Re: connecting up 1 wire ?

[Stuart Poulton <stuart@xxxxxxxxxxxxxx>]

Marcus,

Some time ago I developed a solution for eas of adding sensors to a
1-wire network with some PCB modules with cat5 connectors on

Pictures of the early prototype in use by Q (from IRC) are here

http://awooga.nl/gallery/modding/1wire

I'll find some pictures of the latest revision when I get home.

Stuart

On 11/10/12 12:15, Marcus Warrington wrote:
> Having been playing around with a couple of 1 wire thermometers for
the last few weeks I'm beginning to think of how to wire up something more
permanent
>
> At the moment I just have a USB adapter (DS9490R) plugged into my
NSLU2 (unslung and running OWFS) and have a couple of thermometers
(DS18B20) strung together on a couple of lengths of cat5 cable. One
thermometer is in Node0 and the other just outside in the hallway. The
connections are crudely done by twisting the wire around the legs of the
DS18B20 and securing in place with electricians tape. Both sensors are
running on parasitic power only.
>
> Using a PERL script and RRD I have been able to graph the temps in
Node0 and hallway, but OWFS does seems to crash quite a lot (although it
can run days at a time with no issues) although this may be down to my
rather dodgy connections. I have read that I should have a 4.7K ohm
resistor on the wire but I'm unsure if this is already included in the USB
adapter? I've also read articles that state I should put a small resistor
(100ohm)  on the data leg of each sensor?
>
> Now my 1 wire counter board has arrived from Hobbyboards I'm looking
at pulling a wire from node0 to the front of the house where the Gas meter
is (a distance of about 10 meters). This has gotten me thinking about how
best to connect sensors to a one wire system. Looking around on the net it
seems most people simple crimp RJ45 plugs on the end and then use a 3 port
"Y" converter of some form e.g. http://www.ebay.co.uk/itm/280558030831?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
>
> The trouble (for me) with this is that as far as I understand the
sensor should only be a maximum of 2inches away from the bus i.e. the
convertor must be near the sensor and so I would need to run two cat5e
cables (feed and return from the main bus wire) to each place I wanted a
sensor. Looking at the "standard" use of cat5 cable for 1 wire
implies that even with 12v and 5v feeds only 6 of the 8 wires in cat5 are
used i.e.
>
> 1  5 volt
> 2  5 volt GND
> 3  GND            ** I'm not entirely sure why pin 3 is  GND or indeed
which GND it refers to?
> 4  1 wire Data
> 5  1 wire GND
> 6  N/C
> 7  12 volt
> 8  12 volt GND
>
> Given the above (and assuming I ignore the ground on pin3) could I not
wire up a Y connector such that 1 wire data was sent up on pin 4 but return
on pin 6 and then connected back to pin 4 on the return socket of the Y
connector. The same could be done for pin 5/3 for GND.  All the other pins
would be connected straight through to all 3 ports. This would mean that
plugging in a sensor would actually extend the bus rather than  T'ing off
it.
>
>                       .---.
>                       : .-:-.
>                       V : : V
>
>
>                   1 2 3 4 5 6 7 8
>                   @ @ @ @ @ @ @ @
>
>
>
>
> --in----> 1 @-----+---------------@ 1 ----out--> 5v
> --in----> 2 @-------+--------------@ 2 ----out--> 5v gnd
> --in----> 3 @           ---        @ 3 ----out-->
> --in----> 4 @----------'  `----------@ 4 ----out--> data
> --in----> 5 @------------'     .------@ 5 ----out--> data gnd
> --in----> 6 @         `---------'      @ 6 ----out-->
> --in----> 7 @-----------------+---------@ 7 ----out--> 12v
> --in----> 8 @-------------------+--------@ 8 ----out--> 12v gnd
>
> The big advantage of this is that I could run a single "bus"
wire around any room that I might want a sensor in and then when I want to
install one  I can simply cut the wire , insert a Y connector and the run a
cat 5 cable (of any length) to the exact point I want the sensor.
>
> Marcus
>
>
>
> [Non-text portions of this message have been removed]
>
>



------------------------------------

<*> Join the Automated Home Forums
http://www.automatedhome.co.uk/vbulletin/