Re: [mh] 1-wire Hubs and OXC

[Jim S. <js...@sy...>]

Andy,

 

The power-on reset value of temperature sensor is +85C - that is what it
sends if it has just woken up and not had time to determine the temperature.
If you have a parasitic powered network (just using two wires) this can
because the precharge timing is too short, or the pull up is not strong
enough. In an existing network I would look for a marginal initial design,
corrosion or oxidation on any connectors, and moisture particularly at the
end points. It need not be the sensors that are sending the 85C signal where
the fault is. If you can without disrupting things too much - drop one
connection at a time and see if you can find the leg that is contributing
the problem. Remember all nodes consume the precharge.

 

You might find something useful in this application note on onewire network
reliability  <http://www.maxim-ic.com/an148> http://www.maxim-ic.com/an148.

 

I don't use OXC or OWFS but if you have parameters to control the timing you
might alter those and get back into operation - slowing everything down with
longer precharges will help - unless of course you actually use a powered
network.

 

Jim

 

From: Andy McCallum [mailto:myi...@st...] 
Sent: October 16, 2011 6:59 AM
To: The main list for the MisterHouse home automation program
Subject: [mh] 1-wire Hubs and OXC

 

My 1-wire network has started exhibiting intermittent errors (1 bad hour
every month or so....) after 4+ happy years of operation. It is a poor
electrical layout, so my first effort at fault isolation (or just fixing it)
is to add a HobbyBoards 6 port Hub.

I am using OXC via OWFS to send my temperature (only) data to MH. Now,
apparently OXC doesn't support Hubs.

I have found David
<http://tech.groups.yahoo.com/group/misterhouse/message/40383>  Norwood's
email commenting on Rick Bolen's efforts to integrate a 1-wire hub into MH.

SO, does OXC support hubs via OWFS?  I have seen that v0.5 does not, but I
am hoping that Greg has had time to add it but not yet upload it to his
website....... ;-)

OR is David N. happy to share his patch?

Oh. Any good suggestions on what deteriorates on aging 1-wire networks is
appreciated. The current problem is that between 1 to 3 temperature sensors
report an error by sending a temperature of 85.0 deg C. The sensors are on
different legs of the network and nothing has been changed. A quick
inspection of the "visible" cables shows no obvious damage from vermin,
etc...

Thanks,
Andy.