Electronic Prototype Construction Techniques

8/18/2019 Electronic Prototype Construction Techniques

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Electronic Prototype Construction

Techniques

Peter D. Hiscocks

Department of Electrical and Computer Engineering

Ryerson Polytechnic University

[email protected]

Version 1.2

February 24, 2002

Contents

1 Introduction 2

1.1 The Printed Circuit Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Low-Cost Printed Circuit Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3 Commercial Manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4 Toner Transfer Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5 Prototype Milling Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 Alternatives to the Printed Circuit Board 92.1 Veroboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2 The Protoboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.3 Haywire Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.4 The Dremel Tool Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.5 Radio Frequency Boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.6 Wire-Wrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.7 Vectorboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.8 Terminal Strip Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3 Acknowledgements 21

Bibliography and References 22

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1 Introduction

It is a common situation that an electronic circuit is needed for a student project, to demonstrate a concept, to

validate a simulation or for one specific application. The first part of this paper shows how a printed circuit may

be designed and constructed at relatively low cost.For reasons of time or cost, a full-blown printed circuit board may not be practical or necessary. The second

part of the paper describes different methods of constructing a one-off or prototype electronic circuit withoutconstructing a printed circuit board.

These techniques are well known among the amateur radio and hobbiest community. This paper brings the

ideas together for students in Electrical Engineering.

Several people contributed useful suggestions on publication of the first version of this paper, which havenow been incorporated (see section 3). Thanks, folks. If you have a suggestion or construction technique that is

not mentioned here, you are welcome to send it to me at the email address given above and I’ll consider it forinclusion and credit.

1.1 The Printed Circuit Board

When we think of constructing electronic circuits, we often think of a professional printed circuit board. Anexample is shown in figure 1. Stuffing components into a commercially made circuit board is easy, and the

result looks very professional. However, the design and manufacture of a full-blown printed circuit is a majorundertaking. A double sided board includes the following elements:

top copper traces

bottom copper traces

plated through holes, that connect the top and bottom traces

solder mask, that helps prevent solder bridges between traces

silkscreen, showing component designations and other notes such as the copyright symbol

Using modern methods, the production of a commercial printed circuit board involves a number of steps:

1. Draw the circuit schematic using a schematic editor program. It may be necessary to create some schematicsymbols for the program.

2. Transfer the schematic netlist to a board layout program. It may be necessary to create some packageoutlines for the program.

3. Determine the size and shape of the circuit board.

4. Place the components on the board.

5. Route the circuit board traces, using an autorouter .

6. Add circuit board silkstreen notes.

7. Carefully check that all the holes are in the correct position and the correct size, so that the components fit

properly.

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Figure 1: Professional Quality Circuit Board

8. Generate the gerber files. These describe the board for the manufacturer.

9. Ship the gerbers to the manufacture, cross your fingers, and hope.

Each of these steps takes significant time and require several iterations.

1.2 Low-Cost Printed Circuit Board Layout

It is usually worthwhile to expend some effort on designing the layout of a circuit board, whether or not it will be

used to produce a printed circuit board. Simple boards can be laid out by hand using a computer drawing program,

but the process of designing a complex printed circuit board absolutely requires access to computer-based circuitlayout tools. Full-blown schematic layout and PCB design programs are expensive. For example, the rip-up-and-

retry autorouter in the system I use cost $600CDN. However, there are some limited student-editions that are freeor inexpensive but still useful.

For example, the EAGLE Light Edition from CadSoft Computer GmbH

(http://www.cadsoftusa.com/freeware.htm ) runs under Linux and Windows operating systems and

provides the following features in its downloadable version, which is free to non-profit users or for evaluation1.

1I have no direct experience with the Eagle software - I use a different commercial package - but a number of fourth year EE students at

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Useable board area limited to

mm (

inches).

Two layers maximum

Schematic editor is limited to one sheet

Limited versions of printed circuit layout programs are also available from Ivex Design International, Inc

(http://www.ivex.com/) and Holophase Corp. (http://www.holophase.com).Once you have the board laid out, there are several possible ways to use the circuit-board design:

The gerber file can be emailed to a shop that specialises in quick-turnaround prototype boards. Several of

these companies advertise in Circuit Cellar Magazine (www.circuitcellar.com). (See section 1.3.)

A printed copy may be used in the toner-transfer method. (See section 1.4.)

If you have access to a PCB milling machine, the gerber file output can be used to mill a printed circuit

board. (See section 1.5.)

If you are planning to hand-wire the prototype, the PCB design can be printed at 100% (full scale) and thenglued to the circuit board as a guide for construction. If you are making a double-sided board, print out one

side as is and the other side as a mirror image. Glue them to the top and bottom of the circuit board material

and use them as a guide for constructing the board. This speeds up the process of construction considerablyfrom just ’winging it’. It also provides component annotations that are useful in troubleshooting the board

later. And if it’s a prototype, you can count on some troubleshooting. (See sections 2.1 and 2.7.)

1.3 Commercial Manufacture

Typically a commercial PC board manufacturer will charge about $800CDN for the setup and production of theirminimum quantity, which might be ten boards. However, there are companies such as A.P.Circuits

(http://www.apcircuits.com) that specialize in prototype printed circuits boards. As Howard Franklinwrites:

For AP circuits I use the P1 service which does not have silk screening or solder mask. But, for 2 4in

x 5in boards with their standard drill sizes the cost is $ 105 Cdn excluding tax and delivery. This does

include plated through holes. I sometimes edit the drill file manually to use the free drill sizes. For most work adding a few thousands of an inch doesn’t matter much. The technicians there are quite

good finding an error the pcb package automatic rule checkers missed.

Since a prototype will inevitably have some mistakes, you will have to cut and jumper traces on these boards.

The second run will more likely be mistake free. However, the manufacturer will have a new setup charge, since

the boards will have changed.

1.4 Toner Transfer Method

The toner transfer method provides a simple method of making a printed circuit board from an existing drawing.

Basically, it provides a method of transferring a toner pattern (from a copier or laser printer) to a copper clad

circuit board, where it can act as a resist for the etching process.

Assuming that a single-sided board is being made (the usual case with this method) the process is this:

Ryerson University have used it successfully.

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1. Obtain a size as, (100% scale) copy of the printed circuit board layout. This could be the printed output

from a PCB design program (section see 1.2 above), or it could be the layout that appears in a magazinearticle.

2. Generate the mirror image of the layout.

3. Using a copier, copy a mirror image of the layout onto a special transfer film or, using a laser printer, print

a mirror image of the layout, at 100% scale, onto the special transfer film.

4. Prepare the copper board by carefully cleaning it with steel wool. Use special care to ensure that there is no

grease on the board.

5. Use an ordinary clothes iron to transfer the image from the film onto the copper. The heat setting for the ironis critical and depends to some extent on the toner composition, so some experimenting may be required.

6. Remove the background film. Depending on the type of film, you may have to dissolve or peel it away.

7. At this point, the wiring side of the board should look like the top image in figure 2.

8. Etch the board using ferric chloride or some other echant.

9. When the board is eched, remove the resist using steel wool.10. Tin the board by immersing it in plating solution. This prevents corrosion of the copper tracks and makes it

easier to solder to them.

11. Drill the component holes and mount the components.

The results achievable2 with this process are shown in figure 2. The middle image shows the component side

of the assembled board. The bottom image is the wiring side of the same board. Notice that some traces snakebetween the pins of the integrated circuit, an indication of the capabilities of this method.

Two sources for the transfer film are:

http://www.techniks.com/press-n-peel.html

http://www.dynaart.com/E.DTF/E.DTF1.html

As evident from the photographs of figure 2, an excellent result is possible from this method. There is no

reason why the method could not be extended to a double-sided board, providing both copper patterns could beregistered so that they line up correctly. For most student boards, however, it’s simpler to stick to a single sided

board and put in a few jumpers.

It should also be expected that some experimenting will be required before the proceedure is completelydebugged. Be prepared to throw away a few attempts before a satisfactory board is produced.

2Boards designed and constructed by Peter Kozlowski

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Figure 2: Toner Transfer Application

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1.5 Prototype Milling Machine

Rather than ship the gerber plots to a manufacturer and pay the setup and production charges for a printed circuit

board, it is possible to produce the board on a PC Board Milling Machine. Organizations that do significant

printed circuit board development may be able to justify the $20K price of the machine, in which case they can

generate prototypes very conveniently and quickly.

The milling machine is essentially a very precise X-Y plotter with a cutting tool where the pen would normallyreside. The machine cuts tiny slots into bare PCB stock in order to outline each trace. It also drills the necessaryholes in the board and cuts the board out of the copper stock. A double sided board can be produced on the

machine by milling one side after the other.

An example board produced by this process is shown in figure 3. The top photograph is a mobile robot

prototype, viewed from the component side. The bottom photograph is a closup of the wiring side. Each little

blob is a via that consists of a short length of #30AWG solid wire, soldered to the top and bottom traces. Most of

the copper remains on the board (in contrast to a commercial PC Board). the only copper that is removed is fromthe outline around each trace.

The milling machine has its application niche, and has made it possible for an organization like RyersonUniversity to do quick turnaround development of printed circuit board prototypes. However, there are some

limitations:

The cost is beyond the reach of an individual, so the machine has to be available through an organization.

There are significant operating costs: the milling bits have a very limited life, especially if large areas of

copper need to be removed.

Operation of the machine requires some skill to produce reliable boards. For example, the PC board stock must not be warped or the traces will have short circuits between them.

The prototype board does not have such amenities as plated through holes, solder mask, or silkscreen

markings. Hand wiring the plated through holes is tedious and must be done very carefully not to createshort circuits3.

It’s not unusual to inadvertently create a short circuit between traces or a trace and ground. Finding and

fixing these can be very time consuming.

In spite of these limitations, a milled prototype is useful in many prototyping situations. It is excellent for

generating radio-frequency prototypes where circuit elements such as inductors and stripline resonators must befabricated in the printed circuit board copper. It’s feasible to do small production runs if the board can be kept

to one layer. It’s often very useful to have a prototype that is essentially the same size and shape as the final PC

board version.

One very useful application of the milling machine is in producing adaptor carriers for surface mount compo-

nent integrated circuits. Many surface mount integrated circuits are difficult to wire to because of the tiny size of

the package and pins. The adaptor carrier is a small circuit board that has a connection pattern that matches theintegrated circuit and brings the connection points out to a 0.1 inch grid that can be wired into a protoboard or

other circuit.

It should be kept in mind that any printed circuit board produced on a milling machine must be designed using

all the steps discussed in the previous section. For a student project this can be a time-consuming distraction from

the main objective, which is to get a working circuit.

3I once wired a prototype with over 300 plated through holes. It took several days to accomplish and I’ll never do it again. The board hadone intermittent that took some 7 hours to find.

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Figure 3: Milled PC Board Prototype

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2 Alternatives to the Printed Circuit Board

The process of designing and constructing a printed circuit board is justifiable when the circuit is going to be

produced in large numbers or there are compelling engineering reasons why a printed circuit board is necessary.

However in many situations, especially in the student project environment, a printed circuit is overkill.In the quest to produce a professional looking circuit board, it is common for a student electrical engineer to

become sidetracked from the main objective of a circuit design project, which is to get the thing designed andworking.

The remainder of this paper shows some alternatives to the commercial-process printed circuit board.

2.1 Veroboard

I was introduced to Veroboard while in high school, back in the 60’s, so Veroboard has been around for a while.

Veroboard is a product out of the UK and is excellent for constructing discrete component circuits such as the

audio amplifier shown in figure 4. As you can see, the result is a professional looking circuit. Veroboard is widely

known and used in the UK, but almost unknown in North America for some reason.Veroboard is phenolic board, punched on 100 mil (0.1 inch) centres, bare on the top and with copper strips

on the bottom. To construct the electronic circuit, you lay out the components in a north-south direction. Thetraces run in an east-west and are broken as part of the construction process in order to isolate the various circuit

connections.Vero have a special tool for breaking traces, but I’ve long since lost mine. A 3/8” drill bit works just fine. Push

it up against a trace and twist, and the trace is broken. In the wiring side view of figure 4 the traces are running

north-south, and you can see where they have been broken. In the component side view of figure 4 you can see

the jumpers on the component side of the board that connect traces on the wiring side.An example of a schematic and its corresponding Veroboard layout, is shown in figure 5. The horizontal traces

are the Veroboard copper strips on the wiring side of the board. The vertical traces are jumpers that are used toconnect the various traces.

Another Veroboard example is shown in figure 6. After cooking an expensive microprocessor, I installed this

device between the outside world and the microprocessor to limit the voltage on each microprocessor line with aseries resistor and clamping diodes.

Veroboard is surprizingly rugged. Components can be soldered and unsoldered a couple of times before the

copper traces lift. I’ve even seen it used in small production runs.

Veroboard is not well suited for complex digital circuits. It’s main area of application is analog circuitry.I find it useful to use the xfig drawing program to plan out a Veroboard layout before constructing it. When

the layout is completed, I print it at 100% scale and glue it to the component side of the board. This then acts as a

guide in constructing and troubleshooting the circuit4.

Veroboard may be becoming obsolescent, probably because readily available computer-based layout toolshave made it easy to do printed circuit board layouts. The local distributor - Electronic Packaging in Kingston

Ontario - have indicated that only a limited selection is available. Howard Franklin tells me that a ’veroboard

clone’ is available from Sayal Electronics here in Toronto.

4It would be useful in these days of computer circuit board layout programs, to have a program that would automatically translate a

schematic into a Veroboard layout. As far as I’m aware, such a program does not exist. Alternatively, an existing commercial PCB layoutprogram might be set up in such a way as to generate a veroboard layout.

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Figure 4: Veroboard Audio Amplifier, Component and Wiring Sides

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+

- R2 5k1

+

-

+

-

+

-

D2

1N4001


Revision: 0.1

Motor Speed Controller

Peter Hiscocks, October 30, 1997

File: motcon2.fig

Print at 70%

1

U1

B C E

Q1

R2

25k 21

3

D11N4148

Speed

5k1R3

R4

5k1

9

10

8

5k1R5 R6

C1100n

12

1314

R7

3k9

R8

1k0

5

67

11

4Q1

TIP120

C2

16u, 10V

R175k

Supply

5VDC

Motor

0.2 ohm

800mA, 1 ohmR9

NOTES:

Q1 may be any NPN type TIP series Darlington transistor.

Q1 must be on a heat sink, area 3 inches squared

Op amps are from Quad Op Amp, LM324N or LM324AN (DIP package).Recalculate resistor values to suit other components.

For D1, any small signal silicon diode may be substituted

For D2, any 1N4000 series diode or 1 amp diode may be substituted.

10k

U1AU1C

U1B

U1D

R9 is 5, 1 ohm resistors in parallel

R 4

R 6

R 5 R

9 A

R 9 B

R 9 C

R 9 D

R 9 E

R 7

R 2

D 6

R 8

D 1

R 3

R 4

R 6

R 5 R

9 A

R 9 B

R 9 C

R 9 D

R 9 E

R 7

R 2

D 6

R 8

D 1

R 3

R 1

C 2

R 1

C 2


Revision: 0.1

Motor Speed Controller, Vero Layout

Print at 80% for full scale print

File: motcon-layout.fig

Peter Hiscocks, Oct 30, 1997Motor-Motor+

Pot WiperPot Gnd

Pot Supply

VccGnd

Motor-Motor+

Pot WiperPot Gnd

Pot Supply

VccGnd

U1

C1

Q1

2.9"

1.6"

U1

C1

Q1

Figure 5: Example Schematic

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Figure 6: Cable Adaptor, Component and Wiring Sides

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2.2 The Protoboard

If you’ve done any work in electronics, you’ve probably used a prototyping board. A small protoboard circuit is

shown in figure 7.

The board consists of a number of groups of holes. In the centre of the board, you can see that there are

groups of 5 holes running vertically. Each of these has a connection strip below the plastic, so that anything lead

plugged into one group of five holes is connected to another lead in the same group. There are also larger groupsof holes that run along the top of the board. These can be used as power supply busses. Connections are madewith jumpers of #22AWG solid wire.

The prototype board is a wonderful invention. It allows one to throw together a circuit in minutes. Experi-

menting is easy, and requires very few tools. (A pair of needle-nosed pliers for pushing leads into the sockets, and

a pair of side-cutters for trimming component leads, are both handy.) One nice aspect of the protoboard is that it

can be set up to mimic the layout of a schematic, with a positive power bus at the top, ground in the middle and a

negative power bus at the bottom5

Figure 7: Protoboard

For low frequency work, the protoboard is an essential tool. However, it does have some limitations in critical

applications. Where large gains or high frequencies are involved, the protoboard does not provide very predictablegrounding paths, and this may lead to noise pickup and oscillation. There is a small capacitance between each of

the connector rows, and this can upset some high frequency circuits. The current capacity of a protoboard is very

limited – I wouldn’t use it for anything much more than 500mA. If you force large diameter leads into the holes,the contacts are bent back so they don’t make reliable contact, and this can be difficult to troubleshoot.

For a student project, the protoboard is a good place to start. But for a circuit that has to be reliable (when

5Always, always decouple the power busses to the ground bus with 100nF capacitors. Larger capacitors, such as 10 F electrolytic, are

also a good idea.

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carried around in a student knapsack), some other method of construction should be used. A useful strategy is to

debug certain parts of a circuit on a protoboard, and then migrate that circuit to some other construction technique.

2.3 Haywire Technique

This technique uses bare copper printed circuit board as a platform for the rest of the circuit. The printed circuit

board functions as a low impedance ground plane for the circuit. Components are soldered to the ground plane orto each other. Integrated circuits are mounted dead bug style onto the copper and components soldered directly to

the IC pins. An example of a haywire circuit is shown in figure 8.

Figure 8: Haywire Circuit 1

If you look carefully, you can see where component wires are soldered directly to the ground plane, and the

integrated circuits mounted pins-up. The circuit is an experimental variable-gain preamplifier for an oscilloscope,

where high frequency behaviour is important. The protoboard version of this circuit functioned after a fashion,

but it was necessary to build this prototype to get it to operate up to its specification (4MHz). The three toggleswitches select one of 8 gain settings.

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A second example is shown in figure 9. In this circuit, the board has been divided into three strips, one

Figure 9: Haywire Circuit 2

each for the positive power, ground, and negative power. Notice the decoupling capacitors at the left end of the

circuit, where power enters the board. The twisted wires in the forground are a gimmick capacitor – an adjustable

capacitor of a few picofarads.

Of course, modifications to the circuit require use of a soldering iron. The haywired circuit is more reliablethan a protoboard circuit. You don’t have to worry about flaky connections when leads are soldered. The haywired

circuit has fewer problems due to stray capacitance and the large ground plane area minimises problems due to

indictive or resistive voltage gradients.

2.4 The Dremel Tool Method

When a circuit is not too complicated (ie, can be laid out with a single copper layer) and includes some large,

odd-sized components, the milled circuit technique shown in figure 10 is useful.

In the traditional method of laying out a circuit board, the traces are usually fine lines. But when you think

about it, the large empty space between traces is not necessary – the copper could be increased and the spacedecreased, providing everything can be made to fit. Then each wire in the circuit becomes an area on the circuit

board, and the areas are separated from each other by thin gaps. Putting it technically, each wiring node on the

schematic is allocated an area on the printed circuit board.

This leads to some advantages in circuit board construction.

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Figure 10: Milled Circuit: Dremel Tool Method

The areas can be separated from each other by hand, using a Dremel tool with a milling bit to cut a gap that

isolates each circuit area in the copper.

Each copper conductor is now a large area, so it can safely carry a heavy current.

The board can take a fair amount of abuse with a soldering iron and is the copper is still unlikely to lift(unlike boards with delicate traces), since there is a large area holding it to the substrate.

Each area represents a relatively large target, so component holes can be drilled without worrying too much

about alignment.

The circuit shown in figure 10 is an SCR light dimmer circuit that was built by theatre technology students.This particular technique was appropriate because the students could each mill out their own board by hand, the

board could take some inexpert soldering without being damaged, and it could handle line current of several

amperes.

The position of the milling lines were transferred to the copper layer using carbon paper and then milled out by

hand. Another template, showing drill sizes and positions, was glued to the component side and used as a drilling

guide. The same Dremel tool that was used for milling out the traces can now be used to drill the componentholes.

Notice in figure 10 how the mounting hole areas in the four corners are isolated from the rest of the circuit.

The circuit gaps are plainly visible from the component side of the board, which aids troubleshooting.

It’s important when milling the board that all the circuit areas are completely isolated from each other. It’s

easy to overlook a copper whisker connecting two areas. After milling is complete, it’s a good idea to check forany short circuits with an ohmmeter or continuity checker.

Depending on the size of the copper area, soldering to this type of board may require significant heat. A large

copper area may take some time to come up to temperature. So the board should be carefully cleaned beforesoldering, and solder joints should be carefully inspected after soldering.

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2.5 Radio Frequency Boards

A related technique for board construction is shown in figure 11.

Figure 11: Radio Frequency Circuits

These are two radio frequency circuits, a 50MHz amplifier on the left, and a section filter on the right. In

both these boards, areas have been milled out using a Dremel tool and then components soldered to the copper

areas. The amplifier board was divided up into squares and the copper squares used as terminal points for the

components. This way, the circuit can be modified and components added without having to change the circuit

board.Notice the copper board shield that is soldered to several areas on the main board, often necessary to isolate

output from input in an RF circuit. (At radio frequencies, stray capacitance between output and input can turn anamplifier into an oscillator.) Component lead lengths can be kept short. The material used is double-sided board

stock. One side is used for attaching components, the other as a ground plane. Where necessary, holes in the

board can bring traces from the top side to the ground plane.

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2.6 Wire-Wrap

Wire-wrap is a the technique traditionally used for a complex digital prototypes. It supports an extremely high

wiring density, so lots of circuitry can be packed into a small board. In these days of accurate, powerful digital

simulations, the wire-wrapped prototype is not as common as it used to be. After a successful simulation it usual

to migrate the design to a printed circuit board without a wire-wrap prototype. However, wire-wrap is still useful

where there are many IC’s to be interconnected and a printed circuit board is overkill.Views of a wire-wrap board are shown in figure 12. The first part of the figure shows a component view of the

Figure 12: Wire Wrap Board

board, together with the wire used, #30AWG, and a wire-wrap tool, an unwrap tool, and needle-nosed tweezers –

a useful accessory. The second part is a closeup of the wire-wrap pins and wiring.Each integrated circuit sits in a wire wrap socket. The wire-wrap socket has square pins of about a centimeter

in length, which project into the wiring side of the board.

Connections are made with #30AWG solid wire. The end of the wire is stripped for about 1.5cm and then fed

into an offset hole in the end of the wire-wrap tool. The center hole of the wire-wrap tool is then placed over apin and twisted. This results in a spiral wrap of 7 or 8 turns of the wire around the pin. The square corners of the

pin cut into the wire, ensuring a gas tight connection that will not degrade with time. Wire-wrap was originallyinvented to be used in the telephone system, so it is known to be reliable.

If discrete components need to be mounted on the same board, T44 pins (see section 2.7 below) can be

pushed into the board so that the component is soldered to the top and wire-wrapped to the bottom. Alternatively,

components can be soldered to an IC carrier - a small platform with pins that fit into an IC socket. The carrier is

then plugged into an IC socket and connections wire-wrapped to the pins of that socket.

It’s easy to get lost in the forest of pins and wires of a wire-wrapboard, and mix up IC numbers or pin numbers.

It’s possible to get little plastic labels to go on each IC, but these are expensive. A better alternative is to design

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the layout on a computer, showing the integrated circuit numbers and pin numbers. Print it out at 100% scale,

glue it to the wiring side of the board, and poke the sockets through the board and paper. This kind of roadmapwill be very welcome when trying to find a particular signal to probe.

2.7 Vectorboard

The Vector company produces a number of diffirent circuit boards that are useful in the construction of electronicprototypes. In this section, we’ll look at an application of their bare perforated board. The component and wiring

sides of an example are shown in figure 13.

Figure 13: Vectorboard Application

This board is typical of many electronic circuits. It contains a single chip microprocessor, analogue signal

conditioning circuits and a variety of external connections.

Integrated circuit wire-wrap sockets are fastened to the circuit board using hot-gun glue6. The component

leads themselves cannot be used for wire-wrapping, because they are round in cross-section. If you do wrap to

a round cross section wire, it will probably work for a while and then fail when oxide forms on the wire and

component lead. If you do wire-wrap on a circular cross-sectional lead, you should solder the connection to make

it reliable.

6Don’t use cyanoacrylate (aka Crazy-Glue, Super-Glue), because it tends to wick up into the IC socket and make the socket unuseable.

Guess how I discovered this .. .

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A special Vector pin, the type T44, is used to mount discrete components. The square cross section tail of the

T44 pin cuts through oxide on the wire wrap wire and makes a reliable connection. The T44 pin has a fork at thecomponent end, a shoulder that fits snugly into a Vectorboard hole, and a long tail that is used for wire-wrapping.

The fork section of each T44 pin holds one end of a component such as a resistor or capacitor. The component

leads can be bent to solder to adjacent pins and component leads.

The overall result is a respectable looking circuit, at least when viewed from the component side.

2.8 Terminal Strip Construction

The terminal strips shown in figure 14 are useful in a variety of circuit constructions. A wide variety, at very low

cost, are available from Cinch-Jones7.

Figure 14: Terminal Strips and Application

Figure 14 also shows two circuit board constructions that use terminal strips. The left-most circuit is a jig for

measuring inductance. The wiring is supported by the terminals of four binding posts and a BNC connector, plus

a 5-way terminal strip.

The right-most circuit is the remnants of a power supply zener regulator and capacitor filter.Terminal strip construction is especially effective when there are only a few components to be mounted. Often,

the components can be completely mounted on one terminal strip or between two terminal strips. As in all circuitconstruction, a little planning pays off in a neat result.

7I was unable to find a WEB reference to these devices. There is, however, a picture in the Electrosonic Catalogue, reference [9], page

484.

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3 Acknowledgements

Special thanks to Jim Koch, who brought my attention to student versions of the printed circuit board layout

programs. Peter Kozlowski showed me the very important toner-transfer method of making printed circuit boards

and provided examples for the photographs. Howard Franklin provided useful information on the construction of PC boards.

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References

[1] Prototyping techniques help verify analog-circuit performance

Walt Kester

EDN Design Feature, Feb 15, 1996Makes the point that prototyping is essential to verify the predictions of simulations and describes prototyp-

ing techniques for high speed op-amps.

[2] The ARRL Handbook

American Radio Relay League

Published annually, always contains one chapter on construction techniques. Reasonable price, a must-have.

[3] High Speed Amplifier Techniques

A Designer’s Companion for Wideband Circuitry

Jim Williams

Linear Technology Application Note 47

1993 Linear Applications Handbook, Volume II, pp 47-1 to 47-132

Linear Technology CorporationAn invaluable reference on high frequency amplifier wiring techniques, theory and practice.

[4] Layout and probing techniques ensure low-noise performanceJim WilliamsEDN Magazine

(issue unknown)

Construction and probing techniques for switching power supplies.

[5] Handcrafting Design IdeasJeff Bachiochi

Issue #70, May 1996, Circuit Cellar INK, pp 62-67

Covers much the same ground as this paper.

[6] A Surface-Mount Technology Primer – Part 2Bryan P. Bergeron

QST Magazine, January 1991, pp 27-30The use and soldering of surface mount passive components.

[7] Prototyping with smds (Surface Mount Devices)

Nick Wheeler

Electronics World, January 1998, pp67-69

Prototyping with fine-pitch surface mount integrated circuits.

[8] Analog Breadboarding

James M. Bryant

Chapter 9, The Art and Science of Analog Circuit Design

Jim Williams, Editor

Butterworth Heinemann, 1995

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[9] Electrosonic Catalogue 991

Electrosonic Supply1100 Gordon Baker Road, Toronto, M2H 3B3

416-494-1555

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Documents

Electronic Prototype Construction Techniques