[ale] [OT] how do I monitor the "weather" in my computer room

Michael H. Warfield mhw at WittsEnd.com
Thu May 30 15:13:05 EDT 2013


On Wed, 2013-05-29 at 17:47 -0400, Ron Frazier (ALE) wrote: 
> Hi all,

> I have a computer in a downstairs room that runs all the time. The
> processes I have it doing generate lots of heat; and there is no hvac
> thermostat there. There is a heating / air vent and return though, so
> it gets some air circulation. I need to monitor the temperature in the
> room from upstairs.

> I bought an Acurite backyard weather thermometer from home depot with
> remote sensor. I put batteries in the sensor and display and verified
> that the sensor is transmitting. I sat both units a foot apart in the
> living room maybe 12 feed from the honeywell thermostat on the wall. I
> trust the temperature reading of the honeywell more than any other
> sensor I have.

> The honeywell says it's 73 in this room. It doesn't show decimals.
> My fairly nice Oregon Scientific weather station shows 73.6 in this
> room.
> A cheap Lacross Technology weather monitor that I use to monitor
> humidity in the basement says 73.9 in this room.
> And a cheap Lacross Technology (I think) wall clock shows 73.0 in this
> room.

> It's actually annoying that all these sensors within 12 feet of each
> other are so different. I guess I'll assume that the actual
> temperature is between 73 and 74; and I think it's more toward 73.

Sound to me like they're dead on for what they're designed for.  Most of
those sensors are using devices similar to what you find in the cheaper
1-Wire sensors.  They're basically going to be in the accuracy of +- 1F
(or sometimes only +- 1C / +- 2F) with a precision of +- .1C.  If you
want a good example of why precision exceeding accuracy is a bad thing,
you're looking at it.

Look at your device specs.  I think you'll find they really are in the
spec'ed range.  To get something with a true accuracy down to .1F is
going to be an expensive unit and not a cheap consumer grade device
though you can pick up some relatively inexpensive 1-Wire components
that are decent if you want to go the roll-your-own route.

> My NEW weather monitor is showing 74 or 75 on both indoor and outdoor
> temp with both sensors in the same place, which probably about 1-2
> degrees high. This one doesn't display decimals.

> In any case, while that's not ultra critical, I'm considering
> returning it.

> So, I'm looking into other alternatives.

I just bought a nice Mead TE523W-M off Amazon.com.  This has an internal
sensor and barometer, plus atomic clock receiver, plus remote anemometer
(wind speed and direction), plus remote UV, plus remote temp and %
relative humidity (%RH) sensor, plus supports up to 4 more remote T/%RH
sensors which can be internal or external at about a 300' transmission
range.  It also has a USB port and Linux software is available.  I
currently have it plugged into one of my RPi's.  They're not
inexpensive.  That was about $180 plus another $10-$20 for additional
remote sensors (depending if I get the ones with 10' remote temperature
probe cables like what I would use for my pool water temp).

http://www.amazon.com/gp/product/B004UI2FYC/ref=oh_details_o02_s01_i00?ie=UTF8&psc=1

If you want to "roll your own" these are some decent DTH22 1-Wire
temperature / humidity sensors that will interface directly to a
Raspberry Pi or Arduino and claim an accuracy of .1 (presumably C) and
only set you back $11 per sensor.  Doesn't say what the accuracy of the
humidity part of the sensor (hygrometer) is but the precision is down to
+- 1%.  Relative humidity is a real iffy thing to measure and calculate
and a "sling psychrometer" is still the gold standard.  In most cases,
the accuracy of your temperature sensor will bear a direct impact on the
accuracy of your hygrometer.

http://www.amazon.com/Appliance-Digital-Temperature-Humidity-Measurement/dp/B00CDHH3WQ/ref=wl_it_dp_o_pC_nS_nC?ie=UTF8&colid=3CMJ5PZC70J2O&coliid=I3D7WBJ9139NAW

You just gotta wire'm up and rock and roll.

You can get cheaper.  The DTH11's are dirt cheap but less accurate and
less range.  Some of the reviews of the DTH11's claim their %RH can be
off as much as 15% (gag).

> 1) Buy another more expensive weather station, like another Oregon
> Scientific. That would cost $ 50 - $ 75.

I looked at the Oregon Scientific devices and I have had their products
in the past.  They're ok.  Their wireless range is more limited than the
Mead.  I like the Mead better for what I got but it is definitely
pricier.

> 2) Buy a wifi or lan attached temperature sensor. That way, I could
> just display the weather sensor's web page from a local 192.168.x.x
> address and see the temperature in the basement room.

Those are pricey and unlikely to be any more accurate.  The Mead
equivalent is nothing more than the TE523W-M attached to a little server
for which they charge you $200 more.  I don't think so.

> 3) Use a rpi plus a sensor to do the same thing as number 2. Would
> probably cost more.

Maybe.  Not so sure.  The sensors can be cheap enough but you'll have to
wire them in.  The wireless interfaces for the RPi is less than $10.

> 4) Attach a USB temp sensor to the pc downstairs and run a web server
> on it to display the temperature.

> Other than having a more accurate stand alone unit like the one I
> bought, I like option 2 best. That way, I could set a web page up in a
> small window on my monitor upstairs to show the downstairs temperature
> and set it to auto reload every few minutes. Also, I could run a
> script on the downstairs computer to poll the sensor periodically and
> send me an email if the temperature exceeds a preset limit.

> Anyone know what I might use to get this done?

> By the way, when I was researching how to monitor my basement
> humidity, I found out that any humidity sensor less than about $ 300
> is probably rubbish for precision. The tolerance is usually + / - 5%.
> I think that's ridiculous, but I guess it's hard to do much better for
> cheap.

Champagne taste, beer budget.

Seriously, +- %5 is not bad considering what you're measuring.  You
could move from one end of a room to another and vary by as much as that
just due to airflow and temperature differentials.  You're not dealing
with chemical engineering here.  Most of the time, if you're not drawing
static sparks or condensing moisture, you're probably in the ball park
on that one.

> Thanks in advance.

> Sincerely,

> Ron
> 
> 
> 
> --
> 
> Sent from my Android Acer A500 tablet with bluetooth keyboard and K-9 Mail.
> Please excuse my potential brevity if I'm typing on the touch screen.
> 
> (PS - If you email me and don't get a quick response, you might want to
> call on the phone.  I get about 300 emails per day from alternate energy
> mailing lists and such.  I don't always see new email messages very quickly.)
> 
> Ron Frazier
> 770-205-9422 (O)   Leave a message.
> linuxdude AT techstarship.com
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Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
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