Encoder Reading using LabVIEW and Arduino

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 Fall 2016

TABLE OF CONTENTS 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 4.2. PROTEUS SIMULATION 4.3. EXERCISE 4.4. COMMUNICATION WITH LABVIEW 4.4.1. ARDUINO CODE 4.4.2. LABVIEW VI 4.4.3. LABVIEW BLOCK DIAGRAM

2 4 6 6 6 6 7

5. RESULTS

8

6. FURTHER EXERCISE

8

7. REFERENCES

9

LIST OF FIGURES FIG. 1 ARDUINO UNO R3 BOARD ........................................................................................................... 1 FIG. 2 SIX POLES, TWO CHANNELS MAGNETIC ENCODER ................................................................................ 1 FIG. 3 LIQUID CRYSTAL DISPLAY .............................................................................................................. 2 FIG. 4 ARDUINO USB CABLE .................................................................................................................. 2 FIG. 5 ENCODER LIBRARY BY PAUL STOFFREGAN ......................................................................................... 2 FIG. 6 PROTEUS MODEL......................................................................................................................... 5 FIG. 7 ARDUINO CODE AND PROTEUS ....................................................................................................... 5 FIG. 8 SIMULATION RESULT .................................................................................................................... 6 FIG. 9 COM PORT CONNECTIONS ............................................................................................................ 7 FIG. 10 LABVIEW BLOCK DIAGRAM......................................................................................................... 7 FIG. 11 LABVIEW - ARDUINO CO-SIMULATION FOR ENCODER READING.......................................................... 8 FIG. 12 GITHUB COURSE REPOSITORY ...................................................................................................... 9

MCT 432 Hybrid Control

Lab 1: Reading Quadrature Encoder Position

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.

Fig. 2 six poles, two channels magnetic encoder

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


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

Fig. 5 Encoder library by Paul Stoffregan

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After installing the library, create a new sketch and copy the below code, then save it with any name appropriate. #include #include const int encaPin=2; const int encbPin=3; int oldPosition char buffer[6];

= -999;

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 #include

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MCT 432 Hybrid Control 


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

𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛𝑃𝑃𝑅 = (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.



LCD module connected to Arduino as instructed in code. P a g e 4 | 12

MCT 432 Hybrid Control 


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

Run the simulation and watch results P a g e 5 | 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.

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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

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

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 You can get all files of lab 1 from GitHub repository of the course [3].

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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-visa15.0.1/5693/en/ [3] F. Tolbah and W. El-Badry. MCT 432 Hybrid Control Repository. Available: https://github.com/wbadry/MCT432-Hybrid-Control

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Encoder Reading using LabVIEW and Arduino

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