Business Card
I often take an approach to understand new concepts through working with my hands and create something. -My business card is one of the outcomes of this approach.
Capacitance soil sensor is one of the simplest, most popular principles to measure soil moisture from its dielectric permittivity. Throughout the summer of 2022, I taught myself the principles of these sensors while designing one as a learning experience.
My business card has a capacitance probe (towards right) and a simple oscillation circuit with a 555 timer. By applying a voltage of 5V/3.3V through a connector on the top left, it returns the change in dielectric constant of the probe in analog values.
Galleries
PCB design (KiCad) 
Circuit design 
Parts list
All parts are 0603 SMD size (except D2 - SOD123).
| References | Value |
|---|---|
| C1, C2, C5 | 1uF |
| C3 | 10nF |
| C4 | 0.1uF |
| D1 | LED |
| R1, R2 | 330 |
| R3 | 1.5k |
| R4 | 1M |
| R5 | 1M |
| U1 | XC6206P302MR |
| U2 | TLC555xD |
Warning
Please acknowledge that this is part of my learning process. The parts and design may change over the course to further improve the sensor.
- Sensor sensitivity to moisture seems to be low at this moment. I believe this is due to the suboptimal combination of a probe size and a resistor that comprise the RC circuit (I re-designed the probe after I determined the initial schematics).
- The sensor value can be highly affected by salt contents. This is primarily due to the cost compromises; limited by the maximum square wave frequency that 555 timer IC can generate.