On 10:53 PM 12/3/2001 +0100, Christoph Brudy wrote:
>can somebody recommend a way to handle components that I want to appear
>in the schematic, but are not mounted on the PCB (e.g. switches, lamps,
>fuses ...).

For moderately complex system designs, I have generally created at least one separate 
"interconnect" schematic, in which the assembly's (or subassembly's) off-board 
components are accurately represented and connected to the board-level "devices", 
which are in turn represented by *rectangles (sheet symbols) containing accurate 
representations of the off-board connection headers, solder-pads, etc., as well as 
either representational or text-based functional description(s) of the PCB(s) 
involved. Offboard wiring is almost always color-coded for additional understanding 
(troubleshooting, fabrication, etc.) FWIW, I also generally include wire-gauges and 
expected current loads to the wiring description by "improper" use of netlist 
designators...(It makes it easy to "fix" the text to a given wire or cable, even if it 
causes PCB-designers to shudder...)

The above allows for a relatively complete understanding of the design by both the 
casual and technicaL "reader".

An added advantage to this technique is that one can link the sub-circuit 
representations to the actual PCB-based electrical schematics for more thorough 
analysis of the subcircuitry by those 
readers capable of said analysis. (Though they have almost always wanted more than a 
simple picture of the buttons they must push and knobs they will twirl, most of my 
historic customer-base has had limited ability to absorb much detail beyond a 
comprehensive interconnect schematic, as their technical expertise lay outside the 
realm of electronic design, ie, fluids, combustion, and materials science, as well as 
mechanical and process engineers and associated scientific management personnel, all 
of whom are generally anything but dullards, (there have been notable 
exceptions...;)...) but who are often not really up to breezing through detailed 
electronics schematics without extended effort...) Anyway, this allows for "hiding" 
system complexity from those who would otherwise be daunted by its inclusion, and yet 
making that complexity available to those who aren't.

In cases where there is little complication to the overall design, and in which I have 
been responsible for manually routing the PCB component of the design, and when, in my 
estimation it would be less productive to work on the above than complete the design 
and mfg of said object(s), the entire design has generally been placed on a single 
page. (for instance, a 3-amp PCB with an offboard pot or two, a power switch, pwr, 
input, and output connectors, and an LED or two, or a simple DC/DC converter PCB with 
a couple of connectors and a pot) Granted, I've done this for significantly more 
complex circuits than the examples, but it should outline some boundaries...

My gut feeling is that the lion's share of electrical design work accomplished with 
packages like this are not 1000-5000 component designs, as might be assumed from 
discussions from many of the PCB-designer-house authored discussions often held within 
this group, but in actuality are quite modest in scope, (perhaps a hundred PCB 
components), which are handled from concept to layout inhouse by a single individual 
or integrated team, and which generally don't demand significant adherence to the 
canon of the PCB-designer school of thought on the subject of "proper design 
technique" (ie, everything must have a netlist, and the schematic and PCB designs MUST 
be cross-linked) It is for that reason that the second alternative is often more valid 
than one might assume at first glance. No one method of design is ALWAYS the most 
productive or economical...


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