‘URESControl Your Audio/VideoConnections with theAVMux

Control YourAudio/VideoConnections Steve Ciarcia

Exploring the VerticalBlanking Interval

Employer Ownership of

with theAVMux

Employee and ConsultantWork Product

4b0

bout nine yearsago, the concept of

an entertainment(a.k.a., media) room

became a heavy topic in audiophileand videophile circles. Ret rooms losttheir pool tables and pinball machines,and relatives expecting the same (free)svare bedroom were shown the YellowPages under “motels.” Home builderswho had just come to grips withjamming jacuzzis into the masterbedroom closet now had to come upwith a home theater to entice thesophisticated home buyer.

Aside from the physical roomitself, the reality of a dedicatedentertainment space was primarily amatter of assembling the components.Virtually all of the equipment (projec-tion television, CD player, laserdisc,VCR, amps, etc.] was available off theshelf, but implementing the physicalconnections among the componentspresented a problem.

Virtually all of the equipment ofsufficient quality for this purpose alsohad singular applications. Good stereosystems (“good” is interpreted asmeaning audiophile quality) consistedof individual modules such as a tuner,preamplifier, amplifier, CD player,sound field processor, subwooferamplifier, DAT player, and so forth. Itwas not uncommon to have to useeight or ten of these electronic sub-systems to create the proper sound andvideo atmosphere in a true entertain-ment room.

The unfortunate truth back thenwas that while the concept of coordi-nated media was easily understood, anadequate means for channeling theaudio and video signals among all

14 Issue #45 April 1994 The Computer Applications Journal

these subsystemsthat wouldultimately resultin the desiredeffect was nosmall task. Infact, it was awiring maze. Toease the wiringcongestion andsimplify overallinterconnection, Idesigned acombination 8x8audio and videomultiplexer.

Photo l-The finished AVMux and hand-held control unit add both sophistication and class to any home theater

The AVMux, as I called it, was(and is) exactly as the name implies. Itwas an electronic cross-matrix ofswitches which channels specificinputs to designated outputs. In thecase of an 8x8 multiplexer, the inputsto it (commonly called the froms)come from the outputs of the varioussignal-generating subsystems, such asCD players, VCRs, laserdisc, taperecorders, and so forth (subsystemswith both audio and video outputswould use the appropriate audio orvideo input side of the multiplexer).Similarly, the output side of theAVMux was connected to the inputs ofvarious other system components(called tos): preamplifier, amplifiers,surround decoder, soundfield decoder,tape recorders, and so forth.

Using the AVMux and a series ofpush-button settings like “From 2 to6 ” “From 3 to 5,” and “From 3 towould, for example, channel the

7,”

laserdisc into a system combination ofthe preamp, amplifier, and subwooferamp (we presume speakers are alwaysconnected to a particular amplifier). Tochange the source from the laserdisc tothe CD player, we might enter “From1 to 6” on the control. This “erases”the “From 2 to 6” connection andreplaces it with “From 1 to 6” instead.

A SOLUTION NOW LACKINGA PROBLEM?

Nine years later, the scenario isquite different. Consumer audio andvideo equipment have made signifi-cant advances such that the borderlinebetween true “audiophile” and “high-end” consumer quality is fuzzy at best.

To obtain superb sound and video inthe past, the only solution was to usemore expensive modules and exter-nally connect things through an elec-tronic multiplexer like the AVMux.

the equivalent separate boxes.. .

Today, stereo manufacturers havesucceeded in providing some realpower and quality in a single enclo-sure. It is not hard to find the equiva-lent of the tuner, preamplifier, twoloo-watt stereo amplifiers, subwooferamplifier, a Pro-Logic surrounddecoder, and a dedicated audio/videomultiplexer in one enclosure. AMitsubishi unit I looked at recentlyincluded all this for $1400. When Icompare this to the $10,000 I spent on

The greatestattribute oftoday’s “inte-grated compo-nent” single-boxstereos [providedit is of sufficientquality) is thatthey contain anintegral dedicatedmultiplexer. Withexternal inputdesignations likeVCRl, VCR2,TAPE 1, TAPE2,CD, AUXl, and

AUX2 (remember, the tuner andsurround decoder are already in thebox, so they don’t need externalinputs), a simple push button orremote tells the internal multiplexer(frequently a relay) to channel theappropriate input through the preampinto the surround decoder and amplifi-ers. The outputs of this system areusually just speaker terminals and thedirect video from the designatedsource. This video goes to a separatemonitor such as a projection TV.

multiplexer is always a Nxl and the

Depending upon the brand and thecost, you can find a variety of input/output configurations. Because theyhave a dedicated avvlication. the audio

Basic serial-controlled AVMux

Video

Audio

Expanded multi mode controlled AVMux

Tzr%tal 7

optional dKeypad unitwith LED connection

)E} A u d i o

16

Figure l--The A VMux sefup can be as simp/e as a seriaial terminal controrolling it, or as complex as using wirelesscontrols, user displays, and the HCS /I to make a fruly powerfuful system.

The Computer Applications Journal Issue #45 April 1994 15

OptionalAudio x 1 amp

1 1 Video Amp

video rarely more than a4x1 or 4x2. The Nxlaudio configuration isbecause all the amplifi-ers are in the one box.Any sound created in thesystem has to be ampli-fied by this box and allspeakers are wired to it.If there are eight audioinputs and only a singleoutput that goes to theamps, then we have an8x1 audio mux. Simi-larly, since this inte-grated system does notincorporate its ownmonitor, the manufac-turers facilitate anexternal connectionthrough the mux. With four videosources and two outputs, we have a4x2 video mux equivalent.

Vi&oInputs

OUT 1

OUT 8

t Video AmpPWR (8 total)

i

8 7x2Video

Outputs

Figrue P-The Circuit Cellar A VMux uses a pair of chips (one from Analog Devices and the other from Maxim) designed specifically fordoing audio and video multiplexing.

channel to 120 W per channel, or,using the same CD player, channel itsoutput to a different set of speakers.

OK, enough beating around thebush. If you want to put together anentertainment room and you are on alimited budget, these integratedsystems are the only way to go. Onehundred watts channeled throughefficient speakers can sound quite goodin any room.

While the integrated system hasgreatly reduced the introductory costof an entertainment room and satisfiedbottom-up multiplexer execution to agreat extent, it has done little forapplications that don’t fit the “mold.”

right elements, it didn’t have any-where enough power and its internalswitch multiplexer (or that on virtu-ally any integrated unit) was far toolimited for the I/O selection I have.

The problem comes when youwant to do something that is not partof the basic box. The instant you wantto connect three video inputs whereyou only have two available, changethe front surround speaker poweroutput capability from 20 W per

As you might already haveguessed, very little that I do fits any“mold.” Let me explain.

Recently I decided to revamp ourentertainment room. I thought ofusing an integrated surround systemlike those I described, but even the350-W Mitsubishi unit didn’t quite fitthe bill. While it contained all the

In all truth, if I didn’t already haveall the amplifiers and many of thesubsystem components, I might wouldhave changed the rules to fit thesolution, but the disparity in perfor-mance was still there. My attitudetoward surround sound movies is tocreate an environment as close to thepictured event as possible. When wewatch Top Gun, only the lack ofexhaust fumes and salt spray keepsyou from actually believing you are ona carrier deck. To achieve this soundenvelope requires considerably morethan 5 W through a 6” x 9” oval TVspeaker. In my opinion, it also takesmore than the 300-400 watts availablefrom the current top-of-the-lineintegrated units.

Photo 2-While the circuit isn’t complex, wiring the projecf can be a major task since a// the cab/es must beshielded.

My entertainment room techniqueinvolves using separate modules(preamp, surround decoder, etc.)instead of the integrated unit. The factthat a stand-alone surround decoder/sound field processor has all its signaloutputs available, gives me the optionof using any size amplifiers I want.Being brief, let me just say that I’musing about 1200 watts on the dozenspeakers comprising the surroundsystem. Included among them is a pairof 200-W subwoofers that guaranteeyou don’t miss an F-14 fly by.

1 6 Issue #45 April 1994 The Computer Applications Journal

What finally convinced me to Take away all the sound effectsredesign and further employ an processing, decoding, and electronicexternal AVMux was the implementa- signal manipulation and true soundtion of dual systems. I’m sure you’ve quality of any stereo is simply anheard the saying, “If it ain’t broke, audio source, amplifier, and a pair ofdon’t fix it!” Well, that can apply to speakers. In my opinion, the soundstereo systems as well. produced by a pair of B&W 808

ANALOGINPUT/OUTPUT

SIN

1 +72v -12v +5uSERIAL DATA IN

ANALOGOUTPUTS/

INPUTS

BUSSED CLOCK SERIALLINES DATA

TO NEXTSTAGES

16 x 16 ARRAY OF SWITCHES,LATCHES AND SHIFT REGISTERCELLS (ONLY TWO LOCATIONS

ARE SHOWN FOR CLARITY)

DGND

‘yDGND

SERIALDATAFROMPRIOR

STAGES

BUSSEDCLOCKLINES I

Y15 cANALOG

t 4

SWITCH SHIFTREGISTER

CELL #l

P&K StLK S&T

IN0 IN1 IN2 IN3 IN4 IN5 IN6 IN7l-OF-8 OUTPUT

BUFFERS

/\

* EDGE/LEVEL

SEWPARI 1st.RANK REGISTERS

Figrue 3-The Analog Devices AD75019 (top) is a 16x16 switch matrix idea/ for useMaxim MAX456 (bottom) is an 8x8 witch meant for video.

in audio applications while the

RELAY(INTERRm

@NNECTS TO RS-2S#)

AR-10 RELAY INTERFACE 16&Juts

chmnd) . . . . . . . . . . . .are fxovilw fof 8Q*9s

ANALOG T ODIGITAL

&” ( CONNECTS TO ~3.232)

ADG16 AID CONVERTER*ADC-8G AID CONVERTER*Input voltage, amperap, pressure. energy “saga,

joysticks and a wide vartety of other types of analogsignals. RS-422/R&466 available (lengths to 4.W).Call for info on other A/D configurations and 12 bitconverters (terminal block and cable sold separately).ADC-IE TEMPERATURE INTERFACE’ (8 ch)..S 139.95Includes term. block 8.6 temp. sensors (-40’ to 146’ F).STA-8 DIGITAL INTERFACE* (8 channel) . . . . . . . . . S 99.95Input on/off status of relays, switches, HVAC equipment,security devices, smoke detectors, and other devices.STA-6D TOUCH TONE INTERFACE’................ $ 134.90Allows callers to select control functions from any hone.PS-4 PORT SELECTOR (4 channels RS422)....Q79.95Converts an RS-232 port into 4 selectable RS-422 ports.CO-485 (RS-232 to RS-422/FtS-485 convertar)......S 44.95

l EXPANDABLE...expand your interface to control andmonitor up to 512 relays, up to 576 digital inputs, up to126 anal0the PS-4. i

inputs or up to 126 temperature inputs usingX-16. ST-32&AD-16 expansion cards.

FULL TECHNICAL SUPPORT...provided over thetelephone by our staff. Technical reference&diskincluding test soltwara & programming examples inBasic, C and assembly are provided with each order.

HIGH RELIABILITY...engineered for continuous 24hour industrial applications with 10 years of provenperformance in the energy management field.

CONNECTS TO RS-232, RS-422 or Fl%WS...use withIBM and compatibles. Mac and most computers. Allstandard baud rates and protocols (50 to 19.200 baud).Use our 800 number to order FREE INFORMATION

PACKET. Technical information (614) 464-4470.

24 HOUR ORDER LINE (800) 842-7714Visa-Mastercard-American Express-COD

International & Domestic FAX (614) 464-9556Use for information, technical support & orders.

ELECTRONIC ENERGY CONTROL, INC.360 South Fifth Street, Suite 604

Columbus. Ohio 43215-5436

#IO6The Computer Applications Journal Issue #45 April 1994 1 7

Photo 34nside the finished AVMux you can see the controller (let?), multiplexer electronics (center), and HCS /I

Reference Speakers [running at another1200 watts) comes close to perfectaudio. I like classical music straight,while rock music seems better with allthe effects. That means I have onesystem configuration for classical anda completely different one for rock.

Keeping a dual redundant systemlike this requires a sophisticatedmultiplexer to allow a common set ofAV sources to be routed among allinput combinations.

A SIMPLE MUX DESIGN WITHMANY OPTIONS

The new AVMux has improvedperformance primarily because it usesnewer technology. Like the originalunit, this is an 8x8 stereo audio and8x8 video multiplexer. Unlike itspredecessor, however, this mux allowsthe user to select independent orcoordinated control of the audio andvideo sections. You can have eightaudio sources with only three corre-sponding video signals and still use theother five video inputs for unrelatedactivities. Audio and video channelscan be routed independently.

Due to its particular architecture,which allows independent audio andvideo operation, you can choose tomake just a video-only or audio-onlymultiplexer. Control is realized withan 80C52-based microcontroller whichallows considerable expansion options.As outlined in Figure 1, the newCircuit Cellar AVMux can operatethrough simple, direct, serial RS-232control; operate with a wirelessinfrared remote control; operate with ahand-held keypad and LED connectionmatrix display; display an ASCII list of

connected points during operation; andallow network connection (using aDIO-Link) with functional controlprovided by the Circuit Cellar HCS II.

As you can see, this is a long listof functions. It also incorporatesfeatures that involve considerablymore software than I cared to write. Tofinish in a reasonable time, I draftedJeff Bachiochi to help. I’m glad I didand I’d further have to say that thisnew AVMux has as many features as itdoes because of his added expertise.Since we worked together, Jeff will becovering certain AVMux aspects in hiscolumn as well.

For this month, I’ll describe thebasic AVMux components and thecontroller design. Next month, Jeffwill fill in more on how the softwareworks, with particular emphasis onthe remote keypad/LED connectionmatrix unit. I’ll conclude next monthwith the wireless remote controlinterface specifics.

NEW SINGLE-CHIPMULTIPLEXERS

Any rational person would noteven attempt to make an 8x8 multi-plexer if it were not for the availabilityof some new highly integrated multi-plexer chips from Analog Devices andMaxim. The configuration of the basicAVMux using these chips is outlinedin Figure 2. Regardless of all the otheroptional features, this basic circuitstays the same. The two sections-audio and video-are also divisible andyou could build each separately.

The audio multiplexer is thesimpler of the two, both in conceptand construction. Employing an

Analog Devices CMOS AD7501916x16 crosspoint switch array (itsfunctional block diagram is in Figure3) allows the complete circuit to befabricated with just that single chip.

Unlike its video companion, an8x8 stereo audio multiplexer involvesswitching 16 signals (8 left channeland 8 right channel). I chose theAD75019 specifically so I would nothave to use two 8x8 devices. TheAD75019 contains 256 analogswitches in a 16x16 array. Any of theX or Y pins may serve as inputs oroutputs. Any of the X pins can beprogrammed to connect to any Y pinsand vice versa. The switches allowamplitudes up to the supply voltagesand have a typical resistance of 150ohms.

Figure 4 shows the actual circuitconnections. To keep things simple,we designated all X pins as inputs andall Y pins as outputs: X0-X7 are rightchannel inputs l-8, X8-X15 are leftchannel inputs l-8, YO-Y7 are rightchannel outputs l-8, and Y8-Y 15 areleft channel outputs l-8. I know thatchip designations use “0” instead of“1” as the first signal line, but try totell someone unfamiliar with electron-ics that and you’ll get a blank stare.Zero to seven is for the builder and oneto eight is for the user.

Connecting input X2 to output Y7is accomplished by closing thecrosspoint switch at their intersection.Each of the 256 crosspoint switches iscontrolled by a shift register cell. If thecell contains a 0, the switch is open. Ifthe cell contains a 1, the switch isclosed. The contents of all the cells,describing the crosspoint matrix map,is a 256.bit data packet.

The data is loaded serially via theSIN input (DATA) and clocked intothe 256-bit shift register via SCLK(CLK). When all 256 bits have beenentered, data is transferred in parallelto the switch latches on the high-to-low leading edge transition of PCLK(ALD). One caution to note here: theserial shift register in the AD75019 isdynamic and the minimum clock rateis 20 kHz (the maximum rate is 5MHz). With a high-level languagecontroller, an assembly languageroutine is often used to send data to

18 Issue #45 April 1994 The Computer Applications Journal

+SJ0

d (1 FID75019lN5819 PCLK -1

0.luF‘: 42 ucc

SIN 3”I\

AL0 P 1 . 3DATA P1.O

7 &‘JDDSCLK-’ CLK P1.l

Input 1 ; l5 x023-X8

SOIJI .g

Y8 l4 ; Output 1 *

Input 2 ; 16-x124 x9 ;A.:: ; OUtPUt 2 *

Input 3 ; l7 x225 x1018.x3

y:g :z ; O u t p u t 3 *

RInput 4 L

26 x11 y;; :: "L OutPut 4 *

InPut 5 ; 19.x427 Xl2 Output 5 *

RInput 6 L 20.X528 x13

Y;; Ii L"

21.X6Y13 g

RL Output 6 S

RInput 7 L2g x14

Y637 R

RInput 8 L 22 x7Y14 * L Output 7 *

30.x15Y7 38

Y15 7RL Output 8 *

DGND USS43 4

0.luF. 1; 0

L = 0 -5ulN5819

_=

1009

* Optional VoltageFo l lower Bu f fe rAmp LM2904,LM324. e t c .maw be added to eachof the outputs shown.

tlgure 4- /ne actual connections to the AD75019 are numbered l-8 rather than O-7 to make it easier on the user.

this chip. Once programmed, however,operation is static and the switchesstay programmed for as long as thepower is on.

One final note on this chip. Whenpowered on +5 V, the AD75019 has atypical switch resistance of 300 ohms.Many applications may be unaffectedby this added resistance and you canuse the circuit as is. If you are unsureor desire extra output protection, addthe voltage follower buffer amplifier toeach output channel (16 amps total) asnoted in the schematic.

A NEW MAXIM MULTIPLEXERIf you look closely at the spec

sheet on the AD7.5019, you’ll note thatit has a switch frequency response of20 MHz. While I could have used it forboth sections, I opted to use a chipspecifically designed for video.

I decided to make the AVMuxvideo section using the new MaximMAX456 CMOS 8x8 crosspoint switch(functional block diagram in Figure 3)specifically designed for video. Itcontains a similar register, latch, andswitch arrangement as the audio mux,but the MAX456’s connection logicprohibits illegal switch connections.

The MAX456 is an 8x8 matrix, andthere are indeed 64 separate switches,but in video applications, not allcrosspoint connections are allowed.Video outputs should not be tiedtogether, for example.

In the MAX456, each outputconnection command is thought of asa combination of the binary address ofthe selected l-of-8 inputs and datasuch as whether the buffer is on, off, orgrounded. This data combinationresults in a 4-bit value for each outputchannel. To program 8 channels,therefore, only requires 32 bits.

The MAX456 is unique in that itcan load this switch register data byeither parallel or serial means. To keepprogramming consistency, I chose thelatter. The 32 bits are applied to theDO/SER IN (DATA) line as the l WR(CLK) line is clocked (these are thesame two lines that are connected tothe audio mux). At its conclusion, thedata is latched on a high-to-lowleading-edge transition of the LATCHpin (VLD). Using common data andclock control lines with separate videoload (VLD) and audio load (ALD)allows just four control lines to controlthe whole AVMux.

Yes, that’s right! HTE has dropped theprice of it’s popular 8031/32 EnhancedDrylCE from $269 to $149. Now youcan’t afford to be without one! ThisICE performs single step, real-timeexecute to breakpoint, disassemblyand more. 8K user code space,expandable to 32K. Order yours today!

Our DrylCE Plus has so many featuresthe price is unbelievable. 48K of user codespace, real-time execution, antexpandability to nearly all of the 805’family processors. We are novsupporting pods for the 803112, 87518OCL51/32, 8051Fx, 8OC154, 8OC410/18OC451, 8OC528, 8OC550, 8OC5358OC537, 8OC552/562, 8OC575, 8OC6528OCL781/2, a n d 8OC851. W i t h p o d !priced at only $149, going to a differenthigher integration processor is easy. Potand base unit are just $446 complete

At $149, our 552SBC-10 OEM board hasthe price and features you need rightnow! It’s an 8051 core processor with aneight channel, IO-bit A/D, two PWMoutputs, capture/compare registers, 16digital l/O, one RS232 serial port, fourJEDEC memory sockets. Add options liket w o m o r e RS232/422/485 po r t s , 24more digital l/O, real-time clock, serialEEPROM, and battery-backup for clockand RAM. Start with the Developmentboard; all the peripherals and a debugmonitor for only $349. Download anddebug your code, assembly or ‘C’, righton the SBC, then use the low-cost OEMboard of your choice for production. Wealso do customs - call for a freequotation.

aoci 88 s18cMEW! Starting at only $249. Two serialG23214221485, Parallel, expand to 16:h. 12-bit A/D, 8 ch. 12 bit D/A, Keybd,-CD, Relay I/F, more. Call for details!

pFJ 1-1

HiTech Equi ment Carp

HTE z?$;~$$2zI

- (619) 566-l 892 -70662.1241 @ compuserve.com

HO9The Computer Applications Journal Issue #45 April 1994 19

Figure 5-While the circuitry around the MAX456 video mux is simple, having to use shielded cable complicateswiring. The MAX457 video amps are used for impedance matching.

Video Frame Grabberl $495 Including Software with “C” Library _l Half Slot Card for Compact Applicationsl Real Time Imaging with Display Outputl 8 Bit (256 Gray Levels)

One additional note on theMAX456. While it does have internalvideo buffers, they can only drive 400-ohm loads. Since most video applica-tions require 75-ohm impedance,additional external buffer amplifiershave to be added. The dual-ampMAX457, which has a 70.MHz unity-gain bandwidth, is the perfect choice.As connected in Figure 5, the MAX457is configured for a closed-loop gain of2. The gain selection resistor is set at1.05k instead of I k to make up foropen-loop gain loss. The 6.8-pFcapacitor helps eliminate phase delayat high frequencies.

We have to be careful to properlymatch the cable impedances even in ahand-wired prototype. This particularcircuit allows us to drive a doublyterminated 75-ohm line. The combina-tion of the series 75ohm resistor andthe 75ohm termination at the outputconnector produces a low-noise 75ohm external connection with theappearance of unity-gain amplification.

A FAMILIAR CONTROLLER FORTHE AVMUX

As I mentioned, it takes just 4wires from the controller to theAVMux chips to do everything. Figure6b is an 8OC52-BASIC-basedmicrocontroller circuit which is morethan adequate for the task. Together,they represent the configurationoutlined in Figure 1. I used aMicromint RTC52 and RTCIO as thecontroller rather than spending thetime and effort to build one. At theprice I get them, it wasn’t a hardchoice.

We chose to use BASIC (withassembly language calls) here becausethis is not a speed-intensive controlapplication. Using a high-level lan-guage also expedited development andmade certain expansion options easier.For example, since BASIC-52 supportsa serial printer output, presenting anASCII connection list for terminaldisplay was as easy as adding anLPRINT (PRINT#) command.

The controller circuit has twosections: basic controller with oneserial port and one parallel port (Figure6a), and the same basic configurationwith more parallel ports and nonvola-

#llOIssue #45 April 1994 The Computer Applications Journal

tile memory (Figures 6a and 6b). Sincethis circuit has been presented onnumerous occasions, I will not belaborit. The initial circuit is suitable foroperating the AVMux through a serialterminal. A simple connection displayand command menu prompts the userto designate the desired From-Toconnections. More later.

PROTOTYPINGSuccess here is not just a function

of interpreting the schematic correctly.Experience counts.

As you can see from the photos,even though this is only a six-chipcircuit, it is a wiring nightmare. Tokeep signals from radiating or pickingup the radiation from adjacent signals,all input and output wires should beshielded cable [now you might under-stand the reason for doubly terminatedvideo buffers). I even used shieldedcable from the MAX456 to the bufferamps. The enclosure should be metalto serve both as an EM1 shield and as alarge noise-reducing common ground.It can also function as the heatsink foryour power supply.

Ordinarily, I wouldn’t discuss thepower supply in any detail. In anapplication where limiting electricalnoise is critical, I believe it a notewor-thy exception. First of all, I suggest

you use a linear supply only and not aswitching regulated unit. Without thebenefits of printed circuit board layout,ground planes, single-point termina-tion, and proper shielding (all of whichare incorporated in a production unit),a switching power supply is justanother source of unwanted noise(herringbone pattern on the video andbuzz in the audio).

Getting from here to there can bean interesting journey, however. Idesigned my AVMux as a totallyenclosed unit. My intention was to useone of those cheap wall-module powersources and an internal regulator. TheAVMux operates on +5 V and -5 V.Unfortunately, all the cheap wall-modules seemed to be 2-wire output.

Since I couldn’t just throw in aswitching regulator or charge pumpinverter to get -5 V, I concluded thatmy only option was an elaborate dualtracking regulator with a concoctedground. Would I have to resort to anexternal power supply and pipeeverything in instead?

The answer turned out to be reallylow tech. Shown in Figure 7, theAVMux power supply is just a regu-lated-output AC-to-DC converter. Wecan get by with a 2-wire voltage sourceif it is AC. The AC is then half-waverectified and stored as separate positive

CS

RDW R

AIfA0

PA0PA1PA2PA3PF14PA5PA6PFl7PB7PB6PBSPB4

D7D6D5D403D2

PB3PB2PBlPB0 >PC7PC6PC5PC4PC3PC2PC1

~PC0 4

DFITA

c=

From DIOP r i n t e rOutwt

3

DATA

c=

F r o m W i r e l e s s

STBR e m o t e C o n t r o l

Figure Ga--To add either HCS /I or wireless remote control to fhe A VMux, an 82C.55 must be added to the corecontroller in Figure 66.

1994 120 page catalog for PC, VME,and &us data acquisition. Plus infor-mative application notes regardinganti-alias filtering, signal condition-ing, and more.

NEW Software:LabVlEW @, LabWindows*,Snap-MasterTM, and more

NEW Low Cost l/O Boards

NEW Industrial PCs

NEW isolated Analog andDigital Industrial l/O

New from the inventors ofplug-in data acquisition.

Call, fax, or mail for yourfree copy today.

ADACAmerican Data Acquisition Corporation70 Tower Office Park, Woburn, MA 01801Phone: (800) 648-6589 Fax: (617) 938-6553

Ml1The Computer Applications Journal Issue #45 April 1994 21

Figure Gb--The confrol section of the AVMux uses the same &XXX-BASIC core seen in many other projects. Connections to the outside world are done through FL/l 1 jacks

and negative supplies with a commonground. Two three-terminal regulatorssimply convert this to +5 V and -5 V,respectively. The one notable circuitpeculiarity is that each regulator hasbeen configured for voltage outputadjustment with a pot. By referencingthese pots to the opposite supplies, theoverall input-output differentialnecessary for these three-terminalregulators is reduced. Rather than a 12.VAC input, a 9-VAC will work justfine. The benefit is reduced powerdissipation and a cooler AVMux box.

AVMUX OPERATIONThe AVMux is designed to operate

in a variety of modes. With just thebasic serial controller, all user interac-tion is through a terminal. Wheninitialized, the program displays aconnection matrix. To set a connec-tion, the user designates whether it is(A)udio, (V)ideo, or (B)oth. Answering(A) displays the audio matrix while (V)or (B) displays the video matrix. Thenext entries are the From and Tochannel numbers, or cancel. Theprogram then repeats the display,

showing it with the new connections(Jeff’s program is on the Circuit CellarBBS for anyone building the AVMux).

As I mentioned, by using BASICwe have a serial printer output alsoavailable. One program functionphysically documents the entire From-To connection list, by componentnames (such as From ADS CD PlayerTo Nakamichi Preamp Aux 2 input).This is for people who don’t want tocarry a component list to rememberchannel numbers or for those whowant to have space in their stereocabinet and want a unique terminaldisplay.

EXPANDING AVMUX FEATURES-THE HCS CONNECTION

Adding the 8255 PPI to the basiccontroller circuit facilitates otherAVMux features. Initial operation isthrough a serial ASCII terminal.Considering that the communicationis simply the 12 characters typicallyon a telephone keypad, other methodscan be employed to communicatethese characters.

The first option we thought of wasa hand-held remote that presented adisplay of the connected channels onan 8x8 LED array. It also had anintegral keypad to enter commands.

LM7805

Figure 7--The power suppty section creates quiet positive and negative supplies for the amplifiers from an ACsource.

22 Issue #45 April 1994 The Computer Applications Journal

This construction of this unit and adescription of its software will bepresented by Jeff next month.

The next brain storm we had wasto connect the AVMux so it couldwork independently from, or inconjunction with, the HCS II and thetrainable infrared MCIR-Link. Theconnection is accomplished using theDIO-Link.

Normally, the DIO-Link is used asan 8-bit, bit-programmable I/O port onthe HCS II’s RS-485 network. TheDIO-Link can also be set to drive aparallel printer. In this configuration,all bits are outputs and each charactertransfer is accompanied by a strobepulse. Character transfer timing isprogrammable within the DIO-Link.

Port A and one bit of Port C areused to receive the parallel data. TheHCS can command the AVMux bysimply sending an ASCII string, suchas “A35” (make an Audio connectionfrom 3 to 5), to the DIO-Link printerport. It’s as easy as that.

Since we were accepting paralleldata inputs anyway, it didn’t seemoutrageous to consider an additionalsource. The total 12-character vocabu-lary could also be represented as 12combinations within a 4-bit code. Itshouldn’t be too hard to communicatethese codes using readily availableremote control transceiver chips. Infact, next month I’ll demonstrate sucha wireless remote interface design. )&

Steve Ciarcia is an electronics engi-neer and computer consultant withexperience in process control, digitaldesign, and product development. Hemay be reached at steve.ciarcia@circellar.com.

Some components of this projectmay be purchased from

Pure Unobtainium13109 Old Creedmoor Rd.Raleigh, NC 27613Phone/fax: (919) 676-4525

401 Very Useful402 Moderately Useful403 Not Useful

Real-Time Emulation to 16MHzComplete system for 16C5x only $895.00’

Introducing RICE16-5x, real-time, non-instrusive in-circuit emulatorfor the PIC16C5x family microcontrollers: a feature-filled developmentsystem at an affordable price. a Suggested Retail for US only

l Real-time Emulation to 16MHz l Single Step, Multiple titep, To Cursor,l Non-instrusive Operation Step over Call, Return to Caller, etc.l PC-Hosted via Parallel Port l Search Capability in Source Code,l 8K Program Memory Program Memory and Trace Bufferl BK deep by 24 bits wide Trace Memory l On-line Assembler for Patchingl Source Level Debugging Instructionl Unlimited Breakpoints l Support; 16C71 and 16C04 with

l External Trigger Break with either Optional Interchangeable Probe Cards“AND/OR” with Breakpoints . Comes Complete with TASM16 Macro

l Trigger Outputs on any Address Range Assembler, Windowed 5of%ware, Powerl 12 External Logic Probes Adapter, Parallel Adapter Cable andl User-Selectable Internal Clock from User’s Guide

40 frequencies or External Clock l 30-day Money Back Guaranteel Easy-to-use windowed s&ware l Made in the USA.

Call our BBS at (2141660-0067 to download DEMO:RlCEl6.ZIP

Advanced Transdata Corporation Tel (2141980-296014330 Midway Road, Suite 104, Dallas. Texas 75244 Fax (214) 900-2937

The Computer Applications Journal Issue #45 April 1994 23