Without anything being fitted the the analogue input is floating and so picks up electromagnetic radiation from radiated signals. That is exactly how radio works, your Arduino is acting as a radio receiver.
Now that first post is way too long, edit it to just a page at the longest.
Second do not post in the troubleshooting section as that is only for getting the IDE to work. I have moved your post here.
You can use a potentiometer to simulate a device that provides an analogue signal. If you don't have a potentiometer, you can use a wire and connect A3 to GND or 3.3V. If your board is a 5V board (e.g. Uno), you can also use the 5V.
Your previous post makes no sense.
This picture reminds me of a user who created endless topics about nothing a couple of months ago. He was eventually banned...
@shuvra100 , in topics that you created under a different nickname others explained to you in great detail how to get the CO2 concentration from the values of your sensor.
Please do not start again.
If you don't understand something, ask specific questions.
I need 2 things to know -
1)OLED display of sensor data
2) How to measure voltage from multimeter& associated logic % for co
Seller told me that it is work fine with AC supply .Please suggest for relay operations
Seller told me that it is work fine with AC supply .Please suggest for relay operations
Please
Whereas It is working properly for
Looks like a 110V/220V cable; what is the other side?
Disconnect the relay module, run the program and check the output level with a multimeter.
//Edit
I thought I answered your question (post #4). Maybe I misunderstood? Please elaborate on your original question in the topic title. If I indeed did provide the solution what the question was about, leave this topic alone.
Other side is Plug & another sode is solenoid valve for pressure regulator for gas.
How to to check with multimeter ? I am using 12 V DC relay .
Obviously I did not understand your question in the topic title. Please elaborate.
What plug?
Measure voltage. Connect one probe to GND and the other one to the output pin. Let your program run so it activates the relay and observe the different measurements (with and without relay active).
Hi,
This is ridiculous.
Asking all the same questions here;
Tom... 
int analogPin = A3;
int Rawval ; // variable to store the value read
int Scaleval ;
int RELAY_pin = 10; // Relay is connected to pin D10
void setup()
{
Serial.begin(9600); // setup serial
pinMode(RELAY_pin, OUTPUT);
}
void loop()
{
int Rawval = analogRead(analogPin);
Serial.print("Rawvalue from Analog input =");
Serial.print(Rawval);
// For 3V3 input to read 100%, 3V3 of 5V ref = (3.3 / 5) * 1023 = 675
Scaleval = map(Rawval, 0, 675, 0, 20);
Serial.print(" Scaled Value =");
Serial.println(Scaleval);
/// === RELAY code ===
// raw value 675 correspond to 20%, so for 5% we will get 169
if ( Rawval < 169) digitalWrite(RELAY_pin, HIGH);
else digitalWrite(RELAY_pin, LOW);
}
Whereas it is operational
Seller (solenoid valve)told that it is functioning when it will get AC
Your topic was MOVED to its current forum category which is more appropriate than the original as it has nothing to do with Installation and Troubleshooting of the IDE
Please help
Hi,
Your relays are 12V coils, what are you powering the assembly with?
Tom...
I have merged your cross-posts @shuvra100.
Cross-posting is against the Arduino forum rules. The reason is that duplicate posts can waste the time of the people trying to help. Someone might spend a lot of time investigating and writing a detailed answer on one topic, without knowing that someone else already did the same in the other topic.
Repeated cross-posting can result in a suspension from the forum.
In the future, please only create one topic for each distinct subject matter. This is basic forum etiquette, as explained in the "How to get the best out of this forum" guide. It contains a lot of other useful information. Please read it.
Thanks in advance for your cooperation.