BITS N BYTES – Arduino Encoder Control - How-to

12 Jan 2016

Example Rotary Encoder

I have recently acquired a piece of hardware from a friend. The item in question is a really cool, high current triple output power supply. I have big plans for a remote control head for this unit that will turn it into a really cool bench power supply. Before I get to that project, I am in the midst of building a few bits and pieces with intentions of adding them all together for the power supply.

In my opinion a simple to use, intuitive user interface is always the best approach when designing an instrument type of project. This little gizmo may prove useful to you. Using a simple rotary encoder to adjust values and to navigate menus is just one approach to this goal. I have a number of CUI Inc. ACZ16 Series mechanical rotary encoders lying around, so I have decided to use this device for my project. Of course an optical encoder is probably more ideal, but my decision here is purely one of convenience. Besides they are cheap!

Some Theory on Encoders

Basically, what we are about to do is detect when a major transition step occurs within the encoder. Depending on what transition occurred, we can tell if the encoder was rotated clockwise or anti-clockwise. Refer to Figure 1 below for the timing (switching) diagram. The output of our encoder will produce two square waves. One signal from the A and one signal from B terminal. These two signals are produced out of phase by 90 degrees. When we observe a low-to-high transition on terminal A, we can then look to terminal B to see if the signal is high or low. If B is high we know that the encoder was turned clockwise. If B is low, we know that the encoder was turned anti-clockwise. Now, since we are human and by nature slow, this algorithm works for us. If transitions are missed or any number of strange occurrence happen, we should not care in this application. Things should happily move along unnoticed. If you are looking for a more precise control method or your application is accuracy dependent (Like for example, a position encoder on an electric motor) – this bit is probably not for you.

Figure 1: Arduino Encoder – Output Waveform Data

Arduino Encoder – Test Circuit

ARDUINO – CODE EXAMPLE

Rotary Encoder Control for Arduino - with Interrupt 
 
 
 
 
Arduino
 
1 
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
 
/* 
 Encoder Demo with LCD - Interrupts enabled
 Richard Galambos - August 7.2014
 
 Demonstrates the use of a CUI ACZ16 Encoder with a 16x2 LCD display.
 Interrupts enabled
 
 The LiquidCrystal library works with all LCD displays that are
 compatible with the Hitachi HD44780 driver with the 16-pin interface.
 
  Connections:
 - LCD RS pin to digital pin 13
 - LCD Enable pin to digital pin 12
 - LCD D4 pin to digital pin 8
 - LCD D5 pin to digital pin 7
 - LCD D6 pin to digital pin 4
 - LCD D7 pin to digital pin 2 
 - LCD R/W pin to ground
 
 - Encoder output A pin 3
 - Encoder output B pin 10
 
 */
 
// include the library code:
#include <LiquidCrystal.h>
 
// define encoder pins
#define encoder0PinA 3
#define encoder0PinB 10
    
    // initialize variables for Encoder
    int encoder0Pos = 0; //initialize encoder position
    int encoder0PinALast = LOW; // last state variables
    int n = LOW;
    
    // initialize the library with the numbers of the interface pins
    LiquidCrystal lcd(13, 12, 8, 7, 4, 2);
 
void setup() {
  // set up the LCD 
  lcd.begin(16, 2);
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("POSITION: ");
  lcd.setCursor(11,0);
  lcd.print(0);
  
  // Set up I/O Digital Pins  
  pinMode(encoder0PinA, INPUT); 
  //digitalWrite(encoder0PinA, HIGH);      // turn on pullup resistor
  pinMode(encoder0PinB, INPUT); 
  //digitalWrite(encoder0PinB, HIGH);      // turn on pullup resistor
 
  // Setup the interupt
  attachInterrupt(1, EncoderChanged, CHANGE);  // encoder pin on interrupt 1 - pin 3
}
class Human {
    private int age = 0;
    public void birthday() {
        age++;
        print('Happy Birthday!');
    }
}
//Main code
void loop() { 
      delay(500);
      }
//Encoder interupt routine
void EncoderChanged() {
  n = digitalRead(encoder0PinA);    //temporary read value of A on Encoder
  // Check to see if previous value was low and if the current value is high 
  if ((encoder0PinALast == LOW) && (n == HIGH)) {    
    // if the condition is true then increment the position counter 
    if (digitalRead(encoder0PinB) == LOW) {
      encoder0Pos++;
    } 
    // Otherwise decrement the position counter
    else {
      encoder0Pos--;
    }
      // set the cursor to column 5, line 0
      // (note: line 0 is the first row, since counting begins with 0):
      lcd.clear();
      lcd.setCursor(0,0);
      lcd.print("POSITION: ");
      lcd.setCursor(11,0);
      lcd.print(encoder0Pos);
      
  } 
  // set the Last Pin State 
  encoder0PinALast = n;
  
}

ARDUINO – Wiring and Prototyping

SEE MORE AT WWW.TECHMAESTER.COM