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'[EE] Temperature and Humidity sensors'
2011\06\25@164430 by V G

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Hi all,

I'm looking for a relatively cheap (~$10 for humidity sensor, ~$5 or less
for temperature sensor) for my project.

Right now, I'm looking at the following:

Temperature: DS18B20 (
ca.mouser.com/ProductDetail/Maxim-Integrated-Products/DS18B20+/?qs=sGAEpiMZZMvbyeSUH4qH%2fLbikZ7SIep9
)

Humidity: HIH-5031-001 (
ca.mouser.com/ProductDetail/Honeywell-Microswitch/HIH-5031-001/?qs=sGAEpiMZZMseu6oguAZpqee7rmuRi3v3z4pHD5zNNiU%3d
)

Requirements:
- Low voltage (3.3V compatible).
- Easy to interface (digital bus outputs are nice, such as SPI, I2C, 1wire,
etc), I don't want to be measuring capacitance or frequency. I can work with
linear voltage measurement.
- Humidity range: 0-100% RH.
- Temperature range: nothing special, anything standard will most likely do..
- Cost: as mentioned above. I don't want to be spending $40 for a chip.

Can anyone recommend better? Have any experience with a particular product

2011\06\25@165433 by V G

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On Sat, Jun 25, 2011 at 4:44 PM, V G <spam_OUTx.solarwind.xTakeThisOuTspamgmail.com> wrote:

{Quote hidden}

Also, the LM75 doesn't look too bad:
http://ca.mouser.com/ProductDetail/NXP-Semiconductors/LM75ADP118/?qs=sGAEpiMZZMucenltShoSngZctQqH05qEYl3RXUhBUpg%3

2011\06\25@170203 by John Ferrell

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On 6/25/2011 4:44 PM, V G wrote:
{Quote hidden}

LM34/35
Less than $5.

--
*John Ferrell W8CCW*

**

*'A man's feet should be planted in his country, but his eyes should survey the world. '*

*George Santayana*

**

2011\06\25@171248 by Mike Harrison

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On Sat, 25 Jun 2011 16:44:14 -0400, you wrote:

{Quote hidden}

I looked at that recently & came back with  LM75 and HIH-503x as cheapest. NB price on HIH-503x varies a lot between distributors so worth shopping around

2011\06\25@173307 by John Byrnes

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There are a few combined sensors out there like this one.
http://www.adafruit.com/products/385&zenid=1858fee8067021c742610fa2e713375a

A bunch of online shops sell them.

Best,
John

On Sat, Jun 25, 2011 at 17:09, Mike Harrison <.....mikeKILLspamspam@spam@whitewing.co.uk> wrote:

{Quote hidden}

>

2011\06\25@175106 by V G

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On Sat, Jun 25, 2011 at 5:09 PM, Mike Harrison <mikespamKILLspamwhitewing.co.uk> wrote:

> I looked at that recently & came back with  LM75 and HIH-503x as cheapest..
> NB price on HIH-503x varies a lot between distributors so worth shopping
> around
>
>
Thanks. Yeah, I like the HIH-5031 because it can work in condensing
environments. I'll probably go with that. Looks like it's good quality.

As for the LM75, I'll have to compare it to the DS18B20. I don't mind
spending a couple more dollars on the DS18B20 if its easier to interface

2011\06\25@180132 by Veronica Merryfield

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Years ago I used a 1N4148 for temperature sensing and made a humidity sensor using inter-digiting fingers on a PCB.
If this is a one off project, that could work for you. The diode I think is done my measuring voltage across it for a constant current, but the spec sheet would help here, and the PCB humidity sensor is a resistance measurement, which will need calibrating. Both comply linear voltage measurement.

On 2011-06-25, at 1:44 PM, V G wrote:

{Quote hidden}

> -

2011\06\25@183918 by Oli Glaser

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On 25/06/2011 21:44, V G wrote:
> Hi all,
>
> I'm looking for a relatively cheap (~$10 for humidity sensor, ~$5 or less
> for temperature sensor) for my project.
>
> Right now, I'm looking at the following:
>
> Temperature: DS18B20 (
> ca.mouser.com/ProductDetail/Maxim-Integrated-Products/DS18B20+/?qs=sGAEpiMZZMvbyeSUH4qH%2fLbikZ7SIep9
> )
>

I've used the DS18B20, I found it to be pretty easy to use and quite accurate.
If you haven't used 1-wire before, it can be a bit fiddly to get going depending on what uC/language you are using, but it's no big deal. Basically you need to make sure you are running fast enough to meet the timings, as it's all done in firmware. Also you need to decide whether you will be using parasite power or not.
It's a particularly useful system if you want to save pins and have multiple sensors (you can have many on one wire IIRC)


2011\06\25@194911 by V G

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On Sat, Jun 25, 2011 at 6:38 PM, Oli Glaser <.....oli.glaserKILLspamspam.....talktalk.net> wrote:

>  I've used the DS18B20, I found it to be pretty easy to use and quite
> accurate.
> If you haven't used 1-wire before, it can be a bit fiddly to get going
> depending on what uC/language you are using, but it's no big deal.
> Basically you need to make sure you are running fast enough to meet the
> timings, as it's all done in firmware. Also you need to decide whether
> you will be using parasite power or not.
> It's a particularly useful system if you want to save pins and have
> multiple sensors (you can have many on one wire IIRC)
>

Yup, I've used it a few years ago on a breadboard and it worked well. I just
need to remember the code for it again and rewrite it for the PIC32. I'll
probably go with the DS18B20

2011\06\25@195032 by V G

picon face
On Sat, Jun 25, 2011 at 6:01 PM, Veronica Merryfield <
EraseMEveronica.merryfieldspam_OUTspamTakeThisOuTgmail.com> wrote:

> Years ago I used a 1N4148 for temperature sensing and made a humidity
> sensor using inter-digiting fingers on a PCB.
>
> If this is a one off project, that could work for you. The diode I think is
> done my measuring voltage across it for a constant current, but the spec
> sheet would help here, and the PCB humidity sensor is a resistance
> measurement, which will need calibrating. Both comply linear voltage
> measurement.


The project is for a university, so accuracy is a requirement. But your
method definitely seems interesting. Could you please describe it more? What
is the configuration of the PCB fingers and how is humidity measured? What
is the approximate precision and accuracy

2011\06\25@195610 by Marc Nicholas

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> Yup, I've used it a few years ago on a breadboard and it worked well. I just
> need to remember the code for it again and rewrite it for the PIC32. I'll
> probably go with the DS18B20.

They're wonderful devices. Have been a huge fan for years.

Agree with the earlier comment that getting the code right can be a
challenge, but once it's working you open up a whole world of devices
and the 1-wire protocol itself is quite something.

Ahhhh, I'm starting to reminisce about the hay-day of DalSemi ;)

-

2011\06\25@221055 by cdb

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I'm a big fan of the Sensirion sensors, combined humidity and temperature. The original series use a modified I2C data transfer method and the new ones use real I2C or PWM depending on the type.

Price is around US$ 25 - 30 .

Futurlec, Mikroelectronica, Parallax, Mouser etc stock them.

Colin --
cdb, colinspamspam_OUTbtech-online.co.uk on 26/06/2011
Web presence: http://www.btech-online.co.uk   Hosted by:  http://www.justhost.com.au
 

2011\06\25@231141 by V G

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On Sat, Jun 25, 2011 at 10:10 PM, cdb <@spam@colinKILLspamspambtech-online.co.uk> wrote:

> I'm a big fan of the Sensirion sensors, combined humidity and temperature..
> The original series use a modified I2C data transfer method and the new
> ones use real I2C or PWM depending on the type.
>
> Price is around US$ 25 - 30 .
>
> Futurlec, Mikroelectronica, Parallax, Mouser etc stock them.
>

I was looking into them. Two problems:

1. Price.
2. Mouser doesn't stock them. I don't want to pay an extra shipping fee on a
different distributor on top of the already high cost

2011\06\25@233624 by cdb

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:: 1. Price.

As you could say this is for a university project they might be willing to send you a sample.

:: 2. Mouser doesn't stock them
Ah, must have been Digikey i saw them at then, mind you Element14 and Newark stock them and here in Ozland freight is free so long as the order is placed via the internet.

I have a couple of SHT71's which with suitable negotiations you could acquire if you so wished.

Colin
--
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Web presence: http://www.btech-online.co.uk   Hosted by:  http://www.justhost.com.au
 


2011\06\26@035438 by Ruben Jönsson

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> Hi all,
>
> I'm looking for a relatively cheap (~$10 for humidity sensor, ~$5 or less
> for temperature sensor) for my project.
>
> Right now, I'm looking at the following:
>
> Temperature: DS18B20 (
> ca.mouser.com/ProductDetail/Maxim-Integrated-Products/DS18B20+/?qs=sGAEpi
> MZZMvbyeSUH4qH%2fLbikZ7SIep9 )
>
> Humidity: HIH-5031-001 (
> ca.mouser.com/ProductDetail/Honeywell-Microswitch/HIH-5031-001/?qs=sGAEpi
> MZZMseu6oguAZpqee7rmuRi3v3z4pHD5zNNiU%3d )
>
What are your requirements for accuracy?

You can make a 1-wire temp/humidity sensor using a DS2438 + the HIH-5031-001. The DS2438 also contains a temperature sensor but it is only accurate to +/-2 degrees C while the DS18B20 is accurate to +/-0.5 degrees C, if I remember correct.

Here is the circuit:
<www.sensorsmag.com/sensors/humidity-moisture/a-1-wire-humidity-sensor-
1080>

Note that the HIH sensors give you relative humidity and not absolute. You also need to do some calculations to get from voltage to RH. This is a lot easier using a high level language and floating point.

/Ruben

==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
RemoveMErubenTakeThisOuTspampp.sbbs.se
==============================

2011\06\26@043315 by Oli Glaser

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On 26/06/2011 08:54, Ruben Jönsson wrote:
> while the DS18B20 is accurate to ±0.5 degrees C, if I remember
> correct.

I *think* it is actually 0.0625 (1/16 deg C)
IIRC it is 12 bits for -55 to +128, represented by a signed char followed by 4-bits fraction.
The number of bits accuracy is adjustable between 8 up to 12 if you don't need the higher resolution.
The tradeoff is quicker sampling time (up to 750ms for 12-bit IIRC)

2011\06\26@043658 by Oli Glaser

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On 26/06/2011 08:54, Ruben Jönsson wrote:
> DS18B20 is accurate to ±0.5 degrees C, if I remember
> correct.

Sorry disregard my previous mail - I noticed you said *accuracy*, not resolution, which is what I was talking about.
The DS18B20 is indeed accurate to 0.5 deg C.
Sorry for the confusion.+/-

2011\06\26@051252 by V G

picon face
2011/6/26 Ruben Jönsson <spamBeGonerubenspamBeGonespampp.sbbs.se>

> Note that the HIH sensors give you relative humidity and not absolute. You
> also
> need to do some calculations to get from voltage to RH. This is a lot
> easier
> using a high level language and floating point.
>

RH is fine, that's what I want.

And I'll be writing in C, so those calculations are no problem, especially
on a PIC32

2011\06\26@092946 by RussellMc

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part 1 2378 bytes content-type:text/plain; charset="iso-8859-1" (decoded quoted-printable)

Method of measuring temperature, using a silicon diode junction, that
could change your life ;-).
Cheap, easy, no calibration needed, 10 x more accurate than typical
diode based methods.

     : http://www.smsc.com/media/Downloads/Application_Notes/an1014.pdf

________________


> Years ago I used a 1N4148 for temperature sensing

There is a surprisingly little known method using any silicon diode
that is cheap, easy, needs no calibration and which is typically an
order of magnitude better than you will usually get with cheap
sensors.
(Choose any four !!!!)

ANY silicon diode can be used.
Accuracy of 0.1% easy enough [tm] to get.
Need to be able to set a current to two values and measure a voltage.
NO calibration is required and any silicon diode can be substituted
anytime desired.

This method is used by (at least) NatSemi to measure processor die
temperature using an embedded diode that is usually used for the much
less accurate ingle current diode voltage drop method that Oli
mentioned. They are exceptionally mealy mouthed about how the IC works
- presumably hoping that inobservant competitors will not copy them.

The method is based on the same  principle which the band gap
reference is based.
The CHANGE in voltage across a silicon junction with a known change of
current is a property solely [tm] of temperature and the properties of
silicon.

Delta V_junction = K.T.ln(Ihigh/Ilow)
T = absolute temperature.
See attachment and below.
As Ihigh and I low are fixed this reduces to

      Delta Vjn = K.T

Yeeha!
I ratio can be selected  to get a convenient scale factor.

Be ware of die heating (or allow for it).

The method is used by SMSC in their equipment and described in their
AN10.14. Note that this application note varies - the formula is NOT
given in older versions.
Bad: 1086, 2006
Good:  2009
I have a copy of the good version but so far no source.

Delta Vjunction = Z.K.T / Q . ln (Ihigh/Ilow)
See attachment for details.
Note Z :-(.
Still very good.

This is an application note for their EMC2105 which used this method.
           http://www.smsc.com/media/Downloads/Application_Notes/an171.pdf

Antiparallel diode sensing allows two temperatures to be sensed per
wire pair !!!

     Good (2009) :
http://www.smsc.com/media/Downloads/Application_Notes/an1014.pdf



Russell McMahon


part 2 12194 bytes content-type:image/jpeg; (decode)


part 3 181 bytes content-type:text/plain; name="ATT00001.txt"
(decoded base64)

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2011\06\26@130557 by Gaston Gagnon

face
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On 2011-06-25 23:11, V G wrote:
> On Sat, Jun 25, 2011 at 10:10 PM, cdb<TakeThisOuTcolinEraseMEspamspam_OUTbtech-online.co.uk>  wrote:
>
>> I'm a big fan of the Sensirion sensors, combined humidity and temperature.
>> The original series use a modified I2C data transfer method and the new
>> ones use real I2C or PWM depending on the type.
>>
>> Price is around US$ 25 - 30 .
>>
>> Futurlec, Mikroelectronica, Parallax, Mouser etc stock them.
>>
> I was looking into them. Two problems:
>
> 1. Price.
> 2. Mouser doesn't stock them. I don't want to pay an extra shipping fee on a
> different distributor on top of the already high cost.
Newark sells Sensirion
canada.newark.com/jsp/search/browse.jsp?N=500001+1003484&Ntk=gensearch_001&Ntt=sensirion&Ntx=mode+matchallpartial
Gaston

-- Gaston
http://public.fotki.com/Gaston-Gagnon/

2011\06\26@155146 by Joe Wronski

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 On 6/26/2011 9:29 AM, RussellMc wrote:


It's been too long since studying or using any semiconductor theory.  Is q = electron charge a constant?  I know the rest are, except for the ideality factor, which I would hope are in the spec sheet or can be calculated empirically.

Also, in your math notation, as in:
> Delta Vjn = K.T
Is t he . dot a multiplication, what I would expect to be '*'?

Joe W

-- Joe Wronski
Stillwater Embedded Engineering
http://www.stillwatereng.net

2011\06\27@032438 by cdb

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Here we go Future (I believe are still in Canada)

Combined temp and humidity sensors starting form US$8.46

www.futureelectronics.com/en/Search.aspx?dsNav=Ntk:PlainTextSearch|h
umidity|3|,Ny:True,Nea:True,N:637

Colin
--
cdb, RemoveMEcolinspamTakeThisOuTbtech-online.co.uk on 27/06/2011
Web presence: http://www.btech-online.co.uk   Hosted by:  http://www.justhost.com.au
 

2011\06\27@071515 by RussellMc

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> Is the . dot a multiplication, what I would expect to be '*'?

Yes, I used "." for std basic multiplication. (No vectors harmed in
the writing of that formula).

The less keen would build a system and derive K overall from measurement :;-)

> It's been too long since studying or using any semiconductor theory.  Is
> q = electron charge a constant?

A far more profound question than may at first be obvious :-).

A: Only if the fine structure constant is constant and maybe not then.
If not, the sky is falling and I'm off to see the king. (Does anyone
want to buy an acorn?).

There is ongoing uncertainty about the constancy of the F.S.C. and
whether it is spatially isotropic across the universe. But, for we
mere mortals, it can be assumed that all of the current physical
constants are so. At least close enough to constant across ranges of
time and space liable to be encountered in terrestial applications.

FSC = alpha = 2.Pi.q^2 / (CP)

   q = electron charge
   C = light speed !!!!!!!!!!!!
   P = Planck's constant

http://en.wikipedia.org/wiki/Cosmological_principle

They were at it in 1962 :-)
"The significance of spatial isotropy."
http://prola.aps.org/abstract/PR/v127/i2/p629_1                 <- Ref
http://astrophysics.fic.uni.lodz.pl/100yrs/pdf/07/026.pdf       <-paper

http://www.ebtx.com/ntx/ntx215.htm   <- Danger Will Robinson

" ...  using the Bekenstein-Sandvik-Barrow-Magueijo (BSBM) theory. ...
dark energy ..."
Must be good, then.
http://arxiv.org/abs/astro-ph/0401631

On Feynman (long ago) & Webb & King (2010)  on FSC
NB FSB <> FSM but it may sometimes be hard to tell :-).
http://www.economist.com/node/16930866


> I know the rest are, except for the
> ideality factor, which I would hope are in the spec sheet or can be
> calculated empirically.

I doubt if many spec sheets cite non a non-ideality factor, alas.


                   Russell

2011\06\27@085250 by Spehro Pefhany

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At 07:14 AM 6/27/2011, you wrote:

>I doubt if many spec sheets cite non a non-ideality factor, alas.

I doubt if even one does.

Diode-connected transistors don't have that problem (n=1).

The next factors in line limiting accuracy are the base spreading resistance
(rbb), which is a (typically unspecified) transistor parameter (use a part
such as MMBT4401 or 3904) and wire resistance. A third current can be used
to eliminate those, with some increase in complexity and additional
sensitivity to component values.

The sensitivity (microvolts per degree) of this approach is not that much
higher than that of Pt100 RTD or thermocouple, and the complexity is not that
low. Since the output is proportional to absolute temperature, a 0.1% error
represents several degrees C, but a single-point adjustment could be used.

In a way, this idea is similar to the internal circuit in your garden-variety
band-gap voltage reference, except rather than using two closely matched
(fabricated on the same monolithic substrate) BJTs operating at different
currents, a single device is used with a switched current.

It's a fine technique for certain high-volume niche applications (such as
measuring CPU die temperature, but I'm not sure I see much in the way of
general application areas for it given the limitations it has.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffEraseMEspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2011\06\27@093115 by PICdude

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Code is indeed challenging, again! -- I originally wrote the code for  a 18F and it worked nicely, but now I'm trying to port to an enhanced  16F and ripping my hair out over some odd results.  They'll be nice  deviced again, after I get the code working again.

Cheers,
-Neil.



Quoting Marc Nicholas <EraseMEgeekythingspamgmail.com>:

> They're wonderful devices. Have been a huge fan for years.
>
> Agree with the earlier comment that getting the code right can be a
> challenge, but once it's working you open up a whole world of devices
> and the 1-wire protocol itself is quite something.
>
> Ahhhh, I'm starting to reminisce about the hay-day of DalSemi ;)
>
> -m

2011\06\27@131105 by RussellMc

face picon face
> ... and wire resistance.

Kelvin sensing. Annoying.

> The sensitivity (microvolts per degree) of this approach is not that much
> higher than that of Pt100 RTD or thermocouple

No calibration needed for sensible sensor choices.

Sensor cost trivially low.
Pt100 cost would make you think it used a precious metal ! :-)
Thermocouples this good are getting costlyish and need moderate
processing power for linearisation.

> and the complexity is not that
> low.

Certainly non zero.
ADC measurement is a nothing in modern environments.
Differential constant currents annoying but can probably be PWM out
and one op amp.
ie you will probably need an opamp for good precision but most other
requirement is on IC in modern micro controller.

> Since the output is proportional to absolute temperature, a 0.1% error
> represents several degrees C, but a single-point adjustment could be used..

And it's not temperature dependent :-)

> In a way, this idea is similar to the internal circuit in your garden-variety
> band-gap voltage reference, except rather than using two closely matched
> (fabricated on the same monolithic substrate) BJTs operating at different
> currents, a single device is used with a switched current.

Yes. Although temperature needs to be factored into the bandgap device.

> It's a fine technique for certain high-volume niche applications (such as
> measuring CPU die temperature, but I'm not sure I see much in the way of
> general application areas for it given the limitations it has.

Seems potentially useful to me.
Once you have basic system going you can eg monitor N sensors with
little more effort and minimal delta cost. Switching issues to be
sorted.
..

2011\06\27@221132 by Joe Wronski

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 Thanks Russell,

My first electronics job was in semiconductors at Sprague Electric, now Allegro.  If I had stayed on that path in the R&D lab, I might actually understand some of your references and links.  I was looking into a job opp where the company wants someone with low noise analog expertise, and I think it's time for some refreshers.

I signed up for  an Analog Devices  webinar for starters:
<http://www.newark.com/jsp/bespoke/bespoke7.jsp?bespokepage=newark%2Fen_US%2Flanding%2Fwebinar%2Fadi%2Fadi.jsp>

Joe W



On 6/27/2011 7:14 AM, RussellMc wrote:
{Quote hidden}

-- Joe Wronski
Stillwater Embedded Engineering
http://www.stillwatereng.net

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