Schematics

Drafting schematics wasn't always my favorite part of creating electronics, but I've actually started really enjoying the process. The following write-up demonstrates how it has evolved for me and where it could be heading.

Workflow

Getting an idea down on paper is important. It doesn't have to start big, it just has to start somewhere. Even the most complicated projects can be broken up into bite size pieces, which is how I typically put them together. The idea is to focus on one aspect of the project at a time, get it working, then move on to the next part. By the end of it, there will be a large, fully functioning product that will be ready for PCB layout.

The following image shows an IC in a specified configuration according its datasheet, with some modifications to suit the my needs. Often times some notes will be written down on the schematic with any pertinent information and a date for reference. The important thing to take away here is that it's simple. There's nothing too complicated to follow along with, just a couple components. This simple schematic can then be built upon to make something more complicated, that completes more tasks. I tend to draft a lot of my schematics by hand, simply because I have a preference for it. I do utilize schematic drafting software, just not as often. I think the most important thing to note is that if hand drawing a schematic is the choice, do it neatly and understandably.

A simple schematic for an optocoupler

I didn't take any special courses for schematic drafting, I've just done so many that I developed a style. I also spent a lot of time researching circuits and looking at professional schematics, which is what I try to emulate when I draft my own. Recently I came across an article that presented clear rules to drafting schematics, written by a professional that goes by "jonk" on StackExchange. I'll sum them up, but if you'd like to see an in depth look at them, check here.

When arranging a schematic, the current should flow from top to bottom.
The overall flow of signal should be left to right - this makes the schematic much easier to read.
Drawing connections to power and ground signals everywhere in the circuit should be avoided.
The schematic should be drafted coherently. It needs to "look right".

When I began drafting my own schematics, I wasn't aware of these rules. I did however notice a theme in all the best looking and professional schematics I had looked at. They appear to follow these rules. This is the type of schematic that I emulated which is why my schematics follow these rules as well. If I am developing a large circuit and it's being drawn by hand, I will use Gimp and turn on grid view to make sure all my lines are neat and straight. Then I draw a single component of each type and copy/paste them into place, rather than drawing them each time. From there I just put together the individual parts of the circuit and find a flow that makes sense, working from top to bottom and left to right.

A schematic demonstrating the hand drawn style, making sure the lines are neat and coherent

I am not opposed to using drafting software for my schematics. I do like how they look when they are completed, I just have a preference for hand drawn. Recently I've been using Eagle for my drafting and PCB design. Honestly it's not the most intuitive software, in my opinion, but it is undeniably powerful. The schematic below was drafted in Eagle and then used to build a PCB in the same software. You can see that the circuit flows from left to right and top to bottom, making sure that only the necessary connections are physically connected to maintain neatness and the overall appearance of the schematic "looks right". It's also important to note that the schematic is documented on the bottom right, displaying the name of the circuit, its revision number, and the date it was created.

A schematic created inside of EAGLE for the motorcycle turn signal project

Recently I stumbled across a circuit simulator that I really like. I've used a couple of free simulators in the past, like LTspice, but I never really liked them. They felt clumsy to me, like the keyboard shortcuts and mouse controls never made sense. They've all been difficult to work with as well. Circuit Simulator at falstad.com has been incredibly easy to use and intuitive. This simulator has made putting together new projects an absolute blast. I will certainly continue to work with this as my primary simulation software. It's also been good for general drafting, but it's not something that will replace my usual drafting software like Eagle. I may still use it as part of my drafting workflow, however.

Below is a video demonstrating the use of the circuit simulator software to draft and test my aquarium temperature controller circuit.

Developing a New Workflow

I'm always looking for ways to improve my process and with my last major project I wanted to try something new. As was stated previously, all of my circuits can be broken up into smaller components. I took advantage of this fact and decided to box out those sections and describe their function with a visual representation of the circuit available, rather than using a separate document to describe how the circuit functions. This may or may not be something that I continue to use in the future, but I do like its simplicity and the fact that I have the schematic to reference while reading about the function.

A new method to describe how the circuit works attached to the schematic

Developing a decent workflow has been key to the success of my projects over the years and I'll continue to find ways to keep improving my workflow.

Next Up: Board Layout

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