[sdiy] SSI2130

Pete Hartman pete.hartman at gmail.com
Sat Sep 19 19:40:58 CEST 2020


I was inspired last night to take a crack at the idea of a breakout that
could have the chip pre-soldered.  I don't normally do a lot of work with
finer pitch SMD so I found I had to use fairly fine traces to route to the
pins with the chip rotated (which seemed to make the most sense, since
going to a DIP form factor).  Necking in KiCad is not something I've
mastered and I didn't spend a lot of time when I found it wasn't working
the way I thought the descriptions online said it should.  PS: not looking
for a debate about CAD packages ;).

I'm curious if any of the more experienced would have any opinions they'd
care to offer?  Full disclosure: the intent is for this to be sold as a DIY
tool, so if providing advice for what might become a low volume commercial
product is a concern, by all means, don't feel like you are obligated to
comment.

First the images.  I'm also sending pictures to the list for the first
time, so if for some reason this doesn't work, I can always throw links to
my google drive up pretty quickly.

[image: Screen Shot 2020-09-19 at Sep 19 12.05.02PM.png]       [image:
Screen Shot 2020-09-19 at Sep 19 12.06.12PM.png]

I liked the idea of having the regulator(s) on board, so I dug around to
find a couple that seemed likely.  I did find that -V regulators were
significantly more expensive (Q100 of both of these are under $0.30,  Q10,
and I didn't look for Q100, of even a pretty basic - regulator was on the
order of $3.00).  Since the chips tolerates up to -18V I decided to forego
a regulator on the negative rail.

The V+ equivalent pin feeds the TLV1117-50, and that 5V feeds the
MCP1700-25 as well as the actual V+ pin on the chip.  I figured someone
might want to use their own different 2.5V reference so I put a normally
closed set of jumper pads that could be cut if preferred (like the USB
power on a teensy, for example).  This also allows you to take the 2.5V
reference *off* the pin if you wanted to use it for expo scaling, or
through zero, etc.  Sitting here this morning I am thinking it might be a
good idea to provide an extra pin at the top edge so the 5V reference could
be treated similarly.  I don't think I could do exactly the same thing
because there has to be some way for the higher voltage to get onto the
breakout.

All the caps are 0603, which is about as small as I'd want to hand solder;
although I do not intend to hand solder it myself, I figured leaving the
option open even if just for prototyping seemed like a good idea.  Same
idea behind using "handsolder" footprints for the regulator & reference.

It's half an inch between the rows of pins and .7" wide by 1.7" long total.

Thoughts?

Thanks!

Pete
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