DS18B20 reports -196.60°F when temp < 4.1°F w/ DallasTemp library only about arduino-temperature-control-library HOT 2 CLOSED

The rawToCelcius() and rawToFahrenheit() functions (which get called when you grab the temperature) compares the raw value (fix point scaled -7) out of the device to constant DEVICE_DISCONNECTED_RAW (-2032). I couldn't quickly figure how this constant was derived, but it's wrong (at least for a 12-bit resolution DS12B20). If the output of the device is less than this constant, the DEVICE_DISCONNECTED_C (-127) or DEVICE_DISCONNECTED_F (-196.6) constant gets returned.

If we convert the constant, which is supposed to be the lowest allowed value, to a temperature:

-2032 * 2^-7 = -15.875C = 3.425F

Since the lowest temperature the device can produce is actually -55C, the correct value for this constant should be -7040:

-55 * 2^7 = -7040

Therefore, in file DallasTemperature.h, if you change the value for constant DEVICE_DISCONNECTED_RAW from -2032 to -7040, the library will report temperatures down to -55C.

from arduino-temperature-control-library.

See https://github.com/milesburton/Arduino-Temperature-Control-Library/tree/tommi-tuovila-temperature-fix

from arduino-temperature-control-library.