External temperature & humidity sensor..

External temperature & humidity sensor.. - Printable Version

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RE: External temperature & humidity sensor.. - werk_ag - 23-08-2015

Hi, zitoune

Please check the user config options in the TX software.

For the SH21 it should be:

Code:
// -------  Define type of Temperature Humidity for Sensor 0 and Sensor 1 --------------

#define TH_Sensor0  0      // 0 for SHT2x sensor, 1 for HTU21 sensor, 9 for Not Used

#define TH_Sensor1  9      // 0 for SHT1x sensor, 1 for DHT22 sensor, 9 for Not Used

For the DHT22 it should be:

Code:
// -------  Define type of Temperature Humidity for Sensor 0 and Sensor 1 --------------

#define TH_Sensor0  9      // 0 for SHT2x sensor, 1 for HTU21 sensor, 9 for Not Used

#define TH_Sensor1  1      // 0 for SHT1x sensor, 1 for DHT22 sensor, 9 for Not Used

You also can keep both connected:

Code:
// -------  Define type of Temperature Humidity for Sensor 0 and Sensor 1 --------------

#define TH_Sensor0  0      // 0 for SHT2x sensor, 1 for HTU21 sensor, 9 for Not Used

#define TH_Sensor1  1      // 0 for SHT1x sensor, 1 for DHT22 sensor, 9 for Not Used

You should also check/define in the RX user config options which one will be your main temperature / humidity sensor.

Code:
#define MainOutTH_Sensor 0   // 0 for sensor type SHT21 or HTU21D, 1 for sensor type SHT1x or DHT22

RE: External temperature & humidity sensor.. - zitoune - 24-08-2015

Oh yes you are totally right, I set the TH_SensorX flag to a wrong value (1 and 9 instead of 0 and 9). I corrected it and it works well now.
Thanks!

RE: External temperature & humidity sensor.. - werk_ag - 24-08-2015

Is good to know. Smile

Thank you

RE: External temperature & humidity sensor.. - zitoune - 24-08-2015

I am still puzzled why the DHT22 went completely crazy with the humidity reading while the temperature seems fine.

I use two other same sensors, with the RX and the WD units which are both inside the house.
However, the humidity level is less important where the WD unit is stationed (due to air-conditioned). But the RX unit is exposed to as much humidity as the outside TX unit..

RE: External temperature & humidity sensor.. - werk_ag - 26-08-2015

(24-08-2015, 15:08)zitoune Wrote: I am still puzzled why the DHT22 went completely crazy with the humidity reading while the temperature seems fine.

IIRC the DHT22 (as the DHT21) uses a thermistor for the temperature and a separate sensor for humidity. If one of them gets faulty, it's possible that the other can continue to function.

Many times I saw problems with the humidity readings from the DHT2x sensors family (seems that the DHT22 in this matter is worse than the DHT21). It works great inside, and seems to last forever, but when used outside, in frequent high humidity environments, it last only some months.
During the first year of operation of the Meteocercal Weather Station I used a DHT22 for outside readings, after one year I was tired of changing the sensor, it was then that I added support in WeatherDuino Pro2 for SHTxx series of Sensirion, and changed the outside TH sensor to a SHT21. In the last two years, I never had any more problems.
I have also an SHT11, working without problems, for two years too.

RE: External temperature & humidity sensor.. - laulau - 20-11-2015

Hi,
Which finally is the best choice?
SHT21, DHT22 or HTU21D ?
Thanks

RE: External temperature & humidity sensor.. - werk_ag - 21-11-2015

For outside readings, my recommendation is using an SHT1X.
SHT10, SHT11 or SHT15 depends on your budget.
The SHT2x range is also very good, but you should understand that connecting and using a SHT2X it not as easy as a SHT1X.

For inside readings an DHT22 is just fine, an HTU21D is better.

RE: External temperature & humidity sensor.. - laulau - 21-11-2015

Why is connecting and using a SHT2X not as easy as a SHT1X ?
The SHT21 is mounted on a little board :http://www.ebay.fr/itm/SHT21-Digital-Humidity-And-Temperature-Sensor-Module-Replace-SHT11-SHT15-top-/221685877037?hash=item339d82092d:g:AzcAAOSwBLlU2Cdv
Laurent

RE: External temperature & humidity sensor.. - werk_ag - 22-11-2015

Maybe I have not used the correct terms.
The question is, the SHT2x series communicates using the I2C protocol, which implies that you also have to install the I2C bus extender Philips chip on the TX unit, which is not required for the SHT1X series.
Some care with the cables must also be taken.

RE: External temperature & humidity sensor.. - hornychz - 27-07-2016

Hi,

Maybe for someone it can be a useful overview of temperature and humudity sensors that use. Probably not complete, perhaps not even entirely accurate. Certainly, it is necessary to preview the datasheets:

[Image: Sensors.jpg]

Please note! All this is not recommended sensors, it is only an overview of those that occur frequently in e-shops. Another informations are here.

And here is to possible download the original spreadsheet:

The original spreadsheet

For any addition or correction thank you.
(Sorry for using comma instead of dot in my spreadsheet Wink

Regards