T & RH sensor

A project log for konijntje-thermo-humi

Gadget that shows room temperature & humidity on a LED-bar

Christoph TackChristoph Tack 06/03/2018 at 20:020 Comments

Temperature & relative humidity are key factors for climate control.  That temperature is important, is evident, but how does relative humidity influence people's comfort in a room?  Let's give an example: While increasing the relative humidity and keeping the temperature constant, most people will perceive this as "it's getting hotter".  This is due to the fact that the human sweat, to cool the body, evaporates less easily when the relative humidity increases.  As a result, the human body doesn't cool so efficiently and people will feel hot.

Relative humidity

Extensive research has been done in the past to determine what temperature and relative humidity values people feel as comfortable.  According to Wikipedia, relative humidity values should be between 50 & 60% ideally.  30-70% is acceptable.


Wikipedia has an article related to room temperature: "The World Health Organisation's standard for comfortable warmth is 18 °C (64 °F) for normal, healthy adults who are appropriately dressed."  To be honest, that's rather cold, so it will be shown in red on this gadget.  The maximum temperature is determined by the number of LEDs available.


In this project the SI7021 will be used as I had plenty of these lying around.  If you're interested in a comparison of RH&T-sensors.  You can have a look here.


The SI7021 has been implemented and tested on a STM32F103 Nucleo for ease of debugging.