ok I bought 2 sensors from a local store and now it found them....
so probably a bad batch.... where can you see the batch?
Thank you all for trying to help me with this!
Sagirokach:
Ok wait isn't that what I posted?
Sorry, I missed it.
Congrats, I am glad you solve it.
If they are real DS18B20 sensors, they should have writing on the flat face of the device which should look like this:
DALLAS
18B20
1218C4
4007A
The first two lines are obviously the important ones. If there's no writing at all, it's probably a dud, one way or another.
Pete
on 9 of the 10 I have this written:
DALLAS
18B20
1541C4
+233AA
And those won't engage.
the last one has this written:
DS18B20
1433B1
MALAY
507AF
and this one will get extermly hot when I put it in the right way as the other and as the new sensor that I bought today.
so about the other 9 what can be the problem?
Apparently correct figure does not mean anything. The fakes on ebay frequently looks like original and in addition they works. Some time ago it was very discussed chip FT232RL. It has exactly same package. Firstly there was visible difference in printed label and mark while original has it engraved by laser. Lately, the fakes was also engraved. Fake chips works so normal user cannot recognize between. FTDI released the drives which disabled fake FT232. It means internally they differs.