Introduction: Digital Potentiometer MCP41100 and Arduino

By Mohannad Rawashdeh
About: Maker, PCB designer , electronics instructor from Jordan just one word ! I Adore electronics follow me on FB https://www.facebook.com/Mohannad-Rawashdeh-Raw-774983565988641/

We know the analog potentiometer , is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider .

Potentiometers Many application such like :

1)volume controls on audio equipment.
2) Control the amplifier Gain and offset .
3) Transducer " displacement  transducers ".

and many Other application , But did you you want to control the resistance value by Microcontroller instead  of using analog one ?

Analog potentiometers have some problem with MCU ,  Microcontroller doesn't have an easy way to interface with them . 

The Digital Potentiometer ,  give you an ability to adjust the resistance ,allowing you to control a voltage splitter with digital signals

In this simple instructable I will show you how  to control Digital Potentiometer MCP41100 Using Arduino IDE .

Step 1: Material


we will need :

1) Arduino Board .
2)Digital Potentiometer MCP41100 .
3)Resistor 100 Ohm
4)LED 
5)BreadBoard.
6JumperS

The pin Configuration for MCP41100 above , very easy .

Data sheet for MCP41100 here

This IC using SPI Protocol to communicate with Arduino Board .


Step 2: Calculate the Resistance .

Ok , now we will look at this table , which is show who we can Calculate the Output resistance .

MCP41100 Have a sensitivity of 8bit , 256 taps for each potentiometer will taken from .

The MCP41100 Nominal resistane equal 100K ohm "Rab" and from the Datasheet , The wiper resistance is 125 ohm"Typical" ,

For example , if we write 222 to MCP41100 ,The resistance will equal :

Rwa= (100*10^3)*(256-222)/256 + 125 = 13.41K ohm . (corrected by Spacebrain,big thanks )

Step 3: Arduino Code

The arduino Code  below :

/*
this program taken from arduino Example .
  modified by By Mohannad Rawashdeh
  http://www.genotronex.com
https://www.instructables.com/

  This code used to control the digital potentiometer
  MCP41100 connected to  arduino Board
  CS >>> D10
  SCLK >> D13
  DI  >>> D11
  PA0 TO VCC
  PBO TO GND
  PW0 TO led with resistor 100ohm .
*/
#include <SPI.h>
byte address = 0x11;
int CS= 10;
int i=0;

void setup()
{
  pinMode (CS, OUTPUT);
  SPI.begin();
  // adjust high and low resistance of potentiometer
  // adjust Highest Resistance .
   digitalPotWrite(0x00);
   delay(1000);

      // adjust  wiper in the  Mid point  .
   digitalPotWrite(0x80);
   delay(1000);

   // adjust Lowest Resistance .
   digitalPotWrite(0xFF);
   delay(1000);
}

void loop()
{
    for (i = 0; i <= 255; i++)
    {
      digitalPotWrite(i);
      delay(10);
    }
    delay(500);
    for (i = 255; i >= 0; i--)
    {
      digitalPotWrite(i);
      delay(10);
    }
}

int digitalPotWrite(int value)
{
  digitalWrite(CS, LOW);
  SPI.transfer(address);
  SPI.transfer(value);
  digitalWrite(CS, HIGH);
}

Step 4: Simple Applications :Motor Drive Controller and LED Controller

This Is a simple example to control the speed of DC Motor using555 timer  ,  PWM Technique

the arduino Code :

/*
this program taken from arduino Example .
  modified by By Mohannad Rawashdeh
  http://www.genotronex.com
  This code used to control the digital potentiometer
  MCP41100 connected to  arduino Board
  CS >>> D10
  SCLK >> D13
  DI  >>> D11
  PA0 TO VCC
  PBO TO GND
  PW0 TO led with resistor 100ohm .
*/
#include <SPI.h>
byte address=0x11;
int CS= 10;

void setup()
{
  pinMode (CS, OUTPUT);
  SPI.begin();
  // adjust high and low resistance of potentiometer
  // adjust Highest Resistance .
   digitalPotWrite(0x00);
   delay(1000);

      // adjust  wiper in the  Mid point  .
   digitalPotWrite(0x80);
   delay(1000);

   // adjust Lowest Resistance .
   digitalPotWrite(0xFF);
   delay(1000);
}

void loop()
{
    for (int i = 0; i <= 255; i++)
    {
      digitalPotWrite(i);
      delay(10);
    }
    delay(1000);
    for (int i = 255; i >= 0; i--)
    {
      digitalPotWrite(i);
      delay(5);
    }

}

int digitalPotWrite(int value)
{
  digitalWrite(CS, LOW);
  SPI.transfer(address);
  SPI.transfer(value);
  digitalWrite(CS, HIGH);
}


Video :