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A 5V Single-Channel Relay Module is an interface device that bridges the gap between low-voltage control electronics and high-voltage or high-current loads. This article will discuss the working principles, components, pin configuration, specifications, internal operation, application circuits, troubleshooting methods, advantages, limitations, and practical uses of the 5V Single-Channel Relay Module.
A 5V Single-Channel Relay Module is an electromechanical switching device. It is designed to allow low-voltage control signals to operate high-voltage or high-current loads safely. Commonly used with microcontrollers such as Arduino or Raspberry Pi, enabling them to control appliances, motors, lights, or other electrical equipment that they cannot drive directly.
The module works by using a 5V input signal to energize an internal relay coil through a driver circuit. When activated, the relay switches its internal contacts, either opening or closing the connected load circuit. Built-in components such as a transistor, flyback diode, and indicator LEDs ensure stable operation and protect the control circuit from electrical damage. With terminals labeled COM, NO, and NC, the module offers flexible switching options for different applications.
• Terminal Block - Provides a secure screw-type connection for external loads. It supports AC mains and high-current DC wiring and connects directly to the relay’s COM, NO, and NC contacts for flexible load control.
• 5V Relay - Acts as the main switching element. When energized by a 5V supply, it mechanically opens or closes the contacts to control the connected circuit. The printed ratings indicate the maximum allowable voltage and current for safe operation.
• Switching Transistor - Amplifies low-current control signals from microcontrollers so the relay coil can be driven reliably without overloading the control pin.
• Freewheeling Diode - Protects the circuit by suppressing voltage spikes generated when the relay coil is switched off, improving long-term reliability.
• Input Pins and Jumper - Supply power to the module and accept the control signal that triggers the relay, allowing easy interfacing with digital controllers.
• Power LED - Indicates that the module is powered and ready for operation.
• Relay Status LED - Lights up when the relay is activated, providing instant visual confirmation of switching activity.
| Pin / Terminal | Label | Description |
| Load Terminal | COM (Common) | Common connection point for the load. It switches between the NO and NC contacts depending on the relay state. |
| Load Terminal | NO (Normally Open) | Disconnected from COM when the relay is OFF. It connects to COM only when the relay is activated. |
| Load Terminal | NC (Normally Closed) | Connected to COM when the relay is OFF. The connection opens when the relay is activated. |
| Control Pin | VCC | Supplies 5V power to the relay module, including the relay coil and indicator LEDs. |
| Control Pin | GND (Ground) | Ground reference for the power supply and control signal. |
| Control Pin | IN (Input) | Control signal pin. A HIGH or LOW signal, depending on module design, triggers the relay to switch states. |
| Parameter | Specification |
| Operating Voltage | 5V DC (typical) |
| Supply Voltage Range | 3.75V to 6V |
| Quiescent Current | ~2 mA |
| Operating Current (Relay ON) | ~70 mA |
| Control Signal Type | Digital (HIGH or LOW trigger depending on module design) |
| Relay Type | Electromechanical relay |
| Maximum Contact Voltage (AC) | 250 VAC |
| Maximum Contact Voltage (DC) | 30 VDC |
| Maximum Switching Current | 10 A |
| Contact Configuration | SPDT (COM, NO, NC) |
| Isolation | Electrical isolation between control and load |
| Indicator LEDs | Power LED, Relay Status LED |
| Typical Relay Model | SRD-05VDC-SL-C or equivalent |
Multi-channel relay modules such as dual-channel, four-channel, and eight-channel versions are direct alternatives that operate using the same 5V control voltage. Each relay typically supports load ratings up to 10A at 250VAC or 30VDC, with mechanical isolation between the control and load sides. These modules are suitable when multiple devices need to be switched independently while maintaining simple microcontroller compatibility.
Solid State Relay modules also accept 5V-compatible input signals and use semiconductor switching instead of mechanical contacts. They commonly support AC loads from 24VAC up to 380VAC, with current ratings ranging from a few amps to several tens of amps. SSRs offer silent operation, fast switching, and long service life, making them ideal for applications requiring frequent switching.
TRIAC- and SCR-based switching modules can also be driven by 5V logic signals. TRIAC modules are designed for AC-only control and are often used for dimming and power regulation, while SCR modules handle higher power levels and latching AC control. These options are preferred in high-power or speed-sensitive applications where mechanical relays are less suitable.
The 5V Single-Channel Relay Module is designed to operate directly from a 5V logic supply, making it ideal for use with common microcontrollers such as Arduino, ESP8266, ESP32, and Raspberry Pi GPIO (with proper level control). This allows reliable switching without additional voltage regulators or interface circuits, simplifying circuit design.
This module contains one relay channel, enabling it to control a single load independently. It is well suited for applications that require simple on/off control, such as turning lights, pumps, fans, or small motors on and off using a low-power control signal.
Many 5V single-channel relay modules include an optocoupler that electrically isolates the control side from the load side. This isolation helps protect sensitive microcontrollers from voltage spikes, noise, or short circuits generated by high-voltage or inductive loads.
The onboard relay is typically rated to switch higher voltages and currents, commonly up to 10A at 250VAC or 30VDC, depending on the relay model. This allows the module to safely control mains-powered devices or higher-power DC equipment while keeping the control circuit low voltage.
A built-in LED indicator provides visual feedback on the relay’s operating state. When the LED is on, the relay is energized, making it easy to monitor operation during testing, troubleshooting, or normal use without additional measurement tools.
The relay output terminals are clearly labeled as Common (COM), Normally Open (NO), and Normally Closed (NC). This standard configuration gives flexibility in wiring, allowing the load to be either off or on by default depending on the application’s requirements.
The input pin is designed to be driven directly by digital I/O pins from microcontrollers. Depending on the module design, it may support active-high or active-low triggering, enabling easy integration into automation, IoT, and control projects.
The circuit illustrates the internal working principle of a single-channel relay module. Power is applied through the VCC and GND pins, which supply energy to the relay coil, indicator LEDs, and the control transistor. When a signal is applied to the INPUT pin, it passes through a resistor and reaches the base of the NPN transistor. This small input signal is enough to turn the transistor on, allowing current to flow from VCC through the relay coil and down to ground. Once the coil is energized, it creates a magnetic field that mechanically switches the relay contacts.
This circuit also includes two LEDs with current-limiting resistors. The power LED turns on as soon as the module receives power, confirming that VCC and GND are correctly connected. The relay status LED lights up only when the relay coil is energized, clearly showing when the relay is active. A flyback diode is connected across the relay coil to protect the transistor. When the relay turns off, the collapsing magnetic field generates a voltage spike, and the diode safely absorbs this spike to prevent damage to the transistor and surrounding components.
The relay itself is a single-pole double-throw (SPDT) device with COM, NO, and NC terminals. In the idle state, COM is connected to NC. When the transistor activates the relay coil, COM switches to NO. This internal structure allows the module to switch loads while keeping the low-voltage control side electrically isolated from the high-power side.
The circuit shows how the single-channel relay module is used in real-world applications to control an AC load using a microcontroller. The control side of the relay module is connected to the microcontroller using three pins: GPIO, VCC, and GND. The microcontroller provides a low-voltage signal through the GPIO pin. When this pin is activated, it triggers the internal transistor inside the relay module, energizing the relay coil and switching the relay contacts.
On the load side, the AC source is wired through the relay’s COM and NO terminals. When the relay is OFF, the circuit between the AC source and the load is open, and no current flows. When the relay turns ON, COM connects to NO, completing the circuit and allowing AC power to reach the load. This setup enables the microcontroller to turn devices such as lamps, fans, or appliances ON and OFF without directly handling dangerous AC voltages.
This circuit highlights the main advantage of a single-channel relay module: safe electrical isolation. The microcontroller operates at low voltage and low current, while the relay contacts safely handle higher voltages and currents. This makes the module suitable for automation systems, embedded projects, and industrial control where safety and reliability are critical.
Catalogue
FPGA / CPLD
Memory
MOS 
MCU 
DSP
OCEP
Secondary 
Other