Re: Home Grown ActionTec Development Daughterboard

Scott,

> Say 50 people want one and we make a "group buy" of all the goodies.

I made up a Digikey parts list spreadsheet last night.  We have a system 
that turns an Excel BOM spreadsheet into a Digikey automatic ordering Web 
page.  I'll be puting it up on the "Wiki".

It looks like the parts are ~$22 in quantities of 10 (usually a Digikey 
"price-break" point), plus ~$7 per PCB in groups of 9 from ExpressPCB 
(which, with a simple layout change, could be 12 PCB's per ExpressPCB 
"miniboard" fab run).

The 3.3V RS-232 converter is the biggest cost element at $5.63 each.  If 
anyone knows a good cheaper alternative, I'd like to know.

Alternatively, the RS-232 "level shifting" can be done with a few 
resistors and the left-over inverters in the 74AC04 hex inverter chip.  I 
do this all the time.  However, you don't get true negative RS-232 signal 
transistions this way.  Nevertheless, modern PC serial ports don't 
care...0-3.3V signaling is fine with them!

We now just need a "groupie" to make a Digikey and ExpressPCB order and 
distribute the parts! (Read *not me*!)

> It would be easier for end users if the layout changed slightly on the 
> connectors, so for "revision 2" of the pcb I would like to make a 
> friendly suggestion, armchair quarterback-style!  :-)

Better is the enemy of good enough! :-)

I got bored looking at all the possible I/O options, and made a "command 
decision" to do what I did, and assumed that I'd either solder wires 
point-to-point into the serial/reset/boot mode/USB connector holes, or I'd 
put in a 12-pin 0.1" dual-row right-angle header and makeup cables with 
mating plugs on the end...much like you see with PC motherboard connectors 
to the "reset" switch, speaker, power switch, etc.

> If the pcb had a 10 pin (5x2) header for the serial port, then we could 
> use off-the-shelf IDX to DB9 serial cables often used for taking a mobo 
> serial header to a PC slot cover plate.  I have the proper mapping for 
> this I can supply.

In my many years of using these serial port IDC ribbon cables, I've been 
burned many times with the pinouts changing.  If here *really* is a 
"standard" now, that may make sense...ignoring the fact that the PCB is 
tiny and a 10-pin connector may be hard to fit.  (I guess the PCB can 
always be made a bit longer.)

> Same idea for the USB header; 5 (or 6?) pin SIP.

Is there a standard for USB on PC motherboards?  Maybe there is and I 
haven't paid attention.  When I'm building PC's "from scratch" at home, I 
usually don't add the "front panel" USB wiring.  The last PCB case I got 
had individual 1-pin connectors for each and every USB signal wire.  This 
makes me think that every PC motherboard is different in this area!

> As well as a separate 2x2 header for the BOPT & reset switches.

In fact, that's the situation now.  The "headers" are just real close 
together! :-)

> They could be soldered on as right angle so it all still fits inside the 
> case.

That's my current plan...in fact I'm pretty sure you can solder the RA 
dual-row 12-pin header to the underside of the PCB.

> Bottomline, if we slightly rearrange how many pins (a few extra), and 
> how they are wired (some will be n/c), then it becomes plug-n-play for 
> connection.

A laudable goal, let's fine tune it if and when this PCB works.  Your 
feedback and ideas are welcome!

Best regards,

Bruce

-- 
  Bruce D. Lightner
  Lightner Engineering
  La Jolla, California
  Voice: +1-858-551-4011
  FAX: +1-858-551-0777
  Email: lightner-2huV/[email protected]
  URL: http://www.lightner.net/lightner/bruce/

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