SHT15 Readings Offset (..?!)

Hardware
1

I am trying to use the SHT15 Temp/RH surface mount component in my PCB footprint with an Electron (with 10K pull-up; all precautions for ventilation taken.). According to the datasheet and the SHT1x library in the Particle Web IDE, it looks like you should be able to use any two digital pins as Clock and Data lines for the sensor since you manually toggle the signal for synchronization anyway ( got this from the sendCommandSHT() function in SHT1x.cpp ).

  1. Is my understanding right?

  2. I am trying to use the following configuration with the SHT15:

       #define dataPin  B0 //DATA
   #define clockPin C0 //SCKL

I have an SHT10 running parallely on another Electron on D5 (Data) and D4 (SCKL). The SHT15 readings are at least 10 deg F higher than those from the SHT10 even though they are right next to each other. Although the SHT15 is responsive to temp/RH change, the values seem to be offset somehow…

Any thoughts on why this may be the case?

2

Any thought? @Dave @rickkas7 @peekay123

3

Yup, the protocol is bit-banged so you can assign any two pins. As for the temperature difference are you running the electrons physically side-by-side. Is there a difference in how the SHT1x is mounted? Are these breakouts or do you have them mounted on a pcb?

All this to say that conduction and convection heating from adjacent components can create an increase in temperature. From the specs:

If the SHT1x shares a PCB with electronic components that produce heat it should be mounted in a way that prevents heat transfer or keeps it as low as possible.

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4

I’ve found that almost all of the inexpensive sensors are wrong by some amount. Some caused by the sensor itself, and some because of how I’ve mounted it.

Since I generally measure room temperatures with them, I just calibrate them with a constant offset, which has been close enough for my purposes.

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5

Thank you @peekay123 @rickkas7 . Appreciate your help! :slight_smile:

6

The SHT15 was the first pro version Temp / Humidity sensor I purchased and it was accurate and stable.

I would recommend the New SHT31 sensor in the future, it runs on real I2C and there is already a working Particle library for it.

7

I am using the SMD SHT15 directly on my PCB. I did ensure that the module is far away from the power circuit and other heating components on the board. Maybe elevating it using headers might improve the ventilation around the module. I’ll try it out.

8

My PCB was a breakout so it was not attached to any PCB that had other components that were heating up. I would think that could easily cause the readings to be higher than real temps.

9

I didn’t realize the effects would be this drastic. #PCBdesignNoob

I will try to use long headers and post my results here for others to benefit. :slight_smile:

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