OVERVIEW
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.
PARTS USED
Bourns EAW Contacting Encoder
I2C Expander Module
EasyDriver Stepper Driver
Stepper Motor NEMA 17
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QUICK OVERVIEW
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.
CONNECTIONS
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
THE CODE
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 / https://Brainy-Bits.com
This code is in the public domain...
You can: copy it, use it, modify it, share it or just plain ignore it!
Thx!
*/
#include <LiquidCrystal_I2C.h> // I2C LCD Library by Francisco Malpartida https://bitbucket.org/fmalpartida/new-liquidcrystal/wiki/Home
#include <AccelStepper.h> // AccelStepper Library https://www.arduinolibraries.info/libraries/accel-stepper
#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 BACKLIGHT_PIN 3
#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> // https://github.com/arielnh56/ACE128
#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.setBacklightPin(BACKLIGHT_PIN,POSITIVE);
i2c_lcd.setBacklight(HIGH);
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.setCursor(0,0);
i2c_lcd.print("Encoder: ");
i2c_lcd.setCursor(9,0);
i2c_lcd.print(multiturn_encoder_value);
i2c_lcd.print(" ");
i2c_lcd.setCursor(0,1);
i2c_lcd.print("Stepper: ");
i2c_lcd.setCursor(9,1);
i2c_lcd.print(stepper.currentPosition());
i2c_lcd.print(" ");
}CONCLUSION
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!
TUTORIAL VIDEO
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Copy and Paste the above code/sketch in your Arduino IDE software.
Link to the libraries used in this tutorial:
I2C LCD library by Francisco Malpartida: https://bitbucket.org/fmalpartida/new-liquidcrystal/wiki/Home
AccelStepper library by Mike McCauley : https://www.arduinolibraries.info/libraries/accel-stepper
Bourns EAW Encoder library: https://github.com/arielnh56/ACE128
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