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 <G>
>
>   Mark

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...  A
mechanically activated switch would be nice... but... remember the 5 yrs
old skinny frekles face boy poking the connector with a pencil.  I
thought also to use a transistor open collector to drain the loop-back
wire, base polarization cut off by the GroundRet from the next module,
if no next module it floats, the transistor then will follow base
polarization by a second resistor connected to Data Out pin....the PIC
needs to understand that the DataReturn wire has an inverted data bit
signal, also easy to do, right?

I still reading posts solutions about to turn each "operator module"
somehow inteligent, when it doesn't need it.  The main point here is
just to transport the math expression sequenced by the blocks into just
one inteligent block that will do the simple math.  It is just a
sequential input of digits and operators and a simple syntax
pre-evaluation to make multiplication and division first, and evaluate
the result at the left side of the "=" module with the right side, as
well, to check if operator modules are unique between numbers, to avoid
1234+-1234 or 1234*/1234 or similar errors.

It is the same as if you are inputing an equation to a calculator in
serial mode, nothing else, pretty and simple.  Sincerelly, this is a one
hour assembler programming and it's done.

Wagner.