Arduino UNO R4 - Relay

Hardware Preparation

Or you can buy the following sensor kits:

Overview of Relay

A relay is a switch that you can program, controlled by devices like Arduino UNO R4 or other micro-controllers. It lets you turn devices on or off automatically, especially those that use high voltage or high current.

The relay is a bridge between Arduino UNO R4 and high-voltage devices.

Relay Pinout

A relay consists of two sets of pins: the input pins, which use low voltage, and the output pins which use high voltage.

• The pins in the input group are connected to the Arduino UNO R4 and include three pins:
• DC- pin: connect this to GND (0V).
• DC+ pin: connect this to VCC (5V).
• IN pin: this accepts the control signal from the Arduino UNO R4.
• The pins in the output group connect to the high-voltage device and also have three pins (usually found in a screw terminal):
• COM pin: this is the common pin used in both the normally open mode and the normally closed mode.
• NO pin: this is the normally open pin. It is used in the normally open mode.
• NC in: this is the normally closed pin. It is used in the normally closed mode.

In practice, we usually do not use all the pins in the high voltage group. We only use two of them.

• For normally open mode, we use only the COM pin and the NO pin.
• For normally closed mode, we use only the COM pin and the NC pin.

Also, if the relay can use both LOW and HIGH level triggers, there is typically a jumper to choose either LOW level trigger or HIGH level trigger.

※ NOTE THAT:

Different manufacturers may arrange the pins on the relay module in different orders. Always check and follow the labels on the relay to connect it correctly. Make sure to look carefully!

How to Connect the High Voltage Device to Relay



How It Works

A relay might works in different ways depending on the manufacturer and how the user installs it.

The input mode: There are two input modes that make the relay function oppositely:

• LOW level trigger mode
• HIGH level trigger mode

The output mode: There are two output modes that make the relay work oppositely:

• normally open mode
• normally closed mode.

The term “normally” refers to the condition when the "IN pin" is connected to "LOW (0V)". Let's start with some quick information:

• The normally open mode and normally closed mode work in opposite ways.
• Most relay modules support both normally open and normally closed modes.
• The LOW level trigger and HIGH level trigger modes work in opposite ways.
• Not every relay module supports both LOW level trigger and HIGH level trigger modes.
• At any given time, the relay module can operate in only one mode, either LOW level trigger or "HIGH level trigger."

The combination of input modes and output modes leads to many use cases. For beginners, we suggest choosing HIGH level trigger mode and normally open mode.

The LOW level trigger and HIGH level trigger modes function in opposite ways. Next, we will describe the HIGH level trigger mode in detail. The LOW level trigger operates in the opposite manner.

HIGH Level Trigger - Normally Open Mode

To set this mode, connect the high voltage device to both the COM pin and the NO pin.

• When the IN pin is connected to LOW (0V), the switch is open and the device is OFF.
• When the IN pin is connected to HIGH (5V), the switch is closed and the device is ON.


HIGH Level Trigger - Normally Closed Mode

To use this mode, connect the device with high voltage to the COM pin and the NC pin.

• When the IN pin is connected to LOW (0V), the switch is closed. This means the device is ON.
• When the IN pin is connected to HIGH (5V), the switch is open. This means the device is OFF.


Summary

Input modes	Output Modes	IN pin (programmable)	Output pins	Relay state	Device state
HIGH Trigger	Normally Open	LOW	COM and NO pin	⇒ open	⇒ OFF
HIGH Trigger	Normally Open	HIGH	COM and NO pin	⇒ closed	⇒ ON
HIGH Trigger	Normally Closed	LOW	COM and NC pin	⇒ closed	⇒ ON
HIGH Trigger	Normally Closed	HIGH	COM and NC pin	⇒ open	⇒ OFF
LOW Trigger	Normally Open	LOW	COM and NO pin	⇒ closed	⇒ ON
LOW Trigger	Normally Open	HIGH	COM and NO pin	⇒ open	⇒ OFF
LOW Trigger	Normally Closed	LOW	COM and NC pin	⇒ open	⇒ OFF
LOW Trigger	Normally Closed	HIGH	COM and NC pin	⇒ closed	⇒ ON

There can be as many as 8 use cases. This might seem overwhelming. But if you are a beginner, you only need to focus on the first two cases. These involve the HIGH level trigger and normally open settings. This tutorial will mainly cover these two cases.

Arduino UNO R4 - Relay

The Arduino UNO R4 uses a relay to control a device that operates at high voltage.

To control a relay is easy. We just need:

• Attach the pin from the Arduino UNO R4 to the IN pin on the relay.
• Program the pin to be LOW or HIGH to operate the relay.

Wiring Diagram

This image is created using Fritzing. Click to enlarge image

How To Program For Relay

• Set up the digital output mode for an Arduino UNO R4 pin using the pinMode() function. For instance, for pin 3:

• Set the pin to LOW (0 volts) using the digitalWrite() function.

• Set the pin to HIGH (5V) using the digitalWrite() function.

Arduino UNO R4 Code

Detailed Instructions

Follow these instructions step by step:

• If this is your first time using the Arduino Uno R4 WiFi/Minima, refer to the tutorial on setting up the environment for Arduino Uno R4 WiFi/Minima in the Arduino IDE.
• Wire the components according to the provided diagram.
• Connect the Arduino Uno R4 board to your computer using a USB cable.
• Launch the Arduino IDE on your computer.
• Select the appropriate Arduino Uno R4 board (e.g., Arduino Uno R4 WiFi) and COM port.
• Copy the code and open it in Arduino IDE
• Click the Upload button in Arduino IDE to send the code to Arduino UNO R4
• Check the LED strip: it should be blinking

Video Tutorial

Function References

• pinMode()
• digitalWrite()
• delay()

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