On May 23, 2011, at 5:38 AM, V G wrote:

> What suggestions would you guys have for saving space and designing =20
> for
> better efficiency?

Don't use a UBW32 ?  Seriously; that's going to be a major factor =20
limiting how much you can shrink the board.   Mmm.  Could be that the =20
new ChipKit boards change your equation...

There are a lot of components on there, and I don't think you'll be =20
able to shrink the board very much just by better routing and =20
placement.  Protection circuits are annoyingly large :-(

In general, your passives are further apart than they need to be.  A =20
set of signal-protecting diodes, resistors, and caps (as you have on =20
the left edge) can generally fit on a 0.1 inch grid unless there are =20
other reasons (power dissipation, isolation) for keeping them far apart.

Consider quad opto-isolators instead of one-per-package devices.

Consider resistor arrays (SIPs) where appropriate (current limiting =20
for LEDs, especially.)

I can't quite figure out what your TTL devices are, but it looks like =20
you have one 20pin DIP  (eg U8) driving four LEDs, which is pretty =20
awful, density-wise.  Use higher efficiency LEDs and the PIC32 can =20
probably drive the LED directly (4mA).  I don't know if you can get =20
optos for low drives or not  (Hmm.  How much CAN the pic32 drive on IO =20
pins?  I see a 25mA absolute max, but not a "recommended" value...)  =20
You could stick in something like a TLC5940 LED driver and drive 16 =20
leds from a 28pin chip (with internal current limiting, so you get rid =20
of the resistors as well.)

The other thing to think about is that $65 is NOT a lot of money.  =20
About one day's worth of labor at minimum wage, or less than a =20
billable hour for a research project.  (of course, it's REAL money of =20
the sort that escapes the university instead of going around in =20
circles making everyone look good, but still...)   A TH design that =20
costs an extra hundred bucks that is robust and can be put together =20
easily may be preferred over a crowded SMT board that was cheaper but =20
more difficult to assemble)

BillW


BillW

--=20
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