Schematic – Just drawing a circuit?

21 Mar

Is there more to it?

Having used a few CAD packages, including DesignSpark PCB, I was curious to look around to see how people work on drawing schematics. I was not interested in the way they draw or the design itself, but was only looking at the importance they attribute to drawing and configuring their schematics.  The general practice seemed to be – draw the circuit, translate to PCB and let’s work out things on the PCB side. I was wondering whether this approach was right.

The schematic is the closest in context to the design and layout provides the necessary connections physically. Whenever, we need to look into the design, our first action would be to refer to the schematic.

The most important aspect of a  PCB layout, perhaps, is the width of the track. Tracks are drawn based on the properties of the Nets specified in the schematic. For example, when we connect two component pins through a net, we can change the width of the track according to the current carrying capacity needed. We do this by clicking on the net and pressing ‘S’. We get to change the width in mils or the units we have chosen.


For VDD and VSS, we may draw tracks with 60 to 80 mils whereas for a I2C signal such as SDA and SCL, we may go below 15 mil too, depending upon the size of the board.

As the schematic gives us a better idea about the current and voltages involved in a particular part in relation to the end design, specifying track widths would help us  to pre-fix the track widths to the appropriate values.

DesignSpark – 18/08/2011




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