PCB Design

PCB design is an essential skill to know as an electrical engineer. It enables you to get your circuit ideas down on a physical medium that will stand the test of time. PCB design is however glossed upon in the classroom and these almost never go through the tools you will use. This workshop will assume you know the basics of layout as you would have most likely already learnt things such as the use of supply planes, digital and analog routing as well as integrated circuit decoupling however they will be quickly touched upon. 

The tool we will be using here is EAGLE by Cadsoft. There are other tools on the market such as Altium Designer and their freeware Circuit Maker however EAGLE is arguably more beginner friendly. Do look at the other options as Altium gives you access to their vault which is a massive library which can save you time.  

There will hopefully be a screen recording of the workshop assuming everything works. Look forward to seeing this if you missed out. 

To begin, you must have already created a schematic and have chosen the packages you intend on using. 

Circuit to be built

The schematic to the right is a 555 timer acting as a square wave generator connected to an operational amplifier as an integrator. The output of the op-amp is a triangle wave. 

The parts are:

  • LM555 - DIP-8

  • OPA342 - SOT23-5

  • R1, C1 - SMD 1206

  • R2, R3, C2, C3 - Through Hole 0207

  • Headers

circuit_orig.jpg

We chose these to cover the main components packages you may encounter.

Datasheets

OPA342

SOT23-5

SOT23-5

DIP-8

Device Creations

Device creation involves three steps. 

  • Package >> Getting the physical footprint ready

  • Symbol >> Getting the schematic symbol

  • Device >> Combining the package and symbol

​​If you want a step by step guide for this, there is a great guide from SparkFun. 
https://learn.sparkfun.com/tutorials/designing-pcbs-smd-footprints 

Schematic Drawing

This bit is probably the most important. Errors here will end up coming back to you. Double check, triple check, understand how your schematic works. Schematic drawings are as you'd expect. This is very similar to doing SPICE simulations. Plop the parts on the page and join the pins between parts. The only thing of note is to join things using the NET tool, not the wire tool. The wire tool is really a line tool for drawing things. The net tool connects things together electrically. 

One very convenient thing here is if you were to miss something in the schematic step, and add it in later, it gets updated to the layout file so you just need to place the part. 

Once again, for an in depth look:
https://learn.sparkfun.com/tutorials/using-eagle-schematic

PCB Layout

This is the most important part of PCB design and where a lot of the thought process will be. Some tips here are:

  • Take into account your manufacturer and set the design rule checker

  • Group modules up if possible. This makes it easier to route parts and troubleshoot.

  • Separate digital and analog circuits

  • Use starred ground planes 

  • Decoupling capacitors close to your device

  • No sharp turns

  • and others I have certainly missed. Looked up your electronics notes. 

The step by step: 
https://learn.sparkfun.com/tutorials/using-eagle-board-layout

Useful Resources

elsoc.lbr

elsoc.sch

elsoc.dru

elsoc.cam

elsoc.brd