Story
This project is an advanced 4-channel relay module designed for home automation and IoT applications.
Unlike standard relay boards, this design integrates an LM2596 buck converter for onboard 12V-to-5V power regulation, making it compact, efficient, and safe.
It includes reverse polarity protection, ON/OFF jumper control, improved LED indicators, and optimized PCB track widths for handling up to 10A per relay channel.
- ✅ 4 Independent Relays (SRD-05VDC-SL-C) – each rated 10A @ 250VAC / 30VDC
- ✅ Onboard LM2596SX Buck Converter – accepts 12V DC input and outputs regulated 5V
- ✅ ON/OFF Control Jumper (H1) – enable/disable relay board manually
- ✅ Reverse Polarity Protection with SS14 Schottky diode
- ✅ Flyback Diodes (1N4007) across relay coils
- ✅ Indicator LEDs with optimized 680Ω resistors for better brightness
- ✅ MMBT2222A NPN Transistor Drivers for reliable switching
- ✅ Compact & Efficient PCB Layout with 3D preview
- ✅ High-current tracks (4mm+) for relay outputs, safe for up to 10A
Each relay is driven by a transistor with flyback diode, LED indicator, and input header.
LM2596-based buck converter powers the relays and logic from a 12V input.
- Relay coil traces (5V): 0.8mm
- Relay output traces (COM/NO/NC): 4mm (supports 10A)
- Separate high-voltage (AC) and low-voltage (5V) sections
Visual representation of the final PCB design:
| Component | Value / Part No. | Qty |
|---|---|---|
| Relay | SRD-05VDC-SL-C | 4 |
| Driver Transistor | MMBT2222ALT1G | 4 |
| Flyback Diode | 1N4007 | 4 |
| Indicator LED | XL-3216SURC | 4 |
| LED Resistor | 680Ω | 4 |
| Base Resistor | 1kΩ | 4 |
| Buck Converter IC | LM2596SX-5.0/NOPB | 1 |
| Inductor | 33µH | 1 |
| Schottky Diode | SS54 | 1 |
| Reverse Protection | SS14 | 1 |
| Input Capacitor | 680µF / 35V | 1 |
| Output Capacitor | 220µF / 16V | 1 |
| Ceramic Capacitors | 100nF | 2 |
| DC Jack | 5.5mm × 2.1mm | 1 |
| Screw Terminals | WJ128V-5.0 | 6 |
- 🏠 Home Automation – fans, lights, appliances
- ⚙️ Industrial Projects – pumps, motors, solenoids
- 💡 IoT Devices – WiFi/ESP32/Arduino-based controllers
- 🔋 DIY Electronics – safe switching between microcontroller and AC/DC loads
This 4-Channel Relay Module with onboard LM2596 regulator is a complete, safe, and compact solution for powering and controlling AC/DC devices with a single 12V input.
It’s perfect for Arduino, ESP8266, ESP32, Raspberry Pi, and other microcontrollers.
👨💻 Designed by ElectroIoT
🔗 Website: https://electroiot.in
▶️ YouTube: ElectroIoT-IN
📸 Instagram: @electroiot_in
📧 Email: electroiot.in@gmail.com
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