Summary
Detect Power‑On Reset and Insufficient Power for DS18B20
Contributed by @Laxilef, reviewed by @RobTillaart
Changes:
- Added detection of two special error conditions specific to DS18B20 sensors:
- Power‑On Reset (85°C) – Returns DEVICE_POWER_ON_RESET_RAW when the sensor reports 85.00°C and scratchpad[6] == 0x0C. This identifies the well‑known “85°C glitch” on power‑up (common with counterfeit or mis‑wired sensors).
- Insufficient Power / Conversion Failure (127.94°C) – Returns DEVICE_INSUFFICIENT_POWER_RAW when the sensor reports 0x07FF (127.94°C), indicating a failed conversion (e.g., parasitic power without Vdd grounded, voltage drops).
Implementation details
- The logic is borrowed from the Linux kernel driver and verified by community testing.
- Only applies to DS18B20 family devices.
- Existing getTempC() still returns the raw value; advanced users can check the specific error codes via the new constants.
Credits
Thanks to @Laxilef for the contribution and @RobTillaart for in‑depth technical review.
Contributors
RobTillaart and Laxilef