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1 opyright 00, Wimborne Publishing Ltd (Sequoi House, ingwood od, Ferndown, Dorset BH AU, UK) nd TechBites Interctive Inc., (PO Box, Mdison, Albm, USA) All rights reserved. The mterils nd wors contined within EPE Online which re mde vilble by Wimborne Publishing Ltd nd TechBites Interctive Inc re copyrighted. TechBites Interctive Inc nd Wimborne Publishing Ltd hve used their best efforts in prepring these mterils nd wors. However, TechBites Interctive Inc nd Wimborne Publishing Ltd me no wrrnties of ny ind, expressed or implied, with regrd to the documenttion or dt contined herein, nd specificlly disclim, without limittion, ny implied wrrnties of merchntbility nd fitness for prticulr purpose. Becuse of possible vrinces in the qulity nd condition of mterils nd wormnship used by reders, EPE Online, its publishers nd gents disclim ny responsibility for the sfe nd proper functioning of reder constructed projects bsed on or from informtion published in these mterils nd wors. In no event shll TechBites Interctive Inc or Wimborne Publishing Ltd be responsible or lible for ny loss of profit or ny other commercil dmges, including but not limited to specil, incidentl, consequentil, or ny other dmges in connection with or rising out of furnishing, performnce, or use of these mterils nd wors. EADES TEHNIAL ENQUIIES We re unble to offer ny dvice on the use, purchse, repir or modifiction of commercil equipment or the incorportion or modifiction of designs published in the mgzine. We regret tht we cnnot provide dt or nswer queries on rticles or projects tht re more thn five yers old. We re not ble to nswer technicl queries on the phone. POJETS AND IUITS All resonble precutions re ten to ensure tht the dvice nd dt given to reders is relible. We cnnot, however, gurntee it nd we cnnot ccept legl responsibility for it. A number of projects nd circuits published in EPE employ voltges tht cn be lethl. You should not build, test, modify or renovte ny item of mins powered equipment unless you fully understnd the sfety spects involved nd you use n D dptor. OMPONENT SUPPLIES We do not supply electronic components or its for building the projects fetured; these cn be supplied by dvertisers in our publiction Prcticl Everydy Electronics. Our web site is locted t We dvise reders to chec tht ll prts re still vilble before commencing ny project. To order you copy for only $. for issues go to

2 onstructionl Project BIOPI HEATBEAT MONITO JOHN BEKE Te pee t the rhythmic wveforms tht eep you ticing! B EFOE joining EPE, the uthor ws on short-term contrct with lifesupport equipment mnufcturer. Of prticulr interest were the hertbet wveforms displyed on the hert defibrilltor screens, which hd to mtch certin softwre criteri before electric shoc tretment could be given to ptients. The vrious ctegories of wveform could be simulted electroniclly, but in ctive service the system would monitor ptient s hert vi chest electrodes. BEATING HISTOY Inspired by the simplicity of the hert monitoring circuits, the uthor designed one for EPE. This ws published in Feb/Mr s the Biomet (which loosely trnsltes s Life Meter). PI microcontrollers were unherd of to hobbyists t tht time nd the three-bord design required i.c.s. Hertbets were monitored cross the chest using simple electrodes. Pulse rtes could be monitored seprtely by hndheld sensor tht detected the opcity of the thumb, which chnges s blood pulses through it. A ½ digit liquid crystl disply (l.c.d.) showed the pulse rte. Dt could lso be output to computer for wveform disply. MODENISED MONITOING Although hert monitoring techniques my not hve chnged fundmentlly since tht design, the methods for processing the dt hve moved on drmticlly. The Biopic design presented here tes dvntge of PIF microcontroller s cpbilities nd uses n lphnumeric l.c.d. screen, plus n electriclly-isolted seril dt lin to P-comptible computer. There re only five i.c.s. The probes nd contct pds used re those sold inexpensively by mjor chemists for use with proprietry TENS (pin relief) mchines. The design cn be used s hndheld unit without using P. In this role it outputs hertbet wveforms to the l.c.d., which is used in the sme grphicl fshion s with the uthor s Micro-PIscope (simple oscilloscope) of April 00. The disply lso shows the hertrte in bets per minute (BPM) nd rel-time pulse bet vi flshing steris nd l.e.d. When used with P, the design switches off the l.c.d. wveform nd outputs dt s 00 bud seril strem to progrm written for QB (QBsic or QuicBASI). The Biopic softwre is selfcontined nd does not require QB itself to be instlled. The QB progrm cn be run in DOS mode or under Windows.,, nd ME (other Windows versions hve not been tested with it nd no dvice cn be offered for them). Exmple of thumb-monitored wveform on the Biopic. P WAVEFOM DISPLAY A composite photo of severl typicl hert wveforms displyed on P screen is shown on the next pge. Whilst the subject is believed to be in good helth, medicl opinion of the wveforms hs not been sought. Normlly rel-time wveform strts t top left (zone ), continues to the right, recommences in zone, continues right, etc. At the end of zone 0, zone is clered nd the disply continues from the top gin, ech zone then clering in sequence s the wveform strts t its beginning. The BPM rte is clculted cross ech zone, nd the vlue displyed t the screen s top right. This vlue is updted ech time zone line is completed. The BPM nd rel-time clender/cloc disply re updted simultneously. At the bottom of the screen, detils of the OM port in use re shown. The OM port ddress (shown here s OM ) cn be chnged by pressing eybord ey <> (more lter). The bud rte nd its formt cnnot be chnged s this is set within the PI softwre s well s in the QB progrm. The spn between screen dt plotting points cn be chnged to vry the disply detil, using the <> nd < > eys. The Everydy Prcticl Electronics, June 00

3 HEAT POBES SK IGHT INPUT HEAT LEFT INPUT S Sb 0 00n 00n 0 M M TL0 I Ib TL0 0 V D N n Id TL0 D N 0 PEAMP BALANE µ I TL0 0 00n 00n Ic 0 TL0 K V M µ TL0 GAIN Ib K µ µ I PIN (A0) S V LD OP FINGE POBE PL TIP ING SK 0 00n µ V rnge is / to /0, the ltter showing wveforms closer together. The smpling rte itself is not ffected by these chnges, the result is purely cosmetic on the P s screen. Pressing <H> turns on the hold function. The disply then puses when it reches the fr right of its current zone. Pressing ny ey then lets the disply run gin. Pressing <Q> cuses n exit from the progrm nd return to the screen from which it ws first clled. 0 00n 0 LEVEL 00n Pressing <L> enlrges the disply to cover just one nerly full-screen line. Pressing <L> gin returns you to 0-line mode. When run under Windows, wveforms cn be cptured for sving to dis nd printing to pper (vi Pint). ANALOGUE IUIT The Biopic effectively hs two circuits, the sensor input nd signl pre-conditioning circuit, plus the PI-controlled disply nd dt output circuit. The nlogue circuit digrm is shown in Fig.. Probes from the subject whose hert is to be monitored re connected into socet SK. The circuit is not erthed for sfety resons nd differentil mplifiction technique is used. The probes re ech connected seprtely to the non-inverting inputs of two op.mps, I nd Ib, vi resistors nd. Both inputs re bissed t bout V (hlf the nominl V supplied by PP bttery) vi resistors nd, which hve high vlue to minimise the voltge drop cross nd. A pumping hert is ccompnied by smll electricl field cross the chest. This cn be detected by using two electricl contct pds nd probes. One pd is plced below the hert, ner the bottom left of the subject s rib cge. The other is plced on the subject s right towrds the top of the chest. It is worth experimenting to find the best position. The self-dhesive pds hve terminls to which the commercilly purchsed probe leds re clipped. As the hert bets, the electricl field is detected s voltge difference between the probes, nd thus by their mplifiers. The difference in potentil between the probes is extremely smll nd needs considerble mount of mplifiction. Initilly, the difference is d.c. mplified by fctor of two, s set by resistors, nd, lthough this is complicted by the intercoupling between I nd Ib vi (see Tech-In 00 Prt (Mr 0) for n explntion). Further mplifiction of bout is given when combining both pths vi differentil op.mp Id. The blnce between the two signls cn be set by Everydy Prcticl Electronics, June 00 Ic 0 TL0 µ I IN LD OP Fig.. ircuit digrm for the nlogue stges of the Biopic Hertbet Monitor. omposite of severl hert wveform trces s shown on the P screen. In norml running the wveforms run continuously. 0 V TO V EQUIVALENT IUIT FO FINGE POBE. FINGE TIP IS PLAED BETWEEN LIGHT SOUE AND LD.

4 V IN (SIG IN) I L0 OM 00n OUT V D N 0p. X MHz 0p preset V. High-frequency cut-off is provided by cpcitor. Still s d.c. voltge, the signl is fed to the first stge of low-pss filter vi resistor, with cpcitor providing some preliminry upper-frequency cut. Hertbets normlly te plce t round one per second, nd seldom bove two per second except under extreme conditions. Wheres the previous Biomet used switched-mode filter (MF0), Biopic uses purely nlogue filter. This is vrint of the Third Order hebyshev low-pss filter from the Filter Hndboo by Stefn Niewidomsi. It is formed round op.mps I nd Ib nd removes prcticlly ll frequencies bove those tht re to be expected from hertbet wveform. Its output is.c. coupled by cpcitor to the finl gin stge, formed round Ic. Here the gin cn be vried between bout 0 nd 000 by potentiometer V. pcitor gives stbility to Ic t high gin levels. The finl output is.c. coupled by cpcitor to one of the AD inputs (A0/AN0) of the PI microcontroller (Fig.). THUMB Still referring to Fig.. The circuit cn be switched to monitor pulse bet detected vi thumb probe, detecting blood flow s mentioned erlier. The fmilir OP light dependent resistor (l.d.r.) is used. This is bissed cross the V/ power rils vi resistor. An equivlent circuit of the sensor configurtion is shown in the inset of Fig.. As the blood pulses, the mount of light pssing to the l.d.r. through the thumb vries. This cuse the resistnce cross the l.d.r. to chnge minutely. The resulting fluctuting voltge t the l.d.r./ junction is.c. coupled vi 0 to 0 VE A0/AN0 A/AN INT/B0 A/AN/VEF B A/AN/VEF B A/TOK PGM/B A/AN/SS B I PIF B PGLK/B PGDA/B OS/LKIN TOSO/TKI/0 TOSI/P/ P/ SK/SL/ SDI/SDA/ 0 OS/LKOUT SDO/ TX/K/ ML X/DT/ GND GND VPP DATA LK POGAMME potentiometer V. This sets the mplitude tht is fed vi to op.mp I nd switch S. Amplifiction tes plce s before, but with Ib not used. ONTOL IUIT In the control circuit of Fig., the principl component is the PIF microcontroller, I. This is cloced t MHz s set by crystl X. The mplified nd.c. coupled signl from Ic is fed to the PI s A0/AN0 nlogue-to-digitl converter (AD) input. The input is bissed to bout V (hlf the PI s nominl V supply), by resistors nd. When no signl is present, the AD conversion vlue red by the PI is bout deciml, out of possible -bit rnge of 0 to (the PI s full 0-bit rnge is not needed in this design). From the incoming vlues, the PI clcultes the BPM rte ccording to n internl cloc. It does not ttempt to determine which pulses re truly hert-generted nd which hve been cused, for exmple, by movement of the thumb on the l.d.r. The twin hert-probe pth is less prone to extrneous conditions. The pulse bets re displyed by l.e.d. D, which is buffered by resistor nd controlled by PI output. The clculted BPM rte is output to the l.c.d. vi lines B0 to B, the disply being operted in conventionl -bit mode. Preset V djusts the l.c.d. screen contrst. The softwre lso outputs grphics dt to the l.c.d. for disply on line in cells to s simple wveform (s shown erlier nd on the finl pge). The technique ws first used by the uthor in the l.c.d. disply for his Micro-PIscope. eders fmilir with lphnumeric l.c.d.s will be wre tht the disply hs severl internl chrcter genertor registers tht cn N D0 N D N D 0 N D D D D D S E /W be progrmmed by the user. Dt is written from the PI into these registers such tht the pixels show moving disply of the hertbet wveforms. It hs to be emphsised, though, tht the l.c.d. shows less detil thn cn be displyed on the P screen. Nonetheless, for simple hndheld use of the unit, the l.c.d. cn produce informtive results. SEIAL When the PI detects tht its pin hs been set high vi switch S, it switches from l.c.d. output mode to seril output mode vi pin, feeding to opto-isoltor I. This hs n integrl l.e.d. tht is controlled by nd buffered internlly. The l.e.d. s behviour controls n opto-sensor coupled to I s internl buffer. The resulting logic level chnges re output from pin to the seril connector SK, nd thence to the P. The buffer within I drws its power directly from the P. The positive supply is pssed vi bllst resistor nd diode D to I pin. Zener diode D ensures tht the voltge cross the buffer cnnot exceed V nd cpcitor smooths this supply. As result, the dt logic levels output to the P stys within its cceptble rnge of nominlly to V. The PIFx series ll hve seril communictions routines built into them, nd the protocol (e.g. Bud rte etc.) cn be chnged s detiled in this PI fmily s dt sheets. The rte hs been set t 00 bud, -bit, 0 prity, stop bit. This configurtion dt is lso set into the Biopic s QB softwre tht controls the P s seril reception mode. Ech PI-generted AD conversion is sent to the PI s seril dt output register nd then to the P, which receives ech dt byte nd processes it s discussed lter. The l.e.d., D, is not ctive in this mode. Everydy Prcticl Electronics, June 00 0 SEIAL * S 0Ω D Fig.. The Biopic s control circuit detils. V 0 V I 0L000 ONTAST OPTOISOLATO * SEE TEXT D N. ma D V VE X L..D. MODULE GND 00Ω * µ X * VE SEIAL SK

5 D D D D LEFT POBE PAD GAIN IGHT POBE PAD V V SK PL I 0 I OPTO-ISOLATION I S 0 OM V 0 D OUT The importnce of using n opto-isoltor cnnot be over-emphsised. The most dngerous route tht n electricl current cn te cross the humn body is vi the chest. The voltges nd currents tht cn be lethl cn vry between subjects, but cn be s low s nd 0mA. It is therefore impertive tht ny unit which requires pir of electrodes to be secured cross the chest when tht unit is lso connected to mins powered piece of equipment, such s P, must provide totl electricl isoltion between them. HEAT IN PL SK S. IN (. mm) I X TO POGAMME (SEE TEXT) ML DATA B LK B FLAT BATTEY V LD MOUNTED AT END OF JAK BODY (SEE TEXT) V D S X V (/W) E S D D D D I SEIAL D EA VIEW SEIAL OF PINS Any designer must ensure tht his units nd their users cnnot be hrmed by mins power fults. The opto-isoltor specified for the Biopic is stted by the mnufcturer to provide isoltion up to 0, well in excess of the.c. present on norml UK.c. mins supply. The reson for using seril connection between the P nd the Biopic ws to simplify the isoltion circuit. To hve used the prllel port s the connection pth (esier in some respects) would hve required using n isoltor for ech dt line. Also for electricl sfety resons, the Biopic MUST NOT be powered from OMPONENTS esistors,,,, 0 ( off),, M ( off),,, to ( off), 0, to ( off) 0,, ( off) 0W Approx. ost Guidnce Only 0 excluding chest electrodes Everydy Prcticl Electronics, June 00 SK L..D. D LD Fig.. Printed circuit bord component lyout nd full-size mster trc pttern, plus off-bord connection detils.. IN (. mm) See SHOP TALK pge 00W (see text) OP light dependent resistor Potentiometers V min. preset, round V, V min. preset, round, or pnel mounting, lin. (see text) ( off) V 0 min. preset, round pcitors,,,, 0,, 00n cermic, mm pitch ( off) n cermic, mm pitch,, m rdil elect. V ( off) m rdil elect. V,, m rdil elect. V ( off), 0p cermic, mm pitch ( off) Semiconductors D to D, D N signl diode ( off) D red l.e.d. D V 00mW Zener diode I, I TL0 qud op.mp ( off) I PIF-P microcontroller, pre-progrmmed (see text) I L0 V 00mA voltge regultor I 0L000 logic-to-logic opto-isoltor Miscellneous S, S min. s.p.d.t. toggle switch ( off) S min. d.p.d.t. toggle switch SK, SK mm jc socet ( off) SK -pin seril connector PL, PL mm jc plug ( off) X MHz crystl X -line x -chrcter (per line) l.c.d. module Printed circuit bord, vilble from the EPE PB Service, code ; TENS replcement electrode pds ( off, minimum), plus twin connecting led; -pin d.i.l. socet; -pin d.i.l. socet ( off); - pin d.i.l. socet, nrrow;.mm plstic jc plug cp (see text); plstic cse 0mm x 0mm x 0mm; PP V bttery plus clip; nobs (see text) ( off); connecting wire; solder, etc.

6 mins operted power supply of ny type. Only bttery power must be used. The sfety of the person to whom the probes re connected must be the prime considertion. DO NOT IGNOE THIS SAFETY ADVIE. ONSTUTION The component nd trc lyout detils for the Biopic, plus the off-bord wiring, re shown in Fig.. This bord is vilble from the EPE PB Service, code. Socets must be used for ll d.i.l. (dulin-line) i.c.s, but do not insert the i.c.s until the correctness of the power supply regultor hs been proved. Assemble the other components in ny order you prefer, but it is recommended tht they should be inserted nd soldered in order of scending size. It is up to you whether you use preset potentiometers for V nd V, mounting them on the p.c.b. in the holes provided. The lterntive is to use pnel mounted rotry potentiometers with nobs. The former is neter, but the ltter provides esy externl control of signl mplitudes. On considertion, the uthor opted for V s rotry pot. If you do not intend to use P with the Biopic, connect the led tht would otherwise go to the pole of switch S to the connection. A plstic cse mesuring 0mm 0mm 0mm ws used for the prototype. A viewing slot for the l.c.d. ws cut in its lid, nd holes drilled for the controls nd socets. POBES The OP l.d.r. for thumb pulse monitoring conveniently hs dimeter tht llows it to be inserted in the plstic cp of mm (¼in) jc plug. Solder suitble length (sy hlf metre) of twin lowvoltge cble to the l.d.r. s pins, pss the cble through the hole t the end of the cp nd gently push the device into the cp until it is flush with the rim. Secure the l.d.r. with suitble glue or dhesive-bced tpe, such s insulting tpe (s ws done with the prototype). onnect mm plug to the other end of the cble. Polrity does not mtter. The hert monitoring pds re liely to be sold in multi-pcs two pirs in the pc bought by the uthor. They re intended s replcements for use with proprietry TENS mchines nd their existing cbles. Spre cbles cn be purchsed, however. Two were in the pc supplied for the prototype, hving pressstuds tht clip onto the pds t one end, nd -pin femle plug t the other. The uthor mde no ttempt to buy suitble mle connector for use with the Biopic. Insted, the plug ws cut off nd the twin wires soldered to mm jc plug. Agin polrity does not mtter. PELIMINAY HEKS Hving completed the bord ssembly, thoroughly chec tht ll components re in the right plce nd tht their polrity hs been correctly observed s pproprite. Py gret ttention to the soldering, especilly for those components in the physicl region of opto-isoltor I. Interior detils of the Biopic enclosure. It is impertive to ensure tht no solder bridges or hirs occur in tht re. The isoltion vlue quoted erlier only holds true if the mnufcturer s pin seprtion distnce is mintined. The bord re in tht region (bove nd below) must be scrupulously clen to mintin its own electricl isoltion qulities. With d.i.l. i.c.s nd the l.c.d. omitted, pply bttery power to the bord. hec tht V exists t the output of regultor I nd t strtegic points round the bord. If the voltge is not correct, within bout five per cent or so, switch off nd investigte the reson. When stisfied, nd with the bttery disconnected, insert the remining i.c.s., ensuring their correct orienttion in the socets. onnect the l.c.d. Apply power ompleted Biopic, plus hert monitoring probe pds, nd thumb pulse detector. Typicl exmple of hert wveform shown on the P when the progrm is in enlrge mode. The two horizontl lines indicte the trigger zone used for ssessing bet rte. 00 Everydy Prcticl Electronics, June 00

7 gin nd rechec tht the regultor still outputs V. If you hve Toolit M or M (TK) you cn now progrm your PI while in situ, ming the required connections vi the connections provided. The PI configurtion is for crystl XS, PO on, WDT off. For those who do not hve progrmming fcilities, pre-progrmmed PIs cn be obtined s stted on this month s Shoptl pge, which lso gives detils of obtining the softwre itself.. ATIVE TESTS Once the progrmmed PI is running, djust preset V until messge is visible on the l.c.d. With mode switch S in the Pulse setting, line should show the word BIOPI on the right, to its left nothing recognisble is liely to be displyed. Line should red ATE followed by Exmple of hert wveform monitored cross subject s chest. Another exmple of pulse being monitored vi the thumb probe (the lc of uniformity is due to the subject s slight gittion!). The Biopic s screen while it outputs pulse wveform dt to the P. numericl vlue nd perhps n steris. It is best to chec the unit while using the thumb-pulse detector, with the first messge on disply. Plug the l.d.r. ssembly into socet SK nd switch S to Pulse mode. Set preset V midwy nd potentiometers V nd V for mximum signl gin. Move your hnd bc nd forth cross the l.d.r. s fce in resonbly welllit room, so putting the l.d.r. in nd out of shdow. Observe l.e.d. D while you do so. It should flsh on nd off in response. If it does not, chec tht you hve set V nd V in the correct direction. Looing t the l.c.d. screen, the steris t the right of line should lso go on nd off in response to light chnges. On line pulsed wveform should now be seen, corresponding to the high nd low light levels s the shdow crosses the l.d.r. Gently plce your thumb cross the l.d.r. fce nd point the top of your thumb towrds the light. As your blood pulses, so the l.e.d. should flsh, ccompnied by meningful detil on the l.c.d. screen. You must eep your hold of the l.d.r. gentle nd stedy to void flse triggering. It my either be necessry to come closer to the light or to reduce the setting of V until n even l.c.d. wveform is shown, Another enlrged wveform, displyed horizontlly on wider scle. together with resonble BPM vlue on line. A certin mount of prctice is needed to get the technique right. HEST POBES TESTING To chec the chest probes mode, switch S to Hert. Plug the hert sensor cble into its socet. Attch the TENS monitoring pds to your chest, s described erlier, nd clip the cble to them. Next, stop moving, relx nd observe the l.c.d. screen. If you hve positioned the pds on your chest correctly, you should see your hert wveform begin to pper on the l.c.d. It my te few seconds to stbilise. Adjust potentiometer V until distinct pulses re seen. Your pulse rte should gin be indicted numericlly, together with flshing steris, nd the l.e.d. flshing in sympthy. Agin, it tes bit of prctice to remin in sufficiently pssive stte for the disply nd BPM rte to remin stble. Hving set V for wht ppers to be resonble gin setting, return to using the thumb monitor nd if necessry redjust V to compenste for the chnge in V s setting. If you hve n oscilloscope, preset V cn be djusted to blnce the gin between the two input signl pths. If not, leve V set midwy. P MONITOING Instructions for loding the P with its progrm for monitoring the Biopic re to be found in the text file BIOPI.TXT tht ccompnies the softwre. This file my be red vi text editor such s Notepd or MS-DOS Edit. Follow the instructions, omposite of severl typicl pulse displys when the thumb pulse monitor is used. Slight involuntry movement of the ptient cuses unevenness. connect seril cble between the P nd Biopic, using the type required by stndrd modems. Set the Biopic for thumb monitoring nd switch S for seril output. Then run the progrm. On first running, it my be tht the softwre nd P hve different ides on which OM port to use. If the P screen does not show series of wveforms such s pper in the screen photos, press ey <> to chnge the OM ddress used by the Biopic s P softwre. Pressing <> gin reverts to the previous OM port ddress, of which there re two, OM nd OM. It is not nown if Ps cn hve more thn two OM ports if yours hs, consult its Help file for more informtion. Do not chnge ny of the settings within the Biopic s P progrm unless you now wht you re doing. SEEN DUMPING When the progrm is run from within Windows, the disply cn t ny time be cptured nd psted into the Windows Pint progrm, from where it cn be sved to dis or sent to printer (i.e. screen dump such s shown in on this pge). Screen dumps cnnot be creted from within DOS, nor cn other forms of screen output to dis or printer (there re methods to do so, but discussing these is beyond the scope of this rticle). To cpture screen, press the Print Screen function ey. Now press the Windows-symbol ey, nd select the route Progrms > Accessories > Pint > Edit > Pste > Sve As. If you re not fmilir with Pint, explore its rnge of options. MEDIAL GUIDANE Biopic should not be used s substitute for seeing your medicl prctitioner. It is not climed tht the wveforms it displys ccurtely mimic those tht would be displyed by fully professionl hert monitors. The displys re purely for interest. They should not be ten s n indiction of nyone s true stte of helth. If you hve ny reson to believe tht nyone s hert is not behving s it should, see prompt medicl dvice. EFEENE Filter Hndboo prcticl design guide. Stefn Niewidomsi. Heinemnn Professionl Publishing. ISBN 0. Everydy Prcticl Electronics, June 00 0