ENGR43Lab2

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ENGR 43 Lab Activity Student Guide LAB 2 – Voltage, Current, and Resistance Measurements Student Name: ___________________________________________________ Overview In this lab activity, you will make voltage, current, and resistance measurements on the BOE-bot robot trainer. You will compare your measurements to specifications and determine if your BOE-bot is ready for its run on the racetrack. You will monitor its operation on the track and evaluate its performance based on your measurements and manufacture’s data. Before Starting This Activity Review the following online learning modules on the Wisc-Online website (www.wisc-online.com):  Introduction to the Digital Multimeter  Voltmeter Circuit Connections  Ammeter Circuit Connections  Ohmmeter Measurements Links to these learning modules are on the GoogleDocs listing ( http://tinyurl.com/engr43-lablinks ) . Learning Outcomes for Activity Relevant knowledge (K), skill (S), or attitude (A) student learning outcomes K1. Identify the proper meter connections and circuit conditions for measuring voltage, current, and resistance with a digital multimeter (DMM) K2. Compare measured data with specified limits K3. Evaluate voltage of a series battery S1 . Measure voltages with a DMM in a functioning system S2. Measure current with a DMM in a functioning system S3. Measure resistance of components from a deactivated system S4. Compile data into a test report. A1. Recognize the positive impact of well- organized and neatly prepared report. Time Needed Lab Performance: It should take students approximately 2.0 hours to work through the entire lab. Lab Deliverables: It should take students approximately 2.0 hours of homework time to create the lab report summary. Lab 2 – V, I, R Measurements © 202 ENGR 43 1

ENGR 43 Lab Activity Student Guide Equipment & Supplies Item Quantity BOE-bot robot trainer 1 Optical sensor course tracking board 1 DMM and test leads 2 BOE-bot power monitor test cable 1 AA alkaline cells (batteries) – installed in BOE-bot 4 Special Safety Requirements  The BOE-bot wheels can present a pinch hazard when moving. Keep fingers and loose parts away from the wheels.  Incorrect connection of an ammeter can create a shorting hazard, with possible overheating and damage to the BOE-bot and meter. Ask the instructor to double-check your connections before connecting power to the BOE-bot Lab Preparation 1. The lab instructor will set up the BOE-bot racetrack for the final performance test. 2. The BOE-bot must have the program follow-line.bs2 loaded on the BASIC Stamp microcontroller. The instructor will confirm that you have the correct software loaded. 3. The BOE-bot must have the optical sensor course tracking board installed. Verify that the board is mounted securely on the front of the robot. Introduction You are the technician responsible for preparing the BOE-bot for the “Engineering 500 Robo-Race.” You will verify that the robot is ready to race by comparing your measurements with specified limits and you will monitor the performance as it runs the test course. Your final report will evaluate the race performance and predict the chances of your robot completing a longer endurance race. Task #1 – Battery Voltage Measurements Follow the steps to measure the individual cell voltages and battery output voltage. 4. Download the lab worksheet E50lab2.xlsx from the Canvas site. Open the file in Excel. 5. Place the BOE-bot upside-down on the lab bench, with the rear ball wheel facing left. If AA cells are not already in place, install 4 cells in the battery holder. Refer to Figure 1. Figure 1 6. Set the DMM to measure voltage, and if it is not an auto-ranging meter, set the range to the closest value greater than 10 V. Measure the voltages where cell terminals contact the battery holder. Refer to Table 1 on the worksheet and Lab 2 – V, I, R Measurements © 202 ENGR 43 2

ENGR 43 Lab Activity Student Guide Figure 1 above for the locations of the red (+), and black (-) leads. Enter your measured values in Table 1. You may round your values to the nearest hundredth of a volt (example: round 1.325 to 1.33 volts). Take turns with all your lab partners so that everyone makes several voltage measurements. 7. As you enter the values in Table 1, the values in the green cells are copied into Table 2. Compare these values to the minimum specified voltage. If any of the cells are out of spec, ask the instructor for a replacement AA alkaline cell. Once all cells are in-spec, proceed to the next step. 8. Turn the BOE-bot right side up, unplug the power plug from the power jack (labeled 6-9VDC). Measure the voltage between the center contact and outer ring of the power plug. Refer to Figure 2. Determine the polarity (+ or -) of the center contact relative to the outer ring. Enter your findings in the area to the right of Table 2. Figure 2 Task #2 –Resistance Measurement The “eyes” of the robot are light-sensitive resistors. We will verify that the robot can “see” by measuring the resistance. 1. Remove the green and red jumper wires from the “P3” and “P6” connector sockets as shown in Figure 3. Leave the other ends of the wires connected to the proto-board. Connect an additional 22 AWG solid wire to the same row as the black wires on the proto-board. 2. Set the DMM to resistance mode, and if the meter is not auto-ranging set the range to 200 k ohm (or higher). Place the black meter leads on the black lead of the opto sensor board harness and the red meter lead on the red wire. Place an opaque object over the face of the left (with the ball in at the back of the car) photoresistor and measure the “dark resistance.” Enter the value in Table 3. Remove the object, measure the “light resistance,” i.e. photo-resistors are pointing towards a light, and enter the value in Table 3. Move the red meter lead to the green wire. Repeat dark and light measurements for the right photo- resistor. Figure 3 When you have completed the resistive measurements, plug the green and red Lab 2 – V, I, R Measurements © 202 ENGR 43 3

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ENGR 43 Lab Activity Student Guide jumper wires back into P3 and P6 connectors. Figure 4 Task #3 –Current and Voltage Measurements Follow the instructions carefully! Ask the instructor to check your connections before connecting the battery pack power plug to the Power Test Cable! 1. Connect the BOE-bot power monitor test cable to the power jack on the circuit board. Do not connect the power plug from the battery pack until instructor checks your connections! Set one meter to measure voltage and the other to measure current. Connect the meters as shown in Figure 4. 2. After the instructor has checked your connections, plug in the power plug. With the power switch on the BOE-bot in position 0 (off), measure voltage and current and enter the values in Table 4. Set the power switch to position 1 (microcontroller on, motors off), measure voltage and current and enter the values in Table 4. 3. Pick up the BOE-bot so that the main wheels can spin freely. Set the power switch to position 2 (microcontroller and motor power on). Both main wheels should spin. Measure voltage and current and enter the values in Table 4. 4. Turn the BOE-bot so that the photo- resistors are pointing towards a light. Put your finger or an opaque object on the face of the left photo-resistor. The left wheel should stop spinning. Take your finger off the photo-resistor. The left wheel should start spinning. Repeat for the right photo-resistor and wheel. Congratulations! By completing these steps you have verified that the power supply, motors, and control systems are ready for the race track. 5. Set the power switch to 0 (OFF). With the power monitor test cable, voltmeter, and ammeter still connected, carefully transport the BOE-bot to the race track. 6. Place the BOE-bot with the photo- resistors straddling the black course line. Route the cable from the test cable so Lab 2 – V, I, R Measurements © 202 ENGR 43 4

ENGR 43 Lab Activity Student Guide that it will not interfere with the path of the robot on the track. 7. Set the power switch to position 2. After one second your robot will start on the course. Measure the voltage and current when your robot is on one of the straight-aways. Enter your values in Table 4. Pick up your robot and set the power switch to position 1. 8. The instructor will place the track on an incline. Run your BOE-bot on the course, and measure the voltage and current when the robot is going uphill and downhill, and enter these values in Table 4. 9. In this system, the AA batteries are the power source and the BOE-bot electronics and motors are the load. We can calculate the total resistance of the load by dividing the current into the voltage, R = V / I. When you divide volts by milliamps, the resistance is in kilohms (k ohm). Calculate the resistance for the 5 conditions listed in Table 4. Deliverable(s) Save your completed Lab 1 Worksheet and your Performance Report (at the end of this document) in your Lab Activity Binder. Lab 2 – V, I, R Measurements © 202 ENGR 43 5

ENGR 43 Lab Activity Student Guide Lab 2 – V, I, R Measurements © 202 ENGR 43 6

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ENGR 43 Lab Activity Student Guide Lab 2 BOE-bot Performance Report Student Name: ___________________________________________________ Battery Voltage Measurements What can you conclude about the relation between the individual battery voltages and the total voltage supplied to the BOE-bot? The total voltage supplied to the BOE-bot is the sum of the individual battery voltages. Refer to the voltage measurement table on your lab worksheet. Can you match the position of each battery (identified by the letters at each terminal) with the schematic of the battery pack? What would happen if one of the AA cells were installed backwards? Voltage measures the difference in electrical potential between two points. If the middle battery was installed backwards, the difference between that battery, and the one next to it would be 0. Therefore, the total voltage of the 4 batteries now become half of the previous value. If the outermost battery was installed backwards, the total voltage would be the difference between two ends of the battery pack, which is going to be of the same polarity. Consequently, it would be 0. Lab 2 – V, I, R Measurements © 202 ENGR 43 7

ENGR 43 Lab Activity Student Guide Photo-Resistor Test Can you positively determine if the photo-resistor is working properly from the test you performed? What conditions, other than the photo-resistor itself, may affect the measured values you recorded? Lab 2 – V, I, R Measurements © 202 ENGR 43 8

ENGR 43 Lab Activity Student Guide Voltage and Current Measurements What is the difference between how the voltmeter and the ammeter are connected in the test circuit? What would happen to the circuits and to the meters if the ammeter and voltmeters swapped positions (that is, if the ammeter were connected as a voltmeter and the voltmeter were connected as an ammeter)? Voltmeter is connected in parallel, and ammeter is connected in series. Since an ideal voltmeter has a very high resistance, connecting the voltmeter in series would result in an open circuit. Connecting the ammeter in parallel would cause all the current Why was it not possible to calculate the resistance for the power switch in the 0 position? The switch is at position 0, there is no current flows through the circuit. Therefore, we cannot calculate the resistance. Lab 2 – V, I, R Measurements © 202 ENGR 43 9

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ENGR 43 Lab Activity Student Guide How did the voltage and current change for the different test conditions? If the capacity of the AA battery pack is 1 AH (1,000 mAH), how long would the Boe-Bot run on a straight course? Use the formula: Endurance = mAH ÷ mA Lab 2 – V, I, R Measurements © 202 ENGR 43 10