Autonomo Temp Sensor

[Liamo]

Hi...

this probably seems like a very basic question but here goes....

I purchased the Autonomo LoRA kit with grove temp sensor. All works fine except for the temperature sensor. It is marketed "v1.2" and the readings are about 2 to 4 degrees too high when compared against other sensors. Here is the code I'm using:

// settings for Grove Temp Sensor (v1.2) http://www.seeedstudio.com/wiki/Grove_-_Temperature_Sensor_V1.2
const int B = 4275;               // B value of the thermistor
const int R0 = 100000;            // R0 = 100k
const int pinTempSensor = A2;     // Grove - Temperature Sensor connect to A2

...and...

String takeTempReading()
{
  int a = analogRead(pinTempSensor );

  float R = 1023.0 / ((float)a) - 1.0;
  R = 100000.0 * R;

  float temperature = 1.0 / (log(R / 100000.0) / B + 1 / 298.15) - 273.15; //convert to temperature via datasheet ;
  return String(temperature);
}

Right now it says the temperature in my office is 25.25 degrees and it is definitely not that hot.

L

[GabrielNotman]

I think it might be due to the above calculations based on a 5.0V reference.

Try this:

float R = 1023.0 / (((float)a) * (3.3 / 5.0)) - 1.0;

[Liamo]

I tried that. That is yielding temps of circa 10 deg while the ambient temperature is circa 22 deg.

Are these Grove sensors known to be pretty reliable?

[GabrielNotman]

If you have a look at the datasheet, the thermister is rated to within 1% accuracy. Additionally, the nonlinearity seems to be lowest around the 25C range. The +-1.5 degrees is at the extremes of its measurement range.

I believe the issue is to do with the differences between the ADC on the Autonomo and the Uno. The example code is designed with a 5.0V reference on a 10bit ADC. The Autonomo uses a 3.3V reference, and the default resolution might also be 12bit.

[GabrielNotman]

Can you try explicitly setting the read resolution to 10 bits:

analogReadResolution(10);

Then if you could provide me with one or possibly a couple of readings. It would be useful to have the output from the example sketch, the expected temperature, as well as the raw analog readings.

[LulaNord]

Hi...i am a new user here. It seems the issue is to do with the differences between the ADC on the Autonomo and the Uno. The example code is designed with a 5.0V reference on a 10bit ADC. The Autonomo uses a 3.3V reference, and the default resolution might also be 12bit.