There are many things that should be stored at a more or less specific relative humidity. If not, they will dry out or get moldy. There are solutions for this, such as Bodeva. These packets absorb or release moisture to maintain equilibrium at a specific relative humidity. The problem is that these things wear out over time and stop working. But how do you know? You can put indicator paper in the container, but unless it’s clear you have to open it to check, and that messes up the equilibrium.

The answer? Technology, naturally. Goals for this project:

  1. Audible alert if the relative humidity is too high or too low
  2. Low power, last months on a single battery charge
  3. No larger than a small jar


Parts List

This project uses the following parts:

1 x Adafruit Trinket M0
Adafruit Trinket M0 - for use with CircuitPython and the Arduino IDE
1 x TPL5110 Breakout
Adafruit TPL5110 Low Power Timer Breakout
1 x Si7021 Breakout Board
Adafruit Si7021 Temperature and Humidity Sensor Breakout Board
1 x Piezo Buzzer
Piezo Buzzer - PS1240
1 x Battery Connector
JST-PH 2-Pin SMT Right Angle Breakout Board
1 x LiPo Battery
Lithium Ion Polymer Battery - 3.7v 500mAh
1 x LiPo Charger
Adafruit Micro Lipo - USB LiIon/LiPoly charger - v1

This guide was first published on May 21, 2018. It was last updated on Jul 17, 2024.

This page (Overview) was last updated on Mar 08, 2024.

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