# Humidity sensing

Available for checkout from the ITLL are three main types of humidity sensors, and this week I decided to test them against each other.

HIH-4030 (code available on my [Github](https://github.com/squid-lattice/sensors/tree/main))

[![image.png](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/scaled-1680-/FkLeWPlGYWbYQH9D-image.png)](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/FkLeWPlGYWbYQH9D-image.png)

DHT-11 (code available on my [Github](https://github.com/squid-lattice/sensors/tree/main))

[![image.png](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/scaled-1680-/S4J74QHtXpQyNnvT-image.png)](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/S4J74QHtXpQyNnvT-image.png)

Indoor 2-in-1 Humidity/Temp monitor

[![{5FF7F381-2652-4CC0-9BC5-F7D1663AA9FD}.png](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/scaled-1680-/IXsJiz6f1SZ8An8r-5ff7f381-2652-4cc0-9bc5-f7d1663aa9fd.png)](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/IXsJiz6f1SZ8An8r-5ff7f381-2652-4cc0-9bc5-f7d1663aa9fd.png)

[![{DB636874-176D-4A6F-8DD5-29B8C721D8A3}.png](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/scaled-1680-/PRhQJW0rmRYLwUhF-db636874-176d-4a6f-8dd5-29b8c721d8a3.png)](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/PRhQJW0rmRYLwUhF-db636874-176d-4a6f-8dd5-29b8c721d8a3.png)

*Humidity data comparing two identical HIH-4030 sensors - the red data corresponds to a broken sensor. When I generate humid air near the sensors, readout plummets to zero (red data) on the broken sensor.*

The HIH-4030 and the DHT-11 both use a capacitive element to detect changes in humidity. They have a stated accuracy of 5%. I found that two identical HIH-4030 sensors gave output that varied by ~4%, which is within the claimed accuracy. However, one of them appears to be broken because when I placed the sensors next to each other and generated humid air near the sensors, the RH% signal increased on one sensor (as expected, blue data above/red data below), but the other sensor's output plummeted to zero before rising.

[![shared image (17).jpg](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/scaled-1680-/aFSerp97h4KGffsU-shared-image-17.jpg)](https://itll-wiki.colorado.edu/bookstack/uploads/images/gallery/2026-10/aFSerp97h4KGffsU-shared-image-17.jpg)

*I know the y-axis is impossible to read in image above; room RH% is ~40% on top (blue) trace, and ~36% on bottom (red) trace. Blue data plummets to zero when exposed to humid air source, suggesting sensor failure. I retired sensor from our inventory. The linear plot on left I pulled from the datasheet for the HIH sensors and used this plot to write code to convert Arduino's analog signal to RH%.*