Custom PCB Shield for Multi-Zone Security System

A custom two-layer Arduino Mega shield PCB designed to replace the breadboard prototype of the Multi-Zone Smart Security System. The board consolidates all control and sensing connections into a single, permanent, and reliable hardware platform.

🔗 Firmware Repository: Multi-Zone Smart Security System

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Table of Contents

• Overview
• Schematic
• PCB Layout
• 3D Render
• Design Specifications
• Bill of Materials
• File Structure
• License

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Overview

This project is a direct continuation of the Multi-Zone Smart Security System. The breadboard prototype, while functional, was not a reliable or permanent form factor. This shield was designed in KiCad to produce a clean, manufacturable PCB that sits directly on top of the Arduino Mega 2560 and exposes all the necessary connectors for the system's peripherals.

The design follows standard Arduino shield dimensions, ensuring mechanical compatibility with the Mega footprint. All components are through-hole (THT), making the board straightforward to solder by hand. The schematic was drawn as a single sheet with clear net labeling, and the PCB layout was routed with dedicated power and signal trace widths, a ground copper pour on the back copper layer, and a defined keep-out zone to avoid interference with the Arduino's onboard components.

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Schematic

The schematic captures the complete connectivity of all shield components in a single sheet. Each peripheral is connected to the appropriate Arduino Mega pins, with net labels used throughout to keep the diagram readable and avoid long crossing wires.

Key connections documented in the schematic:

• RFID Reader (MFRC522) — SPI bus (MOSI, MISO, SCK) with a dedicated chip-select pin
• ESP8266 Wi-Fi Module — Serial1 hardware UART (TX1 / RX1, pins 18–19)
• LCD Screen — 4-bit parallel interface
• 4×4 Keypad — 8 digital I/O pins (4 rows, 4 columns)
• PIR Sensors & Reed Switches — Digital input pins, one per sensor across all three zones
• Buzzers — Digital output pins, one per zone
• Power distribution — 5 V and 3.3 V rails routed from the Arduino's onboard regulators to the appropriate peripherals

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PCB Layout

The PCB is sized to match Arduino Mega shield dimensions, with connectors positioned to align with the Mega's header rows. Components are placed on the front side only (all THT). A keep-out zone is defined over the Arduino's onboard USB and power jack area to prevent clearance violations.

Routing highlights:

• Signal traces routed at 0.25 mm width
• Power traces routed at 0.5 mm width
• 12 vias used to transition signals between layers where needed
• Ground copper pour applied to the full B.Cu (back copper) layer, connected to the GND net
• All 5 V connections made through dedicated routed tracks on F.Cu

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3D Render

The images below show the KiCad 3D render of the board before fabrication. All component footprints are placed on the front side of the board.

Front

Back

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Design Specifications

Board Stackup

Layer	Type	Thickness	Material
F.Silkscreen	Top Silk Screen	—	—
F.Paste	Top Solder Paste	—	—
F.Mask	Top Solder Mask	0.01 mm	—
F.Cu	Copper	0.035 mm	—
Dielectric 1	Core	1.51 mm	FR4
B.Cu	Copper	0.035 mm	—
B.Mask	Bottom Solder Mask	0.01 mm	—
B.Paste	Bottom Solder Paste	—	—
B.Silkscreen	Bottom Silk Screen	—	—

Total board thickness: 1.6 mm | Solder mask color: Green

Board Dimensions

Property	Value
Width	100.584 mm
Height	78.232 mm
Area	7,863 mm²

Routing Rules

Parameter	Value
Signal trace width	0.25 mm
Power trace width	0.50 mm
Minimum clearance	0.2 mm
Copper to edge clearance	0.075 mm
Minimum via diameter	0.4 mm
Minimum drill (through hole)	0.3 mm
Hole to hole clearance	0.25 mm

Board Statistics

Item	Count
THT components	27
Through-hole pads	170
NPTH (mounting holes)	6
Through vias	12
Total components	33

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Bill of Materials

The table below lists the components used on the shield.

Reference	Value / Description	Footprint	Qty
DS1	WC1602A (LCD Screen)	IDC Header 2×8, 2.54 mm	1
J1	Power Header	Pin Header 1×8, 2.54 mm	1
J2	PWM Header	Pin Header 1×10, 2.54 mm	1
J3, J5	Analog Headers	Pin Header 1×8, 2.54 mm	2
J4	PWM Header	Pin Header 1×8, 2.54 mm	1
J6	Communication Header	Pin Header 1×8, 2.54 mm	1
J7	Digital Header	Pin Header 2×18, 2.54 mm	1
J8	ESP-01 (ESP8266 Wi-Fi Module)	ESP-01 Module Footprint	1
J9, J10	Connectors 1×8	Pin Header 1×8, 2.54 mm	2
J11, J13, J14	Screw Terminal 3-pin (PIR Sensors)	Phoenix PT 1×3, 5.0 mm	3
J12, J15, J16, J17, J18, J19	Screw Terminal 2-pin (Reed Switches)	Phoenix PT 1×2, 5.0 mm	6
J20, J21	Socket Connectors 1×6	Pin Socket 1×6, 2.54 mm	2
D1, D2, D3	LED 5 mm (Zone Alarms)	LED THT, D5.0 mm	3
R1	Resistor 220 Ω	Axial DIN0207, 7.62 mm pitch	1
RV1	Potentiometer (LCD Contrast)	Bourns 3386P Vertical	1

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File Structure

├── kicad/
│   ├── Security System Arduino Shield.kicad_pro   # KiCad project file
│   ├── Security System Arduino Shield.kicad_sch   # Schematic
│   ├── Security System Arduino Shield.kicad_pcb   # PCB layout
│   └── fp-lib-table                               # Footprint library references
├── images/
│   ├── schematic.pdf                              # Schematic PDF
│   ├── pcb_layout.png                             # PCB layout screenshot
│   ├── 3d_front.png                               # 3D render, front side
│   └── 3d_back.png                                # 3D render, back side
├── LICENSE
└── README.md

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License

This project is licensed under the MIT License.