[plug] Dallas One Wire systems

[Gavin Chester]

On Mon, 2006-12-18 at 10:07 +0900, Timothy White wrote:
> On 12/18/06, Jim Householder <nofixed at westnet.com.au> wrote:
> >
> > I'm not using it, but I have noticed options for it in the kernel's
> > .config.  Check it for strings containing DALLAS.  If they are not
> > set you will have to build a custom kernel.
> 
> I had noticed them a while ago as well. So I was more concerned with
> locating parts, and what client side software was available.
> For now, I've requested a sample from Dallas of the temperature chips
> I need, and I'll have a go with the serial circuit Greg pointed me to.
> I'm a little concerned though, that I can only run maybe 3 temperature
> chips off the serial port, if using parasite power, as I would ideally
> like to run 5-10 probes.

YMMV, but you may find that injecting a small external power source into
your 1-wire system may be inevitable, and there are references to doing
this.  This is because many UART16550 RS232 chips are only giving
microamps of current through the port and the days of extracting power
that way are long gone.  I say this from consultation with an
electronics engineer who designs the sensors and data loggers that I
build into systems for sale.  If you know what you're doing, or can find
reference online, you're far better off considering the USB port, which
is a serial transfer process, of course.    

> As for locating these chips in Aust, I'm not doing too well yet, but I
> guess research is all I can do, and if I do get a sample and they work
> well, then start calling every electronics company to see if they will
> do retail! I have found one company that is apparently a representing
> for Dallas, but have yet to contact them.

I don't know if it's the same selling scenario with all the 1-wire
products versus just the "ibutton" range of 1-wire products, but I've
found getting them wholesale is frustrating.  I got some from Farnell
and also RS Components stock them.  Range is limited from those two.

IIRC, if you start from the Dallas website there are links to
distributors in Oz.  I found that because the hardware is so cheap, most
distributors I researched make money by bundling it with their own
software solution, but YMMV.

As for the 1-wire weather station you mentioned in your OP, I remember
reading on a weather watcher's forum in Oz that it can't and won't be
imported into Oz for some reason, so you'll have to try buying it from
USA suppliers.  Google is your friend.

I'd be interested in you posting more updates here as you go because I
am interested in the 1-wire products for commercial sales, but found it
too hard to bother.  It looked as though I really had to develop a
hardware/software product virtually from the ground up, and I'm not
capable of doing that combo alone :-(  Maybe we could collaborate after
you've done some more research - I need a good programmer on hand who
can work with addressing minimalist, customised hardware setups ;-)

Gavin