1102- EPE Hybrid Computer - Part 1.pdf

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HYBRID computers employ bothmajor categories of electronic sys-tems, the analogue and the digital.

As is true with every type of system, eachhas its advantages and disadvantages. Thehybrid system is an attempt to combine thebest of both worlds.

Many people imagine analogue comput-ers to be antique units stored away inUniversity laboratories. But not many peo-ple realise that in some cases the analoguecomputer can solve a problem withadmirable elegance, ease and simplicity,

while the solution of the same problem onthe digital computer may be virtuallyimpossible.

A few analogue amplifiers connectedtogether in a few minutes can give thesolution to a complex problem with theunits producing results in real time. Asimilar problem may take months to beprogrammed on the digital computer, pro-vided the programmer has the skill to solvethe equations.

For the digital computer to execute theprogram, millions of iterations have to beperformed, and not in real time. Granteddigital computers are now very fast, but

those tiny periods of time necessary to per-form the iterations add up to considerabletime periods. If anyone is still skeptical,visit the following site on the internet:

www.indiana.edu/~rcapub/v21n2/p24.html

There, you will meet Dr JonathanWayne Mills, associate professor of com-puter science at Indiana University,Bloomington, and director of the AdaptiveSystems Laboratory, whose patented newanalogue computer uses radically simpli-fied electronic components and “continu-

ous value logic” circuits, that make hiscomputer able to work incredibly fast andprocess more sensory inputs than a digitalcomputer can handle.

An analogue computer uses voltage as

the analogue to represent a physical quan-tity, in the same way that the height of themercury column of an old fashioned mer-cury thermometer represents temperature.

The analogue computer is designed tosolve mathematical equations, in particulardifferential equations, which are especially

difficult to solve manually. Differentialequations describe the behaviour of physi-cal systems, such as the suspension systemof a motor car or the flight of a rocket.

The variables involved in such systems,such as the stiffness of the springs in thefirst example, or the thrust of the engine inthe second, can be varied by simply turn-ing the dial of a potentiometer. In this waythe behaviour of the systems can be simu-lated, and many experiments carried outwithout going to the expense of construct-ing and testing real models.

Other advantages of the analogue com-puter are the speed with which it carriesout the processing, and the relative sim-plicity with which one can formulate theproblem on the computer. The disadvan-tage is that the range of voltage variation islimited and the measurement of that volt-age is prone to errors. However, engineer-ing is not an exact science and the ana-logue computer is a useful tool in thedesign of many engineering systems.

In contrast to its analogue counterpart,

the digital computer works by manipulat-ing discrete voltage pulses, instead of con-

tinuously varying voltages. It has theadvantage of high accuracy and repeatabil-ity of results. On the other hand, it isdifficult and time consuming to program adigital computer to solve differential equa-tions and, moreover, the programmer must

798 Everyday Practical Electronics, November 2002

Ten analogue amplifiers Each amplifier can be operated as an

Adder or Integrator Eight coefficient multipliers

Over-voltage indicators on allamplifiers

Three modes of operation, Compute,Hold and Reset

Automatic or Manual mode control Offset null on all amplifiersATOM microcontroller:

8k Flash program memory384 bytes of RAM15 I/O pinsRS232 serial link Analogue-to-digital converterPWM and Timer functionsBASIC compiler programmingIntegrated Development

Environment (IDE)

Part 1



have the mathematical ability to solve the

equations in order to write the program.The EPE Hybrid Computer employs anATOM microcontroller system, whichoperates in conjunction with the analoguesystem and can be programmed to controlit. Moreover, it can be programmed toanalyse and transmit information to a PCfor the display of results or for further pro-cessing if required. Fig.1 shows a diagramof the arrangement.

The analogue system is programmed byconnecting its modules using wiresthrough a patch panel. The microcontroller(MCU) has access to the control circuits of the analogue computer through the patchpanel. Programming of the MCU is carried

out in BASIC by means of a BASIC com-piler resident in the PC (see later).Communication is through a serial link.

The MCU sends and receives datathrough its input and output ports and hasthe capability to convert analogue signalsto digital by means of the built in ana-logue-to-digital converter (ADC).

Coefficient MultiplierThe Coefficient Multiplier (Fig.4) is

used to multiply a voltage by a constantnumber between zero and one. This math-ematical operation is usually performedwithout the use of an op.amp. A poten-tiometer is connected as shown in Fig.4. Atone extreme of the slider’s travel Vo

= Vin

,i.e. V

inis multiplied by one, whereas at the

other extreme Vo= 0 , i.e. V

inis multiplied

by zero.

Any intermediate value can be set up bymoving the slider. The dial of the poten-tiometer can be calibrated to facilitate this.However, because of the effects of loadresistance, it is usual practice to measurethe potentiometer output after the circuithas been connected and to ignore the scaleon the dial.

By choosing suitable values for theinput and feedback components, Addersand Integrators can also be arranged toapply a multiplication factor to the inputvoltages. Fig.5 shows the symbols and thefunction of each unit used in the EPE Hybrid Computer.

The circuits just described form the

fundamental building blocks of an ana-logue computer. Other specialised cir-cuits, such as four-quadrant multipliers,and various non-linear circuits, can beused to simulate effects such as back-lash , fr ic tion, dead space, abso lu tevalues, etc., although they are not thesubject of this design.

Everyday Practical Electronics, November 2002 799

The heart of the

analogue computer isformed around severalhigh gain d.c. ampli-fiers, or operationalamplifiers (op.amps).

By connecting theop.amps to variousinput and feedback

components, certain mathematical opera-

tions can be performed. These are, addi-tion (and subtraction), integration, andmultiplication by a constant. Differentia-tion can also be performed, but is general-ly avoided due to problems associated withnoise generated by components.Addition circuit

The diagram in Fig.2 shows theAddition circuit in which resistors areconnected to the input and feedback loop of the op.amp to perform inputvoltage addition. The output voltage isgiven by:

Vo= –

Rf V

1+

Rf V

2+

Rf V

3+

Rf V

4(R1 R2 R3 R4)

Integrator circuitWith the Integrator circuit (Fig.3), with

capacitor Cf in the output voltage is given by:

Vo = –1

V1dt +1

V2dt +(R1C

f R

2C

f

1V3dt +

1V4dt

R3Cf R4Cf

ANALOGUECOMPUTER

MICROCONTROLLER

PATCHPANEL

PERSONALCOMPUTER

PERIPHERALS

Fig.1. Block diagram of EPE Hybrid Computer.

V1

V2

V3

V4

R1

R2

R3

R4

RF

VOA

V1

V2

V3

V4

R1

R2

R3

R4

CF

VO

A

VO

VIN

VR

Fig.4. The Coefficient Multiplier

Fig.3. The Integrator circuit.

Fig.2.The Addition circuit.

COEFFICIENT MULTIPLIER

INVERTER

ADDER

SUMMER INTEGRATOR

MULTIPLICATION OF A VARIABLE BY A

POSITIVE CONSTANT COEFFICIENT

0<k>1

SIGN REVERSING, I.E. MULTIPLICATION

OF A VARIABLE BY -1

ADDITION OF VARIABLES INCLUDINGMULTIPLICATION BY 1 OR 10

SUMMATION OF THE INTEGRALS OFVARIABLES WITH RESPECT TO TIME

INPUTS

INPUTS

INPUT

INPUT

X

X

X

X

Y

Y

Z

Z

W

W

OUTPUT

OUTPUT

OUTPUT

OUTPUT

(X+Y+10Z+10W)

X

kX

1

1

1

1

10

10

10

10

k

(X+Y+10Z+10W)

Vic

Ric Ric

HOLD RESET

Fig.6. Circuit changes for integrators for the Hold and Reset modes.

Fig.5. Analogue computer units, their function and symbols.



Circuits which control the mode of oper-ation of the analogue computer are neces-sary. The EPE Hybrid Computer can beoperated in three modes, Compute, Hold,and Reset. In addition, an overload warn-ing system is included which monitors theoutputs of all amplifiers and gives a warn-ing when they are about to saturate.

In the Compute mode the computer car-ries out the solution of the problem. Priorto this, the computer is placed in the Reset,or initial conditions mode in which thevariables are allowed to take their initialvalues before computation begins. Thismode of operation is also called “problemcheck”. It is sometimes desirable to stopthe computation to take some measure-ments. This is achieved by placing thecomputer into the Hold mode.

In the case of Adders, no change in thecircuits is necessary for mode control.However, the Integrators have to be modi-fied as shown in Fig.6.

The circuit diagram for the Analogue

Amplifier is shown in Fig.7. Ten copies of this circuit are required.

Many op.amp i.c. types can be used tomake an analogue computer circuit, fromthe ubiquitous 741, to advanced auto-zeroed chopper stabilised op.amps such asthe Microchip TC901. The device selectedfor this amplifier is the OPA177 high

precision op.amp,which gives verygood performance ata reasonable cost.

Resistors R1 to R4are the input resistorsand R5, plus capaci-tors C1 and C2, arethe feedback compo-nents. The valueschosen give a multi-

plication factor of ×1and ×10, to signalsconnected to therespectively notatedinputs.

Moreover, whenthe amplifier operatesas an Integrator, theprogrammer canchoose C1 or C2 to bethe feedback capaci-tor, by connecting leads to the appropriatepatch panel sockets. If C2 is selected theninput signals are multiplied by an addition-al factor of 10. In computer jargon this isknown as an amplifier with a “nose gain”of 10. This means that input signals con-nected to resistors R1 or R2 will be multi-plied by a factor of 10, whereas signalsconnected to R3 or R4 will be multipliedby a factor of 100.

Switches S1a, S1b, S2a and S2b, andrelays RLA and RLB enable the amplifiersto be operated as Adders or Integrators, andadditionally allow the selection of the threemodes of operation. Relays are used

instead of solid stateswitching to providethe total signal isola-tion as required. Table1 shows the positions

of these switches andrelays to achievethese conditions.

Switches S4 and S3are used to operaterelays RLA and RLB

respectively. In the position shown in thediagram the amplifiers are operating in theCompute mode but if the patch panel sock-ets are connected to the ATOM I/O(input/output) pins, then the ATOM has

control and can place the analogue ampli-fiers in the Hold or Reset modes underprogram control.

Transistors TR1 and TR2 are necessaryto amplify the signal, as the 10 relays candraw a large amount of current. Diodes D1and D2 protect the transistors from theback e.m.f. created by the collapsing cur-rent in the coils of the relays as these areswitched OFF.

Overload warning systemThe Overload Warning circuit is shown

in Fig.8 and is built around the 1458 dual

op.amp. Reference voltages of +13V and–13V are produced across resistor R12 asset by potentiometers VR11 and VR12, andapplied to the inverting inputs of IC11 toIC20. The output of each amplifier (IC1 toIC10) is applied to the non-inverting inputs


b

c

e

b

c

e

COMPUTE/ AUTO RESET

RESET

COMPUTE/ AUTO HOLD

INTEGRATE

INTEGRATE

C2

ADD

RLA1

RLB1

S2b

S1b

S1a

S2a

VOUT

VOUT

VOUT

HOLD

x1

x10

x10

x1

IC11 TO IC20PINS 3 AND 5

+5V

OPEN = ADDERCLOSED = INTEGRATE

INITIALCONDITIONS

INPUT

D2

IN4005

D1

IN4005

R8

82Ω

R9

82Ω

a

a

k

k

RLB

1

RLA

1

GND

R1

1M

R2

1M

R3

100k

R4100k

R7100k

R6

100k

C1

C1100n

C210n

VR1

TOVR10

20k

NC IC1 IC10TO

OPA177

+

5

2

3

1

8

7

4

6

R51M

+15V

15V

GND

S3A

S4A

S3B

S4B

MANUAL

RESET

MANUAL

HOLD

TR1

TR2

BFY51

BFY51

3

2

4

5

6

8

1

7

+15V

15V

IC11

1458

R10

R11

1k3

1k3

TOIC20

D3

D4

OVER

UNDER

TOIC12 TO IC20

VR11

VR1222k

22k

R12100k

IC1 TO IC10

PIN 6

TO

a

a

k

k

+

+

Fig.7. Circuit diagram for the Analogue Amplifier. Ten copies of this circuit are required to be built.

Fig.8. Overload warning circuit, ten are used.

Table 1.The position of switches and relays for mode control.

Adder Integrator Switch Compute Hold Reset Compute Hold Reset

RLA 1 2 2 1 2 2RLB 1 1 2 1 1 2S1a 1 1 1 2 2 2S1b Closed OpenS2a Open ClosedS2b Open Closed







correct orientation into the p.c.b. (note thatthe polarity of l.e.d. D4 is opposite to thatof l.e.d. D3). Carefully press the p.c.b. ontothe switches and then solder as required.Then align the l.e.d.s in position, andsolder them.

Remove the p.c.b. from the front paneland solder the remaining components, i.e.capacitors, relays, potentiometers and1mm pin-header strip connectors.

Thoroughly check for defects in compo-nent positioning and soldering. If every-thing is satisfactory, attach the p.c.b. back onto the front panel.

Pass the patch panel sockets into thefront panel holes carefully (and patient-ly!) pushing their rigid wire extensions

through the p.c.b. holes and solder inposition.

Note that it is preferable to use patchpanel sockets which have the securing nut ontop, i.e. on the same side as the switches.Otherwise, if the nuts are on the opposite

HYBRID COMPUTER MAIN P.C.B.

Approx. Cost Guidance Only £220

excl. case

ResistorsR1, R2, R5 1M 2%

(30 off)R3, R4, R6,

R7, R12 100k 2%(41 off)

R8, R9 82 (2 off)R10, R11 1k3 (20 off)R13, R14 1k (2 off)R15 5k6R16, R17 22k (2 off)

All 0·25W carbon film, 5% except wheremarked.

PotentiometersVR1 toVR10 20k (or 22k) lin., p.c.b.

mounting, vertical,rotary (10 off)

VR11, VR12 22k, min. preset, round(2 off)

VR13, VR14 300k (or 330k) lin., panelmounting, rotary (2 off)

VR15 10k lin., panel mounting,rotary (8 off)

CapacitorsC1, C5 100n ceramic, 5mm pitch

(11 off)

C2, C3, C4 10n ceramic, 5mm pitch(12 off)

SemiconductorsD1, D2 1N4005 rectifier diode

(2 off)

See

SHOPTALK page

D3, D4 red l.e.d., 5mm (20 off)TR1, TR2 BFY51 npn transistor

(2 off)IC1 to IC10 OPA177 dual precision

op.amp (10 off)IC11 to IC21 MC1458 dual op.amp

(11 off)IC22 Basic Micro ATOM

microcontroller(see text)

MiscellaneousRLA, RLB d.p.c.o. relay, p.c.b.mounting, 5V coil(10 off)

S1 to S4 min.d.p.d.t. toggle switch,(22 off)

S5 min. s.p.d.t. toggle switchS6 min. s.p.s.t. push-to-make

switchME1, ME2 ±100 A panel meter (2 off)LS1 piezo buzzerSK1 9-way D-type female

connector

Printed circuits boards, available from theEPE PCB Service, codes 375 (Main), 376(ATOM); 1mm patch panel sockets, black (84off); red (88 off); power supply sockets (see

text) (4 off); 0·8mm (dia.) solder pins (seetext); plastic case with sloped panel, (seeFig.16); knobs with skirts marked 1 to 10 (8off); small knobs (10 off); medium knobs (2off); 1mm pin-header strips, cut to lengthrequired; connecting wire; solder; etc.

Care must be taken when assembling that the switches, potentiometers, l.e.d.s and sockets align with the front panel holes.The sockets need to be mounted last, their extension leads going into the holes just visible in the upper part of the above photo.A socket functions diagram will be given in Part 2.

Edge-on view showing front panel and p.c.b. relationship.

Everyday Practical Electronics, November 2002 803



s o c k e t c onn e c t s vi a a s ui t a b l e l e a d t o t h e

P C ’ s C OM2 s e r i a l p or t .

A t t a c h t h e p a n e l m e t e r s , p o t e n t i om e t e r s ,

r e m a i ni n g s wi t c h e s a n d s o c k e t s t o t h e f r on t

p a n e l .Dr i l l h ol e s i n t h e b a c k p a n e l t o a c c e p t

t h e p o w e r s u p pl y s o c k e t s a n d t h e s e r i a l l i nk

s o c k e t S K1 . C u t r i b b on c a b l e t o t h e r e q ui r e d

l e n g t h a n d s ol d e r t h e e n d s t o t h e a p pr o pr i a t e

c onn e c t or s .M a k e c a b l e h a r n e s s t o c onn e c t :

P o w e r

s u p pl y s o c k e t s t o t h e 1 mm p . c . b .

pi n-h e a d e r c onn e c t or s .

S K1 s e

r i a l s o c k e t t o p . c . b . c onn e c t or .

P . C .B .

c onn e c t or s t o c o e f f i c i e n t m ul t i -

pl i e r p

o t e n t i om e t e r s a n d t h e r e t ur n t o

e a r t h .

P a n e l

m e t e r wi r i n g . N o t e t h a t p a n e l

m e t e r s

m a yh a v e c onn e c t or s f or i l l umi -

n a t i on

of t h e d i a l s . U s e e i t h e r t h e +1 5 V

or t h e –1 5 V t o s u p pl y t h e b ul b s .T h i s i s

u s e f ul a s t h e p a n e l m e t e r l i gh t s f un c t i on

a l s o a s p o w e r oni

n d i c a t or s .

P h o t o gr a ph s of s om

e a s p e c t s of t h e c a s e

a s s e m b l y a r e i nP a r t 2 .

T h e AT OM p . c . b .

( F i g .1 7 ) i s s ol d e r e d

t o t h e f r on t p a n e l

s o c k e t s i n a s i mi l a r

E v er y d a yP r a c t i c a l E l e c t r o n i c s , N o v e m b er 2 0 0 2

8 0 5

8 0 4

E v er y d a yP r a c t i c

a l E l e c t r o n i c s , N o v e m b er 2 0 0 2

s i d e ( b e h i n d t h e f r on t p a n e l ) , t h e n on c e s ol -

d e r e d

t h e p . c . b . wi l l n o t b e a b l e t o

b e

r e m o v e d f r om t h e f r on t p a n e l .

T h e c om p u t e r w a s h o u s e d i n a b ox wi t h

a s l o pi n gf r on t p a n e l .F i g .1 5 s h o w s t h e

d e s i gn

of t h e f r on t p a n e l wi t h

a l l t h e

l o c a t i on s n e c e s s a r y t o d r i l l t h e h ol e s f or t h e

c om p on e n t s .

T h e g e n e r a l d i m e n s i on s of t h e b ox a r e

s h o wni nF i g .1 6 , b u t m a y v a r y d e p e n d i n g

on t h e s o ur c e of t h e c a s e .T h e l a y o u t of t h e

r e a r p a n e l i s s h o wni n t h e ph o t o gr a ph .T h e

f o ur p o w e r s u p pl y c onn e c t or s w e r e 4 mm

s o c k e t s i n t h e pr o t o t y p e , a n d s h o ul d b e

l a b e l l e d a p pr o pr i a t e l y .T h e 9 - w a yD- t y p e

++

1 0

. 5 1

0 1

0 1

0 1

0 1

0 1

0 3 3

2 2 9

1 0 . 5

1 8

3 7

3 6

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1

2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 .

5

1 2 . 5

1 2 . 5

1 2 . 5

1 2

. 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2

2 2 . 5

3 7 . 5

2 0

2 6

3 2

1 7

1 8

2 5

2 5

2 5

2 5

2 5

2 5

2 5

2 5

2 5

3 2

3 7 . 5

6 1

3 1

1 5 . 5

3 2 . 5

2 0

2 3

. 5

3 2

1 4

3 2

9 2 3

3 4

1 6

1 0 3

2 8

3 8

3 8

3 8

3 8

3 8

3 8

3 8

2 3

1 0

. 5

1 0

. 5 2

5 3 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 2 . 5

1 0

1 0

1 0

1 0

1 2 . 5

3 9

. 5 4

6 2

5

3 9 DI A

3 9 DI A

4 2

0

7 3

1 6 3

P 0

P 1

P 2

P 3

P 4

P 5

P 6

P 7

P 8

P 9

P 1

0 P 1 1

P 1 2

P 1

3

P 1 4

P 1

5

A X

0

A X 1

A X 2

A X

3

C R

O S S DE T E

C T I ON

A UDI O

M ODE

MA N

UA L

RE

S E T

H OL D

C OMP

UT E

/

A UT

O

RE

S E T

A UT

O

H OL D

MA N

UA L

C OMP

UT E

/

ME 1

V R1

3

ME 2

V R1 4

P 1

P 1 w

A T OM

A 1

A 2

A 3

A 4

A 5

A 6

A 7

A 8

A 9

A 1

0

A DD

I NT E

GRA T E

OF F

S E T N

UL L

OV E RL

OA D

+

P 1

P 2

P 3

P 4

P 5

P 6

P 7

P 8

R UN

P R O GRA M

RE S E T

E P E

HY B RI D

C OMP UT E R

P 2

P 2 w

P 3

P 3 w

P 4

P 4 w

P 5

P 5 w

P 6

P 6 w

P 7

P 7 w

P 8

P 8 w

ME 1

ME 2

+1

5 V

1 5 V

F i g.1 5 .Di m en s i on s an

d d r i l l i n g p o s i t i on s on t h ef r on t p an el .N o t e t h a t t h e a c t u al

p an el s i z em a y v ar y d e

p en d i n g on t h e s o ur c e of t h e c a s e.

3 7 mm

1 6 5 mm

7 3 mm

4 2 0 mm

7

0 mm

2 4 0 mm

F i g.1 6 .

G en er al c a s e

d i m en s i on s

( s e e t ex t ) .



way to the main board. The ATOM i.c.used in the prototype had four small padsat the back of it (these are the ADC pins),which must be connected with four shortwires to the p.c.b. (see photo).

This is a very delicate operation andmust be done with extreme care

as thepads are tiny and very close together. Use avery small soldering iron tip and melt asmall amount of solder onto the wire ends.Then looking through a magnifying glasshold the wire end on the pad and touch thetip of the soldering iron on the wire andpad momentarily to make the connection.

Whilst “carrying the solder” on the ironis not normally recommended, if you do sowith sufficient haste (but with care) thesolder quality should not deterioratesignificantly.

Once complete, use a multimeter tocheck that a solder bridge has not beenmade between the pads.

In the concluding part next month, test-

ing the various aspects of the design isdescribed. Examples are then given illus-trating how the computer can be used tosimulate real-world engineering problems,such as encountered when loading a spring,or demonstrating the take-off and landingof a Harrier jump jet!

VB6 software for this project is avail-

able for free download from the EPE ftpsite, or on CD-ROM (for which a chargeapplies) from the EPE Editorial office,see the EPE PCB Service page fordetails. Software for the ATOM can besupplied on CD-ROM when you buy thismicrocontroller (see this month’sShoptalk page for details) or can bedownloaded from www.basicmicro.com.


15V

15V

a

a

k

k

FROM

S3

FROM

S4

+5V

+15V

+15V

+

GND

GND

SPEAKER

2

3

4

5

DB9

PINS

RESET

SWITCH

L.C.D.

DISPLAY

(PROVISION)

S3

S4

IC22

D1

D2

TR1

TR2 e

e

b

b

c

c

R14

R13

R15

C4

C3

R16

R

17

IC21

NC

NC

NC

TO MAIN PCB

NC

NC

Fig.17. Component layout details for the ATOM microcontroller p.c.b.

Prototype ATOM p.c.b.

C5

Documents

1102- EPE Hybrid Computer - Part 1.pdf