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practicalarduino / SHT1x

Arduino library to support SHT1x-series (SHT10, SHT11, SHT15) temperature / humidity sensors from Sensirion
http://www.practicalarduino.com/
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Difference Reading with USB5v and DC 5v, USB Power = Wrong reading. #2

Open c2h2 opened 13 years ago

c2h2 commented 13 years ago

I have constantly different reading figures, on the sensors side I have used typ 3.3v to SHT15 sensors.

on USB5v. The reading seems always 3-4 degrees higher. (tested on many machines).

While on the DC power, readings are very similar to other instruments for calibrating.

serialc commented 11 years ago

Using 3V3 should only put off your Celsius degrees off by 0.33 as far as I can see. This library is calibrated for 5V.

LittleHelper00 commented 8 years ago

If the Sensirion sensor SHt1x or SHT7x is supplied with a VDD = 3.3V, then you need to use a different conversion coefficient D1 in formula to convert the digital readout (SOT) to the temperature value. Interpolating the D1 coefficient values listed in the Sensirion datasheet table 8, the linear intepolated values to be used in the .cpp file are:

In case of degrees Celsius readTemperatureC() const float D1 = -39.66; // for 14 Bit @ 3.3V

In case of degrees Fahrenheit readTemperatureF() const float D1 = -39.42; // for 14 Bit @ 3.3V

Ciao, Giulio https://twitter.com/giuliotamberi

serialc commented 8 years ago

Looking at the code I see that this improved accuracy will impact the relative humidity more than the simply shift of 0.33 degrees Celsius for temperature. This makes @giuliotamberi's edits as comments worthwhile.