[chbot] Stampalike progress, microchip direct, and a toaster oven.

[Chris Hellyar]

Well, I changed my mind again....

(Another long email, I'm a man of leisure at the moment!)

After piddling about with the 18F2520 design for quite a while, and
getting the board practically as small as I could single sided to keep
the cost down I emailed the files for a quote, and _almost_ had them
made.....

A bit of a segway is in order here, to make this story complete.  Segway
as in change of subject, not over-grown dancebot with a geek standing on
it.

For my old business I got all of my low volume boards done at Huntsbury,
and decided I should go down and see him about these new boards, it's
nearly 5 years since I had any boards done.  I wanted to check that he
could use the gerber files I was creating with kicad, and to catch up,
shoot the breeze, talk rubbish, you know how it is...

Well, after about 30 minutes of catching up and shooting the breeze I
decided that I should switch to SMD, or maybe Tim decided for me?
Something new for me as I've only ever done repairs to SMD stuff, I've
never done an SMD board from scratch.  I like new stuff.

I also got to stand around and sniff ammonia fumes, and took a look at
his plate through line which is interesting if you're into chemistry.
All the baths were empty while I was there as it was having a bit of
maintenance, but it's interesting to see how it all works, and the setup
cost must have been horrendous....

As an aside, looking at the overseas vs local circuit boards thing;  For
small boards in low volume I'm sticking with Tim @ Huntsbury.  If I get
keen and manufacture something in volume again I'd probably look to go
off shore.

I used the online quoting tool for a couple of the large Asian PCB
houses and without freight it was cheaper, but if you took the freight,
and the inability to visit the factory and shoot the breeze the local
option is far better.  Obviously your mileage may vary if you're doing
boards, but that's where I'm going.

The down side of going to smd is that I have about $5k in through hole
components sitting around in the garage which are only surface mountable
when you drop them on the floor.  The PCB's are cheaper though, if you
don't have to drill them full of holes, and in most cases SMD is smaller
as well.  I'm sure you all know the advantages, thermal coupling, more
robust, lower inductance, blah blah blah.

Back from the segway now. (how damned cool is that word?)

Not wanting to go too far out on a limb with my first SMD venture I
decided to do a PIC16F88 based stampalike.

In a nutshell, a PIC16F88-I/SO, reset switch, ISCP/Serial header and
regulator and some caps on a 50x20mm board, with a 20pin 'SIL' plug to
stick it into a socket or verboard / breadboard.  (hence 20 pins, I
can't get 19 pin SIL sockets cheaply)

http://www.cpix.co.nz/myio/myStamp88smd.png

I don't have the 3d modelling right, and that shows a through-hole tact
reset switch 'cause I've not got the pad spacings for the SMD one yet,
but you get the idea.  The board is single sided to keep cost down, and
will just be solder masked on the SMD side and screen printed on the
other with the pinout and some other guff.

So I've got a few thousand squitty little 0805 (2x1.5mm) resistors, and
the monocaps, and I signed up with microchiponline to order the SMD
PIC16F88's, and a couple of through-hole ones just for the sake of it.
(More on that later)

The tact switches are on their way, as are the SO8 regulators, diodes
and electros.

Hmmm, what are we missing?  Oh yeah, a toaster oven....

Three or four folks I've visited over the last couple of years were
doing SMD reflow using toaster ovens in varying states of modification.
A bit of googling will find a few references to this as well, so it's
not as odd as it sounds.  So I'm off to cash converters, to buy a
toaster oven later on today.

The trick being accurate temperature control, for which I've ordered a
thermocouple from ebay. I've not decided if I'll use a 4-20ma
transmitter or a custom amplifier for it yet, but basically I'll stick a
relay on the oven, and write a simple process control loop in C on a PC
to control the temperature profile.  Might be a good use for my
'bs1rtu' (as per http://ohmark.co.nz/080405.html ).  I'll be able to
graph the profile real time etc, blah blah blah.

The total cost of this little doofer will be a shade over $15 inc GST,
including an RS232 bootloader cable and 20PIN sil socket for your
veroboard, which given that we're talking low volume component
purchasing is pretty neat. My intention is to mark them up a bit and
sell them on Trademe, but if anyone on the list is interested they can
have em at cost, which for just the board with no cable will be under
$13.  Bearing in mind a 16F88-I/P from South Island is $11.88+GST I
think it's good value to put smarts on a breadboard or veroboard
quick'n'dirty project.

Which leads me to the microchip online thing, via a price the reference.

In a thread a wee while ago I asked about microchip direct, and peoples
experience with it.  Last night I placed my first order on there, for
the SMD pics, and I'd have to say as online shopping experiences go it
was pretty cool.

Their online interface is good, it flows well, and there's lots of
information as you go along.  You can all look for yourself at the
prices, and the conversion rate is about 1.29 $NZ to the US at the mo.
( www.microchipdirect.com )

As part of this process I checked with my old PIC supplier here in NZ
(trade supplier, not retail) and although their prices are close to the
online ones I'd have to buy quite large MOQ's (minimum order quantities)
of the parts to get better than the 1-25 part cost from microchip
direct.  Even taking into account the possibility of being charged GST
on entry to NZ.

A very interesting side benefit, which I knew about but had forgotten
totally is the sample program.  When you sign up to microchip direct you
get access to their sample program which essentially gives you up to 10
devices a month for free.

I'm not sure how long they would keep on sending you bits if you never
actually ordered something, but it's certainly worth thinking about if
you want a few free PIC's to play with.  I intend to get the 18F2520's
for my larger stampalike via that once I've managed to not incinerate my
PIC16F88 version. :-).

I'll keep you posted on my progress, and the arrival of the microchip
direct stuff.

Cheers, Chris H.