TerraBlade Sensor PCB

🌱 TerraBlade Sensor - Hardware PCB

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• TerraBlade - Modular Soil Scout (Software)
• TerraBlade - Modular Soil Scout (Enclosure)

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TerraBlade is a professional-grade, ultra-low-power capacitive soil moisture sensor designed around the Seeed Studio XIAO ESP32-C3.

This repository contains the complete KiCad 9 hardware design files, manufacturing plots, and mechanical Inkscape references for the PCB assembly. This board is designed using a "PCBA-Driven" workflow, meaning the electronics were engineered first, acting as the structural core for a modular 3D-printed enclosure.

Created by BJD Solutions.

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Key Engineering Features

• True Digital Capacitive Sensing: Ditching the noisy, drifty analog peak-detectors of standard cheap soil sensors. The FR4 PCB blade acts as the timing capacitor for an industrial-grade TLC555IDR oscillator. It outputs a raw, clean frequency directly to the ESP32's hardware Pulse Counter (PCNT) for flawless, high-resolution moisture data.
• Zero-Leakage "Parasitic" Power: The 555 timer is powered directly by an ESP32 GPIO pin. The ESP32 wakes up, powers the sensor, takes a reading, and kills the power before going back to sleep. Sensor quiescent current: 0.0µA.
• Panelized 3-in-1 Design: The Radio PCB, Power Hat, and Sensor Blade are all designed to be manufactured on a single 100x100mm panel connected by mouse-bites to save on fabrication costs.
• Mortise & Tenon Assembly: The Sensor Blade features a custom "tenon" tab that slots perfectly into the main Radio PCB and is soldered directly at a 90-degree angle, requiring zero wires.
• Pogo-Pin Power Hat: Handles the mechanical shear force of a plunging outdoor sensor by using through-hole Pogo Pins (spring-loaded contacts) rather than weak SMD conical springs.
• Low-Voltage Optimized: Features an ultra-efficient 573nm Yellow-Green LED that requires only ~2.0V to light up. It will reliably flash in "Config Mode" even when the 3x AA batteries are nearly dead. Includes a precision 1% 220kΩ voltage divider for highly accurate battery monitoring.

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📂 Repository Structure

• Full KiCad 9 project files (.kicad_pro, .kicad_sch, .kicad_pcb).
• Ready-to-order plot files, drill files, and the solder paste stencil map.
• High-resolution PDF exports of the schematic and PCB layers.
• Original Inkscape (.svg) files used to perfectly calculate the complex Edge.Cuts curves, alignment notches, and Mortise & Tenon joints.

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🛠️ Assembly & Manufacturing Notes

If you are ordering these boards from a fabricator please note the following:

1. Thickness: Order in standard 1.6mm FR4. The Mortise and Tenon slot on the Radio PCB is routed to exactly 1.7mm to provide a perfect slip-fit for 1.6mm thick material.
2. Solder Mask is Mandatory: Do NOT expose the copper on the Sensor Blade. The blade relies on the green Solder Mask to act as a waterproof dielectric barrier. Exposing the copper to wet soil will cause rapid galvanic corrosion and destroy the sensor.
3. Keyway Notches: The Radio PCB and Power Hat feature an 8-o'clock alignment notch. This is an asymmetrical keyway designed to interface with a matching rail in the future 3D-printed enclosure, preventing the board from twisting or being inserted backward.
4. Solder Paste Stencil: The F.Paste layer has been custom-tailored to remove paste from the structural Mortise & Tenon joints, allowing for clean, manual fillet soldering without bridging.

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🛒 BOM Highlights (LCSC)

The full BOM is included and can be generated from the KiCad schematic, here are the critical components used in this design:

• Microcontroller: Seeed Studio XIAO ESP32-C3
• Timer IC: TLC555IDR (Industrial Temp Range: -40°C to 85°C) - LCSC: C6987
• Pogo Pins (Power Contacts): CHIN-BAN PG1000-01-010P (1A Through-Hole) - LCSC: C49451494
• Config LED: TUOZHAN 0805 Yellow-Green 573nm (1.8V-2.4V) - LCSC: C688885
• Tactile Switch: TS-1187A-B-A-B (4-pin SMD) - LCSC: C318884

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📄 License

This hardware design is open-source. Feel free to build it, mod it, and plant it! Designed by BJD Solutions.

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Schematic:

PDF Version