📝 Introduction

Relay modules are essential in home automation and electronics projects, allowing microcontrollers to control high-power devices like fans, bulbs, motors, and appliances.

In this project, I designed an advanced 4-channel 5V relay module with an integrated LM2596 buck converter power supply, making it compact, efficient, and beginner-friendly. Unlike regular relay boards, this version includes reverse polarity protection, ON/OFF control jumper, and improved LED indicators.

⚡ Key Features

✅ 4 Independent Relays (SRD-05VDC) – each rated for 10A @ 250VAC / 30VDC

✅ Onboard LM2596SX Buck Converter – accepts 12V DC input via barrel jack, converts to 5V for relays & logic

✅ ON/OFF Header Control – enable or disable relay board using jumper

✅ Reverse Polarity Protection with SS14 Schottky diode

✅ Input/Output Terminals for easy wiring

✅ Status LEDs for each relay with optimized 680Ω resistor (brighter visibility)

✅ Transistor Drivers (MMBT2222A) for reliable switching

✅ Flyback Diodes (1N4007) on each relay for coil protection

✅ Compact PCB Layout with 3D Preview

📐 Schematic Diagrams

The module consists of two main sections:

🔹 Relay Driver Section

Each relay is controlled by an NPN transistor with base resistor, LED indicator, and flyback diode.

🔹 Power Supply Section

The LM2596 buck regulator converts 12V DC to a stable 5V rail for relays and logic.

🛠️ PCB Layout

The PCB was designed in EasyEDA with proper track sizing:

Relay coil supply traces: 0.8mm

High current relay contact traces: 4mm+ copper pour (supports up to 10A)

Separate low voltage & high voltage areas for safety

🎨 3D Board Preview

Here’s how the final board looks in 3D:

📦 Bill of Materials (BOM)

Some key components used:

ComponentValue / Part No.QtyRelaySRD-05VDC-SL-C4Driver TransistorMMBT2222ALT1G4Flyback Diode1N40074Indicator LEDXL-3216SURC4LED Resistor680Ω4Base Resistor1kΩ4Buck Converter ICLM2596SX-5.0/NOPB1Inductor33µH1Schottky DiodeSS541Reverse ProtectionSS141Input Capacitor680µF / 35V1Output Capacitor220µF / 16V1Ceramic Capacitors100nF2DC Jack5.5mm × 2.1mm1Screw TerminalsWJ128V-5.06

(You can include your full Excel BOM as downloadable link)

🔧 Use Cases

🏠 Home Automation – control fans, lights, appliances

⚙️ Industrial Projects – motor drivers, pumps, solenoids

💡 IoT Projects – smart switches, WiFi/ESP32 automation boards

🔋 DIY Electronics – safe interface between microcontroller and AC/DC loads

🚀 Conclusion

This 4-Channel Relay Module with onboard LM2596 is a complete, safe, and compact solution for controlling high-power devices directly from a 12V supply. With added features like ON/OFF control, reverse polarity protection, and improved track design, it is a step above traditional relay boards.

👉 Whether you’re building Arduino, ESP8266, ESP32, or Raspberry Pi projects, this module is a perfect addition to your toolbox.

🔗 Download Files:

Click Here

🌐 Author & Contact

👨‍💻 Designed by ElectroIoT

🔗 Website: https://electroiot.in

▶️ YouTube: ElectroIoT-IN

📸 Instagram: @electroiot_in

📧 Email: electroiot.in@gmail.com

PCB FILE Updated Please USE New PCB Thanks To @KhronoSound Audio to fing problem with pcb track c3/c2/r9 track thick

pcb gerber file updated and updated file on github also .