10/01/12 Design process – schematics and PCB design
5 simple ways to diagnose your designer
This part of the design process relates to schematics and PCB design. It can be viewed as the core of electronic design. It is ultimately YOUR design and you should feel able to look at and question it. However, this is an area where considerable differences emerge between designers and their audience.
Accessibility
This is the most important aspect of all. Good design is a specialist skill acquired by education and experience over many years. In spite of that, it is practised by “ordinary” people. You should be able to understand any part of the design either through necessity or pure curiosity.
The process of design, even at the core, should be a process that is informative and perhaps educational. Above all it should make sense or follow a logical path that you can follow with ease.
Cranky words
The technical world is full of strange words and acronyms. Some of the these are necessary and a good designer will use these terms but explain them. Wherever possible more commonly used words and descriptions are employed.
Excessive technical terms or proliferations of pompous expression are not useful. The aim of language is to convey meaning and assist understanding. Good designers stay away from sounding technical even if it makes their job sound simple.
Schematic pictures
Schematics are like simplified maps. They show how the elements of a circuit are connected. The symbols used are strange to the casual observer but they are understood as a world wide “common language”. Reading schematics is like trying to read a book in a foreign language – useless unless you know the language.
In spite of their necessary, specialist, approach there are some things you can tell purely from the schematics. They should have structure. This means that you can see or sense a “flow” from the way that it is presented on the page.
Some circuits take up many pages, so there should be a header page that shows how the various pages are linked. Labels on the header page will also give a view as to the core functions of the circuit groups that follow. The header page will have a logical presentation, usually in a left to right flow of data or signal(s).
Whether a single page is the entire circuit or just a subset of it, there should be a visible organisation to the page. The left/right flow will tend to apply. Some circuits are drawn as blocks and there may be several blocks on a page. These blocks should align top and bottom so that visually there are “sentences” of blocks.
A slave like approach is not required, so that the odd exception is permitted where space or visual clarity is a greater priority. A schematic that has no clear separation between blocks and has “sentences” that have no imaginary ruled lines are indications of less considered design.
Once again the presentation of the schematic(s) should be plain and straight forward even if the symbols are alien.
Printed Circuit Board
The Printed Circuit Board (PCB) is very likely to be the single most expensive part of the assembled circuit. More than that, it is a customised process to deliver you a bespoke end solution. Once created and sent for manufacture it cannot be changed. Once deigned on the computer, your designer should be checking with you to ensure that you are happy for the design to proceed to the next step.
Unlike the simplified map of a schematic, the PCB has to operate in the real physical and electrical world. Mounting holes, control locations and other physical constraints may force the circuit ot be laid out in a prescribed manner. In spite of this there should be ordered groups of components. Where there are multiples of similar circuit blocks, they should like similar instances.
Some circuits are too dense to allow the components to have legends beside them. Other circuits are more dense still and appear to have all components “jostled” up tight to one another. Don't be afraid to ask your designer to talk you thought the circuit.
Whether the process you need is visual or a verbal walk through, you should be able to discern the level of care and consideration given. Very dense circuits may not be as simple to view from a component perspective but there is a common trait to all boards. The connecting tracks should display an order and tidiness. The tracks should all meet pads (component connections) and “holes” squarely to their centre.
The over riding visual appearance of a well designed board is that the track (copper) layers should appear to be “obvious” and not at all complicated. If it looks simple when viewed as a whole, then the chances are a great board is before you.
| Bad Design | Good Design | |
|
1. Language |
Technical/baffling |
Straight forward, terms explained |
|
2. Approach |
Superior |
Educational or “down to earth” |
|
3. Schematics |
Unwieldy, hard to follow any sense |
Organised, neat, sense of flow |
|
4. PCB |
A web of intrigue and chaos |
Ordered and apparently simple |
|
5. In charge |
The designer |
You |
Posted by: Peter Hawkins on 10/01/12.