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Re: a mysterious sensor

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Jan   you might check the data sheet for response time. Most of the ones 
I've seen are very slow.

Hul

Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> wrote:
> Hi,
> been doing some sensor stuff.
> I connect those to a PIC micro and an POE ethernet module, and send UDP data that way.

> Today was the turn for the relative humidity and temperature sensor DHP11.

> It is supposed to be within a few percent accuracy for RH.

> However with 60 % RH it displays 20 %....
> I have 2 and both do the same, software is good and checksum of communication is good.

> So started googling, seems MANY people have the same problem,
> nobody solved it, some people just wrote some correction math...
> That is what I am doing now too (and ordered an other sensor type).

> But, playing with it, trying to find out what I did wrong or what was wrong with those sensors:

> I noticed that if I put my finger on it the reading went way up from 20 % to over 60 %.

> Heat? no, also if I put my finger 5 mm away next to it...
> Tried a light bulb (Edison type), hot, no effect on RH.
> Tried a hot piece of metal: no effect on RH.
> Tried a dark screen, tried a high brightness CREE flashlight: no effect.
> Tried radiation sources (uranium marbles, thorium rods): no effect.

> Tried a wet piece of cloth next to it, way up it goes.
> But but, my fingers are DRY.

> So dry I need to wet those to open a sandwich bag...

> So WTF is going on ?
> Interesting physics, it seems to sense blood THROUGH the skin at a distance?? (theory 1).

> But HOW come these sensors are wrong for so many people ?
> It says in the data sheet that there is an internal lookup table in the on board micro it has for calibration (not use accessible AFAIK).

> Now I remember a discussion here years ago about customs using Xrays to check things, erasing chips,
> could have happened and would explain why so many people have this problem (theory 2),
> especially as datasheet mentions:
>  5) Light Affect
>         long time exposure to strong sunlight and ultraviolet may debase DHT's performance.
>  UV, Xray?

> But a sensor that can detect blood through the skin?
> Or has our body a moisture halo around it all the time?

> Anybody here played with the DHT11?

> Any application for this effect?

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a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-04-30 18:19 +0000
  Re: a mysterious sensor tabbypurr@gmail.com - 2017-04-30 12:08 -0700
  Re: a mysterious sensor Hul Tytus <ht@panix.com> - 2017-04-30 21:49 +0000
  a mysterious sensor pcdhobbs@gmail.com - 2017-04-30 15:04 -0700
    Re: a mysterious sensor Cursitor Doom <curd@notformail.com> - 2017-04-30 23:02 +0000
      Re: a mysterious sensor BM2335 <BM265@DMM.com.au> - 2017-05-01 11:19 +0800
    Re: a mysterious sensor Don Kuenz <g@crcomp.net> - 2017-05-01 03:06 +0000
      Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:17 +0000
    Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:16 +0000
  a mysterious sensor Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-04-30 15:46 -0700
    Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:20 +0000
  Re: a mysterious sensor Jon Elson <elson@pico-systems.com> - 2017-04-30 21:27 -0500
    Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:21 +0000
      Re: a mysterious sensor Jon Elson <jmelson@wustl.edu> - 2017-05-01 14:13 -0500
        Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 19:42 +0000
  Re: a mysterious sensor Frank Miles <fpm@u.washington.edu> - 2017-05-01 02:53 +0000
    Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 08:24 +0000
  Re: a mysterious sensor George Herold <gherold@teachspin.com> - 2017-05-01 05:11 -0700
    Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-01 14:21 +0000
  Re: a mysterious sensor "nuny@bid.nes" <alien8752@gmail.com> - 2017-05-01 13:17 -0700
    Re: a mysterious sensor Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-02 07:46 +0000

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