Schematic

Notebook section:	Hardware technical documents
Purpose:	Diagram all components in your system and show how they are connected together.

Applicability

Schematic documentation is needed for significant electrical/electronic portions of the design. Quality expectations may be adjusted based on the disciplines of engineering students in the team. For example, teams with EE students will be expected to provide higher quality schematics than teams with only ME students. Please contact the instructors for help in determining individual expectations.

Your schematic will describe the electrical connections between all of the components in your system. A complete schematic will show all needed components, and all connections between them.

Tools

You may use any schematic tool you wish. Use the same tool that you will use to layout your PCB if possible. PCB Artist is one such tool; others may work as well.

Appearance

It is very important that your schematic be readable. Please design your layout carefully so that the connections will be readable. Here are three examples to look at:

SDR
Valve Unit
Base Unit

The examples are good models to use. Use busses whenever appropriate (i.e. the Address and Data busses for a microcontroller). Make sure to label the signal names on all nets coming from a bus. You may use more than one sheet if needed for clarity.

Important Notes

	All digital components will require local bypass capacitors to smooth out power spikes. To compute the size of the local bypass cap, use this formula: C = I/[delta(V)/delta(T)], where I is the current used by the component, delta(V) is the maximum voltage deviation allowed for the chip, and delta(T) is the switching time of components in the chip. For example, if a 5V part uses 100mA, can tolerate a voltage drop down to 4.5V, and has a switching time of 5ns, then C = 100mA/(0.5V / 5ns) = 1nF. It is ok to pick values "close by", such as 4.7nF. However, make sure the caps are low ESR. When you try to place bypass caps on your schematic, you'll notice that most symbols don't have power and ground leads. You can just use the VCC and GND symbols from the library to connect your bypass capacitors. They may appear anywhere on your schematic. Please see the schematics for ideas.
	If you have unused inputs on any parts, connect them to power or ground as appropriate. Don't leave them floating.
	If you build custom symbols for new parts, make sure to include all pins, not just the ones you are using.
	If you build custom symbols, label each pin with its name. See examples.
	Include the name of each subnet coming out of a bus. See examples.
	Use connect-by-name for long connections that would be ugly if drawn out.
	Include a fuse in your power supply design. See examples.
	For testing purposes, all of your power supplies must be "isolatable" on both the input and output sides. Make sure to include jumpers or zero-ohm resistors so you can disconnect them from their inputs and outputs for testing.

Kevin Bolding October 27, 2011