Lesson 27 Rotary Encoder Module

Introduction

A rotary encoder is an electro-mechanical device that converts the angular position or motion of a shaft or axle to analog or digital code. Rotary encoders are usually placed at the side which is perpendicular to the shaft. They act as sensors for detecting angle, speed, length, position, and acceleration in automation field.

Components

– 1 * Raspberry Pi

– 1 * Breadboard

– 1 * Network cable (or USB wireless network adapter)

– 1 * Rotary Encoder module

– 1 * 5-Pin Anti-reverse Cable

Experimental Principle

Most rotary encoders have 5 pins with three functions of turning left & right and pressing down. Pin 1 and pin 2 are switch wiring terminals used to press. They are similar to buttons previously mentioned, so we will no longer discuss them in this experiment. Pin 4 is generally connected to ground. Pin 3 and pin 5 are first connected to pull-up resistor and then to the microprocessor. In this experiment, they are connected to GPIO0 and GPIO1 of Raspberry Pi. When it is rotated left and right, there will be pulse inputs in pin 1 and pin 3.

It shows that if output 1 is high and output 2 is high, then the switch rotates clockwise; if output 1 is high and output 2 is low, then the switch rotates counterclockwise. As a result, during SCM programming, if output 1 is high, then you can tell whether the rotary encoder rotates left or right as long as you know the state of output 2.

Experimental Procedures

Step 1: Build the circuit

Raspberry Pi	Rotary Encoder module
GPIO0	CLK
GPIO1	DT
GPIO2	SW
5V	VCC
GND	GND

For C language users:

Step 2: Change directory

cd /home/pi/SunFounder_SensorKit_for_RPi2/C/27_rotary_encoder/

Step 3: Compile

gcc rotary_encoder.c -lwiringPi

Step 4: Run

sudo ./a.out

For Python users:

Step 2: Change directory

 cd /home/pi/SunFounder_SensorKit_for_RPi2/Python/

Step 3: Run

sudo python 27_rotary_encoder.py

Now rotate the shaft of the rotary encoder, and the value printed on the screen will change. Rotate the rotary encoder clockwise, the value will increase; Rotate it counterclockwise, the value will decrease; Press the rotary encoder, the value will be reset to 0.

C Code

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <wiringPi.h>

#define  RoAPin    0
#define  RoBPin    1
#define  SWPin     2

static volatile int globalCounter = 0 ;

unsigned char flag;
unsigned char Last_RoB_Status;
unsigned char Current_RoB_Status;

void btnISR(void)
{
	globalCounter = 0;
}

void rotaryDeal(void)
{
	Last_RoB_Status = digitalRead(RoBPin);

	while(!digitalRead(RoAPin)){
		Current_RoB_Status = digitalRead(RoBPin);
		flag = 1;
	}

	if(flag == 1){
		flag = 0;
		if((Last_RoB_Status == 0)&&(Current_RoB_Status == 1)){
			globalCounter ++;	
		}
		if((Last_RoB_Status == 1)&&(Current_RoB_Status == 0)){
			globalCounter --;
		}
	}
}

int main(void)
{
	if(wiringPiSetup() < 0){
		fprintf(stderr, "Unable to setup wiringPi:%s\n",strerror(errno));
		return 1;
	}

	pinMode(SWPin, INPUT);
	pinMode(RoAPin, INPUT);
	pinMode(RoBPin, INPUT);

	pullUpDnControl(SWPin, PUD_UP);

    if(wiringPiISR(SWPin, INT_EDGE_FALLING, &btnISR) < 0){
		fprintf(stderr, "Unable to init ISR\n",strerror(errno));	
		return 1;
	}
	
	int tmp = 0;

	while(1){
		rotaryDeal();
		if (tmp != globalCounter){
			printf("%d\n", globalCounter);
			tmp = globalCounter;
		}
	}

	return 0;
}

Python Code 

#!/usr/bin/env python
import RPi.GPIO as GPIO
import time

RoAPin = 11    # CLK Pin
RoBPin = 12    # DT Pin
BtnPin = 13    # Button Pin

globalCounter = 0

flag = 0
Last_RoB_Status = 0
Current_RoB_Status = 0

def setup():
	GPIO.setmode(GPIO.BOARD)       # Numbers GPIOs by physical location
	GPIO.setup(RoAPin, GPIO.IN)    # input mode
	GPIO.setup(RoBPin, GPIO.IN)
	GPIO.setup(BtnPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)

def rotaryDeal():
	global flag
	global Last_RoB_Status
	global Current_RoB_Status
	global globalCounter
	Last_RoB_Status = GPIO.input(RoBPin)
	while(not GPIO.input(RoAPin)):
		Current_RoB_Status = GPIO.input(RoBPin)
		flag = 1
	if flag == 1:
		flag = 0
		if (Last_RoB_Status == 0) and (Current_RoB_Status == 1):
			globalCounter = globalCounter + 1
		if (Last_RoB_Status == 1) and (Current_RoB_Status == 0):
			globalCounter = globalCounter - 1

def btnISR(channel):
	global globalCounter
	globalCounter = 0

def loop():
	global globalCounter
	tmp = 0	# Rotary Temperary

	GPIO.add_event_detect(BtnPin, GPIO.FALLING, callback=btnISR)
	while True:
		rotaryDeal()
		if tmp != globalCounter:
			print 'globalCounter = %d' % globalCounter
			tmp = globalCounter

def destroy():
	GPIO.cleanup()             # Release resource

if __name__ == '__main__':     # Program start from here
	setup()
	try:
		loop()
	except KeyboardInterrupt:  # When 'Ctrl+C' is pressed, the child program destroy() will be  executed.
		destroy()