RE: OWFS theoretical limits?

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RE: OWFS theoretical limits?

Alfille, Paul H.,M.D.
I'm forewarding this to the developers list.
 
I've personally built a bus of ~120 sensors, all parasitic, with great
performance. (Continuous polling over 10 days with no problems). In parasitic
mode, the DS1820Ss take about 1 second each to read.
 
A powered bus can trigger them all simultaneously, then read each one quickly --
just set the cache timeout long enough to read them all.
 
You'll want to make sure your program doesn't do anything silly like a directory
listing between each conversion -- that would be slow. Get a list of devices,
store the list, and use that for scanning.
 
OWFS has no fixed limits. It could, in theory, have 2^56 sensors.
 
Actually, with cache, you will store the sensor names for the directory cache,
and their temperature values  -- perhaps 100 bytes apeice. so 100K for your 1000
sensors.
 
 
I've never tried 10 buses, but it should work. Again there is no set limit.
(Well, it's a 32 bit number for the number of busses).If you do try this large
installation, we'd be very interested in your results, and assisting you work
through any problems.
 
Paul Alfille
 

        -----Original Message-----
        From: Wright, Ryan P [mailto:[hidden email]]
        Sent: Monday, May 23, 2005 2:48 PM
        To: Alfille, Paul H.,M.D.
        Subject: OWFS theoretical limits?
       
       

        Hi Paul,

        I am looking at a "large" deployment of 1-Wire temperature sensors with
OWFS and wanted to know if you were aware of where the upper limit might be in
terms of number of sensors on a given 1-Wire bus. For instance, if I had, say,
1000 temperature sensors on a bus, would it work? If so, how long might OWFS
take to read the temperatures from all sensors?

        If this is not a workable solution, what is? 100 sensors? Could I run 10
different instances of OWFS on 10 different USB 1-Wire adapters?

        Thank you very much for your time,

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