Smart Solar Plant Monitor: Track Soil, Light & Humidity Without Recharging

This project is about building a self-sustaining plant monitoring device that never needs manual charging. It continuously tracks your plant’s key stats such as:

1. Soil humidity
2. Air temperature
3. Air humidity
4. Ambient light
5. Battery level (accurate monitoring)

To eliminate the hassle of recharging, the device includes a large 18650 lithium-ion cell paired with a 1W solar panel. The solar panel, together with an integrated charger and lithium BMS, ensures the battery is constantly replenished during the day.

At the heart of the system is my custom Root sensor module, designed specifically for plant applications, combined with the Sprig-C3 ESP32 development board. The Sprig-C3 integrates advanced battery management, a charger, and accurate monitoring ICs. It also offers USB-C programming and seamless integration with Home Assistant for automation and user-friendly control.

The goal is simple: gain insights into your plant’s health without adding maintenance tasks. A plant already requires enough care; you shouldn’t also have to babysit the sensor by charging it regularly.

This system also serves as an excellent playground for:

1. experimenting with smart gardening,
2. collecting and analyzing data, and
3. deploying multiple sensors to map environmental conditions.

Since the Sprig-C3 supports Arduino and Espressif frameworks, you can leverage both WiFi and Bluetooth Low Energy (BLE) to customize the functionality to your needs.

Hardware

1. 1x 3D Printed Enclosure
2. 1x Root - plant monitoring module
3. 1x Sprig-C3 - ESP32 development board
4. 1x Battery mount for 18650 cell
5. 1x Lithium Ion 18650 battery
6. 1x Solar panel 1W
7. 1x JST PH 2.0 battery connector assembly (optional)

Tools & Consumables

1. 3D printer
2. Hot glue gun
3. Silicone sealant
4. Soldering iron & solder wire

Ideally, the enclosure should be 3D printed using a transparent material, to allow some light to hit the ambient light sensor. The air temperature and humidity sensor will inevitably read slightly scewed values due to the enclosure, but most 3D prints are not air tight, so their values will be related to the real conditions. Also, if the sensor will be placed outside, PLA material should be avoided, and PETG should be used instead. We just need to make sure that we use thick walls for this print, to avoid water ingress through the printing layers.

The Root module is designed to attach to our Sprig-C3 ESP32 devkit, therefore we need first to solder some 10pin female headers to it, then attach the Sprig on the Root.

We need to solder a PH2.0 connector to the 18650 battery mount, in order to attach it to the corresponding connector of the Root module. Be careful, because some connector assemblies have reversed polarity. To be sure, solder the 18650 battery mount directly to the B+ and B- battery input pads of the Sprig-C3 as shown in the relevant picture. This is a good time to glue the battery mount to the inside bottom of the enclosure.

In this step, we have to solder some wires to the solar panel's pins (using leftover cables from the 18650 mount is recommended). Next, the solar panel must be glued to the top side of the enclosure's lid, making sure the wires go through the lid's holes to the inside of the enclosure. We can use hotglue for this step, altough silicone sealant might be the better solution for this application. We have to make sure we cover with glue every possible spot where water could enter the enclosure through the lid. In this step, we also have to solder the solar panel's wires to the 5V and GND pins of the Sprig-C3.

In this step, we apply a general amount of silicone sealant on the slit of the enclosure from the inside, and then insert the sensor through it. Inevitably, some silicone will attach to the Root while passing though the slit of the enclosure. We can clean the protruding sensor from extra silicone, and apply some extra silicone to the outside bottom of the enclosure, to ensure no ingress of water can happen.

The easiest and most user-friendly way to monitor our plants with this system is using the Home Assistant platform via the ESPHome plugin. First we create a new ESP32-C3 device in ESPHome and follow the instructions on the screen. Then, inside its configuration YAML file, we copy-paste the contents of the sample configuration file after line 42.

In this final step, we have waited for the silicone to dry, and after we insert an 18650 lithium-ion cell to the battery mount, we close the lid with the solar cell, and we have an assembled monitoring device. We now "plant" it near the root of our plant, and we can monitor our plant's status through the Home Assistant interface.