The Design Process - A High Level View


a) The basic design process is very similar for any product whether it be hardware or software and breaks down into a series of well defined stages as shown in the diagram below. It is also extremely important to separate ‘what is my item going to be/do’ from ‘how is it going to do it’. If you define the ‘what’ part properly, the ‘how’ part follows more easily. Never start with the ‘how’ part.

The worst way to start the process is reaching for the soldering iron / drill / keyboard and saying “I’ll now make something”.

d) You may find that when you have finished a particular step, it is necessary to revisit it or a previous step to make some changes - this is perfectly normal and at the paper design stage is quick and easy to do. At the construction stage it is much more expensive and time consuming so do as much thinking, planning and design as you can at the paper stage. When you have completed this phase go back and check each step. Get a colleague to do a peer review as well.

Each module in the final product should be treated as a ‘black box’ with a functional specification and a defined list of interfaces to other modules - this is more of the “what it does” part. How it does it is another issue entirely and down to the individual module designer. Modules will share some common requirements like temperature, humidity, supply voltage etc.

Other factors in your design are the quantity of the product that that you intend to make, its working environment and its projected life span. High volume brings its own set of requirements, long life span means looking at long term operational life and availability of components for both manufacturing and maintenance spares and difficult environments like high or low temperature, vibration etc directly affect the components and mechanics.

On completion of step 7 for a high volume product you will probably make a small pre-production batch to test the repeatability of the design and the results from this may require that you revisit one or more of the specification and design steps to correct an anomaly (or error!).

Looks easy, sounds obvious? Well, if you do your planning and design properly it is a lot easier than if you don’t! There are a number of different methodologies that you can follow for various types of design task from hardware to software but they are all based on first correctly defining what you are trying to achieve, dividing the whole into a number of cost effective parts and documenting each part.

This is a very high level view of the overall process and does not address the details required in say a receiver or transmitter design. It is intended as a guide to help you to achieve your desired results with the minimum time and costs. Always remember - Keep It Simple because Simple = Lower Cost and Time (and less stress on you). ‘Simple’ also means do not over-complicate it where it is not necessary.


1. Define the product and write the user specification

Treat as a black box – whether it be a garden shed, transceiver, house extension, engine, software program or whatever - this is a specification of what it should be/do.


2. Initial Technical Design

High level view (block diagram etc) of the entire product with appropriate interfaces (including the user interface), estimated costs etc. This is the how it will implement the specification in 1. above.

3. Divide into modules where appropriate

Break down the total functionality into smaller, well defined and cost effective modules

4. Specify each  module

Treat each module as a black box in terms of its interface and define what it should do on its own. Refine costs.

5. Design each module

Designs based on previously defined specifications. Simplify areas of significant complexity / risk.




6. Construct and test each module

When complete, test each module against the specification in step 4

7. Assemble and test the composite product

Progressively connect and test the performance of the modules working together. When complete test the whole against step 1


8. Complete the documentation

Ensure that everything is adequately documented for future maintenance. Update cost totals.

e) Simplify Complex Modules

Commercial production entails making a prototype to establish that the overall design works correctly followed by a small pre-production run to establish any performance variations and required design changes. The majority of home projects are one-offs which increases the risks of this type of error.

Modules/circuit boards may have one or more areas of significant complexity in among much less complex areas. Assess if these complex areas could be constructed as removeable sub-modules/daughter boards so that in the event of a performance problem the entire assembly does not have to be remade.

b) My favourite tools at the start of the design process are a pile of scrap paper, a pencil and eraser - the more time spent in the early stages, the less time will be spent during the prototype build and tests stages when making changes takes longer and costs much more.

c) Why Have a Plan?