I want to control AC bulb with Arduino, 5v-relay. My connections are

enter image description here

My code is

#define RELAY1  7

void setup() 
  pinMode(RELAY1, OUTPUT);

void loop() 
  digitalWrite(RELAY1,LOW); // Turns ON Relays 1
  Serial.println("Light OFF");
  delay(15000); // Wait 5 seconds
  digitalWrite(RELAY1,HIGH); // Turns Relay Off
  Serial.println("Light ON");
  • Red LED is on according to AC bulb.
  • Power LED (Green colored one) is also on as I have given 5v supply from Arduino.

The issues are

  1. Bulb is not following the delay given in the code. The output for the above code is 20sec ON - 15sec OFF -20sec ON - 15sec OFF- 20sec ON -15sec OFF - 1sec ON - 20sec ON - 15sec OFF etc. means apart from 20,15 sec duration there is a duration of 1sec is coming in between as noise. What might be the reason?

  2. On monitor also, only first 3 actions are getting printed after that no printing is observed.

==>The relay I am using is:

enter image description here

  • What relay board are you using? Do you hear the relay clicking?
    – Gerben
    Aug 6, 2015 at 13:29
  • yes I can here the relay clicking.!
    – NShiva
    Aug 6, 2015 at 17:23
  • As Gerben says, please state the relay part number, and give a link to it. Are you sure you connected Vcc on the relay to the +5 V pin on the Arduino?
    – Nick Gammon
    Aug 6, 2015 at 21:46
  • @Nick, I dont have link to relay. But I have uploaded the relay picture in the question it self. I am sure that 5v pin on Arduino connected to 5v pin on the relay.
    – NShiva
    Aug 7, 2015 at 4:51
  • 1
    There is nothing on the back of the board except the metal connections.
    – NShiva
    Aug 7, 2015 at 6:33

2 Answers 2


what i would do is test the parts one by one. so first look if you're signal is good by attaching a led to it. then test you're relay with 5v.

now you should know what the problem is the arduino or the relay


Everything looks good, however Try a different relay, and double check your AC side and be sure the bulb voltage is correct for the AC and the bulb is OK.

You may have a power shortage from your USB or however you are powering it. If you can monitor the 5VDC and be sure it is stable.

Good Luck

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