Trying to connect 12V DC irrigation pump using Relay and power supply

gwareloth:
Maybe you set pin 8 as an output with pinMode, but not pin 10?

Difficult to say though; you should post your code.

I think the problem is using the home power supply but anyway,
Here is my code and thanks:

int sensor_pin = A0 ;

int output_value ;

int valve_pin = 8 ;

void setup ( ) {
Serial.begin(9600);
   Serial.println("Reading From the Sensor ... " );;
   delay (2000);
 } 

void loop ( ) {
  output_value = analogRead (sensor_pin);
  output_value = map (output_value , 1023 , 0 , 0 , 100);
  Serial.println (" Moisture = ");
  Serial.println (output_value);

  if (output_value < 40)
  {
  Serial.println (" Valve: ON ");
  digitalWrite (valve_pin , LOW);    //Relay operates on opposite signal
  delay (1000); 
   }  

  else
   { 
    Serial.println (" Valve: OFF ");
  digitalWrite (valve_pin , HIGH);    //Relay operates on opposite signal
  delay (1000); 
   } 
  delay(1000);
  }