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<div class="moz-cite-prefix">On 05/02/2014 07:13 PM, jonathan
hunsberger wrote:<br>
<blockquote
cite="mid:CAJWx4Yi8eFhn6J0KgNoAp6CZyfkfLiDFSXkaJrC3dqDSSE8adg@mail.gmail.com"
type="cite">
<div dir="ltr">Not sure about the 1-wire. I have some DHT22 /
AM2302 (one signal wire, but not "1-wire" protocol) running
about 16 meters on wire that was once used for security system
sensors. Hooked to an Arduino right now, but they worked
similarly on a Raspberry Pi before I used that for another
project.</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Fri, May 2, 2014 at 4:06 PM,
Grawburg <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:grawburg@myglnc.com" target="_blank">grawburg@myglnc.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
I have an RPi set up with two DS18B20 temperature sensors
- one is fixed on a breadboard and one is the waterproof
unit with about a meter<br>
extension (got from AdaFruit). Works fine as is. I do not
need a waterproof sensor but would like to put the sensor
10 to 15 feet away from the RPi: we are measuring the
temperature at different points in a room. What's the
reasonable limit for extending the sensor away from the
Pi?<br>
</blockquote>
</div>
</div>
</blockquote>
<br>
I was reading over the specs
(<a class="moz-txt-link-freetext" href="http://www.maximintegrated.com/datasheet/index.mvp/id/2815">http://www.maximintegrated.com/datasheet/index.mvp/id/2815</a>) and
see that since this a "parasitic" one-wire device, it derives its
power from the signal line. So therefore, as long as its getting
sufficient power and its signal can be distinguished beyond noise
and delay artifacts, 1-wire buses can be built quite long.
According to this article from Maxim,
<a class="moz-txt-link-freetext" href="http://www.maximintegrated.com/app-notes/index.mvp/id/148">http://www.maximintegrated.com/app-notes/index.mvp/id/148</a>, pulling
up the bus to 5V and using 5V driving signals and using cat-5
twisted pair wiring, the usual configuration is a long bus up to
450-meters with less than 50-meters between stubs and less than
3-meter stubs to the devices should be fine:<br>
<img src="cid:part2.09030505.05040102@gmail.com"><br>
<br>
You can build a bus with long stubs if you shorten the main bus:<br>
<img src="cid:part3.02080606.06000802@gmail.com"><br>
however, due to reflections and such, you should add a resister at
the point where the stub connects to the main bus:<br>
<img src="cid:part4.05060605.00020405@gmail.com"><br>
<br>
For these long buses, you should probably drive it with a
transistor to reduce noise:<br>
<img src="cid:part5.04070709.06060709@gmail.com"><br>
<br>
To isolate the bus from the R-Pi's data pins directly, for small
to medium sized network up to 100-meters you can use a bus driver,
like a DS2480B or DS9097U and a simple R-C impedance matching
circuit:<br>
<img src="cid:part6.08010706.04040202@gmail.com"><br>
<br>
<br>
1-Wire dataspecs and implementation:
<a class="moz-txt-link-freetext" href="http://www.maximintegrated.com/app-notes/index.mvp/id/5134">http://www.maximintegrated.com/app-notes/index.mvp/id/5134</a><br>
<br>
More info here: <a class="moz-txt-link-freetext" href="https://en.wikipedia.org/wiki/1-Wire">https://en.wikipedia.org/wiki/1-Wire</a><br>
<br>
</div>
<pre class="moz-signature" cols="80">--
Scott G. Hall
Raleigh, NC, USA
<a class="moz-txt-link-abbreviated" href="mailto:ScottGHall1@GMail.Com">ScottGHall1@GMail.Com</a>
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