A very cute hack for a 1-wire LCD panel interface, including power!

[Michael O'Dell]

The Dallas one-wire interface is pretty feeble in terms of current available.
To me, the cutest part of this implementation is that there is no voodoo required
to talk to the panel - it’s just 8N1 at 2400 baud which damn near anything can bang-out
with little to no grief. That means I can hang it on a second surreal port as a mini-console
on a one-board-wonder as easily as I can drive it from an Arduino or other digital goober.
everything either has a hardware surreal port or there is bit-banger code that will do it,
and even the most sluggish spring-head can make 2400 baud.

while it would be nice to make the panel auto-baud, the cute hack of looking for
the ASCII NUL with an R/C circuit gets major props for most-est with the least-est
in my book. changing the baud rate would mean the time constant would have to change, too.

	-mo



On Jan 2, 2015, at 3:03 PM, Rob Seastrom <rs at seastrom.com> wrote:

> 
> Michael O'Dell <mo at ccr.org> writes:
> 
>> http://www.edn.com/design/systems-design/4427215/One-wire-brings-power---data-to-LCD-module
> 
> That's a bit interesting, mainly for the cute trick of parasitic
> powering the LCD off the comm line, but 2400 baud is kinda slow.
> Non-overdriven Dallas 1-Wire is 16.3 kbit/sec.
> 
> There are plenty of circuits out there that utilize the Maxim DS2408
> and an HD44780 together, and pre-debugged libraries for writing to
> that combination.
> 
> I see that the cap they use for parasitic poweer is 0.47uF.  Dallas
> 1-Wire stuff typically is powered by an 800pF cap.  I wonder if a
> 1-Wire interface (obviously with fewer stations on the "microlan")
> would source enough power to keep the 44780 and the backlight happy.
> 
> -r
>