Simple code for the Arduino to read data from a GSR sensor and turn on one to four leds based on the reading.

Arduino_GSR_Code

// save pin numbers to variables
int sensorPin = A0;
int ledPin1 = 2;
int ledPin2 = 3;
int ledPin3 = 4;
int ledPin4 = 5;

void setup() {
    // define which pins are used for input and output
    pinMode(sensorPin, INPUT);
    pinMode(ledPin1, OUTPUT);
    pinMode(ledPin2, OUTPUT);
    pinMode(ledPin3, OUTPUT);
    pinMode(ledPin4, OUTPUT);
    // open a serial port connection to computer
    Serial.begin(9600);
}

void loop() {
    // read data from appropriate pin and assign value to variable
    int sensorVal = analogRead(sensorPin);
    // print sensor reading to the the computer via serial port
    Serial.println(sensorVal);

    // set all leds to off
    digitalWrite(ledPin1, LOW); 
    digitalWrite(ledPin2, LOW);
    digitalWrite(ledPin3, LOW);
    digitalWrite(ledPin4, LOW);

    // turn on leds based on value from sensor
    if (sensorVal >= 20) { 
        digitalWrite(ledPin1, HIGH); 
    }
    if (sensorVal >= 40) { 
        digitalWrite(ledPin2, HIGH);
    }
    if (sensorVal >= 60) { 
        digitalWrite(ledPin3, HIGH);
    }
    if (sensorVal >= 80) { 
        digitalWrite(ledPin4, HIGH);
    }
    
    // wait for 20 milliseconds before reading sensor again
    delay(20);
    
}