch S; selects the mode to be used when one or jwo errors are detected dari the charging process—see Table | When So's ints centre position, the pro- cessor uses the standard Lime setting (of charging) of | hour. Its pin 13 is then con: nected 10 earth. IF this meets all your re- quirements, the external clock generator consisting of the 4060 (IC), Rj. Ria. C4. FLEKTOR ELECTRONICS JUNE 1991 Ps il S>, may be omitted. Otherwise, Ry. Ria. Ps, and Cy, set the frequency of the oscillator in the 4060 at 100-150 Hz. The divider on board the 4060 provides the required signal frequencies at ‘outputs Qy and Qu. The charging times of 2 tnd 4 hours respectively associated with these frequencies enable U7 and Ut] size bat teries to be charged in accordance with man ‘ufacturers’ specifications, Preset Ps enables the correct setting of 2 hour (position A} and 4-hour (position B) ‘charging periods. Should that not be possi- ble. the value of C, may be increased (longer petiods orreduced (shorter periods). Ira stan- ard time of 30 minutes is wanted instead oF U hour {S> in centre position), disconnect pin 13 of the L2400B tron earth. MC, is replaced by a 10 nF type. periods of 30 minutes (S> in centre position), | hour (Ss in position A), and 2 hours (S3 in posi tion B), may be selected For trirtle charging the normal charging circe® ed, but the on-off ratio is arWas NiCd CHARGER wf 200200 ° 600 Ne 56 ® © iio) y y a g ” ‘BATTERY 0 | @ Lo) (ele cow on } o ino 4 sarteRy @ 2@u ® ‘STOP ON = ERROR mAH 2 OF CELLSranged at 1:179, which reduces the average charging current of 1800 mA 10 10 mA. The level of the discharge and charging currentsis independent ofthe selected charg- ing period and may be set to six fixed val tues with S,, IF i i required for a battery 10 be charged completely in 30 minutes, the charging current selected musthave twice the value of the battery capcity. The charging current in mA corresponds io the capacities shown on the front pane}—see Fig. 10. That is, in position 500 mAb, the charging cur- Independent of this, the ing Rie with a second 0.1.Q, 1 W, resistor, This may, however, be done only ifthe total consumption, foad joys does not exceed 25 W. otherwise’ the switched-made power supply may become overload. Furthermore, the maximum current through the inductor, the fuse rating (max, 8 A), and the maxi- mun discharge eurrent (max. 10 A) must be observed Construction The battery charger is best constructed on the printed-eircuit board shown in Fig. 9 Pay good atiention to the polarity of number of components and muike sure th firm solder connections are made where large currents are likely to flow. “The components that need cooling, i... ICs, Ds, and Ts, are located at the edge of the board to enable them to be fitted direct toa suitable heat sink (23.2 K W-! at a con- sumption of $25 W), lake sure that the rear oF the LTLO70 is, electrically bonded to the earth connection specially provided between the supply con: nections for C; and ICs, All presels are conveniently grouped at fone side af the board. Resistors Ro3-Ryp are not located on the board, but are soldered direct to the rotary switches. These switches are intended to be fitted to the front panel. Their sections that ‘must be connected 10 the board are marked UNIVERSAL NE-CD BATTERY CHARGER G/H, K/L. and MIN. ‘The sockets for connecting the NTC re- sistor, Rp, the supply (K;) and the batteries (Kz) are located at the right-hand side of the from panel Calibration There are quite a few calibrations ta be c ried out, but fortunately they arenot very erit- ical, In the first place, do not yet fit IC; I. Set Sq t0 500 (mA), Ss to 8 (batteries), Sp to its centre position, and all presets to the centre of their travel, 2 Connect a 12 V, 2 A supply to K, (ob: serve polarity!) 3. Connect an eunitiary supply of 8 V 10 Ka (observe polarity!) 4. Connect a multimeter between the ® pin ‘oF Ky and point G on the board, and ad- just P, until the measured voltage is ex- ‘actly the same as that between the pins of Ka 5. Set $3 to position 10 and adjust P> untit ‘with an auxiliary voltage of 8-8.5 V on K>, a voltage of 053 V is measured be: ‘ween junction P-R-Cyzandearth, This ensures that all batteries are first dis~ charged to an e.t.f. of 0.8-0.85 V. 6, Set $5 10 position 10 and adjust P, until with an auxiliary voltage of 10x the max- imum specified (by manufacturer} cell voltage on K3, potential of 0.53 V ismea- sured between junction P)-R>-C), and earth. The maximum cell voltage is nor- ‘mally about 1.65 V. but may vary from 155 Vt0 1.7, 7. The external clock is adjusted with the aid of P and this is best done onan os- cilloscope. The frequency of the signal al pin 6 of IC) musthe | Hz. Ifyou have no oscilloscope, use a logic tester with LED indication: the flashing of the LED may be compared with the second hand ofa watch. 8. Remove the auxiliary voltage from Ka, switch off the supply vollage, and fit ICy and Rg, fn.an emergeney, a normal | KO Resistors: Ai, Ri9= 1.2ko. R2, R3, R13, 18 = 10 ko R26, R32 = 100.0 Inductors. Ra = 300K. Gi R27, R33= 120.0 Ly = choke 200 pH, 5A St = miniature C/O switehr A5 = 22k ‘28, R34 = 150 'S2 = miniature C/O switch with RE = 1 KNTC 35-Ai43 = 1 KO ‘Semiconductors: centre position 7-220 Pt = 10k9 preset D1 = LED, red ‘S3-= rotary switch, 1 pole, RB, AIS 2700 P2 = 25 ko preset D2=LED..green 42 positions F9=18h0. 3 = 50 ko preset 03=zener,27,V,400mW —_S4= rotary switch, 2 poles, Aid=2000 P4 = 2.5 kX preset D4 = IN54C All = 100 ka PS, P6 = 50 2 preset, DS =BYW 29/100 F1 =tuse, 5A, complete with Ri2=1MQ D6 = zener, 18 V, 400 mW holder Rid = 272 Capacitors: 1h, 12, T3, 15, T6 = BC560B KI, K2 = 2-way terminal block R16, R25, Rat = 86 2 C1, C11, C12, C13 = 100. nF T4=BS170 Heat sink, 1003815 mn RIT =1.5ko. C2=150F T? = BC547B PCB 900134 R20 = 33k C3, C9, C10 = 470 WF 25 V ‘Te isisintended for probes that can cope with input voltages up to £12 V. If sucha probeisnot envisaged, thissection simply be omitted, ‘Mains transformer Trois rated at 5 A to handle the whole analyser. The rating can be reduced by 1 A for each RAM card that is omitted. ‘The five regulators are ofthe well-known ‘7xxtype, but here rated al 2 A (S-type). This isbecausethe current drain of the RAMeards is ust about 1 A and it would be disturbing, ifthe current limiting of the regulator would ‘come into action regularly (low voltage) The PCBforthesupply isshown in Fig, 17. [thas the same format as the bus board and thetwomayzthereforeiftheenclosureallows, be fastened together with the aid of suitable spacers (track sides facing, of course). Such an arrangement would place the 5 V and 12Veonnections ofthe boards close together Atari interface Communication between an Atari and the logicanalyseris via the hard-disk slotemerg. ing at the rear of the computer viaa D-type connector. ‘The present interface is not strictly a spe- cial hard-disk interface, but a DMA inter- face ta which a maximum of eight external apparatuses may be connected in parallel. ‘Addressing the apparatuses separately pro vents any conflict between them. This means alsothat the hard diskmay remainconnected. “The circuit diagram of the interface is m2 78808 eywes ee Fig. 16. Circult diagram of the power supply; the section based on Trt is or use only if probes that ‘accommodate input voltages up to #19 V are to be used. ELERTOR ELECPRONICS JUNE 1991| Tc z s a o Pp Heol eo @ (220) et == 4Fig. 21. Circuit diagram of the IBM interface. =—-, ca rolls ocife eclfe i — 3/0 "SSescroscosey O} Fig. 22. The printed-creult board for the |BM intertace is designed as a slotin card. ELEKTOR ELECTRONICS JUNE 199ELEKTOR, ELECTRONICS oO ao] 50 Hz No. 900094 F1=125mAT F2=2AT No. 900094 F1=125mAT F2=2AT Fig, 2. Suggested labels for the rear panel ofthe logie analyser.LoGIc ANALYSER Fig. 25. The front panel forthe logic analyser is available through our Readers Services. Power supply Capacitors: 667, C70, C73, C76, C79, C82, (C83 = 470 uF, 25 88, C71, 074, C77, C80 = 330 nF C69, C72, 076, C78, C81, Ce4, ‘C85 = 100 nF ‘Semiconductors: | 02-05 = Byw29, 6-09 = 1N4001 IC65-1069 = 78505 \c70= 7812 171 = 7912 Miscellaneous: K23-K29 = 2-way terminal block, S-0m centre Ke2 = 3-way terminal block, 5-cm centre ‘Trt = mains transtormer, 12 V, 3.75 VA ‘Tr2 = mains transformer 8 V. 5 A ‘St = mains on/off switch with Integral tuse holder F1 =fuseholder and fuse, 63 mA, ‘delayed action shown in Fig. 19, The DMA interface can ac ces5 two addresses in the circuit via line AT ‘The control register, ICsz, is at one of these addresses (AI = 0), The address of the appa: ratus must be written in the three most sig- nificant bits ofthis register in order to actu- ate the analyser, ‘The logicanalyser hasaddress 4; whether. thatisstored in thecontrol registerischecked by gates ICaic and IC, ‘The output signal of ICy) enables or dis ables the various inputs and outputs of the interface. The remaining bits of the control register ELEKTOR ELECTRONICS JUNE 1991 bau is F2= fuse, 1 A, delayed action Five heat sinks for |C65~1C69 PCB 900034-7 Atari interface Resistors: R32-A34 = 22k Capacitors: (064-086 = 100 nF ‘Semiconductors: IC59 = 74H0TS74 (C60 = 74HCT138 [C61 = 74HCTOO i062 = 74HCTO2 io63 ~ 74HCTO3 1064 = 74HCT245 are used to address the various registers in the analyser proper: Q0 and QI provide the woaddresslines forthe register, whileQ2-O4 control address decoder ICjo, which gener ates the five card-select signals. When theinterface isactuated by the four highest bits ofthe control register, data may besent toand from thelogicanalyser via bidi- rectional butfer ICyy. The buffer is addressed when Al is high. The direction of the data transport is determined by the read /write> Tine. Thesingle-step signalis produced by ICs and [Cig from the strobe signal for the data ——s aaa Miscellanous: 20 = 19-pole male D connector or 20-way box header (S00 text) IBM interface Capacitors: C1-C7 = 100 nF ‘Semiconductors: } IC1,1C3, IC4= 74HCT245 No2 =74HCTS77 15 =74HCT138 ICB = PAL1618 (Order No. 5972) IC7 = 74HCTO4 Miscellaneous: K1 = 25 pole female D connector tor PCB mounting Fixing plate (see Fig. 22) PCB 900094-1 busand the WR> signal Atari interface board ‘The board for the Atari interface has been designed as asort of adapter plug (see Fig, 20 and 27) that can be inserted at the rear of the computer. The PCB-Lype 19-way maleD con nector for this is, however, ot easily avail- ableinmany locations, Thereis, therefore, the possibility to use a box header (which is much more readily available) in the K20 po- sition. Starting at pin 1, he wires in the cableFig. 27. Photograph of completed Atari interface board. are soldered or crimped as follows: 1 10 1;2 fo 11; 3 t0 2; 4 40 12; 510 3; and so on; only pin 20 of the box header is nat used, No such difficulties are envisaged with Kz The cable between the interface and the logic analyser may be a standard computer accessory:25-way with maleand female con- nesters. Itshould, however, note longer than ‘one metre IBM interface ‘The interface for [BMXTand AT computers Consists oF not much more than a number of digital inputs and outputs—see Fig, 21, The data bus for the computer is butfered by IC} This is nol necessary for the address lines of the computer, since most lines are connected toonly one input. There three addres lines that, dependingon the po- sitionafthejumpers nearIC,,areloaded with Up to two inputs. Circuit IC; is the address decoder of the interface The basic address of the card may be ar- ranged in stepsof ouraddresses from 300, t0.1Cyqs with the aid of jumper verters in lines A2-A4. Fouraddresses emanate from theaddress eceler fa PALI: an enable signal for the re, nevertheless, and iy data bus buffer (E>) and three select signals forcontrolling thethreeindividualaddresses on the interface card: ADR(-ADR2. ‘The address register is found at basic ad dress +0. The address with which acard and a register are addressed on that card is writ ten in the address register. ‘The data register is found at basic address +1, via which data are written to, or read from, the logic analyser, Simultaneous with thereadingor writing, card select decoder ICs is enabled via the ADRI Tine to ensure that the cards of the analyser are connected to the bus only when this really necessary. ‘The IRQ signal (rom the analyser enters via basicaddress +2 on theinterfacecard. This is processed as data, and not asan interrupt IBM interface board The dimensions of the PCB for the IBM in- terface are determined solely by those of the two connectors—see Fig, 22 and 28, Since the electronics clo not need much space, it has been possible to include a table on the board that indicates what jumpersane required to place a certain basic address for the ear ‘To prevent the card being pulled from the slot by the connecting cable, itis essential Fig. 28. Photograph of completed IBM intertace board. that the board is provided with a fixing plate with which it can be fastened securely on to the computer. Such a plate can be made as shown in Fig, 24 For the connection between the interface and the computer the same sort of cable as for the Atari may be used. Overview An overview of the logic analyser and all that may go with it is shown in Fig. 23, ‘Thecontrolcardisalways connected tothe centre connector of the buis board to ensure that when several RAM cards are used, the connections between these cards and the control card remain as short as feasible. Before the RAM cardsare builtin, 0 10k resistor must be soldered al the track side between pins 11 aad 16 of ICxe, This resistor suppresses any reflections that may occur at that end of the clock line to the shift re There is not much wiring in the analyser because most connections are contained on. the bus board. What wiring there Is comes mainly from the power supply, .VIDEO A-D/D-A CONVERTER PART 2: A 30 MHz Si | GATEA GATES VIDEO ADC/DAC aS DEVELOPMENT = S Pal BOARD “Ta =] Following last month's introduction into the basic wool) @) | operation of the two main sa conden integrated circuits in the design, the TDA8708 and the TDA8702, this second 7] and last instalment rakes focuses on the more - practical side of things. “=O a Are you triggered? Here is lL a high-speed video A 8 A-DID-A converter board 71 ae | eleeeeeaes aimed at helping you on 7 Sag the way with your own ext sy abeoscnerey video experiments. P. Godon (Philips Components, inwed from the May 1991 issue ‘orsr02(7 The block diagram of the development Pee #8 oor | board, Fig 8, shows the wo converter ICs any ee an les surrounded by quitea few sockets, switches omen and connectors. The switches, Ki through ke, are actually jumpers that allow different ‘modes of operation to be selected. The BNC Fig. 8. Block diagram of the video processor card. Most of the switches shown here are sockets, Ki0 through KI7, are the analogue wire jumpers to select different modes of operation. Beso SES are opener ies ra Xi umeer——_Gock2 eayed Cock Io BN socket AOC iu 2 RE ccs. Mecsas aes te Ki BNGrekat Clock put ee eatayootmitn| ie lesen cana Se ob seo ee raarcn iis. eNGSaaat | eas gto ee eee Inesnid WeteNC seamen ace ees ow ecreneyamell| mie) © auctiacre cho metese aoa KP ME eccsh cratered Minis rclek Coenen iy” ERERUBGgeinemetcamer lies cprscun. “ce tase iS. URI vie putateaie or Ucar aa tere. Ulbecatoces cameo fio BNE mt ADE destin fae ecdremer Puc rier Kir eNCeeckat_ ADC impute &5—“SEwayDIN_ combined ADC ouput and DAC pat Xie) BNC sea ADU ES | ELEKTOR ELECTRONICS JUNE 1991B RADIO AND TELEVISION video inputs and the digital control inputs, ‘The analogue output signal of the DAC is available on socket Kis, The board is linked to a computer or microprocessor system via connectors K2! and K22, or K23, All digital in- puts and outputs of the board are TTL com: patible ‘The development hoard is connected to analogue and digital 5-V power supplies via zn, Two separate power supplies are re- ‘quired to ensure the best possible decoup- ling of the analogue and digital sections. “The ‘adjustable delay’ block is formed by an integrated circuit that has not been dis cussed last month. This IC, a Type 1505-58 rom Data Delay Devices, cantainsa stepped delay line. The signal applied to the CLxi input of the board, Kis, can be delayed in stepsof Ins toa maximum of Sns. Thedlelay Tine has a dec. resistance of 0.7 © and an im- pedance of about 100 ©. Finally, the resistors shown in the block diagram ensure that video sources are termi- nated in 75 0, and the clock inputs in 50.2. The development circuit The circuit diagram of the video A-D/D-A card is given in Fig. 10, As discussed last ‘month, the TDA870S stores the current anal- ‘ogue value at the first leading edge of the clock signal, after the 1.5-V threshold is ex ceeded. You will also recall that the digital ‘equivalent of the analogue value appears at the output after a delay, Ts, of 8 to 20 ns. At the next trailing edge of the clock signal, the DAC copies the digital information, and supplies the corresponding analogue value after the conversion delay, ty, of 3 ns. Hence, the video input signal is subject to a total delay, Ts, of TeaTys hen At relatively high clock frequencies, say, 30 MHz, it may happen that the minimum. required delay time between the A-to-Dand D-to-A conversions is not available. The DAC requires that the input data remain stable for at least 0.3 ns. Since the time be- tween the leading and the trailing edge is only 17 ns for a 30-MHz. clock signal, itis readily seen that the DAC may have trouble loading stable data when the required delay, Tu, is yet to be subtracted. This potential problem is eliminated by the previously mentioned delay line, ICs, which delays the trailing edgeof theclock 1 to 6ns, depending, ‘onthe selected tap’ jumper K19). This com: pensation ensures the correct operation of the conversion processes when relatively high clock speeds are used. The diagram in Fig. 9 shows the combined timing of the ADC and the DAC, along with the data setup times and associated delays. Construction In view of the speed of the signals involved, the video A-D/D-A circuit is best built on a printed-circuit board of the design shown in Fig. 11, The board is double-sided, but not coum ff \_ fe ‘Anolog Input ADC digital outputs DAC digital inputs one- LOC | ‘ Power staoes | . Output & Second channel ‘enitt | (contusion moet ently ed 909522 -| Fig. 8. period time ofthe triangle is about 100, but the actual value is slightly different for each ofthe four generatorsin the control unit. The differences are such that it takes more than 21 hours (theoretically) hefore the same pat temis repeated Circuit diagram The circuit diagram, Fig, 9, ofthe laser con- trol unit follows the Block diagram quite closely. For the sake of simplicity few books are drawn in Fig. 2 that contain ci cuits discussed in detail further on The unt and signals are applied tothe iru vin sockets Bui to Bus, which are con nected via a potential diver forthe right and Jat channel. This means that the Ls Socket andthe Ne socket net lo it can not be used simultaneously. Fortunately, the high impedance af the potential divider pro- vents damage wequipment when the is and LUNE inputaeacatdentally used atthe same time. The apt signals are firs ed toa com pressor, whose operation is discussed fur ther on “The microphone a small electret type witha builtin FET amplifier is connected to terminate STI, Stand ST3, The micro- phone signal is ampli! by IC before its BLEKTOR ELECTRONICS JUNE 1991 ‘Block diagram of the laser control unit applied to the compressor. The three com pressors are followed by the input selection siitches that enable the signals to be routed in one of two directions: fo the frequency determining circuits, or to the amplitude determining circuits Inthe trequency-determining branch, the signal i first applied to a 150-Hi filer set up around Ty (T3 for the right channel). Then follows another switch, this time for the se lection between the audio source and the generator. After the frequency compensa tion the signal arrives at electronic poten tiometer ICé In the amplitude-determining branch the audio signal is fed to T? and Ts, which form anenvclope detector. The switch contact that follows the detector allows the size of the patterns to be controlled manually or by the ‘envelope waveform of the audio signal, The latter function requires a constant voltage, which is obtained from a regulated supply voltage with the aid of a potential divider. ‘Theamplitudecontrolsignalis subsequently amplified to allow the final size of the laser pattern to be set by the LEVEL control, Rar. Rao, Next, the level information is applied to the control inputs of an electronic poten- tiometer, IC4. The output signal of ICsis buf- fered by [C2 and ICss before it arrivesat the switch contacts that allow you to determine the channel assignment (left/right; L/R) for the horizonal and vertical (H/V) deflection ‘of the laser beam, From the poles of the H/V- L/Rswitches the signal is taken tothe inputs of the two power amplifiers that drive the mirror galvanometers, The generators ‘There are two almost identical generators in Ue laser control unit. The difference be- tyween them is the value of a single resistor. Figure 10 shows the circuit diagram of the generator for the left channel, All compo- rents are numbered from 100 onwards. For the right channel, the corresponding compo- nents are identified as 2xx. Note, however that resistor Ria in the left channel appearsas Rosin the right channel ‘The heart of the generator is formed by two integrated circuits Type XR2206, a well- known function generator from Exar. The frequency of the output sine-wave produced by the generator is determined by a control voltage obtained either from potentiometer Rist-Ris? via an amplifier, or from a gener- ator The circuit for the automatic frequency control of the sine-wave generator may look2 GENERAL INTEREST unusual ata first glance, Fortunately, it oper ates in a rather simple way- Opamps ICioxs ‘and ICjosh form two Schmitt-triggers set up as square-wave generators, Concentrating, fon [Coa for the moment, we see that the ‘opamp is wired to function asa Schmit-trig- gerby means of resistors Ris7, Riwand RI, ‘The Schmitt-trigger is turned into a square- wave generator by components R140 and Chis, A square wave is, however, not what ‘we are after if we want the sine-wave gener alor to produce a continuous frequency range. Fortunately, the capacitor, C!s, has. on ita triangular waveform that does allow true, lineat, VCO (voltage-controlled oscil- lator) function to be realized. The capacitor voltage, which is a triangular waveform with a period time of about 100s, is buffered by opamps ICime and ICiosd. Note that the period time is chosen slightly differently for pai te other generator, This is done to prevent vol the laser repeating the same pattern after é 100 when the ‘automatic’ mode is used. ‘The ditferently set perio times ensure that it takes at least 24 hours before a pattern ts re- peated (this is based on the assumption that ‘component tolerances have no effect The generator circuit is followed by a ‘summing amplifier, ICur, that serves to add the two sine-waves. Electronic switch IC115 allows you to select either the output signal dof ICins only, or the mixed output of the two nerators, The compressor ‘The circuit diagram of the compressor is shown in Fig. 11. The component numbers refer to the left channel — the circuit of the right channel compressor is identical, with ‘component numbers in the 200" range. The component numbers in the microphone ‘compressor start at 300. ‘Opamp ICoib supplies stable and ade- quately decoupled relerence voltage to the circuit. The a. input signal is applied to the compressor via capacitor Clci. Opamp ICjots forms an_amplifier whose gain is determined by FET Tio, which functions as 4 voltage-controlled resistance. The output Signal level of [Cioia is monitored with the aid of a further opamp, ICi0id, whose output sconnected toa rectifier, Dioi-Djx-Cros. To close the auf. level control loop in the com- pressor, the direct voltage supplied by the rectifier is fed to the gate of FET Twot. The gate voltage determines the a.c. resistance of the drain-souree junction, and thus the gain fof ICiota. The compressor has an inverse level control characteristic, which means that its gain is reduced as the input signal level increases. In this manner, the co pressor ensures that {he mirror driver cuits are provided with a reasonably constant input signal Frequency compensation Asdiscussed last month, thedeflection ofthe mirror galvanometers is frequency depend- ‘ain clrcult diagram of the laser contro! unit. Some clreull sections are shown as ent,i.e.,not linear. To linearize the response, modules here. a frequency compensation cireuit is used — ELEKTOR ELECTRONICS JUNE 1991= p, | Tel ried Fig. 11. Compressor circuit bers forthe (identi see Fig. 12. The circuit starts with a buffer, Cia, and ends with a summing amplifier, [Cw The latter adds the signals supplied by a number of filter sections in the circuit ia resistors Ri2z, RI20 and Riv. A filter ‘based on Tie provides a rising filter slope from 50 Hz onwards. The falling slope of the filter response is st to start at about 200 Hz. with the aid of Rizy and Cis, Returning to the low end of the filter response, compo- nents RrisC)0 create a falling slope from 15 Hz onwards, ie, before the rising part ‘which starts at 50 Hz. The las filter section, Ri2sCits,servesto correct thefilter response for frequencies below 15 Hz. The result ofall this filtering and summ- ELEKTOR ELECTRONICS JUNE 1991 left channel). The component num- I) right channel are in the 200 range, and those for the microphone channel in the 300 range. Fig. 12, ing isa virtually linear response of the mirror galvanometers, ie, their deflection is inde- Pendent of the signal frequency when the signal level is held constant, Next time The above descriptions cover most of the operation of the laser and the associated con- {rol unit. In next month's final instalment we \will complete the description by discussing. the way in which the electronic switches are controlled. The article will be closed with a eseription of the way in which the laser control unit is built and operated. a Frequency compensation circuit for the mirror galve: nometer driver in the left channel. number of filters are used to linearize the frequency response of the mirror over a small range. ‘A complete kit of parts for the laser control unit (LSI7000) is available from the designers’ exclusive world- wide distributors: ELV France BP. 40 F-57480 Sierck-les-Bains FRANCE, Telephone: +33 82897213 Facsimile: +33 82838180LIGHT SWITCH WITH TV REMOTE CONTROL Why not use the infra-red remote control, that magic little box supplied with every TV set these days, for applications other than channel hopping and turning the volume up when your favourite pop group appears on the screen? The simple IR receiver discussed here responds to most types of TV remote controls, and can be used to switch lights and other appliances on and off. J. Ruffell, from an idea by M. Dupessey RACTICALLY all TV sets these days are supplied with an infra-red remote con- trol, Provided they have not been dropped too often, or chewed on by our beloved pets {we mean domestic animals including par- rots and budgerigars), these handy little boxes allows ts to remain comfortably seated in front of the ‘tube’ and exercise total con- trolover the channel selection and a plethora of other settings of the TV set. As shown in this article, it is perfectly possible to use a remote control box for an application not foreseen by the manufac turer. The general idea is illustrated in Fig. here, the IR remote control is used to switch a light on and off. In some cases, it is even possible to switch the TV set on and off as Well, although this requires a small change in the receiver. Note, however, that many modern TV sets already have a standby /ac- tive function controlled via the IR box Single-chip IR receiver The IR receivers based on an integrated cir cuit Type TDEI6I from Siemens. The inter nal diagram of the chip is given in Fig. 3, The ‘main technical characteristics are: + Low stand-by current: 650 A + Supply voltage range: 4 V 10 65 V + Frequency range up to 200 kHz + Available with and without demodula- tor output (TDE4Q61 / TDE4060) + No inductor required in external circuit + High ambient light rejection: + Bipolar technology couples good high- frequency behaviour with a low current consumption; + Suitable for battery supply The input of the TDE406I (see Fig, 3) is con- nected toan infra-red photodiode, which un- fortunately notonly ‘sees’ thesignal from the IR remote control box, but also visible light, 100-Hz. interference. from incandescent bulbs, and a part of the light spectrum emitted by fluorescent tubes, ‘The input stage is followed by a bandpass filter that serves to extract the IR remote con trol signals from the interference. The de- modulator block drawn in Fig. 3 is not available in the TDES060. ‘A current sink circuit is provided to sup- press low-frequency currents supplied by the photodiode, and stabilize the bias at the input of the IR preamplifier at 1.4 V. The gain of the preamplifier isautomatically con- trolled to ensure optimum drive of the band: pass filter ‘The ik (infra-red) input of the TDE4061 forms a high impedance, and is suitable for input currents in the nano-ampere range Hence, the anode of the photodiode is con- nected direct to the irk input. ‘The output of the TDE%9e1, @ supplies a demodulated digital signal. An example of an output signal isshown in Fig, 2 for the Ar istona (Philips) remote control Type RCS: Note that the pulse lengths, TI to T4, showr inthe diagram depend on the IR remote con- trol used, Circuit description As shown in Fig. 4, very litle is required to build an IR receiver based on the TDE4061 In the following description, some points will be noted that may be of interest to those ‘of you who want to use the TDE4061 for their ‘own applications, ELEKTOR ELECTRONICS JUNE 1991The IR photodiode, Ds, is a Type BPWSIN from Telefunken. It is forward biased via resistor RS, and supplies a photo- current to the FR input of the TDE4O61 ‘Capacitor Cr and resistor Rs form a low- pass filter at the IF input that serves to sup- press interference. The capacitor at the Crac ‘put of the TDE4061, Cs, determines the time constant of the preamplifier. The value ofthis capacitor is set to 470 nF to suit the bi- phase-coded signals emitted by most mod- em IR remote controls. The capacitor must be made smaller when an IR system is used that does not supply run-in signals for the sain control circuit of the receiver. In the rases, C5 may be reduced to about 10 nF. Do nat golower than this value to prevent oscil: lation, The capacitor at the Cs input of the TDEAN61, C7, gives the preamplifier a high- poss characteristic, and works in conjunction with Gras and the double-T network at the ci and Rc2 connections of the IC. These components determine the settling, beha- viour of the TDE4O61 following fast signal changes. The Cs capacitor tunes the receiver tothe carrier emitted by the IR remote con: trol. Depending on the carrier frequency, C7 1S 100 nF (for 30 kHz systems) or 10 nF (or 120 kHz systems) The banclpass filter that follows the IR preamplifier improves the signal-to-noise ‘ato of the IR signal and reduces the jitteron the digital output signal. The extemal double-T R-C bandpass filter connected to the RCI and RC? pins of the TDE4061 must provide a dc. path, and have a band-stop notch) characteristic. The notch frequency, fo is made equal to the IR carrier frequency. Itis given by =1RQ Hed where R=R6=Ry, and C=Cv=C2. Note that Ri-R/2, and Cs=2C. To keep the voltage drop across the filter within reason, R mvust not be made larger than 100 k. The values Bes Fig. 1. ‘The remote control supplied with the TV set Is used to control a light. ra 13 1 B11 102 —S ™ a= 100ms Fig. 2 Response of the TDE4061 to a typical datasiream produced by @ TV remote control ha]o fa}nc. ome [3 fra}ncr ws hi]ace wera jio}es como [7 Jeo lownoise lated preamp band: pass demodu- PP] tator O J hs oe 910088-12 RCI RC? Ge OND Fig. 3. ELEKTOR ELECTRONICS JUNE 1991 Functional diagram and pinning of the TDE#061 infra-red receiver IC from Siemens,GENERAL INTEREST 7AHCT73 7aHcT132 Ki ra 1N4001 Fig. & of the external filter components may have tobe changed experimentally to suit the pre viously mentioned pulse lengths supplied by the IR remote control. ‘The output of the TDE4061, 0, is of the ‘open-collector type. When the output tran- sistor is switched on, the maximum collector current is I mA. In designs where the output signal is fed back to the input, oscillation ‘may occur if the output current is not kept smaller than about 200 wA, Note that this type of feedback is not applied in the present circuit, The digital pulse train supplied by the ‘TDEAO61 is inverted by a Schmitt-trigger gate, IC2s, and subsequently rectified by D2- Cato obtain an on/off control signal. Every trailing edge of the switching signal sup- plied by ICxa causes J-K bistable IC» to toggle, so that the relay, Ret, is actuated or de-actuated. This creates a simple on/off toggle function Circuit diagram of the remote control receiver. The load to be switched is connected to the contact of relay Ret. ‘The load controlled via the IR system is connected to the contact of Ret. LED Dt lights inthe rhythm ofthe pulses when an IR signal is received. When the Qoutput of ICtb is logic high, transistor Ti conducts, and the relay is actuated. The complementary out put, O, of the bistable is then low, and LED Di lights to indicate the relay status. ‘The response of the receiver to IR control signals is determined by the value of Ct. This capacitor effectively turns the pulse train ELEKTOR ELECTRONICS JUNE 1991LIGHT SWITCH WITH TY REMOTE CONTROL a “s 3 oR I0 exe oCEne of aE off Fig. 5. Single-sided printed circult board for the IR remote control receiver. COMPONENTS LIST Resistors: + é7onF os + 7aHOT7S (c1 1 47a a 1 220pF 6 4 yaHoTia ice 1 200 Re 2 100nF ores 1, TDE¢061 (Siemens) (C3 1 ana Fa + 330pF oe 4 78105 Ica 4 630K Re 4 {uF 16v C10 2 1K0 ASAI2 1 470uF 16V en Miscellaneous: 2 Ka RoR? 1 10, 104 cr + S-yay Sm pitch «i 1 rake Fe OB terminal bock + 200k Ro Semiconductors: 4) 2eway Simm pitch ke 1 az Rio 1 green LED da. amm 01 PCB terminal block 1 3300 Rit + BATES be 1 save300 PCB ust } FN (Tatehankon) relay, 0.9., Siemens capsctors: 1 yo 25d be vasareenio1 fet 1 Tn sole a 1 9Ns148 D5 + ovnisema cB mount 1 2 150pF C209 4 1NA001 De ee riinan pp ee Es Bh a eet PZ 1 Printed circuit board 10048 1 1NF 18V (see text) Ca + 805078 into an on/off pulse with a much longer period. This is achieved by a relatively small esistor and a diode, R-D2, through which the capacitor charges, and a relatively large resistor, Rs, through which the capacitor dis charges. The receiver is completed by a standard 5-V regulated supply based onan 78105, ICs, Construction The IR receiver isa compact unit because all components are fitted on a single printed- circuit board, which is shown in Fig, 5. Start the construction by fitting the three wire links on the board. Neu, fit the resistors, the diodes, the capacitors, and the active compo- nents, Use sockets forthe ICs, which are not ELEKTOR ELECTRONICS JUNE 1991 plugged in until the board is completely as- sembied. Complete the construction of the board bby mounting the transformer, the relay and the soldering pins. The three LEDs are fitted such that their faces protrude from holes in the plastic enclosure. The infra-red diode, D3, is fitted on the front panel of the case. It fs secured such that its light-sensitive area can ‘see’ the remote control. The light-sensi tive area of the BPWAIN is located at the centre ofthe flat front side ofthe device After finishing, the construction of the PCB, connect the mains cable to Ki, a 3-way PCB mount terminal block of which the centre pin is cut off. Next, connect theload to ‘To enable you to experiment with differ ent values, the PCB allows capacitors with ‘hwo different lead spacings to be fited in po sitions C3, Crand Ci Practical use With most remote control boxes the usable range of the receiver will be greater than 5 ‘metres. Since the response time of the re- ceiver is relatively short at a few tens of mik liseconds, the unit must be installed at some distance from the TY set to prevent it being triggered by control commands intended for the TV set. If you still want to locate the re- ceiver close to the of Ci to, say TV set, increase the value 17 uF. This results in a much longer response time to remote control com mands, .APPLICATION NOTES The contents of this article are based on information obtained from manufacturers in the electrical and electronics industry and do not imply practical experience by Elektor Electronics or its consultants. UHF AUDIO/VIDEO MODULATOR TDA5664X (Siemens Components) THE new TDAS664X from Siemens Com- ponents isan integrated circuit that con all functions required to mix and modulate video and audio signals at fre- quencies between 30 MHz and 84) MHz. Thenew TV modulator ICs intended for use in video recorders, cable network conv ters, video pattern generators, closed-circuit ‘TV systems, amateur TV transmitters and personal computers, ‘The advantages of the TDAS664X over its predecessor, the TDAS660P, are: 5-V supply voltage; + nocircuit adjustment required = reduced external circuit = smaller package (DIP14); = also available in SMA package (S014); In addition to these advantages, the TDAS®64X has the following specific fea- tures: - FMsound modulation; = syne-pulse clamping circuit at video input clipping at peak white level; continuously adjustable modulation depth for positive and negative video modulation; high residual carrier suppression; low spurious radiation, Block diagram The composite video signal with negative- going synchroninztion pulses is applied to pin 8 via a coupling capacitor (see Fig. 1). ‘The on-chip clamping circuit fixes the vieleo ignal level relative to the synchroniaztion pullses. When the video signal exceeds 1 V, the peak white level is clipped. Negative AM video signal modulation is selected by leav ing pin 9 of the IC non-connected. When ppin 9 is connected to ground, the RF carrier {s positively modulated. Ifdesired, a variable resistor may be connected between pin 9 and ground to enable the modulation depth to be controlled, ‘The TDAS664X is capable of modulating video as well as sound. The audio signal is capncitively coupled to the AF input of the IC, pin 13. A pre-emphasis network may be connected externally. The output signal of the audio input amplifier is frequency tract hat pelea ] Ye T — Se aaa e7 = ae / | Scoop ea | | See Fig. 7 ‘modulated on to a 6.0 MHz (UK) or 55 MHz subcarrier, The output signal of the subcar- Hier oscillator is mixed with the output signal ‘of an on-board RF oscillator. The operating frequency of the sound subcarrier oscillator is determined by an extemal 1-C parallel tuned circuit connected between IC pins 1 and 14. This tuned circuit may be damped by an external resistor, R5, to set the sound sub- carrier amplitude with respect to the vision carrier amplitude. Block diagram of the TDAS664X modulator IC. ‘The amplifier that forms parto! the RF os- cillator is connected to external frequency determining components via pins 2 and 6 of the IC, At the resonant frequency, the eapa- citive reactance, X,, must be 70 02 between pins 2-3 and pins 5-6, while X, ~ 26 must be observed between pins 3-5. The ground ‘connection of the RF oscillator, pin 4, must bbe connected to the ser ductor, An external oscillator signal may be applied to the TDAS664X via pins 2 and 6. Table 1. Application circuit specification Parameter ‘Min, Max, Unit Supply voltage uy 48 65 Vv Video input frequency fo 0 6 Mie ‘Audio input frequency far «020 kez Output frequency fo 30-880 MHz Operating temperature Tx 9 70 °c Subeartier frequency osc «47 Miz TOR ELECTRONICS JUNE 1991This signal may be coupled induetively or capacitively For optimum operation and minimum spurious radiation, the oscillator pins (2406) mustbescreened from the modulator output pins (10, 1 and 12). The RF attenuation ot ihis screening must be 80 dB or greater Application circuit The circuit diagram of a TDASG64X-based UHF TV modulator is shown in Fig. 2. The balanced mixer outputs, pins 10 and 12, ane connected toa wideband balances-to-unbal- anced (baltin) transformer, which ensures a phase difference of exactly 180°, The basic onstruction af this balun on a two-hole fer- ite core is shown in Fig. 3. The attenuation ofthe device must besmaller than 3dBat the Ce Resistors (SMA): 1 270 RI 4 220ke Re 2 are FaRa 1 12K0 AS 1 75 Re Cepacitors: 2 2pF7 SMA cre203 2 4pF7 SMA acs 2 150 SMA cec7 1. Yon SMA oo 2 InFSMA. c1oc14 2 A700 Sm encr2 1 2205 BMA 13 ‘Semiconductors: 1 Basis ot 1 TDASBESXSMA GY ‘Miscellaneous: 1 B62152.A0008-X0)7 ™ balun (Siemens) 4 FoaieCs-117Bs215 FIL (Toko) ELERTOR ELECTRONIES JUNE 1991 HP TY MoDU $090 DL pFSeC7 avsof]es ow co 1+ +A md 108 inne +5 . 2. Application circuit of the TDASOGAX: a UNF audioivideo modulator The circuit is tuned to the desired TV channel by applying a tuning voltage to the varicap diode, D1 frequency of operation. Because of the impedance change from 270.0 balanced to 302 unbalanced, the RF ‘output voltage of the modulator is about 15 times the RF voltage across Bi, This is based on the assumption that the balors has an attenuation of OdB, Finally, a suggested PCB design for the ‘modulator based on the SMA version of the TDASHbIX is shown in Fig. 2. The design of Fig. 3 this PCB meets the requirements as regards decoupling and minimum stray inductance inthe oscillator as well as the modulator out- put circuitry. The modulator is tuned toa TV channel between 30 and 40 (ie, between 543.25 MHz and 623.25 MHz) by applying a voltage to the TUNING input : Siemens Components issue 28 (3/90). 7 othe Ra we Aba v2}. ase 2p EB : cs ieee OB he ss Bee of AE gn BG. oS c+ TS EP os Op PGB track layout (1-1), component mounting plan (2:1) and balun construction.REAL-TIME CLOCK FOR ATARI ST The Atari ST is a user-friendly computer supported by a massive amount of excellent software. Unfortunately, early models of the ST lack a clock circuit that keeps ticking when the computer is switched off. The LTHOUGH the design of the Atari ST computeris moder by any standard, a real-time clock (RTC) is provided only on the latest models. This is surprising because the ‘main rival of the ST, the IBM PC or com: patible, has had an RTC as an option or a standard feature longer than many of you will care to remember. Owing to the absence ofan RTC, many Atari ST users are forced to sot the date and time, every time the com: puter is switched on. To help out the thou. sands of faithful owners of older ST models, we have developed a real-time clock that is inexpensive and simple to build. One of the most attractive features of the Atari ST is the number of interfaces, One of these interfaces, the printer port, is used here to connect the real-time clock to the com: puter. We hasten to add that you will beable touse the printer as before, since the RTC is inserted between it and the Centronics port, for which only a very small modification is required. Up-to-date with the RTC Of the real-time clock ICs currently avail- able, the MSM5832. from OKI and. the MCI46818 from Motorola are probably the best known and widest used. The Motorola IC has an advantage over the MSM5832 in offering an 8-bit wide databus, and a 30-byte non-volatile RAM (random access memory). Thedata retention is achieved with an exter nal rechargeable battery. Here, the Motorola IC is used, although no useis made of ils internal RAM, The8-bit databus of the RTC chip allows the control software to be kept fairly simple, and in ad: dition affords the possibility to implement further extensions circuits on the Centronics port. The control software for the present project is supplied on disk in the form of a source listing written in C. This program. may be used as the basis for further hard- ‘ware or software functions that you may wish to add. The hardware presented here, and the object code compiled with the aid of the C program, can be used to develop a ‘desk accessory’ to support the new clock function, Returning to the hardware, the circuit di agram of the clock extension is shown in Fig. 1. The heart ofthe circuit is the RTC chip from Motorola, Besides four logic gates and F. Dossche thyo bistables, the circuit contains a handful of discrete parts used mainly to implement a battery back-up function for the RTC. The and one I/O line on the com: puter’s main board serve to direct the data fon the Centronics bus either to the printeror thereal-time clock. Inaddition, one of thebi stables indicates whether the 8-bit word sent totheclock circuits intended toselect an ad dress location, or to be stored as data in the RTC. The real-time clock sits between the Cen tronics port on the computer and the Cen- tronics input of the printer. Hence, it has an input an output connector. At the left in the circuit diagram we find connector Ki which links the eireuit to the computer, Two new signals appear on this connector on pins 16 and 17. Pin 16, nor- mally the RESET line, snot used by the Atari rcuit presented here overcomes this problem. SST, and now carries the computer's 5-V sup- ply voltage. Since the RESET signal is active Tow according to the Centronics standard, placing +5 V on pin 16 has no effect on the printer (anyway, the ST is not capable of is- ing a reset via this line). Pin 17 of K1 is connected to an unused 1/Oline in the computer,and serves to direct, dlata either to the RTC o to the printer. The 1/Olline is found on pin 14 of the sound gen erator ICin theST, the Yamaha YM-2149, Ak though not used in the harcware of the ST, this 1/0 line s supported by the BIOS (asic input output system), which makes it per fect for the present application. Pin 17 on the Centronics connector is chosen because itis not used on the ST or the printer. Do, how. ever, check that the cable between the com puter and the RTC has a wire for the signal fon pin 17. In general, most serial cables for zzz DZDZDZLLT 0 ZZ” fitz” Gitta a Zizi” ft tzREAL-TIME CLOCK FOR ATARIST fb 5 lle ci Fig, 1. Cireull diagram of the real-time clock. [PCs have a wire foreach of the 25 pins, and will therefore, meet our requirement. You ray also decide to make your own 25.way cable, which has the advantage that itean be ‘made shorter than most ready-made eables snlong, and quite bulky for our application. A home-made cable may be produced by a short length of 25.way nibbon cable terminated in an IDC- Style male 25-way D-connector at one end, and a female D-conneetor atthe other end, Returning tothe circuit diagram, thesig- + nal at pin 17 of Kr enables bistable [Cos by making the § ine logic high. This results in any changes atthe set and the eset inputs of IC being ignored, so that the bistable re- mains in the ‘set’ state Because the SET line wasactve last. Als, the strobe signal for the printer (connected to K2) is blocked by gates {Cac and {Cau, and the enable input of the RIC is actuated via transistor Th. Next, an RTC adds is passed to the circuit via the Centronics datalines. The most-significant bit, D7, indicates read oF a write operation tor from the RTC registers ‘A pulse on the robe line (pin 1 of KD is fed to the AS input ofthe RFC chip via bi stable ICxs and gate ICzx This pulse is used to transfer an S-bit word on the Centronics datalines to the RTC, 0 vice versa, as indie cated by the level of databit D7. After the ELEKTOR ELECTRONICS JUNE 1991 strobe pulse, the inverted level of D7 is ap- plied to the R/W input of IC}. When the next Strobe pulse occurs, ICiw toggles because the ‘Qoutput of this bistable is connected to its D Gata-) input. The pulse is subsequently fed to the DS (data strobe) input of ICs via IC Data may be read before the end of the sec- ‘ond strobe pulse. When this is finished, the computer will deactuate the ‘sclect” line (pin 17 on Ki), The printer can then be used Again, and the clock operates. The above se quence is used to store the time and date in the RTC, and also to read these back into the computer, allowing the system clock in the ST to copy the RTC information. Gone are the days when you had to set the system clock every time the ST was switched on. The rest ofthe circuit is fairly simple. The PCB has two options for charging the bat- tery. The simplest is by means of diode D1 When the ST is switched on, the battery is charged via Di and R7, The RTC is also powered via the diode. This must be a Schottky type to ensure a low voltage drop. Remember, the change current can become toosmall when the computer supply voltage js on the low side, when the battery voltage is on the high side, This is prevented by a diode with a low voltage drop. If you can not secure the BATSS or an equivalent Scholtky diode, add the circuit based on T2 and TS. When the computer is switched on, Ts starts to conduct and swit- ches on Ts, By virtue of the relatively low col- lector-emitter voltage of T2, the charge current for the battery is sulficiently high, When the computers switched off, T?blocks and turns off T2, so that the battery takes over the supply of IC), Note thatthe fransis- torbased supply is an alternative to the single Schottky diode — components T2, Ts, Rsand Ro are not fitted if you use a BATSS. “The RESET and PS inputs of IC\ aretaken logic high briefly afterthe supply is switched ‘on, Thisends the low-power standby state of the RTC, and causes it to switch to normal ‘operation, ‘A quartz crystal, Xi, together with C1,C2, Ri, Re and two gates in [C2 form an oscillator that supplies a clock of 32.768 kHz. to the RTC. This frequency is used in most battery- powered clocks and electronic wrist- ‘watches. Construction ‘The construction of the real-time clock unit will present little difficulty if the printed-cir- cuit board shown in Fig. 2 is used. Start the construction by fitting the wire links and the ‘connectors. Note that Ki isa male type, and K2a female type. If you swap them acciden-j0000000000003 90000000000002% B, ° COMPUTERS AND MICROPROCESSORS 000000000000" Roooooococ000s 104, Fig. 2. tally, you willbe unableto connect the circuit properly to the input and output cables Proceed with fitting the remaining parts ‘on the board. IC sockets are not strictly re- quired. If you do decide to.use them, be sure to buy good quality types, The completed printed circuit board fits into an ABS enclosure of 12057030 mm. The side panels ofthe enclo sure are cut to allow the connectors to pro- rude ‘Single-sided printed circuit board for the reablime clock. A small modification is required in the computer before the RTC can be connected. Although the ‘operation’ is really no more than soldering two wires, it may still take you an hour r so to complete because the computer has to be disassembled, After re moving the floppy diskdriveand theswitch: ing power supply module, you should be able to see the printer connector and the Yamaha chip. Take the main board out of the enclosure, and remove the metal screen at Fig. 2. fan ABS enclosure. Completed circuit board fitted into Ceo Moi46818 yaHcTo2 c2 7aHCT74 ica Miscellaneous: 1) 25eway male suD «i ‘connector with angled pins, for PCB mounting 1 25-way female suo-D ke ‘connector with angled pins, for PCB mounting 1 82.768 Kz quartz cystal Xi 1 36VNICabatory Bat 1 ABS enclosure; siza ‘approx. 120<70,20mm 1 Printed cxcutt boars 910006 1 Disketto ith contrel sofware ESS1621 both sides. This means that you have to bend ‘a couple of small metal brackets with the aid of tweezers. Afterturning the main PCB, you should have access to the sound generator connections. Run a wire from pin 14 of the Yamaha chip to pin 16 of the printer connec- tor, and another wire from pin 40 of the Yamaha chip (+5 V) to pin 17 of the printer connector. This completes the modification. Reassemble the computer Software As usual, hardware is never complete with- ‘out the appropriate software. The clock unit described heres supported by a control pro gram on disk, which may be ordered through our Readers Services. The disk con- tains the ready-to-go desk accessory for the clock, as well as the source listing used to compile the machine code. As already men- tioned, this listing is intended for those of you who want extra features for the clock, such as a programmable alarm. You may also want to use the 30-byte non-volatile RAMarea in the RTC chip. The source code can be converted into a control program with the aid of, forexample, the Mark-Williams C compiler. This és not strictly required, though, si ply copy the control program on the floppy disk (supplied by us) to your system disk Every time the computers switched on, the program will automatically copy the RTC data to the system clock, Now, is that up-to- date or not? . BLEKTOR ELECTRONI S$ JUNE 191STEPPER MOTOR BOARD PART 1 PC INSERTION CARD AND CONTROL SOFTWARE Getting a stepper motor to work properly invariably seems to require either a lot of discrete electronics, or an expensive dedicated integrated circuit. However, since the actual commands for stepper motors are almost always supplied by a computer, it is a challenging idea to economize on the hardware, and have the software do the TEPPER motor controls are available in many shapes and sizes, ranging from complex to ultra-simple, and based on a var- ety of integrates! circuits, including the MC3479, the L297/298and the TDA1024, all of which have been used in projects de- scribed in this magazine. By contrast, the control described here is not based on any of theseICs. None the ess, itis versatile, simple tobuild and relatively cheap. ELEKTOR ELECTRONICS JUNE 1991 work. H. Kolter The circuit described has evolved as part of a PC-controlled professional milling ma chine that accepts CNC-format data to the Gerber standard. CNC stands for computer ‘numerical control The concept The above application was aimed at develo: achine for very ac: pinga complete milling curate processing of aluminium, steel and plastic workpieces. When the project was in itiated, there was the choice between (1) “in- telligent’ motor control with relatively simple control software, and (2) a simpler controller with powerful, complex, software. To ensure the best possible resus in regard of speed andl accuracy ofthe system, the first option requires the motor control to be ‘geared accurately to the specific features of the milling machine The second option has theadvantage that changes to the machine, of extensions, are ‘easier to support with appropriate software extensions, Sincethe electronics and the mill- ing machine were developed roughly at the same time, the choice of the stepper motor control was clearly in favour of the second option: simple hardware and complex sot In practice, the computing power re- guired for the system can only be provided by a PC-AT or a compatible machine with a clock speed of at least 16 MHz. The com. puter program consists of an interpreter that reads drill and fraise data produced to the Gerber standard, and converts these into stepper motor commands, The interpreter uses a configuration file that contains various system parameters stich as the type of stepper motor (bipolar or unipolar, rotation per step, maximum step rate, etc), and the main properties of the milling machine (spindle pitch, number of idle steps on spindle reversal, etc.). These parameters can be changed easily and allow the control system tobe rapidly ‘customized fora particular application. In line with the different functions, the lectronies are divided into two parts. One ppart isan insertion card for IBM PCs, the ther a larger board, which is fitted external to the PC, and contains the power drivers. ‘The PC insertion card described here is basically adigital l/O card based on the fam- iliar 8255 PPI (programmable peripheral in- terface) from Intel. The ‘half-size’ insertioncard offers 24 input /output lines, and hasan additional timer/counter IC Type 8253, a {quartz oscillator and two relays. The quart oscillator makes the timing of the 1/O card independent of the computer speed. The two relays have changeover contacts and are suitable for switching mains loads. ‘The power driver board (to be described in part 2 of this article) has a fairly large power supply and 16 optocouplers that af- ford electrical isolation between the com- puter and the stepper motors. TTL buffers are provided between the optocouplers and the Ip power drivers. These butters are also used to drivea LED-based readout that sig nals the active status of all stepper motor windings. The readout will be found par ticularly useful when a machine is first con- nested, or during program debugging, Circuit description ‘The PC interface shown in Fig, 1 isa more or less standard design based on the 8255 PPI Apart from the data and address signals, the extension card uses a few control signals on. the IBM slot, IOWR which indicates write ac- tivity in the 1/O memory area, [ORD which thas the same function form read operations, and, of course, RESET. The extension card is powered by the computer via the extension. bus. Thedatalines are buffered witha 7ALS245 coctal bidirectional driver. The buffered da. talines are connected to the PPI (the 8255) and the PIT (programmable Interface Timer/counter; the 8253). A. single PAL (programmable array logic), ICs, handles all. address decoding. It uses address line A3 through A9 and the ORD and IOWR signals to generate chip select signals CSO, CSI, CS2 and C83, and in addition the enable signal and the direction control signal for the da- tabus butter, ICs The I/O lines of ports A and B of IC1 are available on a double row PCB pin header, Kz, Port Cis connected to the outputs of the programmable timer, ICs. Connections PC and PCSswitch thetwo relays via darlington transistors T-T2. In most cases, a value of TKO will be adequate for Rs and Re. These resistors may need to be made smaller, how- ever, when the relays do not come on re liably. The minimum value of RS and Rois 3300. PPI line PC3 has a special use here as iis connected fo an external emergency switch that stops the entire system. Normally, PC3 isheld at +5 V by a pull-up resistor, Ri. The two remaining port lines, PCo and PC7, are rot used here The intemal block diagram of the 8253, ‘counter/timer is shown in Fig. . The three lo-bit counters, numbered 0, 1 and 2, are identical and can be preset to count down. ‘The counters operate independently and can be programmed separately. The counter values can be read from the 8253 without blocking the clock signal, The preset values areloaded with the aid of four control words stored in the control word register. Since this has only one address, two bits, SCO and SCI, Fig. 1. Circuit diagram of the PC insertion car - = : =] | Laie our? A) Fig. 2, Block diagram of the 6255 Programmable Peripheral Interface (PPI). ELEKTOR ELECTRONICS JUNE 1991o GENERAL INTEREST SSS a @ Ql] xa @ sq p ote 3. St eal | (e3l 3) Ie $ Ble} [eal 2 blo} joo) 3} (33 S| (88) Fig. 3a, Cee cue Resistors: 4 4KQ7 2 1k@ (see text) 2 2x02 1 BedkOT array ARI Ceanecnem 3 100nF cx0203 Semiconductors: + 8255, 2 7aLS205) + eB (ESseot) C3 1 8253 5 2 Bcsi7 Miscellaneous: 1 MHz oscllatorblock Ose 2 POB-mount SV changeover relay 1 16way 20 PCB pin KI header 1 26may2row POBpin—K2 header 2 S-way PCB terminal block 41 printed-creuit board kaka 9100541 Component mounting plan of the PC insertion card. indicate the counter for which the control word is intended, Returning to the circuit diagram in Fig, 1, the CLKO through CLK3 inputs of the 8253 are supplied with a 4MPLz clock signal ‘generated by oscillator block OSC1. All three gate (Gx) inputs of the counter/ timer are tied to 45 V via pull-up resistors. The 8253 is programmed to operate as a frequency divider. Depending on the preset value, a counter divicles the oscillator fre- quency down to a particular value, for in stance, 100 Hz, which is then passed to PPL port C. By loading different counter preset KOR ELI ECTRONICS JUNE 1991values, the step duration of the stepper mo- tors is made independent of the computer's speed ICs, a 741.5245, forms an §-bit input port which is used to signal the status of a set of end switches fitted on the milling machine The eight input lines of the port are held at 45,V with the aid of pullup resistors. The end switches wired to Ki should, therefore, connect to ground when active The address assignment of the ports on. the insertion card, and their functions, are summarized in Tables | and 2 Construction Populating the double-sided through: plated board (Fig. 3) should not cause difficulty, To make sure the card remains secure in the PC slot, you will need to secure it to a metal bracket as found on other insertion cards, Here, itisbest to use (or make)a bracket with a relatively large vertical clearance that allows the two flatcables and the relay wires to pass, Switch the computer off fit the L/O card into a free slot, and secure the card to the metal frame at the rear of the PC. Switch on. the PC, and check that a frequency of 4 MHz ‘s present at pins 9,15 and 18 of ICs. In case the PC will not boot up with the I/O eard in seried, you ate probably faced with a short- circuit on the board, ora faulty IC ‘Thedata in Tables 1 and 2, and a few lines of BASIC oF Pascal, allow the card to be checked for correct operation. For instance, reading address [base+8] (IC) should retum, 1111 Tis, which equals FFy, or 256 deci: mal. Next, connect two or three jumpers to to pull the input datalines logic low. Run the read test again, when the result should match the set bit pattern (a jumper produces logic low) Next, test the PPLby writing tothe control register at address (base+3] (0DE3,). Set all portsto output, then make all port lines logic high. The relays should come on. ‘The scope ofthis article does not allow a more detailed description of the way in which the 8255 and the 8253 are pro- ‘grammed. Fortunately, plenty of literature is available that covers the practical use of these ICs in great detail. Software ‘A number of different, fairly complex com: puter programs are required before the fai {ng machine can be made to work. The first step inmaking a fraised product isto draw it ‘with the aid of a CAD program, such as AutoCAD or AutoSketch, and save the drawing filein the DXF format. Next, a pro- ‘gram called AvioPack-II is used to convert the DXF file into a format suitable for further processing, AutoPack ll is a 2/dimension version of the 3+dimension program Auton Pack. None the less, AutoPackelf allows you to view the workpiece in 3D to the ISO standard. Also, all side views of the work- piece can be displayed atthe same time, and the program is capable of calculating the ELEKTOR ELECTRONICS JUNE 1991 STEPPER MOTOR BOARD <1 G routines supported by CNC-DIN All dimensions in mm, DIN 66025. Example of Synta 10 G00 x17.34 y200.0 20 G01 x10.90 20.90 % Sart of program remark G00 argo point direction characteristic (x.y. 2). Move 10 target point Frise carrer speed, ot Straight interpolation of target point x,y. 2). Fraise ram curent point to indicated targa point Fraise speed. Goz Circle interpolation. clockwise. (Gat. yakt. x, yj) current point txakt, yak), target pont (x,y). centre of ere (i Fraise an are based cee intormation, from currant point to target poi. G03 Circle interpolation, anv clockwise. Seo G02, cos Spindle ice ie (Wie ume n seconds, sa Site of spindle motor relay so ‘Switch on spindle motor rolay, 03, Switch on pur for dil oan. Moo Switch off pump fo ailing cootant. G20 All ansolute data cot Allincramental data cas Spindle shit speed in mmm. (0 ¥. 21 speed indication for single spindle 30 ‘ena of program, Fig, 4 Overview of Gerber commands supported by the CNG-DIN converter program. curve described by the fraise. This curve is called fraise exquidistant because the radius ‘of the raise itself is taken into account The frais file generated by AutoPack-Il consists of a set of so-called Gerber com- mands. The actual control software for the milling machine is a converter called CNC- DIN. Written in C, it reads the Gerber data and converts these into commands for the stepper motor board described here. CNC- DINisavailable from the author, and allows you set a number of parameters related to the hardware. These parameters include the type of stepper motor used (2-phase or 4+ phase), the number of steps per revolution, ‘ete. The parameters and their settings are stored in a configuration file that can be modified as required for your own hard ‘ware. Figure lists the G (Gerber-) functions to DIN-66025 that are supported by CNC- DIN. 4 Part 2 of this article will deseribe the motor driver board. Tables 1 and 2 mentioned here will be included in Part 2 Note: The program CNC-DIN mentioned in this article is available from Kolter Elektronik ¢ Steinstrasse 22 + W-5042 Eristadt * Germany. # Telephone: +49 (2235) ‘707007, Fax: +49 (2235) 72008,