1.3.3 Relay¶

Introduction¶

In this project, we will learn to use a relay. It is one of the commonly used components in automatic control system. When the voltage, current, temperature, pressure, etc., reaches, exceeds or is lower than the predetermined value, the relay will connect or interrupt the circuit, to control and protect the equipment.

Required Components¶

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
Transistor	BUY
Relay	BUY
Diode	BUY

Schematic Diagram¶

Experimental Procedures¶

Step 1: Build the circuit.

Step 2: Open the code file.

cd ~/raphael-kit/c/1.3.3

Step 3: Compile the code.

gcc 1.3.3_Relay.c -lwiringPi

Step 4: Run the executable file.

sudo ./a.out

After the code runs, the LED will light up. In addition, you can hear a ticktock caused by breaking normally close contact and closing normally open contact.

Note

If it does not work after running, or there is an error prompt: "wiringPi.h: No such file or directory", please refer to Install and Check the WiringPi.

Code

#include <wiringPi.h>
#include <stdio.h>
#define RelayPin 0

int main(void){
    if(wiringPiSetup() == -1){ //when initialize wiring failed, print message to screen
        printf("setup wiringPi failed !");
        return 1;
    }
    pinMode(RelayPin, OUTPUT);   //set GPIO17(GPIO0) output
    while(1){
        // Tick
        printf("Relay Open......\n");
        digitalWrite(RelayPin, LOW);
        delay(1000);
        // Tock
        printf("......Relay Close\n");
        digitalWrite(RelayPin, HIGH);
        delay(1000);
    }

    return 0;
}

Code Explanation

digitalWrite(RelayPin, LOW);

Set the I/O port as low level (0V), thus the transistor is not energized and the coil is not powered. There is no electromagnetic force, so the relay opens, LED does not turn on.

digitalWrite(RelayPin, HIGH);

set the I/O port as high level (5V) to energize the transistor. The coil of the relay is powered and generate electromagnetic force, and the relay closes, LED lights up.