[sdiy] Voltage vs current, was Low voltage synthesis?
chris at chrismusic.de
Tue Jan 18 11:17:19 CET 2022
Don't forget ground layout.
I have the habit of separating AGND and DGND in the schematic and have a
solder jumper in between, so I can see and control where the two are to
be connected on the actual board. In a multi-board scenario, this may
even be on the PSU board.
On Tue, 18 Jan 2022 10:29:36 +0100 "usenet at teply.info"
<usenet at teply.info> wrote:
> On 17.01.22 18:06, Ingo Debus via Synth-diy wrote:
> > Yes, probably because itâs easier to measure voltages than currents. For
> > current measurements usually a wire or trace has to be cut. Thatâs often
> > difficult or even impossible (think multilayer PCBs).
> > Thinking in terms of voltage is also reflected in the traditional way
> > schematics are drawn (i. e. the way we all usually draw them). If three
> > points (components) A, B and C are to be connected, itâs perfectly legal
> > to draw either AâBâC or AâCâB, even if it is important that, say, B is
> > in the middle (think rectifier - filter cap - load in a power supply for
> > instance). Since both ways to draw these connections are equivalent, PCB
> > design software cannot tell the difference (at least I donât know of any
> > software that does), so doing a good PCB layout is so much more than
> > just translating the schematics. Maybe it wasnât if there was a more
> > appropriate way to draw schematics?
> In cases where it actually matters (mostly RF/microwave stuff as far as
> I can see), it is pretty common to place PCB traces explicitly as
> elements in the schematic and possibly also the layout. This tends to be
> a bit more work as these extra elements need to have a schematic symbol
> and a footprint in order to be recognized by the layout software, but
> can help a lot when it matters.
> In the end it's a tradeoff. You trade flexibility for reproducibility.
> You can either describe an PCB element as "quarter wavelength at
> f=12.96GHz, Z=25R" or as "trace, 1.2 mm wide, 14.46 mm long". Both cases
> have their use, and they can be transformed into the respective other
> *IF* the PCB stackup and materials are known. But in Audio synths I
> don't see any benefit in doing that extra effort.
> Even the mentioned arrangement of rectifier, filter cap and load hardly
> maters at the frequencies in question for reasonable dimensions. Sure,
> placing the load directly at the rectifier with the filter cap two
> metres away probably doesn't serve the purpose, but at a few dozen
> kilohertz it probably wouldn't make a huge difference.
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