Wagner Lipnharski wrote:
>
> Mark Willis wrote:
> >
> > Wagner Lipnharski wrote:
> > > <snipped>
> > > Each module should has only 6 pins (Vcc, Gnd, GndRet, Clock, Data and
> > > DataReturn) at each side (to propagate the signal).  The GndRet at the
> > > left side connector is just a tied down, so it can tells the module at
> > > its left "I am here".  In the absence of this signal, the module
> > > automatically connects Data to DataReturn wires, using a transistor,
> > > gate logic, whatever is low cost. This is an auto-loop-back.
> >
> > Resistor, would be my thought?  Should work well & cheaply, say 10k or
> > so, then the switching's done "auto-magically."  A pic output pin, or
> > 74HC logic, can overcome a 10k resistor <G>  Fewest parts solution > <snippe
d>
> Hey Mark, I thought to use a simple resistor, but if the equation
> expression is 1234+1234-123+12345=14936 it will have 25 resistors
> driving each shift register output directly to the DataReturn wire... so
> you can think almost 25 in parallel... its a pitty, but it needs an
> active loop-back to be active just at the very end module...

I thought the inputs were PIC pins, set as inputs on code startup, then
as things are figured out, they're set (one by one) as outputs, as
appropriate - Thus a 10k or so resistor would be just fine.  (i.e. a PIC
in each block, with Data Out connected to Data In through said resistor,
if another PIC is to the right it's output pin drives the Data In line,
quite well.  Shouldn't be crosstalk problems, even <G>)  If you have
just one output & the Data line's bussed through all blocks, then you
need an end mounting cap or something (Maybe have this end cap hold the
whole equation in place, and have parentheses do the same, on a plug-in
rail that busses Vcc and Ground to all the blocks?)

Myself, I'm concerned with how to make sure your rightmost (and/or
leftmost) blocks have a good solid ground, and decent Vcc, I'm thinking
a regulator on each block & a 78L05 per block, say 9VDC power in, this
would raise the price somewhat but you could then have cheaper
connectors with higher resistances, perhaps?  (Have an LED on each PIC
chip that glows amber when the block has proper power, WDT turns this
LED off for 1/2 second or so (as would power-up) so if the amber LEDs
aren't on, you know something's wrong...)  That'd cost somewhat, as
would mounting the LED, cheaper than a VReg though.  Maybe just VReg the
"=" blocks, and have the Equals signs not come on for 1/2 second after a
cold / warm / Watchdog startup, so you know there's a problem.

  Mark