Smart Plant Monitor

For my prototypes, prioritizing low power consumption and my fondness for e-paper displays, I opted for LilyGo’s T5 2.13″ e-ink development board. This board features an ESP32 with Wi-Fi and Bluetooth capabilities, a 2.13″ e-paper display, and essential circuitry for battery charging and protection, among other functionality.

Next, I chose the sensors for measuring my plants’ vital parameters. With the intention of simplifying the assembly process by mounting everything on a protoboard and minimizing complexity, I opted for digital sensors. This decision meant I only needed to solder a maximum of four pins (I²C bus + power), with the convenience of receiving measurements in physical units.

My primary criterion was to select sensors that had already been tested and proven compatible with the ESPHome framework. For the light sensor, I selected the Maxim MAX44009, conveniently available on a compact purple module called GY-49. And for the temperature sensor, I repurposed an old GY-BM module containing a Bosch BMP280, which not only measures temperature with an accuracy of ±1.0°C but also provides barometric pressure readings.

Lastly, I chose a standard capacitive soil moisture sensor board with a simple 3-pin interface (GND, VCC, and AOUT). Although the output is analog, I planned to calibrate it as needed.

In the initial design revision, one sacrifice I had to make was omitting the measurement of soil fertility, which relies on soil electrical conductivity (EC) and necessitates adding corrosive-resistant pads to the PCB.

NOTE: Some capacitive soil moisture sensors are poorly designed and may even replace important components with inferior parts to be cheaper. This might result in shorter lifespans and/or wrong measurements. 

With all the materials prepared for assembly, you’ll begin by positioning them on the prototype board as depicted.

The LilyGo module is not mounted directly on the protoboard; instead you’ll use the female headers shown.

In this position, the components will be almost aligned, so you’ll have fewer, and shorter, wires to solder.

With all the components in position, proceed with soldering the connections between the pins and wires according to the Pinout Table.

Since the GY-49 and GY-BM modules have their 4 pins aligned, I decided to stack them and solder them together.

After you solder all the components and connections, I highly recommend that you check your connections with a multimeter. This way you make sure there are no short circuits that can damage the LilyGo T5 ESP32 module, and you can verify the continuity of your connections to avoid hardware errors.

Caution: Always solder in safe environments, paying special attention to ensure that smoke does not drift into your eyes or lungs, and be mindful of the hot parts you’ve recently soldered.

With all the hardware assembled, you can proceed with programming the ESP32. While Arduino is a common choice, for this project I’ve opted for ESPHome, a firmware that’s powerful and easy to configure for home automation projects. One of its standout features is its seamless integration and direct communication with Home Assistant. Since all the selected sensor modules are directly supported as Sensor Components on ESPHome, the configuration YAML file looks similar to this screenshot.

After you flash the LilyGo with the ESPHome firmware, calibrating the soil moisture sensor is necessary. This can be achieved by inserting the probe into soils representing 0% and 100% moisture levels, then noting the corresponding readings. This data allows for later application of a linear calibration.