Encoder Reading using LabVIEW and Arduino

(1)

Ain Shams University Faculty of Engineering

Credit Hours Engineering Program MCT 432 Hybrid Control

LAB 1

Reading Quadrature Encoder

Position

Prof. Farid A. Tolbah Eng. Waleed A. El-Badry

(2)

1. OBJECTIVE OF CONDUCTED EXPERIMENT 1

2. HARDWARE REQUIREMENTS 1

3. SOFTWARE REQUIREMENTS 2

4. PROCEDURE 2

4.1. DISPLAY ENCODER POSITION ON AN LCD 2

4.2. PROTEUS SIMULATION 4

4.3. EXERCISE 6

4.4. COMMUNICATION WITH LABVIEW 6

4.4.1. ARDUINO CODE 6

4.4.2. LABVIEWVI 6

4.4.3. LABVIEW BLOCK DIAGRAM 7

5. RESULTS 8

6. FURTHER EXERCISE 8

(3)

LIST OF FIGURES

FIG.1ARDUINO UNOR3 BOARD ... 1

FIG.2 SIX POLES, TWO CHANNELS MAGNETIC ENCODER ... 1

FIG.3LIQUID CRYSTAL DISPLAY ... 2

FIG.4ARDUINO USB CABLE ... 2

FIG.5ENCODER LIBRARY BY PAUL STOFFREGAN ... 2

FIG.6PROTEUS MODEL ... 5

FIG.7ARDUINO CODE AND PROTEUS ... 5

FIG.8SIMULATION RESULT ... 6

FIG.9COM PORT CONNECTIONS ... 7

FIG.10LABVIEW BLOCK DIAGRAM ... 7

FIG.11LABVIEW-ARDUINO CO-SIMULATION FOR ENCODER READING... 8

(4)

P a g e 1 | 12

1. Objective of conducted experiment

After completing this lab, you will be able to:

 Prepare the necessary hardware for reading motor position (angle) from mounted magnetic encoder.

 Understand the Arduino code for successful reading of encoder pulses and show reading on LCD.

 Transfer Arduino reading to LabVIEW.



Prevent recurring transfer and LCD update when no change in reading.

2. Hardware requirements

 Arduino Uno R3 (or any board with at least two pins supporting external interrupt).

Fig. 1 Arduino UNO R3 board

 Quadrature magnetic encoder. Experiment was conducted using Sha Yang Ye geared motor with onboard encoder available in Mechatronics lab.

(5)

MCT 432 Hybrid Control Lab 1: Reading Quadrature Encoder Position

P a g e 2 | 12

 2x16 alphanumeric LCD.

Fig. 3 Liquid Crystal Display

 USB cable for connecting Arduino to PC.

Fig. 4 Arduino USB cable

3. Software requirements

 Arduino IDE for programming Arduino.  NI LabVIEW 2015 or later.

 NI VISA 16 or later to allow LabVIEW to connect to available serial ports.  Proteus ISIS 7.5 or later for offline simulation.

 FabulaTech Virtual serial port kit or any alternative to allow serial communication between LabVIEW and Arduino.

4. Procedure

4.1. Display encoder position on an LCD

The code will utilize encoder library by Paul Stoffregan which can be downloaded from library manager

(6)

P a g e 3 | 12

After installing the library, create a new sketch and copy the below code, then save it with any name appropriate.

#include <Encoder.h>

#include <LiquidCrystal.h>

const int encaPin=2;

const int encbPin=3;

int oldPosition = -999;

char buffer[6];

LiquidCrystal lcd(12, 11, 7, 6, 5, 4);

Encoder myEnc(encbPin, encaPin);

void setup() {

Serial.begin(9600);

lcd.begin(16, 2);

lcd.setCursor(0,0);

lcd.print("Encoder Count:");

}

void loop() {

int newPosition = myEnc.read(); if (newPosition>231) myEnc.write(0); if (newPosition<-231) myEnc.write(0); if (newPosition != oldPosition) { oldPosition = newPosition;

sprintf(buffer,"%04d", newPosition);

Serial.println(buffer); lcd.setCursor(0,1); lcd.print(" "); lcd.setCursor(0,1); lcd.print(buffer); delay(50); } }

Snippet for reading motor angle from magnetic encoder and display it on LCD

You are supposed to be acquainted with Arduino commands. However, few highlights to comprehend the code flow would be useful.

 Importing both encoder and LCD libraries. #include <Encoder.h>

(7)

P a g e 4 | 12

 Define the encoder pins (channel A and Channel B). It is recommended that both pins are “interrupt pins” for better performance of the library [1]

const int encaPin=2;

const int encbPin=3;

 Read the encoder pulses.

int newPosition = myEnc.read();

The used encoder has 6 poles and mounted on 19:1 gearbox. So encoder resolution is calculated as:

ResolutionPPR =(No. of poles)x(No. of channels)x(Grear Ratio) Eq. 1

𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛_𝑃𝑃𝑅 = (6)𝑥(2)𝑥(19.25) = 231 𝑃𝑃𝑅 Where PPR indicates Pulse Per Revolution.

 Since we measure position not number of revolustions, we override encoder reading if exceeded one revolution in any direction.

if (newPosition>231) myEnc.write(0); if (newPosition<-231)

myEnc.write(0);

 Also LCD is updated only if new reading arrived. This saves the LCD from recurring refresh while encoder (motor ) is at standstill.

if (newPosition != oldPosition) { oldPosition = newPosition;

sprintf(buffer,"%04d", newPosition);

Serial.println(buffer); lcd.setCursor(0,1); lcd.print(" "); lcd.setCursor(0,1); lcd.print(buffer); delay(50); } 4.2. Proteus simulation

Open the file “Encoder Reading Model.pdsprj” accompanied with your lab files. The model comprises five components:

 Arduino UNO model (based on ATMEGA328P).

 Scope (to monitor encoder output and the 90o _{phase shift.}

 Encoder circuit that is composed of LM298 motor shield and DC motor with encoder. Again we are interested in encoder only. This can be however used as a base for closed loop control.

(8)

P a g e 5 | 12

 Virtual COM (for later use with LabVIEW).

Fig. 6 Proteus model

Before you start the simulation, make sure your code is compiled into hex file. Double click on Arduino chip in simulation and point to the generated hex file. It is recommended that you place the hex file alongside your Proteus

model.

Fig. 7 Arduino code and Proteus

(9)

P a g e 6 | 12

a) Scope output showing both channels output signal

b) LCD display

Fig. 8 Simulation result

4.3. Exercise

Modify the Arduino code to display the actual position in radian and degree considering that a 1 𝑟𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛 = 231 𝑝𝑢𝑙𝑠𝑒𝑠.

4.4. Communication with labVIEW

The second part of lab activities is to communicate LabVIEW with Proteus for reading encoder position and plot it on a chart.

4.4.1. Arduino Code

The code discussed earlier has the command Serial.println(buffer)which sends encoder reading as 6 characters to LabVIEW.

4.4.2. LabVIEW VI

As mentioned in earlier, your PC must have NI VISA [2] installed in addition to LabVIEW to allow LabVIEW to detect available serial port. Since there is no connected physical Arduino so far, we will also use virtual com port emulator which virtually connect two com ports together. One will be used on Arduino (inside Proteus) and the other with LabVIEW.

(10)

P a g e 7 | 12 Fig. 9 COM port connections

4.4.3. LabVIEW block diagram

The VI was coded by instructors to provide minimum effort to successfully receive encoder data.

Fig. 10 LabVIEW block diagram

 VISA resource name : to enumerate available com ports. You either select the virtual com port or in reality the Arduino com port.

 Configure serial port : after selecting the com port, we may edit the baudrate and reading timeout

(11)

P a g e 8 | 12

 VISA read : Reading six characters from Arduino (you can change that in Arduino code buffer variable to suit your needs).

 String to Number conversion : Since Arduino passes data as encoded string, this block converts the transmitted characters into single decimal value.

 VISA close : This is to close connection and unlock com port so other applications can use it if needed.

5. Results

Start Proteus simulation and then LabVIEW.

Fig. 11 LabVIEW - Arduino co-simulation for encoder reading

6. Further exercise

Modify the code to calculate velocity in PPR.

7. File repository

(12)

P a g e 9 | 12 Fig. 12 GitHub course repository

8. References

 [1] Encoder Library for Arduino. Available: https://www.pjrc.com/teensy/td_libs_Encoder.html

 [2] N. Instruments. NI VISA. Available: http://www.ni.com/download/ni-visa-15.0.1/5693/en/

 [3] F. Tolbah and W. El-Badry. MCT 432 Hybrid Control Repository. Available: https://github.com/wbadry/MCT432-Hybrid-Control