Negative temperature measures

[kgx123]

Hi Charles-Henri,

I am using your excellent TH02 library on Moteino. I have one sensor outside my house, with minus degrees celsius. However the TH02 lib reports the absolute value, without the minus prefix. E.g. “6.5” instead of “-6.5″. Please advise on what I am doing wrong.

Merci beacoup,
Karim

From the Arduino sketch:

int16_t temp, rh, rh_comp;
 //uint8_t status;
 
 Serial.print(F("Starting Temperature conversion."));
 sensor.startTempConv();
 sensor.waitEndConversion();
 Serial.println(F(".done!"));

 // Get temperature calculated and rounded
 temp = sensor.getConversionValue();
 
 // Display unrounded value (raw)
 Serial.print(F("Temperature = "));
 // this call does not do any I2C reading, it use last reading
 Serial.print(sensor.getLastRawTemp()/100.0);
 Serial.print(F(" C  =>  "));
 // Display now rounded value returned by 1st call
 Serial.print(temp/10.0);
 Serial.println(F(" C"));

[Charles]

Karim,

Would you try to modify the following line (261 to 269) to the library th02.cpp

 if(result >= 5000)
{
  result -= 5000;
}
else
{
  result -= 5000;
  result = -result;
}

by

result -= 5000;

Let me know if it works, I don’t understand why I’ve done like that

[kgx123]

Changes done to th02.cpp. Thanks! Seems to be working fine ::

NEGATIVE TEMP:
Starting Temperature conversion..done!
Temperature = -7.00 C => -7.00 C

Starting Temperature conversion..done!
Temperature = -5.82 C => -5.80 C

Starting Temperature conversion..done!
Temperature = -2.10 C => -2.10 C

Starting Temperature conversion..done!
Temperature = -0.79 C => -0.80 C

POSITIVE TEMP:
Starting Temperature conversion..done!
Temperature = 1.43 C => 1.40 C

Starting Temperature conversion..done!
Temperature = 2.87 C => 2.90 C

[Charles]

Excellent,
I will modify the lib on github
Charles