The DS2438-based humidity sensors (family code 26) use the DS2438 chip for
temperature and voltage readings and a separate humidity chip like the
HIH-4021.
The humidity reading depends on the actual temperature and the voltages
read from the chip. Different generations of humidity chips have a
different formula for the humidity, hence the different numbers.
Unfortunately, there is no way for OWFS to know which humidity chip is in
your device, they all look alike. Thus you need to know the chip type to
know which reading is correct.
The addresses in general correspond the the unique lasered ID for each
1-wire chip ever made. The first 2 digits (the family code) define classes
of 1-wire chips. 26 for the DS2438.
Paul Alfille
On Thu, Feb 14, 2013 at 3:48 PM, Mick Sulley <[email protected]> wrote:
> I asked the same question a while back. The answer from Eric Vickery,
> the Hobbyboards guy was
> 'You should use the HIH4000 for the humidity readings. The sensor used
> on our humidity boards is the HIH-4021 now.' I believe that the others
> are to allow for different sensor chips to be used, maybe other
> suppliers use other chips.
>
> On my sensor at the moment I see
> /humidity 45.7448
> /HIH3600/humidity 44.9991
> /HIH4000/humidity 64.9517
> /HTM1735/humidity 19.1244
>
> So there is a significant difference between them. I don't have any way
> to confirm the actual reading, but I would think that the 64.9517 value
> is the most believable of them.
>
> Cheers
> Mick
>
>
> On 14/02/13 21:44, Terry A. Haimann wrote:
> > Yes I figured it out. A web page I saw misled me into believing that was
> > the correct device. Me bad.
> > What's the difference between HIH4000& HIH 3600, they both have a
> > humidity field. Their numbers are a little different though.
> >
> > On Thu, 2013-02-14 at 19:26 +0000, Mick Sulley wrote:
> >> Wrong device. The Humidity sensor is 26.F59F21010000. The software
> >> setup allows for several actual sensor modules, the one in my
> >> Hobbyboards unit is an HIH4000. The directory layout is a bit different
> >> to temperature sensors, under the 26.F59F21010000 directory there is an
> >> HIH4000 directory and in there is a humidity file, that's teh one you
> need.
> >>
> >> Cheers
> >> Mick
> >>
> >> On 14/02/13 19:39, Terry A. Haimann wrote:
> >>> I am having trouble getting owfs to read the humidity sensor. I have
> >>> probably done something stupid. I am hoping it is just something I
> have
> >>> to change in the config, be kind to me since I am new to owfs. Just a
> >>> fyi, I am running a Hobby Board temp/humidity sensor.
> >>>
> >>> I have owfs running on a Raspberry Pi.
> >>>
> >>> pi@watermelon ~ $ owdir
> >>> /10.6F415B020800
> >>> /26.F59F21010000
> >>> /81.91D630000000
> >>> /bus.1
> >>> /uncached
> >>> /settings
> >>> /system
> >>> /statistics
> >>> /structure
> >>> /simultaneous
> >>> /alarm
> >>>
> >>> I look at the files under /81.91D630000000 and I don't see anything
> that
> >>> looks like the humidity:
> >>>
> >>> pi@watermelon ~ $ ls -l /mnt/1wire/81.91D630000000/
> >>> total 0
> >>> -r--r--r-- 1 root root 16 Feb 14 12:12 address
> >>> -rw-rw-rw- 1 root root 256 Feb 14 12:12 alias
> >>> -r--r--r-- 1 root root 2 Feb 14 12:12 crc8
> >>> -r--r--r-- 1 root root 2 Feb 14 12:12 family
> >>> -r--r--r-- 1 root root 12 Feb 14 12:12 id
> >>> -r--r--r-- 1 root root 16 Feb 14 12:12 locator
> >>> -r--r--r-- 1 root root 16 Feb 14 12:12 r_address
> >>> -r--r--r-- 1 root root 12 Feb 14 12:12 r_id
> >>> -r--r--r-- 1 root root 16 Feb 14 12:12 r_locator
> >>> -r--r--r-- 1 root root 32 Feb 14 12:12 type
> >>>
> >>> I have cat'd all of these files and nothing looks like humidity. I
> have
> >>> also looked at it via the webserver and also don't see the humidity
> >>> there.
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> ------------------------------------------------------------------------------
> >>> Free Next-Gen Firewall Hardware Offer
> >>> Buy your Sophos next-gen firewall before the end March 2013
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> >
>
>
> ------------------------------------------------------------------------------
> Free Next-Gen Firewall Hardware Offer
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