PCB Design schematic
Before you even begin to lay out your PCB, you MUST have a complete and accurate schematic diagram. Many people jump straight into the PCB design with nothing more than the circuit in their head, or the schematic drawn on loose post-it notes with no pin numbers and no order.
This just isn’t good enough, if you don’t have an accurate schematic then your PCB will most likely end up a mess, and take you twice as long as it should. “Garbage-in, garbage-out” is an often used quote, and it can apply equally well to PCB design. A PCB design is a manufactured version of your schematic, so it is natural for the PCB design to be influenced by the original schematic.
If your schematic is neat, logical and clearly laid out, then it really does make your PCB design job a lot easier. Good practice will have signals flowing from inputs at the left to outputs on the right. With electrically important sections drawn correctly, the way the designer would like them to be laid out on the PCB. Like putting bypass capacitors next to the component they are meant for. Little notes on the schematic that aid in the layout are very useful.
For instance, “this pin requires a guard track to signal ground”, makes it clear to the person laying out the board what precautions must be taken. Even if it is you who designed the circuit and drew the schematic, notes not only remind yourself when it comes to laying out the board, but they are useful for people reviewing the design.
Your schematic really should be drawn with the PCB design in mind.
It is outside the scope of this article to go into details on good schematic design, as it would require a complete article in its own right.