Nathan House wrote:
> New schematic:
>
http://www.roboticsguy.com/images/misc/balancing_robot/balancing-robot-boar=
d-schematic-r9.png

That's definitely better, despite what Russell says (Russell feels it's his
mission to apologize for anyone I catch being lazy or irresponsible).

In general that looks pretty good.  The thing I was going to mention was th=
e
1K resistors in series with the driver chip inputs.  If these are regular
digital inputs of IC2 and IC2 and the PIC are on the same board, then there
is no need for them.  They will only slow down the edges.

In some cases you do want to put resistors in series with digital signals,
but that's when they are transmission lines.  In any case 1KOhm is way too
much.  If these inputs go directly to the driver FET gates you might want a
little resistance in series, but more like 10 Ohms.  I would loose them
altogether.

A few other nits:

Why is Vcc on the input side and Vdd on the output side of IC2?  That seems
backwards from your description of those supplies at the top of the
schematic.  Maybe there is a reason that makes sense for that chip.  I
didn't look at the datasheet.  However, if Vdd powers the digital side and
Vcc the power bridges, then that is misleading.

There is no capacitance on Vcc I can see anywhere.  There should be some
right at the input connector, and at least a bypass cap at IC2.

What's with the "buffer amplifier" in the upper left corner?  It doesn't
have a component designator and doesn't look anything like a amplifier.  I
didn't look up a LM358, but from your usage it looks like a regular opamp.
By not using the common symbol, you are going out of your way to say
something about that amplifier, but I have no idea what that is.  This is
adding confusion to your schematic, if for no other reason than people have
to wonder what special thing you mean.  It also takes more time to visually
"decode" what you have versus a normal opamp symbol.  That's why we have
standard symbols.

I just looked at that amp more closely, and it looks like (from the pin
names only) that it's a dual opamp with both amps being used as voltage
followers.  However, both inputs are floating and there is no bypass cap.
Both of those are bad ideas.  If it had been drawn properly, this would hav=
e
been immediately obvious.

Surely you can think of better values for some of the test points than U$n,
which is what Eagle sets it to by default in some cases.  It will be very
useful to have the pads labeled on the board, and this label should be show=
n
on the schematic too.  This is usually done by setting the part value.  Suc=
h
values for connectors or pads become silkscreen text, at least in my Eagle
libraries.


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