Arduino – Rotary encoder (Keyes KY-040)

Hardware

De rotary encoder kan onder meer gebruikt worden om snelheid en/of omwentelingen te meten.

Bij een rotary encoder Hebben we twee blokvormige golf outputs (A en B) welke 90 graden met elkaar uit fase zijn. Het aantal pulsen of stappen welke worden gegenereerd per omwenteling kan varuieren. De rotary encoder van Sparkfun bijvoorbeeld heeft 12 stappen, maar andere kunnen er meer of minder hebben. Het diagram hieronder toont de de relatie van de fasen A en B tot elkaar als de encoder met de klok mee wordt gedraaid of juist andersom.

Iedere keer als de A signaal puls van positief naar 0 gaat, lezen we de waarde van de B puls uit. Wz zien dat wanneer de encoder met de klok mee wordt gedraaid, de B puls altijd positief is. Bij het draaien tegen de klok in, is de B puls negatief. Door het monitoren van beide outputs met een microcontroller (Arduino), kunnen we de draairichting bepalen en door het bijhouden van het aantal A pulsen, ook hoever er is gedraaid. We kunnen nog een stap verder gaan en de frequentie van de pulsen tellen om te bepalen hoe snel er is gedraaid. We kunnen concluderen, dat een rotary encoder een groot aantal voordelen heeft ten opzichte van een potmeter.

De output is een bitreeks van 2-bit, voorbeeld:

Position   Bit1   Bit2
- - - - - - - - - - - 
Step1       0      0
1/4        1      0
1/2        1      1
3/4        0      1
Step2       0      0

Position Bit1 Bit2

- - - - - - - - - - -

Step1 0 0

1/4 1 0

1/2 1 1

3/4 0 1

Step2 0 0

Uitleg van de werking (eng):

Rotating the encoder one step takes the signal a full period, starting at A and B both in the HIGH state, both changing to LOW, and both changing back to HIGH again. If you apply the logic on both transitions, you will do a double +1 for every clock-wise transition:

1. A and B are both HIGH (initial state)
2. A changes to LOW, B is still HIGH, so +1 because A changed and B != A
3. B changes to LOW, no effect
4. A and B are now both LOW
5. A changes back to HIGH, B is still LOW, so +1 because A changed and B != A
6. B changes to HIGH, no effect
7. A and B are both HIGH (final state)

For every counter-clock-wise transition, you will instead do -1 twice:

1. A and B are both HIGH (initial state)
2. B changes to LOW, no effect
3. A changes to LOW, B is already LOW, so -1 because A changed and B == A
4. A and B are now both LOW
6. B changes to HIGH, no effect
5. A changes back to HIGH, B is already HIGH, so -1 because A changed and B == A
7. A and B are both HIGH (final state)

Pinout (Keyes KY-040 module)


Pin:	Functie:
1	GND
2	+5V
3	SW (Schakelaar)
4	DT (Data puls)
5	CLK (Klok puls)

Aansluiten

Sluit de module aan volgens onderstaand schema:

Rotary Encoder pin:	Arduino Pin:
1 (GND)	GND
2 (+)	+5V
4 (DT)	3
5 (CLK)	2

Polling of Interrupts?

Je kan de Rotary Encoder op 2 manieren uitlezen: polling of met interrupts.

Polling
Polling doe je door de stand of beweging van de encoder uit te lezen in de LOOP, het nadeel hiervan is dat je tijdens de loop niet veel kan doen omdat dat de telling verstoord en de pulsen niet goed geteld worden, met polling is het wellicht wel mogelijk om meerdere Enscoders aan te sluiten op een Arduino UNO.

Interrupts
Met interrupts kun je een vallende of stijgende puls waarnemen en een subroutine laten uitvoeren die dan de pulsen telt, op deze manier is het tellen van de pulsen veel nauwkeuriger, het nadeel is dat je 2 interrupts nodig hebt per encoder en dus maar 1 kan aansluiten op een Arduino UNO (3 op de MEGA).

Ps. Bij de Keyes module is 1 “klik/stap” 4 pulsen/tellingen.

Script #1 “INTERRUPT”

Onderstaand script leest de encoder uit via een interrupt subroutine en geeft de waarde weer via de console:

/*  roto_jw4.ino -- JW, 29 September 2015 -- 
*  A 4-state state-machine implementation of rotary
*  encoding for KY-040 rotary knobs.  The state-machine picture at
*  https://e2e.ti.com/support/microcontrollers/hercules/f/312/t/318762
*  in a Feb 4, 2014 7:40 PM post by Anthony Seely shows counts
*  increasing on transitions 10 -> 11 -> 01 -> 00 -> 10 and
*  decreasing on transitions the other way.  Transitions between 00
*  and 11 or 10 and 01 are invalid.  This code detects valid
*  transitions by (abOld xor abNew) equaling 1 or 2.  It detects
*  up-count events by the tri-bit value ABA' (where A' is the new
*  reading on pin A) being equal to 1, 2, 5, or 6 (a bit mask of
*  0x66), and down-count events by ABA' being equal to 0, 3, 4, or 7
*  (a bit mask of 0x99).
*
*  On a KY-040 unit I tested, there are 30 detent positions per turn.
*  With this unit the code generates 60 counts per turn, which can be
*  seen individually as one turns the rotor slowly.  Odd counts
*  appear between detents, even counts at detents.
*
*  Set quadrature-signal pin numbers, via PinA and PinB constants.
*  Set IPINMODE to INPUT_PULLUP if there are no external pull-ups
*  on encoder AB pins, else set IPINMODE to INPUT
*/
enum { PinA=2, PinB=3, IPINMODE=INPUT };
static  byte abOld;     // Initialize state
volatile int count;     // current rotary count
int old_count;     // old rotary count
void setup() {
pinMode(PinA, IPINMODE);
pinMode(PinB, IPINMODE);
attachInterrupt(0, pinChangeISR, CHANGE); // Set up pin-change interrupts
attachInterrupt(1, pinChangeISR, CHANGE);
abOld = count = old_count = 0;
Serial.begin(9600);
Serial.println("Starting Rotary Encoder Test");
}
// On interrupt, read input pins, compute new state, and adjust count
void pinChangeISR() {
enum { upMask = 0x66, downMask = 0x99 };
byte abNew = (digitalRead(PinA) << 1) | digitalRead(PinB);
byte criterion = abNew^abOld;
if (criterion==1 || criterion==2) {
if (upMask & (1 << (2*abOld + abNew/2)))
count--;
else count++;       // upMask = ~downMask
}
abOld = abNew;        // Save new state
}
void loop() {
if (old_count != count) {
Serial.println(count);
old_count = count;
}
}

/* roto_jw4.ino -- JW, 29 September 2015 --

* A 4-state state-machine implementation of rotary

* encoding for KY-040 rotary knobs. The state-machine picture at

* https://e2e.ti.com/support/microcontrollers/hercules/f/312/t/318762

* in a Feb 4, 2014 7:40 PM post by Anthony Seely shows counts

* increasing on transitions 10 -> 11 -> 01 -> 00 -> 10 and

* decreasing on transitions the other way. Transitions between 00

* and 11 or 10 and 01 are invalid. This code detects valid

* transitions by (abOld xor abNew) equaling 1 or 2. It detects

* up-count events by the tri-bit value ABA' (where A' is the new

* reading on pin A) being equal to 1, 2, 5, or 6 (a bit mask of

* 0x66), and down-count events by ABA' being equal to 0, 3, 4, or 7

* (a bit mask of 0x99).

* On a KY-040 unit I tested, there are 30 detent positions per turn.

* With this unit the code generates 60 counts per turn, which can be

* seen individually as one turns the rotor slowly. Odd counts

* appear between detents, even counts at detents.

* Set quadrature-signal pin numbers, via PinA and PinB constants.

* Set IPINMODE to INPUT_PULLUP if there are no external pull-ups

* on encoder AB pins, else set IPINMODE to INPUT

enum { PinA=2, PinB=3, IPINMODE=INPUT };

static byte abOld; // Initialize state

volatile int count; // current rotary count

int old_count; // old rotary count

void setup() {

pinMode(PinA, IPINMODE);

pinMode(PinB, IPINMODE);

attachInterrupt(0, pinChangeISR, CHANGE); // Set up pin-change interrupts

attachInterrupt(1, pinChangeISR, CHANGE);

abOld = count = old_count = 0;

Serial.begin(9600);

Serial.println("Starting Rotary Encoder Test");

}

// On interrupt, read input pins, compute new state, and adjust count

void pinChangeISR() {

enum { upMask = 0x66, downMask = 0x99 };

byte abNew = (digitalRead(PinA) << 1) | digitalRead(PinB);

byte criterion = abNew^abOld;

if (criterion==1 || criterion==2) {

if (upMask & (1 << (2*abOld + abNew/2)))

count--;

else count++; // upMask = ~downMask

}

abOld = abNew; // Save new state

}

void loop() {

if (old_count != count) {

Serial.println(count);

old_count = count;

}

Output

Starting Rotary Encoder Test
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
14
13
12

Starting Rotary Encoder Test

Script #2 “POLLING” met bibliotheek

Wat heb je nodig?
1) Arduino Rotary encoder bibliotheek

#include <Encoder.h>
// Change these two numbers to the pins connected to your encoder.
//   Best Performance: both pins have interrupt capability
//   Good Performance: only the first pin has interrupt capability
//   Low Performance:  neither pin has interrupt capability
Encoder myEnc(2, 3);
//   avoid using pins with LEDs attached
void setup() {
Serial.begin(9600);
Serial.println("Basic Encoder Test:");
}
long oldPosition  = -999;
void loop() {
long newPosition = myEnc.read();
if (newPosition != oldPosition) {
oldPosition = newPosition;
Serial.println(newPosition);
}
}

#include <Encoder.h>

// Change these two numbers to the pins connected to your encoder.

// Best Performance: both pins have interrupt capability

// Good Performance: only the first pin has interrupt capability

// Low Performance: neither pin has interrupt capability

Encoder myEnc(2, 3);

// avoid using pins with LEDs attached

void setup() {

Serial.begin(9600);

Serial.println("Basic Encoder Test:");

}

long oldPosition = -999;

void loop() {

long newPosition = myEnc.read();

if (newPosition != oldPosition) {

oldPosition = newPosition;

Serial.println(newPosition);

}

Output

Basic Encoder Test:
0
1
2
3
4
5
6
7
8
9
10
11
10
11
12
13
14
13
14
15
14

Basic Encoder Test:

Script #3 “POLLING”

Onderstaand vind je een eenvoudig script zonder bibliotheken (bron g7nbp.blogspot.nl)

int clock = 2;             // Define encoder pin A
int data = 3;              // Define encoder pin B
int count = 0;             // pre-init the count to zero
int c = LOW;               // pre-init the state of pin A low
int cLast = LOW;           // and make its last val the same - ie no change
int d = LOW;               // and make the data val low as well
void setup() {
pinMode (clock,INPUT);  // setup the pins as inputs
pinMode (data,INPUT);
Serial.begin (9600);    // and give some serial debugging
}
void loop() {
c = digitalRead(clock); // read pin A as clock
d = digitalRead(data);  // read pin B as data
if (c != cLast) {       // clock pin has changed value... now we can do stuff
d = c^d;              // work out direction using an XOR
if ( d ) {
count--;            // non-zero is Anti-clockwise
}else{
count++;            // zero is therefore anti-clockwise
}
Serial.print ("Jog:: count:");
Serial.println(count);
cLast = c;            // store current clock state for next pass
}
}

int clock = 2; // Define encoder pin A

int data = 3; // Define encoder pin B

int count = 0; // pre-init the count to zero

int c = LOW; // pre-init the state of pin A low

int cLast = LOW; // and make its last val the same - ie no change

int d = LOW; // and make the data val low as well

void setup() {

pinMode (clock,INPUT); // setup the pins as inputs

pinMode (data,INPUT);

Serial.begin (9600); // and give some serial debugging

}

void loop() {

c = digitalRead(clock); // read pin A as clock

d = digitalRead(data); // read pin B as data

if (c != cLast) { // clock pin has changed value... now we can do stuff

d = c^d; // work out direction using an XOR

if ( d ) {

count--; // non-zero is Anti-clockwise

}else{

count++; // zero is therefore anti-clockwise

}

Serial.print ("Jog:: count:");

Serial.println(count);

cLast = c; // store current clock state for next pass

}

Output

Jog:: count:-1
Jog:: count:0
Jog:: count:1
Jog:: count:2
Jog:: count:1
Jog:: count:2
Jog:: count:3
Jog:: count:4
Jog:: count:5
Jog:: count:4
Jog:: count:5
Jog:: count:4
Jog:: count:3
Jog:: count:2
Jog:: count:1
Jog:: count:0
Jog:: count:-1
Jog:: count:-2
Jog:: count:-3

Jog:: count:-1

Jog:: count:0

Jog:: count:1

Jog:: count:2

Jog:: count:1

Jog:: count:2

Jog:: count:3

Jog:: count:4

Jog:: count:5

Jog:: count:4

Jog:: count:5

Jog:: count:4

Jog:: count:3

Jog:: count:2

Jog:: count:1

Jog:: count:0

Jog:: count:-1

Jog:: count:-2

Jog:: count:-3

Bronnen:
arduino.stackexchange.com
heliosoph.mit-links.info
henrysbench.capnfatz.com
martoparts.nl
playground.arduino.cc