Howard Winter wrote:
> I think it may be that a lot of people see the 28-pin format as not
> really a standard choice - because they came from the 16C84 they think
> of 18 pins as being the "normal" one to use.

My reasoning was that if you're going to use something the size of a
QuickProto board anyway, there is no advantage to 18 pins over 28, whereas
40 pins is considerably more klunky.  I think this logic is still correct,
but I'm also starting to realize that logic has little to do with it.
Apparently there is a comfort level with the 16F84 beyond any reason, and
anything that looks too different is averted with a shudder and disgust.  I
suppose I could have put both the 18 and 28 pin footprints on the board, but
I couldn't think of a good reason someone would then use the 18 pin
footprint, considering the extra one time $1 is small even compared to the
low price of a QuickProto.  Oh well.

> Personally I
> tend to use the newer 20/14/8 pin format because they are pin
> compatible as far as their number of pins goes, so a board using a
> 20-pin socket, for say the 16F690, can also be used by the 683, 684,
> 688 8- and 14-pin devices and possibly others,

I'm glad you're mentioning this.  Here's the part I don't get.  You've
already bought a QuickProto for $33 and obviously have some other costs in
parts to make your circuit.  Even if your project could fit in a 16F88, what
is the big deal about plunking down a 16F876A or something which is a
complete superset?  You can ignore the extra I/O lines.  Why isn't a 16F876A
a 16F88 with dedicated debug lines and a few extra I/O pins to ignore?  Is
it really the extra $$ or two, or does it just feel wrong, or something
else?

> A QuickProto-xx which had provision for the 690
> and your strip-connected holes area would be ideal for me! (Hey, if you
> don't ask, you don't get :-)

I'll definitely keep that in mind.  However I think the next QuickProto will
be aimed at USB.  Those only come in 28 or 40 pins so I was figuring to
support the 40 pin flavor (18F4550).  This time I won't try to constrain the
size to Eurocard, since nobody that bought one seemed to care about that.
It will definitely have at least the same size prototyping area, a fully bus
powered power supply providing 5V regardless of USB power, and something a
few volts higher and a few volts negative for opamps.  I'll keep the debug
LEDs and RS-232, but probably simplify the connector area on the right.

> Incidentally I meant to mention a problem I had with the QP-01's that I
> bought when I was staying in New York:  they survived the journey from
> MA to NY (who'd have thought that chinese newspaper was anti-static?
> :-) but on the way home in my luggage two of them suffered damage at
> the tender
> mercies of Newton and the baggage handlers: some of the larger
> capacitors became detached from the board, in one case at both sides
> and in a
> couple of others just one side.  I wonder if it wouldn't be better to
> use through-hole for these, rather than surface-mount?

That would add cost.  Normally things that aren't connectors wouldn't get
that much mechanical stress.  It's possible that those caps weren't soldered
down quite as well as they should have been, but good enough to pass test.

> Since my surface-mount soldering skills are
> dreadful, I haven't tried to reattach the completely detached
> capacitor,

If the solder joint came apart and the capacitor and board are still intact,
then it is really easy to solder back on.  Add a little fresh solder and
heat the pad fully before putting the cap on it, then heat it some more and
add a little more solder until you can clearly see it flow.  Then go around
and do it to the other pin, which will be easier since the cap is already
held in place by the first pin.

> but did consider drilling holes and using a TH device.  Do
> you happen to know if it would be safe to do that through the pads, or
> is there anything passing below them that I can't see?

It is a two layer board, so you can see all the traces.  However, I don't
think doing what you're suggesting is a good idea.  The holes won't be
plated, and there won't likely be the right trace on the bottom to connect
to.  That means you have to solder the leads at the top of the board only,
right under the part.

Try soldering down the SMD parts.  I think you'll find it easier than you're
worried it is.


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