Low-Cost Humidity Sensor?
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Hello,
Parallax is looking for a low-cost humidity sensor. We'll accept the fact
that precision and cost are trade-offs, too. Our target cost is less than a
buck, including any support circuitry. Can anybody provide some direction on
parts we might be able to use for this purpose?
The application is for a simple project designed for the experimenter,
hobbyist or student.
Thanks,
Ken Gracey, Parallax
http://www.parallaxinc.com and http://www.stampsinclass.com
Microcontroller Application Cookbook Vol 1&2 features BASIC
Stamp code examples for almost any interface you can
imagine. $54.95 for both volumes at www.parallaxinc.com/mac
Parallax is looking for a low-cost humidity sensor. We'll accept the fact
that precision and cost are trade-offs, too. Our target cost is less than a
buck, including any support circuitry. Can anybody provide some direction on
parts we might be able to use for this purpose?
The application is for a simple project designed for the experimenter,
hobbyist or student.
Thanks,
Ken Gracey, Parallax
http://www.parallaxinc.com and http://www.stampsinclass.com
Microcontroller Application Cookbook Vol 1&2 features BASIC
Stamp code examples for almost any interface you can
imagine. $54.95 for both volumes at www.parallaxinc.com/mac
Comments
We used some "hygristors" a while back for this purpose. They are little
more than glass plates with some sort of black smear of lithium chloride
or carbon on them. They change resistance with humidity. These were
gov't surplus from some radiosondes. I'm not sure how long these last.
These can't cost much to make, but I have no idea how much new ones are:
http://www.ysi.com/veco/media/temp.gif
Humicaps are also around, but I don't know if you can get them for a
buck. http://www.vaisala.com/
Others:
Ohmic Instruments (MD) http://www.ohmicinstruments.com/sensors.html
Rotronic (NY) http://www.rotronic-usa.com/
Don't know if any of them could go under $1.
That ought to get you started.
Al Williams
AWC
* Floating point math for the Stamp, PIC, SX, or any microcontroller
http://www.al-williams.com/awce/pak1.htm
>
Original Message
> From: Ken Gracey [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=k1fe5n4Frltqak9mXmfMGxZ4P6EAW4N45VW2bOEYkG5y5FH5m4myzqUDV8hy91rcjjo6BBRt_fL4UCcCp-6fRg]kgracey@p...[/url
> Sent: Thursday, August 08, 2002 11:42 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Low-Cost Humidity Sensor?
>
>
> Hello,
>
> Parallax is looking for a low-cost humidity sensor. We'll
> accept the fact that precision and cost are trade-offs, too.
> Our target cost is less than a buck, including any support
> circuitry. Can anybody provide some direction on parts we
> might be able to use for this purpose?
>
> The application is for a simple project designed for the
> experimenter, hobbyist or student.
>
> Thanks,
>
> Ken Gracey, Parallax
> http://www.parallaxinc.com and http://www.stampsinclass.com
>
> Microcontroller Application Cookbook Vol 1&2 features BASIC
> Stamp code examples for almost any interface you can imagine.
> $54.95 for both volumes at www.parallaxinc.com/mac
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
> Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
http://content.honeywell.com/sensing/prodinfo/humiditymoisture/
http://www.geinet.com/
GE Panametrics http://www.panametrics.com/
http://www.cosa-instrument.com/
Phillips
BC Components (these are about $4 in big quantity, if I recall)
Also, a colleague just suggested: http://www.humirel.com/ but again no
idea if $1 is reasonable.
Al Williams
AWC
* NEW: PAK-VIa - Read PS/2 keyboards or mice -- double the buffer, lower
current consumption.
http://www.al-williams.com/awce/pak6.htm
>
Original Message
> From: Ken Gracey [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=KrfMQOBNi2b4lKkY5bNpG9rdTfyekDiDWcKIrbzOQg_5Q5zEugxN1C5OViYuP7iP-BFfCWpRcC1yxA2kSTqAaEas]kgracey@p...[/url
> Sent: Thursday, August 08, 2002 11:42 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Low-Cost Humidity Sensor?
>
>
> Hello,
>
> Parallax is looking for a low-cost humidity sensor. We'll
> accept the fact that precision and cost are trade-offs, too.
> Our target cost is less than a buck, including any support
> circuitry. Can anybody provide some direction on parts we
> might be able to use for this purpose?
>
> The application is for a simple project designed for the
> experimenter, hobbyist or student.
>
> Thanks,
>
> Ken Gracey, Parallax
> http://www.parallaxinc.com and http://www.stampsinclass.com
>
> Microcontroller Application Cookbook Vol 1&2 features BASIC
> Stamp code examples for almost any interface you can imagine.
> $54.95 for both volumes at www.parallaxinc.com/mac
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
> Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
unless you buy a shipping container full. The really cheap sensors
are suseptable to dust/dirt, oils, and prolonged exposure to high
temp/humidity can affect there reliability. Use of a sintered brass
or teflon filter will help prevent dust/dirt from contaminating the
sensing element. The HIH series Honeywell sensors are almost immune
to harsh conditions but the sensors cost $25 each.
Another issue is the linearity of the sensor. A capacitive or
resistive sensor could be used with a 555 timer to vary the frequency
as the RH changes. I suppose if your just looking for a ballpark
figure that would work.
But for a buck........
Maybe 3 bucks if your lucky.
Jason
--- In basicstamps@y..., "Al Williams" <alw@a...> wrote:
> I am assuming all the big names are too expensive:
>
> http://content.honeywell.com/sensing/prodinfo/humiditymoisture/
> http://www.geinet.com/
> GE Panametrics http://www.panametrics.com/
> http://www.cosa-instrument.com/
> Phillips
> BC Components (these are about $4 in big quantity, if I recall)
>
>
> Also, a colleague just suggested: http://www.humirel.com/ but again
no
> idea if $1 is reasonable.
>
> Al Williams
> AWC
> * NEW: PAK-VIa - Read PS/2 keyboards or mice -- double the buffer,
lower
> current consumption.
> http://www.al-williams.com/awce/pak6.htm
>
>
>
>
>
> >
Original Message
> > From: Ken Gracey [noparse][[/noparse]mailto:kgracey@p...]
> > Sent: Thursday, August 08, 2002 11:42 AM
> > To: basicstamps@y...
> > Subject: [noparse][[/noparse]basicstamps] Low-Cost Humidity Sensor?
> >
> >
> > Hello,
> >
> > Parallax is looking for a low-cost humidity sensor. We'll
> > accept the fact that precision and cost are trade-offs, too.
> > Our target cost is less than a buck, including any support
> > circuitry. Can anybody provide some direction on parts we
> > might be able to use for this purpose?
> >
> > The application is for a simple project designed for the
> > experimenter, hobbyist or student.
> >
> > Thanks,
> >
> > Ken Gracey, Parallax
> > http://www.parallaxinc.com and http://www.stampsinclass.com
> >
> > Microcontroller Application Cookbook Vol 1&2 features BASIC
> > Stamp code examples for almost any interface you can imagine.
> > $54.95 for both volumes at www.parallaxinc.com/mac
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@y...
> > from the same email address that you subscribed. Text in the
> > Subject and Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
> > http://docs.yahoo.com/info/terms/
> >
>that precision and cost are trade-offs, too. Our target cost is less than a
>buck, including any support circuitry. Can anybody provide some direction on
>parts we might be able to use for this purpose?
>The application is for a simple project designed for the experimenter,
>hobbyist or student.
>Thanks, Ken Gracey, Parallax
hehe! happy hunting...
How about a good old wet bulb thermometer? All you need is two small
temperature sensors (thermistor? thermocouple?) and a little bit of
wet cotton wick over one. RCtime interface. Hey, add a
stamp-controlled fan to keep the air moving, and how about a
stamp-contolled gizmo to keep the wick wet!?
Here is a cheap trick to make a "discrete" humidity sensor: Coat an
interdigitated grid with a saturated table salt (NaCl) solution, then
dry it out with a hair dryer. The resistance across the grid is high
when the %RH is below 75% but drops dramatically when the %RH is
above 75%. Different salts have different transition humidity, for
example, lithium cloride (LiCl) at 11% or potassium nitrate (KNO3) at
95%. AC xitation with a '555 and COUNT in the Stamp. It is possible
to make formulations of salts and binders that display a continuous
change of resistance with humidity, and these were popular for use in
old radiosondes. But they are fragile and the calibration is
terrible.
Remember cobaltous cloride from your chemistry set? On a piece of
blotting paper it is blue at low humidity and pink at high humidity.
I don't know what you could do with that and one of those new TAOS
color sensors.
Here is another manufacturer with relatively low cost humidity
elements ($5 to $10):
http://www.ohmicinstruments.com/sensors.html
Also, here is a smart sensor (~$20):
http://www.sensirion.com/en/sensors/humidity/default.htm
-- regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...
> >Parallax is looking for a low-cost humidity sensor. We'll accept the fact
> >that precision and cost are trade-offs, too. Our target cost is less than a
> >buck, including any support circuitry. Can anybody provide some direction on
> >parts we might be able to use for this purpose?
> >The application is for a simple project designed for the experimenter,
> >hobbyist or student.
> >Thanks, Ken Gracey, Parallax
>
>hehe! happy hunting...
>
>How about a good old wet bulb thermometer? All you need is two small
>temperature sensors (thermistor? thermocouple?) and a little bit of
>wet cotton wick over one. RCtime interface. Hey, add a
>stamp-controlled fan to keep the air moving, and how about a
>stamp-contolled gizmo to keep the wick wet!?
>
>Here is a cheap trick to make a "discrete" humidity sensor: Coat an
>interdigitated grid with a saturated table salt (NaCl) solution,
Ahaha!!.... I suppose if you "create" an interdigitated "finger
capacitor" by bridging the copper rings on a pref-board of say 3x3 inches,
you would have enough bimetallic difference between the solder and
copper that you could have a measurable difference in capacitance
proportional to humidity without using any salt if you simply include
the "capacitor" in a simple RC oscillator.
>then
>dry it out with a hair dryer. The resistance across the grid is high
>when the %RH is below 75% but drops dramatically when the %RH is
>above 75%. Different salts have different transition humidity, for
>example, lithium cloride (LiCl) at 11% or potassium nitrate (KNO3) at
>95%. AC xitation with a '555 and COUNT in the Stamp. It is possible
>to make formulations of salts and binders that display a continuous
>change of resistance with humidity, and these were popular for use in
>old radiosondes. But they are fragile and the calibration is
>terrible.
>
>Remember cobaltous cloride from your chemistry set? On a piece of
>blotting paper it is blue at low humidity and pink at high humidity.
>I don't know what you could do with that and one of those new TAOS
>color sensors.
>
>Here is another manufacturer with relatively low cost humidity
>elements ($5 to $10):
> http://www.ohmicinstruments.com/sensors.html
>Also, here is a smart sensor (~$20):
> http://www.sensirion.com/en/sensors/humidity/default.htm
>
>
> -- regards
> Tracy Allen
> electronically monitored ecosystems
> http://www.emesystems.com
> mailto:tracy@e...
Beau Schwabe Mask Designer IV - ATL
National Semiconductor Enterprise Networking Business Unit
500 Pinnacle Court, Suite 525 Wired Communications Division
Mail Stop GA1 Norcross, GA 30071
I have an old circular chart recorder, temp and humidity.
they used either human or horse hair and as the humitity changed the
mechanical shaft moved allowing the arm to sweep across the 8"
chart. That is 3 inches of mechanical movement. Now THAT is in the
experimentors category. and it is relativly cheap, pot's with shafts
being more than your target price.
Dave
--- In basicstamps@y..., Tracy Allen <tracy@e...> wrote:
> >Parallax is looking for a low-cost humidity sensor. We'll accept
the fact
> >that precision and cost are trade-offs, too. Our target cost is
less than a
> >buck, including any support circuitry. Can anybody provide some
direction on
> >parts we might be able to use for this purpose?
> >The application is for a simple project designed for the
experimenter,
> >hobbyist or student.
> >Thanks, Ken Gracey, Parallax
>
> hehe! happy hunting...
>
> How about a good old wet bulb thermometer? All you need is two
small
> temperature sensors (thermistor? thermocouple?) and a little bit of
> wet cotton wick over one. RCtime interface. Hey, add a
> stamp-controlled fan to keep the air moving, and how about a
> stamp-contolled gizmo to keep the wick wet!?
>
> Here is a cheap trick to make a "discrete" humidity sensor: Coat an
> interdigitated grid with a saturated table salt (NaCl) solution,
then
> dry it out with a hair dryer. The resistance across the grid is
high
> when the %RH is below 75% but drops dramatically when the %RH is
> above 75%. Different salts have different transition humidity, for
> example, lithium cloride (LiCl) at 11% or potassium nitrate (KNO3)
at
> 95%. AC xitation with a '555 and COUNT in the Stamp. It is
possible
> to make formulations of salts and binders that display a continuous
> change of resistance with humidity, and these were popular for use
in
> old radiosondes. But they are fragile and the calibration is
> terrible.
>
> Remember cobaltous cloride from your chemistry set? On a piece of
> blotting paper it is blue at low humidity and pink at high
humidity.
> I don't know what you could do with that and one of those new TAOS
> color sensors.
>
> Here is another manufacturer with relatively low cost humidity
> elements ($5 to $10):
> http://www.ohmicinstruments.com/sensors.html
> Also, here is a smart sensor (~$20):
> http://www.sensirion.com/en/sensors/humidity/default.htm
>
>
> -- regards
> Tracy Allen
> electronically monitored ecosystems
> http://www.emesystems.com
> mailto:tracy@e...