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Long 1-Wire (MicroLan) networks

By Dale Reagan | July 21, 2011

Long is, of course, relative…  After much tinkering/testing with Arduino and 1-Wire networks I discovered what seem to be some limitations:

Hardware: Arduino & LinkUSB

An Arduino solution is attractive since it could operate in a stand-alone, battery powered, SD card data backup solution.  Of course various Arduino ‘shields’ would also be needed and I may revisit this approach at a later date.

At this time I am using a LinkUSB (iButton) USB 1-Wire interface – this is being used for my (relatively) long 1-Wire network until/unless I can resolve the Arduino limitation (note that it may be possible to use Arduino in ‘hub fashion’ – see previous Arduino/1-Wire posts -  to resolve this limitation; I did a ‘mini-test’ but the LinkUSB option worked ‘out-of-the-box’ and I was ready to deploy…)  My current MicroLan contains 34 temperature sensors with an estimated combined cable length of 400+ feet.

I created three types of sensors which I describe as:

  1. box sensors – the DS18B20 is attached to a keystone jack in either a 2 or 4 port box and
  2. string sensors – the DS18B20 is attached to the end of CAT5e cable.
  3. rope sensors – [update, 7/31/2011] multiple DS18B20s attached to 18 gauge bell wire via ‘quick splices‘ at 10 foot intervals (currently testing two ~40ft ‘ropes’) bringing the active sensor count on this micro-lan to 44 and the micro-lan length increases ~480ft.  Since the wire gauge is heavier (than CAT5e) a terminal block is used on ‘rope ends’ to bridge a connection to the CAT5 cable at a ‘hub’.  Note that DS18B20s were soldered to ~2″ of the same bell wire (similar to what is described below except that pins 1&3 were connected for this group of sensors – as wired, the ‘rope sensor’ will only work using parasite power.)  Also, this connection creates another 8-node star from a stub/star connection (note that this is not the suggested approach using parasite power for ‘long networks’…)

The assembly  of sensor ‘nodes’ was something like:

Materials

Open Source Software for reading 1-Wire devices

** The DS18B20 temperature sensor can operate on ‘parasite’ power using just two lines; for a parasite powered MicroLan you connect pins 2 & 3 (GND + Vdd.)  In this case I opted to assemble the components such that I could ‘convert’ to a non-parasite, powered MicroLan (needed in instances of longer distance that what I am planning or, needed by other types of sensors.)  I do connect GND + Vdd at my data collection point (currently, the LinkUSB interface is connected to a 4 port box with appropriate wires crossed…)

*** Star Topology – network nodes branch off from an existing, original-base-primary network source.  If there is only one additional connection then we have a network ‘stub’ node (an end point.)  In the scenario described above the 4 jack boxes create star nodes that branch from the box using the three wires mentioned above – and yes, this solution could have been done with only two wires.  Also note that the product documentation does indicate that star topologies can be problematic and should be avoided if possible – I will use the star topology approach until I encounter a problem.

Topics: 1-Wire, Computer Technology, Problem Solving, Savannah Georgia (USA), Unix-Linux-Os | Comments Off

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