--On 02/13/2006 01:46:34 PM -0500 MarcLavallée wrote:
I'm new to the 1-wire technology.
I'd like to interface over 30 DS2408 on a 1-wire bus, using ordinary
ethernet cables, arranged in a topology of 2 or 3 branches with 10 or 15
daisy-chained devices. The total length of the cables could be over 100
meters. I need to monitor momentary push-buttons connected to the I/O
pins of the 2408 and I need to know about the chronology of their status
(pressed or released). It would work on Linux, and eventually on OSX.
What are my options?
Thanks for your help
--
Marc
Marc,
What you are doing is certainly doable.
A few things that others didn't say:
With 30 sensors, I would not depend on parasitic power. It means bringing a
3.3 or 5V line to the chips. This allows you to ignore the charging time if
you want to do near continuous polling. Others may have a different opinion
on this, and it may be less of an issue with the 2408 than temp sensors.
With power, you have an odd number of lines so you can get noise pickup on
the wire. I found it easier to pull the power and ground in a true star,
and only daisy chain the signal line. I have done tests with 140m in this
way and no observed problems. I also have a chain in service that has much
more than 100m hanging off a single chain, but I don't have a TDR to
measure the true length. In one part is has 3 runs that go ~15m from the
star point to the sensors, so that 90m of bus length right there.
IButtonlink has a hub product in either serial or ethernet flavors. This is
a 1-wire interface and produces 4 1-wire buses with +5v and +12v. It does
not emulate the logic of the 1-wire switch, which is contorted at best, but
rather makes all the sensors available with no additional coding. I have a
serial version. Paul has added support for the ethernet version as well.
best of luck,
jerry
Jerry Scharf
laguna way consulting
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