The Schematic Diagram: A Basic Element of Circuit Design

by kyaps Barnabas

There seems to be a limitless amount of information that can be learned in the field of electrical engineering. One of the most essential skills for an electrical engineer is the ability to read and create schematics. Before you start learning Ohm’s law, superposition theorem, and delta-wye transforms, you need a basic understanding of how to read (and draw) a circuit schematic.

I like the definition of schematic in Wikipedia: “A schematic, or schematic diagram, is a representation of the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the information the schematic is intended to convey, and may add unrealistic elements that aid comprehension … In an electronic circuit diagram, the layout of the symbols may not resemble the layout in the circuit.”

When creating a schematic, it’s important to make sure you’re illustrating your circuit with the proper level of abstraction. If you’re just trying to convey a high level concept, a napkin schematic might do the trick. If you need to create a schematic for a simulation, then the devil is in the details—you’ll need to be clear about power supplies, signal sources, component values, etc. Or, if you want to create a schematic for a published paper, you’ll need something polished, with the appropriate trade-off between detail and abstraction.

Schematics for Illustration

I’ve created schematics for a variety of reasons, and the tools I use depend on the type of schematics I’m drawing. If I’m drawing something for a report, article, or blog post, my focus is more on a presentation with a clean, professional look that doesn’t necessarily include details required to simulate or build the circuit. One tool that I’ve had some success with is Digi-Key’s Scheme-It. Since it’s an EE-centric schematic tool, it’s pretty quick and easy to pull together circuit diagrams. It’s easy for me to add or omit labels for components, and find symbols that convey the appropriate level of detail for my diagram. For example, when searching for capacitors, I was able to find 19 different symbols.

Schematics for Simulation

For simulation of electrical circuits, you’ll need a tool that you can create a schematic with that will also have an associated netlist. For example, the netlist files that SPICE simulators use will often contain information about the diagram, as well as modeling and simulation information. Generally, you will have to get a little deeper into the specifics of the circuit in order to successfully simulate it. Instead of using a generic op amp symbol, you’ll now need to specify some of the finer details: What voltages will you provide to the supply pins? Which specific op amp do you want to run your simulation with? What is the output of your circuit going to be connected to (in order to observe the effect of loading in your design)?