How to Use KY-019 5V 1-Channel Relay Module with Arduino

By Kunkune | Published: 2026-10-27

Category: How-to Guides

Learn how to wire and program the KY-019 5V 1-channel relay module with Arduino to control high-power devices safely.

Quick answer

Connect the KY-019 relay module's VCC to Arduino 5V, GND to GND, and IN to a digital pin (e.g., pin 8). Use a simple sketch to toggle the relay on and off, controlling external devices up to 250VAC/30VDC.

What the KY-019 can and cannot do

The KY-019 is a 5V 1-channel relay module that acts as an electrically operated switch. It allows your Arduino to control high-voltage or high-current devices like lamps, fans, or pumps safely, because the relay isolates the low-voltage Arduino circuit from the high-voltage load.

However, the module can only switch one device at a time. For multiple devices, you would need additional channels or modules. Also, the relay contacts are rated for resistive loads; inductive loads (motors, solenoids) may require a snubber diode to prevent voltage spikes.

Step-by-step wiring and programming

Connect the power and control pins: Connect the KY-019 VCC pin to Arduino 5V, GND to GND, and the IN (signal) pin to digital pin 8. Use female-to-female jumper wires for a secure connection. Double-check that VCC goes to 5V, not 3.3V, or the relay may not trigger reliably.
Write the Arduino sketch: Set pin 8 as OUTPUT in setup(). In loop(), use digitalWrite(8, HIGH) to energize the relay (close the switch) and digitalWrite(8, LOW) to de-energize it. Add a delay(1000) between states to see the relay click. The relay coil draws about 70mA; ensure your Arduino power supply can handle it, or use an external 5V supply.
Connect the load to the relay: Wire your external device (e.g., a lamp) in series with the relay's common (COM) and normally open (NO) terminals. When the relay is energized, the circuit closes and the device turns on. For a device that should be on by default, use the normally closed (NC) terminal. Never exceed the relay's rated load (10A at 250VAC or 10A at 30VDC). Use a separate power source for the load; do not power it from the Arduino.

Product facts

KY-019 5V 1-Channel Relay Board Module for Arduino IOT: KY-019 5V 1-Channel Relay Board Module for Arduino IOT This module is a simple, low-cost way to add relay control to your Arduino projects, with a catalog price of USD 1.05.
KY-019 5V 1-Channel Relay Board Module for Arduino IOT