DS18B20 reading high

[theweissguy]

I have a problem with my GPIO reading any of several DSB20 much too high - a constant 85 deg. C. The device isn't even warm to the touch. Any clues?

[DirkS]

Show us your setup:
* wiring
* configuration
* software you're using to read the sensor

[theweissguy]

Just checked the specs for the DS18B20 - "The power-on reset value of the temperature register is +85°C". It's clearly not getting the correct 1-wire signal from the PI. Wiring problem? Will check it out later today.

[bensimmo]

probably, check against this https://learn.adafruit.com/adafruits-ra ... g/hardware
I can tell you if you wire them up back to front they start to reach 85C on their own, they just don't tell you

[theweissguy]

Problem solved - wrong DS18B20 (PAR version) which only works in parasitic ("true" 1-wire) mode. All works now as it should.

[dentex]

Problem solved - wrong DS18B20 (PAR version) which only works in parasitic ("true" 1-wire) mode. All works now as it should.

Hello.
So are you using the probe in parasitic mode? If yes, could you kindly report some details for its wiring? Thanks!

[theweissguy]

Sorry, you misunderstood. I was setting up a test for non-parasitic use but had a parasitic only device from a old one-wire system.

[dentex]

Ok. So it's not a DS18B20 probe, right?

[theweissguy]

Correct - it's a three pin IC from Dallas Maxim.

[dentex]

Ok thanks.