Resources on writing design documents for software

I am a mechanical engineer by training and new to this whole software development thing. I have finished the actual design for our software project, but now need to write an actual document for it from my scribblings and such; one that will make sense to everyone and seem professional. Anybody have any idea where I can find resources (preferably free) on the net to guide me in this endeavour?

Does your industry (or, more specifically, the industry that the software is used for) have a computing and/or software association? Design documents come in a wide range of flavors, and it’s generally better to stick close to the development lifecycle documentation of similar products.

This is especially true if you’re designing in a regulated field. For those of us producing code in or near the pharmaceutical industry, for example, I would suggest looking at the sample specs made available on the JETT Consortium web site (scroll down almost to the bottom for a sample software design spec document). However, this would be overkill for a lot of other industries.

See if this helps:

Thanks mucho. The two documents complement each other perfectly - one is a template and the other is a sample. I think both of them should see me home safely.