Homebrew PCBs

Robert Hedan wrote:
> I'm interested.
> 
> Let me know what kind of money you want once you've got a detailed breakdown
> of your parts and outsourcing.
> 
> I suppose PayPal would be an acceptable payment method?
> 
> I have my own DIP 16F877s on hand, as well as plenty thru-hole resistors and
> capacitors.  I don't know if you're going all SMD to cut down on spacing,
> but maybe you can offer a kit where we can add ordinary parts.  You could
> include those design-specific parts like the MOSFETs and such, just an idea.
> 
> Robert
> :)
> 
> 


   Well I need to get it laid back out and back before worrying about details 
too much.  But yeah PayPal would work since I'm on Ebay etc.

   The FETs I have 2K on hand.  The 7406s I have 500.  Resistors the same.  For 
what the number would be it'd hardly make sense to leave them out, consider any 
you already had on hand as spare parts.


   The 7406s are DIP, so fairly locked in.  The PIC is the one thing that really 
saves space using a SMT part.  Easy enough to sample a few from Microchip if you 
don't have any.  I have some on hand as well.

   With two copies of the board, I may toss the 5th set of FETs on one board and 
squeeze it to just to 4 phase.  That would likely let the DIP back in if it 
won't squeeze in with 5 phase.


   Note there are a few other things to do before I send it off.  The PSP port 
uses up a lot of pins on the PIC, so many it can't run all 5 phases.  That's 
what one 595 was for, the other for an LCD.

   I plan to scrap the PSP for reading the parallel and switch to serial.  Able 
to do real serial for USB-serial adapter use, or able to use the inverse of the 
595 to read the parallel port pins in a serial manner.  This will let it use the 
same pins to talk to USB or 232 serial, or the parallel port either intelligent 
or just read pin states, all through the same few pins and only jumper a few 
things etc.  More options with the same few pins, and the PSP pins left to 
either run the 5th phase gates or talk to an LCD without an extra part.

   Also consider the original board did have reverse diodes on the FETs.  Only 
problems I had were blowing gates, once I figured out why and did the right 
things to eliminate it I had almost zero problems.  Only a few FETs blown after 
that, from shorting things testing and rough handling.  Took the diodes off one 
set to see and never had any problems attributed to that.  If there is room left 
over, it only takes a tiny bit of spreading to put the holes back in.  Then just 
mount the FETs on top, solder them in, and put the diodes in on bottom.  But 
there is an inherent diode in the FET and it's a 13A FET, don't think you need 
them much with 5 or 7 V 1A motors.  I never had many failures with it when 
running even before I fixed the problem on gate blowing.  Problems all came from 
screwing around with it in odd ways.  Even the gate blowing only really happened 
when I was plugging in motors while it had running patterns going on.  Fixing 
the drive method stopped that.  But again, easy to put them in if there's room, 
easy enough to solder them in place to the transistor leads on bottom even if 
there's not room for holes too.


   There is a lot of stuff to get done before I can even send it off, made worse 
by so many different boards going on it.  None of it is that hard, but it will 
likely be a week before it gets out now.

Alan