1. Analog Input through POT
A potentiometer (variable resistor) is connected to analog pin 0 to an Arduino.
Values presented to pin 0 will vary depending upon the resistance of the potentiometer.
void setup() {
Serial.begin(9600); }
void loop() {
Serial.println(analogRead(0));

2. Arduino-Analog Output-LED
Analog Out put is defined as sending signals from one of the digital pins on the Aurduino board that range between two extremes: 0-255
Out of 13 Digital pins on Arduino board the following pins can be used to signal out Analog output: 3,5,6,9,10,11
These are the pins with PWM label next to them on the board

3. Analog Input-Application
The variable resistor can be replaced with a sensor.
For example, a photo resistor.
Depending upon the light level at the photo resistor:
Turn on a light
Increase or decrease the brightness of an LED (or an LED array)
Most sensors are simply variable resistors, but vary their resistance based on some physical characteristic.
void setup() {
pinMode(9, OUTPUT); }
void loop()
int lightLevel = analogRead(0);
lightLevel = map(lightLevel, 0, 900, 0, 255);
lightLevel = constrain(lightLevel, 0, 255);
analogWrite(9, lightLevel);

4. Sensors Sensors can be both binary or a range.
Usually, sensors that measure a range of values vary their resistance to reflect their detection.
Arduinos can only sense voltages, not resistances.
Sensors that only vary their resistances require a circuit called a voltage divider to provide the Arduino a voltage.

5. Common Sensors Dials on a radio are simply potentiometers Temperature
Light
Angle
Switches
did the user throw a switch or push a button?
Accelerometer (measures motion and tilt)
Infrared sensor & light
Hall effect sensor and magnet
Ball tilt sensor (for measuring orientation)
Force

6. Sensors and Modules Gas Sensor Temp & Humidity Fingerprint Scanner
Flex Sensor
Shields aren't the only way to extend an Arduino board - you can hook sensors to it!  These are some of the hundreds (if not thousands) available.  Many of these are not made specifically for Arduino - some sensors, such as thermistors, you can get from Radio Shack and wire them in!
Sensors can run as low as $0.95 (for a thermistor or light sensor) to $150 (Geiger counter sensor)
Geiger Counter

7. Sensors
Photoresistor, infared, force sensitive resistor, Hall effect, Piezo, tilt sensor..

8. Arduino Types Many different versions Leonardo Due Micro LilyPad
Number of input/output channels
Form factor
Processor
Leonardo
Due
Micro
LilyPad
Esplora
Uno