Devlog #1

Schematic + PCB design

Finished setting up the schematic + PCB of my capacitive soil moisture sensor display. It features a capacitive sensor for detecting soil moisture, and also a capacitive touch sensor for interacting with the OLED display. The PCB features a two copper probe-fingers; one which connects to the MCU and forms a RC circuit, and the other which connects to ground.

How it works

The idea is that when the PCB is embedded in the dielectric soil, and the humidity level increases, the capacitance of the copper probes will naturally increase as well with the presence of water. Through the equation Time = Resistance * Capacitance, we can detect the change in how long the capacitor (the copper probes) take to charge/discharge, and thus approximate the humidity level, with some calibration of course.

The touch capacitance sensor (shown on f.cu) works similarly. When a finger approaches the copper pad, the capacitance of the circuit changes, and that is something we can measure. Only difference is that, for added robustness, I added a 555 timer to convert the capacitance into a frequency that the MCU can read.

Next steps

Since the PCB is already finished, the next step for me is to finish the code and order the PCB to test it out. As this is one of my very first PCBs ever, fingers crossed it’ll work 🤞