Added digital input

examples/Digital_Input/Digital_Input.ino

@@ -0,0 +1,50 @@
+/*
+  MQUnifiedsensor Library - reading an MQ3 using digital input
+
+  Demonstrates the use a MQ3 sensor.
+  Library originally added 01 may 2019
+  by Miguel A Califa, Yersson Carrillo, Ghiordy Contreras, Mario Rodriguez
+ 
+  Added example
+  modified 23 May 2019
+  by Miguel Califa 
+
+  Updated library usage
+  modified 26 March 2020
+  by Miguel Califa 
+
+ This example code is in the public domain.
+
+ Instructions:
+    1. Load the program contained in this example onto your card.
+    2. Let the sensor preheat for 48 hours.
+    3. Generate a contaminated atmosphere, to the point that it is the alert level, this can be done by enclosing the 
+       sensor in a small pot and entering a chemical such as alcohol if it is the case in the form of a spray.
+    4.  Move the potentiometer until the LED on the card lights up.
+    5. Wait until the LED on the sensor card goes out.
+    6. Each time the serial monitor displays an alert, the sensor has detected that the threshold programmed in step 4 has 
+       been exceeded.
+
+
+*/
+
+#define pin 3 // Digital pin connected to your sensor
+
+void setup() {
+  //Init the serial port communication - to debug the library
+  Serial.begin(9600); //Init serial port
+  
+  pinMode(pin, INPUT);
+
+}
+
+void loop() {
+    if(digitalRead(pin))
+    {
+        Serial.println("Alarm high concentrations detected");
+    }
+    else
+    {
+        Serial.println("Status: Normal")
+    }
+}