Aliexpress DS18B20 seem out of spec - Page 1
Forum section: electronics / general

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

author: Ivan7enych
author_rank: Regular Contributor
timestamp: November 05, 2019, 08:12:20 am
content: Sensors can easily heat each other on such a dense board.

author: Rosch
author_rank: Newbie
timestamp: November 05, 2019, 09:47:39 am
content: 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 amAre right next to each other in the middle of the board and the difference between them is more than 2 degrees C

author: magic
author_rank: Super Contributor
timestamp: November 05, 2019, 10:55:56 am
content: Quote from: Rosch on November 05, 2019, 07:34:03 amIt's fake.I mean, seriously, there are fake DS18B20. I have seen them, decapped them, there were even two different versions with different dies.

author: techman-001
author_rank: Frequent Contributor
timestamp: November 05, 2019, 11:06:58 am
content: Quote from: Rosch on November 05, 2019, 07:34:03 amIt 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.

author: magic
author_rank: Super Contributor
timestamp: November 05, 2019, 11:18:46 am
content: If it becomes the Next Big Thing in the hobbyist sphere there will be fakes too.The lesson is mind your suppliers.

author: techman-001
author_rank: Frequent Contributor
timestamp: November 05, 2019, 12:58:50 pm
content: Quote from: magic on November 05, 2019, 11:18:46 amAbsolutely, 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.

author: Rosch
author_rank: Newbie
timestamp: November 05, 2019, 01:57:28 pm
content: 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.Quote from: techman-001 on November 05, 2019, 12:58:50 pmHobby projects however are allowed to take time.

author: DTJ
author_rank: Super Contributor
timestamp: November 05, 2019, 02:02:37 pm
content: 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.

author: Rosch
author_rank: Newbie
timestamp: November 05, 2019, 02:11:01 pm
content: 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

author: magic
author_rank: Super Contributor
timestamp: November 05, 2019, 02:12:51 pm
content: 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.