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8 Pins is too many? How about just 2 pins? Using the Bourns encoder with I2C


In the previous tutorial we had a look at the ‘Bourns EAW’ absolute contacting encoder.

It’s great in many ways but it does require eight pins on the Arduino and if you’re using the Arduino UNO, just can run out of pins pretty fast!

In this quick tutorial we will see how to connect it using two pins instead of eight.

We can do this by using an I2C Expansion board which will enable us to communicate with the encoder using the I2C protocol which uses only two pins.

In the next tutorial we will look at how I2C communcation works and more in depth at this little module.



Bourns EAW Contacting Encoder

I2C Expander Module

EasyDriver Stepper Driver

Stepper Motor NEMA 17

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Like I said we will look at the I2C protocol and this I2C expansion module in more details in the next tutorial, but here’s how we will use it today.

The I2C expansion module has eight pins (P0 – P7) that can be use for input or output, kinda like the ones on the Arduino.

So instead of connecting the eight pins of the encoder directly to the Arduino UNO we will connect them to this I2C expansion module.

The only connections we need to make to the Arduino UNO are the 5V and ground, and the I2C pins (A4-SDA, A5-SCL) to be able to read all eight pins of the encoder through this module.



The connections are the same as in the previous tutorial, except that the encoder pins are connected to the I2C expansion module and not to the UNO.

I2C Expansion module connections: 5V and Ground from the Arduino and A4 – A5 to SDA and SCL on the I2C module

LCD Connections: 5v and Ground from the Arduino and A4 – A5 to SDA and SCL of the backpack

EasyDriver Connections: Pin 10 and 11 of Arduino to DIR and STEP pin of the driver Ground of Arduino to Ground of driver The EasyDriver is connected to a 12V power supply

Bourns EAW connections: P0 to P7 of the I2C module connected to Pin 1 to 8 of the encoder

Ground of Arduino connected to a Common pin of the encoder



We are using the same library as in the previous tutorial, last time we used it with the encoder connected directly to the Arduino, but this library also as the capability to use I2C as a connection.

The code is pretty much the same, but we added the I2C address of the I2C expansion module and the library declaration to use I2C instead of direct connection.

On this I2C module you can select the I2C address with the dip switches from 0x20 to 0x27.

Since we know the I2C LCD backpack uses by default 0x27 we set the I2C expansion module to 0x20 since we can’t have two I2C modules with the same address.

Here’s a table of the possible addresses using the dip switches:

A0  A1  A2 ———— off  off  off      0x20 off  off  on      0x21 off  on  off      0x22 off  on  on      0x23 on  off  off      0x24 on  off  on      0x25 on  on  off      0x26 on  on  on      0x27

/* Control Stepper Motor with I2C 'Bourns EAW' encoder
Created by Yvan /

This code is in the public domain...

You can: copy it, use it, modify it, share it or just plain ignore it!

#include <LiquidCrystal_I2C.h>  // I2C LCD Library by Francisco Malpartida
#include <AccelStepper.h>  // AccelStepper Library

#define lcd_addr 0x27     // I2C address of typical I2C LCD Backpack
#define bourns_addr 0x20  // I2C address of I2C Expander module (A0-A1-A2 dip switch to off position)

// LCD Pins to I2C LCD Backpack - These are default for HD44780 LCD's
#define Rs_pin 0
#define Rw_pin 1
#define En_pin 2
#define D4_pin 4
#define D5_pin 5
#define D6_pin 6
#define D7_pin 7

// Create instance for LCD called: i2c_lcd
LiquidCrystal_I2C i2c_lcd(lcd_addr,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin);

const int pinSTEP=11;  // STEP pin of EasyDriver connected to pin 11 of UNO
const int pinDIR=10;  // DIR  pin of EasyDriver connected to pin 10 of UNO

AccelStepper stepper(1, pinSTEP, pinDIR);  // Stepper setup

// Include the Bourns EAW Encoder library and maps
#include <ACE128.h>  //

#include <ACE128map12345678.h> // mapping for pin order 12345678

ACE128 myACE((uint8_t)bourns_addr, (uint8_t*)encoderMap_12345678); // Using I2C connections
//ACE128 myACE(2,3,4,5,6,7,8,9, (uint8_t*)encoderMap_12345678);    // Using direct connections

int16_t multiturn_encoder_value;  // Variable to hold multiturn value of encoder (-32768 to 32767)

void setup() {
  i2c_lcd.begin (16,2); //  our LCD is a 16x2, change for your LCD if needed
  // LCD Backlight ON
  i2c_lcd.clear(); // Clear the LCD screen

  stepper.setCurrentPosition(0);  // Set current position of stepper at startup to zero
  stepper.setMaxSpeed(1000.0);      // Set Max Speed of stepper
  stepper.setAcceleration(5000.0);  // Acceleration of stepper
  stepper.setSpeed(1000.0);  // Speed of stepper

  myACE.begin();    // initialize the encoder library

void loop() {

  multiturn_encoder_value = myACE.mpos();  // get multiturn value from encoder
  stepper.moveTo(multiturn_encoder_value); // set stepper new position to move to
  while (stepper.distanceToGo() != 0) {  // if stepper hasn't reached new position
    stepper.runSpeedToPosition();  // move the stepper until new position reached

// Display the encoder multiturn and stepper position on LCD
  i2c_lcd.print("Encoder: ");
  i2c_lcd.print("      ");
  i2c_lcd.print("Stepper: ");
  i2c_lcd.print("      ");  


Like before I think this encoder is great for some projects and is pretty cheap for what it can do.

But if you are running out of available pins on your Arduino you might want to use this I2C connection method to use two pins instead of eight.

In my testing I didn’t feel much of a slow down in the response of the encoder when using it, but using I2C does introduce some overhead.

So depending on your project you might still want to use the full eight pin connection, but that would be only in certain cases.

Thank you for stopping by!





Copy and Paste the above code/sketch in your Arduino IDE software.

Link to the libraries used in this tutorial:


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