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General => General Technical Chat => Topic started by: Rosch on November 05, 2019, 07:34:03 am

Title: Aliexpress DS18B20 seem out of spec
Post by: Rosch on November 05, 2019, 07:34:03 am
So I bought a number of  DS18B20 Temperature sensors from Aliexpress.
And built a simple test circuit to test them all. I have attached a picture of the tester.

The values the sensors read in open air deviate a lot. 1.37 degrees C in both directions from the average of all sensors combined.

Could these sensors be genuine but rejected DS18B20?

The location of the sensors on the board does not seem to matter much in terms of deviation.

Code: [Select]
//2100 means 21.00 degrees C same is true for the deviation 100 means 1.00 degrees C
average= 2050
Adr00 = 28 B0 D3 79 A2 16 03 2F  ,  temp =  1987  Dev = - 62 On PIN 02
Adr01 = 28 94 28 79 A2 15 03 C6  ,  temp =  2100  Dev =   50 On PIN 02
Adr02 = 28 5C 30 79 A2 16 03 EF  ,  temp =  1937  Dev = -112 On PIN 02
Adr03 = 28 CA 6E 79 A2 16 03 DB  ,  temp =  1993  Dev = - 56 On PIN 02
Adr04 = 28 2A 43 79 A2 16 03 E6  ,  temp =  2118  Dev =   68 On PIN 02
Adr05 = 28 01 82 79 A2 16 03 47  ,  temp =  1962  Dev = - 87 On PIN 02
Adr06 = 28 91 4A 79 A2 16 03 EA  ,  temp =  1993  Dev = - 56 On PIN 02
Adr07 = 28 91 3E 79 A2 16 03 98  ,  temp =  2075  Dev =   25 On PIN 02
Adr08 = 28 15 40 79 A2 16 03 61  ,  temp =  2068  Dev =   18 On PIN 02
Adr09 = 28 03 13 79 A2 16 03 53  ,  temp =  2037  Dev = - 12 On PIN 02
Adr10 = 28 83 1F 79 A2 16 03 98  ,  temp =  2037  Dev = - 12 On PIN 02
Adr11 = 28 E3 1D 79 A2 16 03 D8  ,  temp =  2112  Dev =   62 On PIN 02
Adr12 = 28 13 35 79 A2 16 03 6C  ,  temp =  2075  Dev =   25 On PIN 02
Adr13 = 28 D3 40 79 A2 16 03 4C  ,  temp =  2043  Dev = -  6 On PIN 02
Adr14 = 28 4B 40 79 A2 16 03 5C  ,  temp =  1950  Dev = -100 On PIN 02
Adr15 = 28 67 4E 79 A2 16 03 35  ,  temp =  2018  Dev = - 31 On PIN 02
Adr16 = 28 77 6A 79 A2 16 03 89  ,  temp =  1950  Dev = -100 On PIN 02
Adr17 = 28 CF 6B 79 A2 15 03 B7  ,  temp =  1975  Dev = - 75 On PIN 02
Adr18 = 28 94 27 79 A2 16 03 FC  ,  temp =  2118  Dev =   68 On PIN 03
Adr19 = 28 3D 2B 79 A2 16 03 17  ,  temp =  2068  Dev =   18 On PIN 03
Adr20 = 28 8C BD 79 A2 16 03 0C  ,  temp =  1937  Dev = -112 On PIN 04
Adr21 = 28 A5 34 79 A2 16 03 14  ,  temp =  2187  Dev =  137 On PIN 04
Adr22 = 28 A0 B3 79 A2 16 03 65  ,  temp =  2081  Dev =   31 On PIN 05
Adr23 = 28 CA 26 79 A2 16 03 0C  ,  temp =  2118  Dev =   68 On PIN 05
Adr24 = 28 12 23 79 A2 16 03 BB  ,  temp =  2062  Dev =   12 On PIN 06
Adr25 = 28 16 1A 79 A2 16 03 10  ,  temp =  2062  Dev =   12 On PIN 06
Adr26 = 28 9B 35 79 A2 16 03 27  ,  temp =  1975  Dev = - 75 On PIN 06
Adr27 = 28 18 03 79 A2 16 03 8C  ,  temp =  2137  Dev =   87 On PIN 07
Adr28 = 28 DE 02 79 A2 16 03 6C  ,  temp =  2156  Dev =  106 On PIN 07
Adr29 = 28 E7 7D 79 A2 16 03 15  ,  temp =  2037  Dev = - 12 On PIN 07
Adr30 = 28 60 41 79 A2 16 03 DF  ,  temp =  2056  Dev =    6 On PIN 08
Adr31 = 28 29 93 79 A2 16 03 E1  ,  temp =  2025  Dev = - 25 On PIN 08
Adr32 = 28 A5 D2 79 A2 16 03 52  ,  temp =  1968  Dev = - 81 On PIN 08
Adr33 = 28 A8 A3 79 A2 16 03 B8  ,  temp =  2137  Dev =   87 On PIN 09
Adr34 = 28 DB AB 79 A2 16 03 47  ,  temp =  2106  Dev =   56 On PIN 09
Adr35 = 28 07 18 79 A2 15 03 AA  ,  temp =  2025  Dev = - 25 On PIN 09
Adr36 = 28 6A 7D 79 A2 16 03 B5  ,  temp =  2156  Dev =  106 On PIN 10
Adr37 = 28 0F 0B 79 A2 16 03 6C  ,  temp =  2025  Dev = - 25 On PIN 11
Adr38 = 28 5A 34 79 A2 16 03 42  ,  temp =  1993  Dev = - 56 On PIN 12
Adr39 = 28 5D 1F 79 A2 16 03 4F  ,  temp =  2143  Dev =   93 On PIN 12
Adr40 = 28 92 00 94 97 10 03 72  ,  temp =  1912  Dev = -137 On PIN 13
Adr41 = 28 06 0D 79 A2 16 03 66  ,  temp =  2175  Dev =  125 On PIN 13
Title: Re: Aliexpress DS18B20 seem out of spec
Post by: Ivan7enych on November 05, 2019, 08:12:20 am
Sensors can easily heat each other on such a dense board.
Title: Re: Aliexpress DS18B20 seem out of spec
Post by: Rosch on November 05, 2019, 09:47:39 am
That is true but these measurements are from one of the first measurements after powering on. And for instance:

Quote from: Rosch on November 05, 2019, 07:34:03 am
Code: [Select]
Adr20 = 28 8C BD 79 A2 16 03 0C  ,  temp =  1937  Dev = -112 On PIN 04
Adr21 = 28 A5 34 79 A2 16 03 14  ,  temp =  2187  Dev =  137 On PIN 04

Are right next to each other in the middle of the board and the difference between them is more than 2 degrees C
Title: Re: Aliexpress DS18B20 seem out of spec
Post by: magic on November 05, 2019, 10:55:56 am
Quote from: Rosch on November 05, 2019, 07:34:03 am
Aliexpress
It's fake.

I mean, seriously, there are fake DS18B20. I have seen them, decapped them, there were even two different versions with different dies.
Title: Re: Aliexpress DS18B20 seem out of spec
Post by: techman-001 on November 05, 2019, 11:06:58 am
Quote from: Rosch on November 05, 2019, 07:34:03 am
So I bought a number of  DS18B20 Temperature sensors from Aliexpress.
And built a simple test circuit to test them all. I have attached a picture of the tester.

The values the sensors read in open air deviate a lot. 1.37 degrees C in both directions from the average of all sensors combined.

It does seem like a lot. I've been using Ti LMT01 two wire temperature sensors and out of the box they agree within 0.1C to one another. They are a pleasure to use.
Title: Re: Aliexpress DS18B20 seem out of spec
Post by: magic on November 05, 2019, 11:18:46 am
If it becomes the Next Big Thing in the hobbyist sphere there will be fakes too.

The lesson is mind your suppliers.
Title: Re: Aliexpress DS18B20 seem out of spec
Post by: techman-001 on November 05, 2019, 12:58:50 pm
Quote from: magic on November 05, 2019, 11:18:46 am
If it becomes the Next Big Thing in the hobbyist sphere there will be fakes too.

The lesson is mind your suppliers.

Absolutely, I don't buy from ebay, aliexpress or China. My suppliers are Arrow.com, Farnell, Avenet etc.

I'd rather pay $100 extra for a bonafide factory chip than spend a week thinking I was the reason my project wasn't working because I can always get more money, but extra hours of life can't be bought and are irreplaceable.

Title: Re: Aliexpress DS18B20 seem out of spec
Post by: Rosch on November 05, 2019, 01:57:28 pm
Yea it is a difficult problem sourcing materials for projects.

How does one know if a supplier is legit. I do not know where the real ds18b20's are made. But loads of parts are made in china. My legit (farnell) attiny 416 eval board is made in china.

Spending money is not my favorite thing to do. If I pay 100 euro extra that would mean i would need to work extra hours of my life.  :P
Quote from: techman-001 on November 05, 2019, 12:58:50 pm
but extra hours of life can't be bought and are irreplaceable.

Hobby projects however are allowed to take time.
Title: Re: Aliexpress DS18B20 seem out of spec
Post by: DTJ on November 05, 2019, 02:02:37 pm
Just for fun, try laying some bubble wrap over and around the temp sensors. Make sure it's not in direct sunlight or close to a desk lamp or other heat source and run the test again.

I've found with much more precise temperature sensors I could not get agreement (to specs) without clipping them to a copper block, insulating it and then waiting a few minutes until it stablises.
Title: Re: Aliexpress DS18B20 seem out of spec
Post by: Rosch on November 05, 2019, 02:11:01 pm
Yea I was thinking about clipping them to a large aluminium heat sink to double check. But these sensors should work in open air.
Quote from: DTJ on November 05, 2019, 02:02:37 pm
clipping them to a copper block, insulating it and then waiting a few minutes until it stablises.
Title: Re: Aliexpress DS18B20 seem out of spec
Post by: magic on November 05, 2019, 02:12:51 pm
That's true, ideally they should be touching each other and isolated from the external world.
But it doesn't matter, these are fake. Another sign is the "serial" numbers which aren't serial but random. So far genuine Dallas chips had their numbers beginning with multiple zeros and (probably) continuous within one production batch.

As for suppliers - Farnell is a big one with relatively inexpensive shipping rate to most of Europe. Or look for local companies that supply components to the industry - in Poland I would be looking at TME (they ship internationally, not sure if competitive against Farnell) or Maritex. Alternatively, small local shops which either sell stock they bought long ago before the fakes plague took off or pledge to only buy from legit suppliers.