On 06/03/13 19:45, David.WE.Roberts wrote:
On Wed, 06 Mar 2013 05:56:05 -0800, dwtowner wrote:

On Wednesday, 6 March 2013 10:03:14 UTC, Tim Watts wrote:
On Wednesday 06 March 2013 09:51 Andy Champ wrote in uk.d-i-y:



On 05/03/2013 19:27, Andrew Gabriel wrote:

I use dallas 1-wire digital thermometers around the house.

These are not wireless, and require a twisted pair



Am I the only person trying to work out how "1-wire" means twisted
pair?



Andy



The name is erroneous - a marketing gimmick - it means "1 wire for +ve
power

and data combined" - you still have a 2nd wire for ground...

There are actually three wires! Ground, data and power. Some 1-wire
devices can derive enough power from the data wire to run without the
power wire, but not all can. 1-wire refers to a single wire being used
for data/signal, unlike other hardware protocols which require data +
clock at least.

I've got multiple 1-wire temperature sensors hanging off my Raspberry
Pi. Some distros for the Pi (e.g, Occidentalis) allow 1-wire devices to
be connected to a GPIO, but I've got mine working off an I2C 1-wire bus
master, which then makes the sensors available through a file-system
interface.

dan.

...errrr.....a data wire but no clock signal wire?
So asynchronous as opposed to synchronous data?


well that depends on what is on the line.


Or is it that it is assumed that data is only going in one direction, so
the usual minimal TXD, RXD, GND (3 wire) configuration for asynchronous
serial data (without any handshaking pins) is cut down to a single data
wire plus earth?

It is a very simple very crude BUS system.

http://en.wikipedia.org/wiki/1-Wire

Not a pint to point bidirectional. Mire HPIB than serial ...


If I remember my asynchronous communications (RS232 or V.24) which I
probably don't after all these years then the signal was a voltage on the
data line with respect to earth/ground.

I see from above a dedicated power line would be to power the remote
device if it had no power source of its own.
Taking power from the data line - not sure how this would work but I
haven't looked at data comms for some years.


the data line is normally high. an 800pF cap in each slave stores
charge when the voltage goes low..

Its designed to be very minimal, pretty slow and needs a master with
most of the intelligence. In practice the master IIRC says 'hello XYZ
address' and the slave says 'here I am and this is my value' and that's IT.

Cutting all power to all devices resets them. Neat huh?


Cheers

Dave R



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.