Timer switch with Relay and LCD Arduino code

A timer switch is an electrical switch that is operated by means of a timer circuit or timer mechanism that measures specific time intervals. It can be used to switch ON or OFF a device after a particular period of time set by the user.

In the below circuit, the output of the Arduino is connected to a relay module that can be used to ON or OFF appliances connected to an external supply like an AC power source, battery supply, etc.

Arduino Switch OFF Timer

This is a basic program to switch off the device after a particular time period since it is switched ON. When we power on the circuit the output pin 9 will be in a low state by default. Hence the Load connected to the relay will remain OFF. In the circuit a push-button is connected to pin2, it is the ON button to turn ON the output. Once it is pressed the output at pin 9 switches to a high state, the relay energizes and the relay contacts switch to NO terminal which switches ON the load or appliances connected to it.

Here in the code, the off-time is initialized as 1 minute; the time value used in the code is in minutes. Once it is turned ON, the device will be turned off after the time specified in the variable “offtime”.

Code

const int switch_on = 2, output = 9;
int offtime = 1, off_timer_start = 0;
void setup() {
  pinMode(switch_on, INPUT);
  pinMode(output, OUTPUT);
}

void loop() {
  int x = ((millis() / 1000) - off_timer_start) / 60;
  if (digitalRead(switch_on) == HIGH) {
    off_timer_start = (millis() / 1000);
    digitalWrite(output, HIGH);
  } else if (x >= offtime && digitalRead(output == HIGH)) {
    digitalWrite(output, LOW);
  }
  delay(1000);
}

Switch OFF timer with time adjust and LCD display

This code is the same as above, but with a few additional options to change the off time, LCD display to show the off time, the present state of the device, and remaining time to OFF.

Here the circuit has two input button switches, one is connected to Pin 2 which is to switch ON the device, and the second button is connected to pin3 to set the OFF-time value; in the above code the off time needs to be declared at first and once the sketch is uploaded then it needs to re-upload again to change the off-time value. Here that disadvantage can be overcome by adding input to change the OFF time.

In the code as long as the pin3 is held ON, the off-time increments by 1 and repeats again from 0 once it reaches the value of 30 minutes. The limit of time, increment value, speed of increment can be modified by adjusting the values in the code; it is specified in the corresponding lines in the code.

Code

#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
uint8_t clock[8] = {0x0, 0xe, 0x15, 0x17, 0x11, 0xe, 0x0};
const int switch_on = 2, input_off_time = 3, output = 9;
int off_timer_start = 0, offtime = 0;
void setup() {
  pinMode(switch_on, INPUT);
  pinMode(input_off_time, INPUT);
  pinMode(output, OUTPUT);
  lcd.init();
  lcd.backlight();
  lcd.setCursor(6, 0);
  lcd.print("OFF       ");
  lcd.createChar(2, clock);
  lcd.setCursor(0, 1);
  lcd.write(2);
  lcd.print((String)" " + offtime + " ");
}

void loop() {
  int x = ((millis() / 1000) - off_timer_start)/60;
  if (x <= offtime && digitalRead(output) == HIGH) {
    int m = ((offtime * 60) + off_timer_start - (millis() / 1000))/60;
    int s = ((offtime * 60) + off_timer_start - (millis() / 1000))%60;
    lcd.setCursor(10, 0);
    lcd.print((String)" " + m + ":" + s +" ");
  }
  if (digitalRead(switch_on) == HIGH) {
    digitalWrite(output, HIGH);
    off_timer_start = millis() / 1000;
    lcd.setCursor(6, 0);
    lcd.print("ON        ");
  } else if (x >= offtime && digitalRead(output == HIGH)) {
    digitalWrite(output, LOW);
    lcd.setCursor(6, 0);
    lcd.print("OFF       ");
  }
  while (digitalRead(input_off_time) == HIGH) {
    if (offtime <= 29) { //change max time limit
      offtime += 1; //change increment by x
    } else {
      offtime = 0;
    }
    lcd.setCursor(0, 1);
    lcd.write(2);
    lcd.print((String)" " + offtime + " ");
    delay(500);// adjust speed of incrementing
  }
}

Arduino ON and OFF timer

This is an expanded version of the above program, here we have additional options to set time to both ON and OFF the device. Here the device is ON after the time set to “ontime” and OFF after the “offtime”.

Here the switch connected to pin3 can be used to change on time and pin4 to change the off time. The pin2 is the same as above to turn ON the device.

#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
uint8_t clock[8] = {0x0, 0xe, 0x15, 0x17, 0x11, 0xe, 0x0};
const int switch_on = 2, input_on_time = 3, input_off_time = 4, output = 9;
int timer_start = 0, ontime = 0, offtime = 0;
String device_status = "OFF";
void setup() {
  pinMode(input_on_time, INPUT);
  pinMode(input_off_time, INPUT);
  pinMode(output, OUTPUT);
  lcd.init();
  lcd.backlight();
  lcd.createChar(2, clock);
  lcd.setCursor(8, 1);
  lcd.write(2);
  lcd.print((String)" OFF" + offtime + " ");
  lcd.setCursor(0, 1);
  lcd.write(2);
  lcd.print((String)" ON" + ontime + " ");
  lcd.setCursor(6, 0);
  lcd.print("OFF       ");
}

void loop() {
  int x = ((millis() / 1000) - timer_start)/60;
  if (x <= ontime && device_status == "TO_ON") {
    int m = ((ontime*60) + timer_start - (millis() / 1000))/60;
    int s = ((ontime*60) + timer_start - (millis() / 1000))%60;
    lcd.setCursor(10, 0);
    lcd.print((String)" " + m + ":" + s + " ");
  } else if (x - ontime <= offtime && device_status == "TO_OFF") {
    int m = ((offtime*60) + timer_start + (ontime*60) - (millis() / 1000))/60;
    int s = ((offtime*60) + timer_start + (ontime*60) - (millis() / 1000))%60;
    lcd.setCursor(10, 0);
    lcd.print((String)" " + m + ":" + s + " ");
  }
  if (digitalRead(switch_on) == HIGH) {
    timer_start = millis() / 1000;
    device_status = "TO_ON";
  }
  else if (x - ontime >= offtime  && device_status == "TO_OFF") {
    digitalWrite(output, LOW);
    lcd.setCursor(6, 0);
    lcd.print("OFF       ");
    device_status = "OFF";
  } else if (x >= ontime && device_status == "TO_ON") {
    digitalWrite(output, HIGH);
    lcd.setCursor(6, 0);
    lcd.print("ON        ");
    device_status = "TO_OFF";
  }
  while (digitalRead(input_on_time) == HIGH) {
    if (ontime <= 24) {
      ontime += 1;
    } else {
      ontime = 0;
    }
    lcd.setCursor(0, 1);
    lcd.write(2);
    lcd.print((String)" ON" + ontime + " ");
    delay(500);
  }
  while (digitalRead(input_off_time) == HIGH) {
    if (offtime <= 24) {
      offtime += 1;
    } else {
      offtime = 0;
    }
    lcd.setCursor(8, 1);
    lcd.write(2);
    lcd.print((String)" OFF" + offtime + " ");
    delay(500);
  }
}