EET-126 Lab 3

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Centennial College *

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126

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Electrical Engineering

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Apr 3, 2024

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Electrical Engineering Technician AMAT/ SETAS Course: EET-126 ,2023.______________________ Lab 3: Operator Control and Process Calibration Overview In this lab, we will start by building the open loop system we developed in Lab 2 – part 1 and add it to a control panel using push buttons. We will then calibrate the push button assuming that our manufacturing process has changed. Components Required (1) x Elegoo Uno R3 (1) x L239D Driver chip (1) x DC Motor (1) x Elegoo power supply (10) x M-M wires (male to male jumper wires) (3) x M-F wires (male to female jumper wires)

Procedure – Part 1 In this lab, we will setup our motor control as was done in Lab 2 – part 1. Remember, the schematic of the circuit looked as shown: Fig 1: Schematic of Open loop system motor control The actual built circuit is shown below: Fig 2: Actual built setup Review the instructions on lab 2 and the video posted if you need help setting this circuit again .

Our goal in this lab is to change the input control of the system to push buttons. Remember, the operator of a system should be able to control the desired process variable from a controller panel generally using buttons or levers. So far, our control change mechanism involved changing the code in the Arduino IDE which is not the most intuitive way of doing things. Moreover, every time we change a setting in the code (example motor speed or direction of the motor spin), we have to re-upload the code to the Arduino Uno, which means the motor first has to stop and then start again. This is not ideal and may not be feasible for application we are running. Therefore, we will modify our system to have a push button control. We will add two push buttons, one push button will increase the motor speed in one direction and another will decrease the motor speed. If the motor speed goes to zero and the push button that reduces the speed is pushed again, the motor will start but in the opposite direction. A good way to visualize the operation is through the following diagram: Fig. 3: Controller output of the open loop system

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Every time we press the increase pushbutton, the speed will increase by a factor called ∆ (pronounced “delta”) and vice versa. It is up to us to choose the value of delta. For this part of the lab, the value of ∆=10. As you remember from Lab 2, the motor speed can go from 0 to 255. Here we have shown the motor speed also going from 0 to -255. This signifies that the motor is changing direction (In Lab 2, we should the operation in having a negative slope, this is another way of representing the same concept). There are a few situations that we must take care of for proper operation of the circuit, these are labeled in Fig. 3  The motor will start at speed of 0. But when the increase speed button is pressed, the motor speed should jump to 100 (remember from Lab 2 that the motor did not start for speeds lower than 100). Similarly, when the motor speed is reduced below 0, the motor must jump to -100  When the motor speed is being reduced, below 100, again we do not want to keep the speed at this level because the motor does not start. Therefore, we must drop the motor speed to zero below 100 and this is shown in the graph of Fig 3 with the sharp increase/drop around 0.  The motor speed must be capped at 255 and -255. So if push buttons are pressed at these edges, we must not increase the speed value beyond 255 or -255. These situations and the corresponding code to deal with them is describe in more detail in the video posted for this lab. Watch the video to setup the pushbuttons and the corresponding code. Once completed answer the following questions 1. This process uses proportional control but the increase is done in discrete increments and is not continuous. Another way of saying this is that the proportional control is digital. Find the proportional gain of this system (hint: remember gain is the slope of the controller outpu and the slope of the curve of Fig. 3 has units of “push” in the x-axis and units of ∆ for the y-axis). Answer:On the y axis, the value goes from 0 to 255 in speed. And in the cx axis, this takes 17 increments of times the button needs to be pressed . So the y axis/ x axis is 255/17. So the propertional gain of this system is =15 2. What is the value of the pushbutton when not being pressed? What is the value of he pushbutton when pressed? (watch the video for clues) Answer: The value of the push button when not being pressed shows up as 1. And when the pushbutton is being pressed or held down, the value shows as 0. You can see this on the serial monitor under tools on the arduino software.

3. In the code provided, what is the purpose of the variable dt ? (watch the video for clues). Answer: It is to delay the reading of the push button. If there was no delay, the arduino board might read a single push as multiple pushes, instead of just 1. The arduino reads the inputs continously so if you put no delay, it might not do what you want exactly.

Procedure – Part 2 The code provided in part 1 is for a ∆=10. Assume that our manufacturing process has changed so that we need to change the speed of the motor by a value other than 10. The value you should choose is based on the following rule  10 + last digit of your student number + 1 For example, if the last digit of your student number is 5, then ∆=16. Modify the code provided to you in part 1 to handle the change in the manufacturing process. Note that you only need to change values provided not any of the code. The video posted gives you hints on how to do this. Answer the following questions: 1. What other reasons may you want to change the value of ∆? (hint: think of reasons why we do calibration) Answer: The goal of calibration is to minimise any measurement uncertainty by ensuring the accuracy of test equipment. So you might need to change the value of delta so that you can get more accurate with your measurements with different types of equipment. Also, in this lab, you might just want to be able to reach maximum speed in either direction faster or slower( more or less increments before maximum speed. 2. Assume that we want the motor to only go to 100 in one direction and to 255 in the other direction. Redraw the controller output as shown in Fig. 3 for this scenario. Deliverables 1. Answer all question provided in each section. You can write your answers on a piece of paper and take a picture of your answer and neatly paste it in the document. 2. Take a picture of your setup in part 2 and include it in your lab report 3. Include the modified code for part 2.

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