ENGG1015: lab 5. A Taste of the Project

Transcription

1 ENGG1015: lab 5 A Taste of the Project 1 st Semester The goal of this lab is further understand the relationship between the input and output (driving) stage of a circuit. You will gain hands-on experience with the project components. 1 Finding your lab partner You will be working with a randomly assigned partner for this lab. To find your assigned lab partner and the assigned table, 1. Log in to Moodle. 2. Select the assignment Lab 5 Partner Please proceed to your assigned table. 2 Basic Rube Goldberg Machine Step Your final Rube Goldberg machine project will consist of a number of interconnected electronic steps. Each step itself can be represented as an electronic system as we covered in class shown in Figure 1. Each of them is consist of 3 stages: input, output, and an optional processing stage. Figure 1: A generic model of an electronic system with input, process and output. This part of the lab is to help you begin constructing circuits for your project. Along the way, you will also learn the importance of isolating the input and output stages to avoid loading effect. 2.1 The Power Need Instead of relying on the FPGA board to supply 3.3V power as Vcc, you will use a power supply to supply power for your project. The power supply you are using for in this class is shown in Figure 2(a). It has 3 output channels, labeled CH1, CH2 and CH3. In this lab, use the left-most channel labeled CH2. A few notes about how the power supply operates: Connect the ground of your circuit to the BLACK terminal, and Vcc to the RED terminal. Ignore the green terminal marked GND in the power supply. Voltage and current output at the terminals are controlled by the 2 knobs in the LEFT. The display shows the live voltage and current output at the terminals. The signal light marked C.V./C.C. (Figure 2(b)) indicates if the output terminal is controlled by current or voltage. In this class, always make sure the light is green, i.e.

2 ENGG1015 lab 5 your output should be controlled by voltage. If it turns to red, then turn up the dial for CURRENT until it turns back to green. The terminal outputs are active only if the OUTPUT button on the top left is depressed. Use this button often. Whenever you are experimenting with the settings on the power supply, make sure OUTPUT is off. Then you can reenable it once the setting is done. (a) Photo (b) C.V./C.C. Indicator Figure 2: Power Supply Do the following: 1. Depress the OUTPUT button so it is OFF. 2. Turn the VOLTAGE dial so the output of the power supply is at 12 V. 3. Turn the CURRENT dial so the output of the power supply is at 1.5 A. Use a digital multimeter (DMM) to measure the output voltage (turn the dial of the DMM to 20). What is the output voltage? Now press the OUTPUT button, what is the reading on the power supply? What is the value you are measuring using the DMM? WARNING: Turn off the power supply output immediately after testing your circuit. In general, always turn off the output of the power supply when you are constructing or debugging your circuit. Only enable output when you are testing the circuit. It helps to avoid causing damage on the lab equipments. 2.2 Switch Solenoid There are many different input and output stages you may utilize in your project. We will start with a simple one here. We will use a mechanical switch (Figure 3(a)) as an input. The output stage we will use is a solenoid (Figure 3(b). The solenoid provides a source of lateral pull force When there is no power, the shaft is extended by default; when turned on, the shaft is pulled into the solenoid via the internal magnetic coil, and hence the shape of a magnetic coil in the symbol. Page 2 of 7

3 ENGG1015 lab 5 switch (a) Switch (b) Solenoid Figure 3: Schematic symbols of a switch and solenoid. Now, take a solenoid, without connecting to anything else, measure the resistance between the two terminals. Record this resistance below. R solenoid = 2.3 Construct the circuit in Figure 4(a). Instead of breadboard, we will use a high-density foam board to provide mechanical support for the circuit and to use heavy-duty terminal blocks for connecting to the power supply. Your circuit should look like Figure 4(b). Figure 4: Simple step with switch and solenoid Now, turn on the power supply OUTPUT. Press and depress the switch to turn on/off the solenoid. When the solenoid is on, record the following from the power supply reading: CURRENT = VOLTAGE = Page 3 of 7

4 ENGG1015 lab 5 WARNING: Never keep the solenoid turned on continuously for more than 30 seconds. 2.4 Turn on Voltage We want to find the voltage at which the solenoid turns on. 1. Turn the VOLTAGE dial on the power supply so it shows 0V 2. Turn on the OUTPUT of the terminals 3. Keep the switch pressed, gradually turn up the voltage supply from 0V to 12V until the switch turns on. Record the voltage (V T,solenoid ). 4. Release the switch 5. Turn off the OUTPUT V T,solenoid = Turn off the power supply when you have completed this part. The solenoid will be damaged if you keep it turned on for a long time. So whenever you are working with it, make sure you DO NOT turn it on for a long time. 2.5 Checkoff 1 Show your complete circuit to your TA and answer the following questions: What is the threshold voltage for turning on/off the solenoid? How do you measure the current running through the solenoid? What is the resistance of the solenoid? 3 Different Input, Different Story Instead of using a switch, most input stages rely on component that changes its resistance according to physical phenomenon. For example in last week, you have used a photodetector that changes its resistance according to the amount of light shining on it. For these kinds of input, we ll use a potential divider circuit similar to last week. To emulate the effect of such potential divider circuit, we ll again be using a potentiometer this week. However, unlike last week, a heavy-duty potentiometer is used. Despite the different size, the function of this potentiometer is the same as the one from last week. 3.1 Connect the circuit shown in Figure 5(a). You should be able to build this circuit by reusing the same foam board from the previous step. Make sure you disconnect the solenoid from the circuit board. Page 4 of 7

5 ENGG1015 lab kω 12V Vout Figure 5: A simple potential divider circuit Measure the voltage Vout. Verify the function of the potential divider circuit by turning the dial on the potentiometer. What is the range of Vout? 3.2 Turn the pot until Vout = VT,solenoid 1 where VT,solenoid is the value you measured above. At this voltage, the solenoid should turn on when connected. Keep the dial of the potentiometer untouched. Construct the following circuit by attaching the solenoid to your circuit. Your result should look like Figure 6(b). 4.7 kω 12V Vout Figure 6: Potential divider input connected directly to solenoid output. Now, turn on the power supply, is the solenoid turned on? What is the value of Vout? Vout = Turn the dial of the potentiometer up and down to see if it has any effect on the solenoid. Page 5 of 7

6 ENGG1015 lab Checkoff 2 Show to your TA your implementation as in Figure 6(b) and answer the following question: Are you able to turn on the solenoid? Why and why not? How does the output voltage change as you turn the dial? 4 Isolating Stages One way to ensure the input output abstraction is not violated as we construct circuit is to isolate the stages. There are many ways to isolate stages. Here, we will use a solid-state relay for that purpose. IN OUT (a) Photo SS-RELAY (b) Symbol IN- OUT- Figure 7: Solid State Relay A sold-state relay is shown in Figure 7(a). We will use the schematic symbol in Figure 7(b) in this class. The function of a SS-RELAY is very simple: When the voltage around the two input terminals (in and in-) is higher than a threshold value(v T,ssrelay ), the output terminals (out and out-) are connected like switch. It is called a solid-state switch because the switching action is implemented electronically. No mechanical part is presented inside the SS-RELAY. As a side note, similar components you may use in the project include magnetic reed switch and relay. These components behave similarly to the SS-RELAY except mechanical switches are used internally. Using a SS-RELAY, extend your circuit from previous step to become the circuit in Figure 8(a). Your final circuit should look similar to that in Figure 8(b). Page 6 of 7

7 ENGG1015 lab 5 OUT IN 12V SS-RELAY OUT- - solenoid IN- V pot V sol - Figure 8: A potential divider input stage connecting to solenoid output stage via a solid-state relay. 4.1 Turn your dial on your potentiometer from one end to another end. Does it turn on/off the solenoid? Now, turn your potentiometer until the solenoid is off. Measure Vpot and Vsol. Then, gradually turn the dial up until the solenoid is just turned on. Measure Vpot and Vsol again. Define the voltage value of Vpot at this point as VT,relay. Solenoid State Vpot Vsol off on VT,ssrelay = 4.2 Checkoff 3 Show to your TA your completed circuit with the SS-RELAY acting as an isolating buffer and answer the following question: Is VT,relay = VT,solenoid? Why or why not? When the solenoid is on, what is the voltage across the two terminals of the solenoid? When the solenoid is on, what is the current drawing from the power supply?... 5 Optional Steps Congratulation! You now possess the basic framework to construct complex Rube Goldberg machine. You may mix and match many different input and output stages as you design your project. Using the circuit above with the SS-RELAY, you will be able to replace the VR with any input stage, and replace the solenoid with other output stages. You may ask your TA to give you the Ball Counter from last week as an input stage. You may also take a motor or a fan to replace the solenoid as an output. Page 7 of 7