Temperature calculation is wrong when using a DS18S20 sensor.

[wecl]

see below

[netpok]

Please fill out the form above, especially the parts about your problem.

[wecl]

To Reproduce
connected a DS18S20 sensor to GPIO14 to a yunshan module and record a time series.

Expected behavior
smooth change of temperature over time.

actual faulty behaviour
when temperature is in- or decreasing the calculated temperature is jumping suddenly about 0.5 degrees at some point in time.

what i did
I looked to the sourcecode of the file xsns_05_ds18x20.ino, function Ds18x20Read() and compared the calculation with the spec of the DS18S20 sensor (https://datasheets.maximintegrated.com/en/ds/DS18S20.pdf).
On page 6 they describe as follow:
"Resolutions greater than 9 bits can be calculated using the data from the temperature, COUNT REMAIN and COUNT PER °C registers in the scratchpad. Note that the COUNT PER °C register is hard-wired to 16 (10h). After reading the scratchpad, the TEMP_READ value is obtained by truncating the 0.5°C bit (bit 0) from the temperature data (see Figure 4)..."

On line 332 of xsns_05_ds18x20.ino, the code fragment
if (data[0] & 1) { temp9 = ((data[0] >> 1) + 0.5) * sign; } else { temp9 = (data[0] >> 1) * sign; }
should be replaced by

temp9 = (data[0] >> 1) * sign;
because it is wrong to add 0.5 in case of calculating resolution greater than 9 bit.

I changed the code accordingly and tested it on my module and the output is as expected.
But i didn't test the calculation when the temperature is lower than 0 degrees.

[ascillato2]

Closing this issue as it has been fixed.

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