Controlling an LED with a Potentiometer

We previously looked at Analog Inputs (here) where we used a photoresistor and LED to make an ambient light sensor. Today, we will still discuss Analog Inputs but we will be using a different component so we see how analog inputs work from another point of view. We will be controlling the
brightness of an LED using a potentiometer otherwise known as a variable resistor.

A particular reason I enjoy this project is because it allows us to combine analog and digital pins in a unique way. On the Arduino, we have digital pins marked with a sinusoidal wave symbol (∿) and these pins are called Pulse Width Modulation (PWM) pins. The Arduino does not have a built-in digital-to-analog converter (DAC), but it can pulse-width modulate (PWM) a digital signal to achieve some of the functions of an analog output. The function used to output a PWM signal is analogWrite(pin, value). pin is the pin number used for the PWM output. value is a number proportional to the duty cycle of the signal.  The PWM on most Arduino boards are 3, 5, 6, 9, 10, and 11.

To map an analog input value, which ranges from 0 to 1023 to a PWM output signal, which ranges from 0 - 255, you can use the map(value, fromLow, fromHigh, toLow, toHigh) function. This function has five parameters, one is the variable in which the analog value is stored, while the others are 0, 1023, 0 and 255 respectively. 

The circuit is simple and straightforward; we have a potentiometer and and LED connected to the Arduino Uno on pins A0 and 9 respectively. The potentiometer is polarized, holding the component facing you from left to right , the terminals are VCC(Positive), SIGNAL(Output), GND(Negative)

So we build the circuit

                                                                                          (Source: Instructables.com)

Now the Code

const int analogPin = 0;//the analog input pin attach to

const int ledPin = 9;//the led attach to

int inputValue = 0;//variable to store the value coming from sensor

int outputValue = 0;//variable to store the output value

/******************************************/

void setup()

{

  Serial.begin(9600);//set the serial communication baudrate as 9600

}

/******************************************/

void loop()

{

  inputValue = analogRead(analogPin);//read the value from the potentiometer

  Serial.print("Input: "); //print "Input"

  Serial.println(inputValue); //print inputValue

  outputValue = map(inputValue, 0, 1023, 0, 255);//Convert from 0-1023 proportional to the number of a number of from 0 to 255

  Serial.print("Output: "); //print"Output"

  Serial.println(outputValue); //print outputValue

  analogWrite(ledPin, outputValue); //turn the LED on depending on the output value

  delay(1000);

We should understand most parts of the code; the comments give a good explanation in case you are a bit confused. The major part we are seeing for the first time is the map(value, fromLow, fromHigh, toLow, toHigh) function. It allows us to map values from 0-1023 to 0-255. The 0-1023 values are what we read (receive) from the analog pin A0 connected to the potentiometer while the 0-255 values are what we write as analogWrite to the digital pin 9. We can use analogWrite with pin 9 because it is a PWM pin. Other PWM pins have been stated as 3, 5, 6, 10, 11.

Once again, I urge you to go a bit further and maybe add another LED or something else. You will learn something new. Ciao.