Sparkfun Weathershield wrong temperature

General
1

Does anybody have experience with the Sparkfun Weathershield for the Photon ?
I have one running with the latest SW from the Sparkfun github and FW 0.4.6.
Everything runs fine, I also added a DS18B20 to the shield and moved the DS18B20 30 cm away from the weathershield. The weathershield measures on average 2,5 degrees of Celcius higher then the 18B20. The DS18B20 measures the same room temperature as my NEST thermostat in the same room.

Am I doing something wrong or do the Humidity/Temperature Sensor - HTU21D and
Barometric Pressure - MPL3115A2 simply get a wrong temperature due to heating up from the Photon ?

2

I believe is the heat of the photon… I see the same thing… Also the barometric pressure is off by 1" give or take… Still investigating if you find something… Let me know.

3

I’ve run the SF Photon Weathershield for about a month (with just the onboard sensor components), and have also noted a similar offset … in my case the Photon will read about 5-6 deg F higher than an adjacent thermometer. (I haven’t been tracking the baro_temp, only the HTU21D reading).

I haven’t investigated the reason for the discrepancy as I haven’t been overly concerned about this level of inaccuracy … your theory of possible localized self heating sounds very plausible though. I think it’s unlikely you are doing anything wrong.

4

@ljd2, @frlobo, thanks for the feedback, indeed I don’t think we are doing something wrong, it is heat coming from the Photon, does somebody has an idea on how we can compensate for that heat or should I simply rely on the DS18B20 ?
KR,
Rudy

5

I think so… THE DS is the best choice for temp, since the photon temp can be variable…

As far as the baro… I don’t know if it’s a calibration issue, or what… But there is a problem with the reading…

6

If it’s mounted on a vertical surface with the temp sensor below the Photon and good ventilation, does that help? Putting the Photon into sleep mode and measuring/transmitting every 10 minutes would probably make a big difference. This is assuming the sensor itself doesn’t consume enough power to affect the reading.

7

@TempHumMeas, thanks for the tip, I’ll give this a try one of the days …

8

experiencing the same.

Shield temp values are about 5-6 degrees F higher than actual…

I does this form cold startup even, i.e. photon was not running, turn on and immediately it reads 5-6 degrees higher than actual…

Any barometric or humidity compensation you need to do?

9

I get most inaccuracies from the barometer…

10

Dear all, I now put the Photon to deep sleep between measurements for 5 minutes and I get correct temperature measurements, so most likely the wrong measurements are due to heating from the photon on the weathershield. So so far so good and issue closed for me.
KR,
Rudy

11

I’m using a DHT22 with the Photon. The DHT22 is mounted on the outside of a small enclosure, but is still influenced by the amount of heat put out by the Photon. I may try the deep sleep approach to see if that mitigates the problem. What approach do you use to put the Photon to sleep for 5 minutes?

12

I’m not an expert on Photon sleep modes by any means, but have been using …

System.sleep(SLEEP_MODE_DEEP, time_interval);

… after setting the system mode - SYSTEM_MODE(SEMI_AUTOMATIC);

I’ve had similar success getting much closer temperature readings. (I happen to be using a 15 minute sleep interval).

13

I too am having higher temperatures on both temp and humidity sensors. I am curious though, what effect does putting the Photon to sleep have on reading wind/rain data?