Design & Technology
Design in electronics
A well-designed and manufactured product starts with good
planning and documentation including a design brief [design
brief: a set of instructions given to a designer by a client. ] and
specification [specification: a statement that tells the designer
exactly what the product has to do and what the design requirements
are. ]. Circuits are first modelled using a prototype board, before
being assembled into a PCB [PCB: Printed Circuit Board ].
Evaluation and testing needs to be built in at critical control points
[critical control points: the predefined points in a manufacture
system where quality control checks take place. ] such as initial
design, breadboard and PCB phases, and at the manufacturing
stage. And you need to be familiar with the ways that CAD[an
error occurred while processing this directive] is used in the
electronics design process.
The design procedure
A design procedure is a series of steps which guide you through any
electronic design-and-make process. Sticking to the procedure will
help deliver a first-class product.
Following a design process
1.
2.
3.
4.
5.
6.
Choose an area of study
Write down in a few words the purpose of the project
Prepare a desin brief
Write down a specification
Carry out research
Use graphics, computer software and other techniques to
generate design ideas
7. Select the best design for further development
Once you have defined the purpose of your project, there are two
important documents you need to write. These are:
 the design brief - a short statement of the problem to be solved.
The brief should outline the design problem you are tackling,
perhaps including one or two of the envisaged design features.
Next comes

the design specification . This is a longer decument, including
full details of the functional and design features of the finished
electronic product - as well as information on weight and size,
maintenance, cost and safety.
The specification for an electronic product should include electronic
factors such as component details, maximum working voltages,
maximum currents, and temperature or frequency ranges.
Ergonomics and aesthetics
The factors which make a product efficient, safe and comfortable to
use are called ergonomics. Considerations of style - the things which
make a product look and feel good - are called aesthetics. You need
to consider both ergonomic and aesthetic factors when planning your
designs.
When designing circuits, for example, ensure that switches and other
control components are placed so that they can be easily reached,
and that output components such as LEDs can be easily seen.
A product's style is a more subjective matter, as different people may
have different ideas of what looks good. Think about contemporary
style, about what is currently fashionable, when designing your
product. You may not want to follow the fashion - but you still need to
know what it is!
Circuit modelling
Circuits can be modelled to make sure they work the way you want
them to. Circuit modelling can be done either using a computer
modelling application, or on a prototype board - also called a
breadboard or veroboard - a board covered with small sockets into
which components can be plugged and connected up.
The graphic shows a breadboard with holes connected in two long
rows at the top and bottom, and columns of five linked holes
elsewhere. Electronic components and wires can be simply plugged
into the board in order to make any required circuit connections. The
top and bottom rows act as power supply channels for the circuit.
breadboard, showing pattern of holes and connections for prototyping
circuits
A breadboard prototype for a 555 monostable timer circuit might look
like this:
breadboard showing a 555 timer circuit layout
Printed circuit boards (PCBs)
Once it has been established that the circuit functions as intended, the
next step is usually to make a printed circuit board.
PCB showing copper connections running beneath the board
Making a PCB
The first step is to draw the circuit on to a mask. This is a kind of filter
which protects the 'positive' parts of the diagram (the connections
between components) and exposes the 'negative' parts (all the rest).
The mask is then placed on the board which has a thin coating of
copper, and the circuit diagram transferred onto the board using an
etch-resist pen. (An alternative technique uses a photosensitive board
which is covered by the mask and then exposed to light.) The circuit is
then etched onto the board using iron (III) chloride in an etching
tank; this removes all the unwanted copper, leaving the req uired
tracks and pads in place on the board. NB - this should only be
done under a teacher's supervision.
Next, a small PCB drill is used to drill out the center of the pads.
Finally the components are pushed through the board and soldered in
place.
The graphic below shows a mask [mask: a filter or partial covering
which protects some parts of a plate, while allowing the remaining
parts to be exposed to acid or light. ] for a 555 monostable timer
circuit, ready for transferring to a board. Note that masks are normally
shown from the component side - that is, as though the board was
transparent and viewed from the side from which the components are
pushed through.
PCB mask of 555 timer circuit
With the components installed, the board would look like this:
PCB with 555 timer circuit components
Soldering
In electronics the main method of joining circuits is soldering.
Electrical solder is made from an alloy of 65 percent tin and 35
percent lead. It also has a flux running through its core. The flux is
needed to ensure that the solder makes a good joint between the
components and the tracks and wires on the PCB.
Evaluation and testing
Evaluation and testing is about making sure that the product stays on
track with the design specification [specification: a statement that
tells the designer exactly what the product has to do and what the
design requirements are. ]. You should plan to evaluate and test your
project at a number of key stages of design and manufacture. These
stages are referred to as critical control points.
The critical control points for evaluation and testing an electronic
product are:
1. Initial design phase. Check that you have used the correct
value components, and that the various systems work together.
These checks can be done using a computer-simulation
package.
2. Breadboard phase. Use the breadboard [breadboard: a
prototype circuit made from a plastic board with holes in which
the components are inserted, linked by conductor traces on the
underside. Also called a veroboard. ] to check whether the
circuit works properly. Test each part of the circuit using a
multimeter or logic probe.
3. PCB layout. Check that the components are in the correct
positions and that you have used the optimum track layout.
Make sure that components are located neatly and that joints
are well-soldered.
4. Manufacturing and packaging phase. After manufacture,
check that the product conforms to its specification. During
packaging, check that the product fits securely in the package,
and that any conducting parts are insulated.
5. Finally, the analysis phase. Look back over the design and
making process. Analyse how well it went, noting down any
modifications and improvements you would make if you were to
do it again. These notes are an important part of your design
portfolio.
Keep notes!
Make a note of each stage in your design process. If possible,
illustrate your notes with digital photographs and/or graphics. Here are
some of the things you should include in your notes:
 The source of your design ideas and how you adapted these
ideas into the intended product.
 The design specification for the product.
 Your design developments. These should include the circuit
designs with annotated notes, circuit diagrams, any computer
program simulation work, evidence of bread boarding and testing
and the design of your packaging etc.
 The testing procedure and evaluation.
ICT in electronics design
There are many advantages to using computers in electronics design.
They speed up the design process, enabling changes to be made
very quickly. They enable circuits and products to be modelled before
manufacture. And they make it easy and cheap to store and edit
design specifications, and then download them onto machines for
manufacturing.
Computer software specially written to facilitate product design is
called CAD[an error occurred while processing this directive] software.
555 timer circuit diagram produced using CAD software
Several different CAD packages can be used to build up and test
circuits on screen, so that you can try out a circuit before making it, or
design a PCB [PCB: Printed Circuit Board ] or vero-board. Crocodile
Clips, Livewire, and PCB Wizard are three common circuit-modelling
packages.
Designers also use CAD to make accurate 2D and 3D drawings of
circuits and products, and for solid modelling [solid modelling: use of
digital drawings based on geometric shapes, used for solid objects
such as car components. ] to show how products will look when
finished. Different colours and textures can be added to the model
and the product can be rotated to show different views.
Computers are often used to design electronic logic gates for PIC
circuits [PIC circuits: circuits controlled by a PIC (Programmable
Interface Controller) - a device which can be programmed by a
computer to control complex circuits ]. PIC programs are usually built
up from a computerised flow chart [flow chart: a graphic outline of the
sequence of operations needed to complete a task ], and then be
burnt or downloaded onto a PIC chip.
Now try a Test Bite
Back to Revision Bite