DS18b20 temp reading too high

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clintebbesen
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Joined: 26 Sep 2016, 02:08

DS18b20 temp reading too high

#1 Post by clintebbesen » 28 Sep 2016, 02:11

Hi,

I have two DS18b20's, one I think the temp is correct or within 1 degree, but the other is reading too high by about 5 degrees. It would be roughly 22 degrees in this room but the device is reading 27 degrees currently.

Both temp sensors are wired the same, they get ground, 3.3v, and data goes to GPIO 0, i havent got any resistors on there. I saw others say you need a resistor, but it seems to work ok without it? Being a digital signal the temp isnt going to change by adding a resistor.

Any ideas on what could it be? Is it just a faulty sensor? maybe i could try use another digital thermometer and measure the temperature probe temp at a few different temperatures, eg 20, 25, 30, 40 degrees and see if the error is consistent and use the formula box to offset the temp? i guess that could work if the error is always the same, but was hoping there is something easier to do

Madbanana
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Posts: 13
Joined: 16 Oct 2016, 20:48

Re: DS18b20 temp reading too high

#2 Post by Madbanana » 24 Oct 2016, 20:59

Hi, obvious first question - are they both 18B20 - or is one 18S20 / 1820?

I ask because I found there was a difference which caused incorrect readings on one - but I think more than you are seeing.

Here's a comparison of the two ... https://www.maximintegrated.com/en/app- ... vp/id/4377 .. which may (or may not help).

I've used dozens of these in the past on a variety of platforms / voltages and never had one malfunction.

Good luck!

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