Rotary selector switch for Arduino using only one analog pin

Arduino is a great developer platform, but you quickly run out of pins, especially the digital ones. And you rarely use all 6 analog pins in an application. This selector switch uses only one analog pin.

The switch is a standard rotary selector switch with 12 positions:



In this example, I have build the switch with 8 x 1K/5% resistors and set the rotary selector switch to 8 positions. The easiest way to build it, is to solder the resistors directly onto the rotary selector switch.

Here is the diagram using 8 x 1K resistors as voltage divider:



Here is the necessary Arduino code for decoding the position:

int selectorPin;

int numOfSteps;

float divider;

void setup() 
{
  //pin for selector switch
  selectorPin = 0;

  //number of physical steps on the rotary switch
  numOfSteps = 8;
 
  //divider for decoding analog input
  divider = 1024.0 / numOfSteps; 
}

void loop() 
{
  //divide and round the input as float
  float selectorValueFloat = round(analogRead(selectorPin) / divider);
  
  //cast to integer for e.g. indexing arrays
  int selectorValue = selectorValueFloat;
}

Now we have an integer value for the position of the rotary selector switch. Hope you like it.