BelfryBoy Clone SHT15 Temperature Humdity sensor

The BelfryBoy SHT15 Temperature/Humidity sensor
I have long been a fan of Davis Instruments weather stations, but sometimes I've just got to have a good hack about. A number of WXforum members were finding that the Davis 7346.166 Temperature Humidity sensor wasn't quite up to their standards, and sometimes the sensor became just plain inaccurate, caused by surface contaminants.

It's hacking time! After digging out the sensor I identified the sensing chip as the Sensirion SHT11. I read the datasheet and came across this interesting (for me at least) graphic.



So I made the simple deduction that If I changed the sensor on my Davis board to the SHT15 chip then I will have a more accurate reading. Significantly, the temperature reading is flatter for the SHT15 chip and the humidity is +/- 2% across a wider range than the SHT11.

But of course it's never that simple. 
After popping the protective cap off I found the sensor was covered in an encapsulating material.
So instead of just digging the material out I decided to make my own board. I found the connections fairly easy to identify once the potting material was removed.

then using Cadsoft Eagle PCB I produced a quick board with the added advantage of using the Sensirion SF1 filter cap to stop contamination. The cable is held in place using epoxy resin and then the entire assembly is protected from condensing moisture with an aerospace grade conformal coating.
A finished Belfryboy SHT15 T/H sensor.
The finished units are given a calibration verification at 33% RH and 75% RH using saturated salt solutions of Magnesium Chloride and Sodium Chloride.





Creative Commons License
BelfryBoy T/H sensor by Rob Smith is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

2 comments:

  1. Any idea if this will work on a 2005 VP2?

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    1. I'm not certain that it will, but there is an easy way to check; remove the white filter cover from your existing sensor, if the the chip looks like the one in the first photo on this page then the replacement will work.

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