Elektor Magazine Schematics & the Lazy Bus: An Extended Rant

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Elektor Magazine Schematics & the Lazy Bus: An Extended Rant

Postby JohnAHind » Mon Aug 29, 2016 11:48 am

I would like to open a debate about the presentation of schematics, particularly for digital circuits, in Elektor. All the examples that follow are from the September & October 2016 edition (although in the English edition at least, some of the page footers claim to be in the May & June edition!). But these are common themes across multiple issues and I could cite many more examples.

Compare the exemplary schematics in the purely analogue "i-Baxandall" article with the unreadable atrocity in another opamp circuit "Opamp Experimenting Kit for myDAQ" where the caption for Figure 1 actually apologises for its unreadability! But this could have easily been fixed. First break up IC4, IC5 and IC6 into individual functional symbols (as has sensibly been done with the quad opamp IC3). Now the switches and isolators can be arranged around the opamp symbols to make the function much clearer. Rearrange the pin layout on the two analogue multiplexers (IC1 and IC2) so the common sits on its own one side of the symbol with the channels on the opposite side and the digital control signals on the top or bottom (or in a separate group on the same side as the common) and draw the switches inside the component symbol. Finally separate connector K1 into an input part on one side of the schematic and an output part on the other and rearrange the order of the pins to "untangle" the connections. With these changes, the lazy use of a bus becomes unnecessary and the individual connections can all be drawn neatly.

The abuse of bus symbols on schematics is my main objection to Elektor schematics. Take the "Swiss Pi" article. This is a very typical "lazy bus" which completely subverts the readability of the schematic. A single bus snakes and branches all over the schematic grouping random signals purely for the convenience of drafting. Worst of all the bus actually hides net connections forcing the reader to search the entire schematic to be sure they have found all the ends of a given net. If you abuse a bus in this way, why bother to draw it at all? Just leave tails in space labelled with net names. And why do Elektor schematics never seem to use more than one bus? Look at the four PWM signals at IC9: these disappear into the one-and-only bus, turn a corner and then reemerge again with just a resistor between each and the output. This bus branch does not contain any other signals, so why on earth is it shown connected to the rest of the bus? With a little rearrangement of the entire schematic, all the connections could be shown explicitly just as compactly and neatly.

A bus should be like an autobahn not a city grid. One legitimate use is for a group of functionally related signals in a multi-drop configuration (SDA and SCL on this diagram, but is a bus worth it for just two signals?). Another use is to take a random collection of signals from vicinity A to vicinity B with no hidden connections. The reader knows that a signal at "A" will have one and only one counterpart at "B". If justified, it should be possible to have more than one bus on a schematic so the grouping of signals actually conveys some useful information to the reader.

End of rant! Comments and excuses please!
JohnAHind
 
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Re: Elektor Magazine Schematics & the Lazy Bus: An Extended

Postby ag » Tue Aug 30, 2016 7:42 pm

Well stated!
Ag
ag
 
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Re: Elektor Magazine Schematics & the Lazy Bus: An Extended

Postby Elektor Editor » Thu Sep 01, 2016 8:43 am

John's criticisms have been copied to our schematic drawing and lab staff for their consideration, their implementation or not is outside the responsibility of the magazine editors like myself.

Frankly this is the first complaint of this nature we received these past 40 years, but valuable still. While appreciating the criticisms on the appearance, I note that the specific way of drawing does not compromise the electrical validity of the schematic, i.e. all connections are present and correspond fully to the PCB design.

Jan
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Re: Elektor Magazine Schematics & the Lazy Bus: An Extended

Postby JohnAHind » Thu Sep 01, 2016 10:49 am

Thanks Jan, hopefully the lab staff will engage here.

I would comment that I am surprised that this is not seen as an editorial responsibility as it is obviously important for the schematic and text to work together for the clarity of the article (and the look of the magazine). This aspect usually works well anyway, but occasionally I notice that text will fall into "describe the schematic" rather than "explain the schematic". Of course the schematic needs to be electrically correct and the lab engineers should have the final say in this. But there are many ways of drawing an electrically correct schematic just as there are many ways of writing a correct text. In each case, some are clearer than others. Elektor does re-draw schematics to a "house style", and it is this process that introduces the possibility of error, since the schematic in the magazine is not now the one used in the design software for the PCB layout. It is also much easier for an error to be missed in a bus or netlist than in a schematic with the nets fully drawn.

EDIT: It occurs that there may have been a misunderstanding: nothing I said was intended to suggest that a circuit should be changed electrically to produce a better schematic. When I say "split the connector" or "rearrange the pins" I mean on the schematic symbols only. For example the schematic symbol for a connector can show the individual pins labelled with their correct pin numbers but not necessarily in the correct spatial arrangement (just as is done for IC schematic symbols).

As for the 40 years, my own Elektor collection goes back less than five years, but I would guess that the "Lazy Bus" has been a growing problem as digital circuits designed at higher than gate level became more prevalent.

Giving credit where it is definitely due, I would hold up the "i-Baxandall" article as a real exemplar of how to use well-drawn schematics in conjunction with text to clearly explain both the evolution and the final workings of a complex circuit.
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