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Recomend any 1-Wire humidity sensors? — Parallax Forums

Recomend any 1-Wire humidity sensors?

jefmjefm Posts: 50
edited 2008-07-16 15:10 in BASIC Stamp
I've been trying to find humidity sensors that work on 1-Wire and so far everything is big and expensive, was wondering if anyone knows about any relatively cheap humidity sensors in DIP size? Sensing temperature would be a plus, temperature alert wires (like the 1620) would close the deal. Thanks for any help!

Comments

  • jeffjohnvoljeffjohnvol Posts: 197
    edited 2008-07-09 15:00
    Check out:· http://forums.parallax.com/showthread.php?p=734148

    He used a SHT15. Not sure of the price, but its one wire and gives RH as well as Temp.
  • jefmjefm Posts: 50
    edited 2008-07-09 18:13
    That is a pretty cool looking project! However at least per the Sensirion paper the SHT15 is a "two wire serial" device. I'm hoping to find something 1-Wire compatible... I did find the DS2438, which is actually a battery monitor but can provide humidity data. However it's a 8pin SOIC and I'm unsure if I can interface that. Too tiny!
  • FranklinFranklin Posts: 4,747
    edited 2008-07-09 19:15
    http://www.sparkfun.com/commerce/product_info.php?products_id=494

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  • jefmjefm Posts: 50
    edited 2008-07-15 17:40
    Hey I might have to eat my words on the 'SHT15' not being a 2-Wire device!
    Maybe half my words. Apparently there are devices about that are I2C-ish but don't call it "I2C" because they'd have to pay royalties to Phillips. Check out this discussion:
    http://www.embeddedrelated.com/usenet/embedded/show/12389-1.php
    (scroll down to the bottom if you want)

    So does this mean the SHT15 is a device that acts like I2C? If someone could assure me that I can individually address a dozen SHT15's on the same set of Stamp pins, I would order them right now. They are expensive but I need lots of humidity readings for my application. Plus Parallax already goes through the trouble of putting it on a board that normal people can use. (Not that the DIY board Franklin recommended above isn't awesome!).
  • Tracy AllenTracy Allen Posts: 6,664
    edited 2008-07-15 18:33
    The SHT15 protocol is similar to I2C, but enough different that the I2C commands on the Stamp cannot be applied. One big difference is that there is no address, so you can't string these out same pair of wires, or with other true I2C devices. No, you can't individually address a dozen of them on one pair of wires. They could share the clock, but not the data line. In my own PBASIC code I bit bang the Start and Ack condition, and then use the SHIFTIN and SHIFTOUT commands to handle the data bytes.

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    Tracy Allen
    www.emesystems.com
  • FranklinFranklin Posts: 4,747
    edited 2008-07-15 19:48
    Jeff, I don't see where the DS2438 can measure humidity, am I missing something? Thanks.

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  • jefmjefm Posts: 50
    edited 2008-07-15 20:08
    Tracy,
    Well, I'm sad now but I do appreciate all the info. Thanks much!

    Franklin,
    it "doesn't", but apparently with it's thermometers and some codery it can output a humidity-like value. It was mentioned as an aside in a tech article, if I find it again I'll put it up. In hindsight it's probably not very good data. (compared to the larger, purpose-made sensirion and it's heated sensor). But it looked workable in desperation.
  • jefmjefm Posts: 50
    edited 2008-07-16 13:42
    Franklin:

    Here's one of the articles I mentioned, using the DS2438 for humidity:
    http://www.sensorsmag.com/sensors/Technologies+In+Depth/Sensors/Humidity/Moisture/A-1-Wire-Humidity-Sensor/ArticleStandard/Article/detail/361379
  • FranklinFranklin Posts: 4,747
    edited 2008-07-16 15:10
    Thanks Jef, I've seen that one. In fact I'm planning on using a MPX4115a and the DS2850 quad adc to do the same type of process.

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