By Cody Shaw | Jul 12, 2013
When designing a circuit board, you will almost certainly use some sort of Electronic Design Automation (EDA) tool. Software programs like Altium and OrCAD can implement design rule checking (DRC), simulation and verification, and allow for seamless transition to PCB layout.
But, there comes a time in every electrical designer’s life when he or she will need to mark up a schematic, analyze a circuit in a notebook, or whip up a quick sketch on a bar napkin. You never know when the ability to hand-draw a schematic will come in handy. While EDA tools have undoubtedly made schematic capture and PCB design much easier, it means that many engineers are now unfamiliar with how to properly draw a schematic by hand.
If you’ve ever looked at a vintage drawing of a LM741 op-amp, or glanced at a CRT TV service manual from 20 years ago, you’ll get an idea of the skill and artistry that goes into a schematic. It’s like a Rembrandt painting, with a healthy dose of science mixed in. Not only can drawing a schematic by hand be really satisfying, drawing it properly will save you time if you need to translate the sketch to an electronic schematic later.
How to draw schematics the Nikola Tesla way:
Go with the flow
Have signals go from left (inputs) to right (outputs), and power run top to bottom on the page. The reader will have a much better intuitive feel for what your design accomplishes. Also, try to avoid using “ports” on paper – it’s best if your schematic is traceable by finger, and very clear.
Consistency is key
Do not draw resistors the Western way (toothed line) and the European way (a rectangle) in the same schematic. Similarly, be consistent with which power or ground symbols you use for a rail.
Dot your Ts
Connect wires at a three-way “T” crossings, and draw a black dot to show that they’re connected. Never use four-way crossings; it’s unclear to schematic reader, and you’ll confuse the electrons. (Kidding.) Also avoid using “humps” to signify a wire not connecting to another; it looks messy, and simply leaving it un-dotted gets the point across just as well.
Sacrifice a tree
Do not cram a circuit into a small space to save paper (or napkins, as the case may be). It’s unlikely that you’ll be drawing really massive or complicated circuits on a piece of paper, so use all the area you need.
Seasoned designers will be able to pick out blocks of a circuit very easily and quickly if you use the classic layout of these designs. If you can identify the structure of an inverting amplifier or an active low-pass filter, for example, you can understand the designer’s intent without having to do any complex circuit analysis. Always draw circuit blocks with a specific function the same way within your design as well.
On top of these points, remember that clarity trumps all. If your schematic would be better understood if you break a rule, then by all means, break the rule! And of course, using a pencil, ruler, and graph paper can help as well. For further reading, The Art of Electronics, by Horowitz & Hill is an excellent resource. Happy drawing!