ECE 2074 Lab 02 Spring 2019 PDF

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ECE 2074 Lab2 - Spring 2019 Name: Wayne Thompson By putting your name on this work sheet, you certify that you have neither given nor received unauthorized aid, and what is presented is entirely your own work and reflects your understanding. No name will result is a score of 0. Why are you making me do this? This lab will familiarize you with basic multimeter measurements and with building circuits on a protoboard. A multimeter is a standard piece of laboratory equipment for ECEs and is used to measure voltage and current as well as resistance. Protoboards are used to quickly build and debug circuits to create a prototype. Circuits meant to be permanent are usually built on printed circuit boards (PCBs).

Parts and equipment needed: • • • •

V79 Digital Multimeter (or similar) and clip leads Resistors: R1 = Brown-Gray-Red-Gold, R2 = Orange-White-Brown-Gold protoboard and power supply Red and Black wires for breadboard and meter probe connections

Note: Show all work. Always include the units for all of your measurements!

A. Resistance measurement. 1. Can you measure the value of a resistor while it is wired into a circuit? (yes/no)

yes

2. Use the resistor color code to determine the nominal values of R1 and R2 in Ω, the tolerance in %, and the maximum and minimum acceptable resistance values for R2. Resistance

Tolerance

Min value

Max value

R1

1.8k ohms

± 5%

-

-

R2

390 ohms

± 5%

370.5 ohms

409.5 ohms

You may calculate the tolerances here:

3. What is the power rating of your kit resistors?

0.5W

What is the maximum voltage that can be safely applied to R2 without exceeding the power limit? 13.61V 4. Use your DMM to measure the resistances of R1 and R2. Value Measured R1

1.879k ohms

Measured R2

387 ohms

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ECE 2054/2074 Lab 1 Page 1 of 6

B. Breadboard Basics If you find that some of your protoboard resistance measurements are higher than 2 Ohms, but not registering as an overflow on your Multimeter, please show this to your GTA as there may be a problem with your protoboard, an issue with your digital Multimeter, or you are using an incorrect method to make this measurement. Any one of these issues will affect your ability to complete this and future labs properly so please address this issue promptly. 1. Set the DMM to measure either Ohms or continuity. Measure the connections within and between the rows, columns, and the power buses on your protoboard. Be sure to orient your breadboard in the same direction as the picture.

2. In Figure 1, draw lines through the breadboard points that are shorted together.

Figure 1 Breadboard connections

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C. DC Voltage measurement. 1. Connect the USB power supply to the board (the pins should plug into the upper and lower power supply rails of the protoboard) and plug the power supply into a USB port on your computer or into a USB power adapter that plugs into an AC wall outlet. 2. Use your DMM to measure the DC voltages of your power supply: +5V and -5V supplies (to ground). 3. Change the meter to measure AC volts and measure the +5V supply voltage. Measurement

Measured Voltage

+5V supply

4.96v

-5V supply +5V supply using AC volts setting

-4.97v .003v

4. Look at the the AC voltage measurement and explain why you must check both AC and DC settings when measuring an unknown voltage? (Imagine a large AC or DC voltage measured with the opposite range!) I.E. the AC voltage will show very low when the DC is high 5. Take a 1M resistor from you kit and insert one end into the +5V power supply rail of the protoboard and leave the other end unconnected. Measure the voltage between the unconnected end of the resistor and ground. If the measured voltage is not equal to 5V, explain why you get the value you measured. Voltage was lower because of dissipation/absorption

D. DC Current measurement. 1. When you measure an unknown current, why should you always first measure the current using the 10A range, and measure for both AC and DC current before you use the mA measurements, and why should you always move the red meter lead back to the VΩHz jack immediately after completing current measurements? The reason for both is so that you don’t accidentally blow out the fuse in the DMM

2. Take a 100 resistor and connect one end to the +5V power supply rail and leave the other end unconnected. If the unconnected end were connected to ground, we would expect 5V/100 = 50mA of current to flow. Set the meter lead and range to measure Amps DC and measure the current that flows between the free end of the resistor and ground. Change the meter range to measure Amps AC and measure the current through the resistor. Change the meter lead and range to measure mA DC and measure the current.

Measurement Resistor current

Range used

Measured Current

A DC

.05A 2/7/2019

ECE 2054/2074 Lab 1 Page 3 of 6

Resistor current

A AC

.00A

Resistor current

mA DC

47.4A

3. Notice how the current appears to be very low or zero on the AC setting. To save your meter fuse, always check an unknown current on both 10A AC and 10A DC before you use the mA scale. Before continuing, move the red meter lead back to VΩHz.

E. Ohm’s Law and Series Resistors 1. Construct the circuit in Figure 2 below on your protoboard. NOTE: Use good wiring practice (short wires, Red for power, black for Ground).

Figure 2: Use the parts list values for R1 and R2. 2. R1 and R2 form a voltage divider circuit, where the source voltage divides proportionally between R1 and R2. The current through R1, R2, and the source are all the same because they form a simple series circuit. Calculate the equivalent series resistance of R1 and R2, the voltage expected across each resistor, and the expected current that should flow through the resistors. Series Resistance

Expected VR1

2190 ohms

4.10V

Expected VR2

Expected I

.89V

2.28mA

Space (if needed) for calculations here.

3. Use the multimeter to measure VR1, VR2, and the total series voltage (VR1+R2). Use your DMM to measure the current that flows through resistor R2. Begin with 10A DC, then move the meter lead and range to mADC only if the current is less than 0.4A. When you have completed the current measurements, unplug the red probe from the meter and record the current measurement. Use Ohm’s Law to calculate the value of R1, R2, and the equivalent series resistance. 2/7/2019

ECE 2054/2074 Lab 1 Page 4 of 6

IR2 Measured

24.29mA

Meter Range used

Resistor

Measured V

Calculated R

R1

4.15

1804

R2

0.88

382

Series

5.01

2178

mA

(Space, if needed, for your calculations below)

How do your voltage and current measurements compare to the expected values from Part E-2. Roughly equivalent How do your calculated resistances compare to the measured resistances in Part A-4. Roughly equivalent

After you have completed the Lab procedure, • •

If you do not understand something or have questions, post a query to Piazza or see a GTA in the OpEL (219 Whittemore) Assignment Submission: Submit this worksheet to Canvas's Assignment 1 before the deadline.

To explore further (optional): How would you calculate the power dissipated in R2 if 5V is applied to R2's terminals. P = _________________ How would you calculate the maximum safe voltage that can be applied to R2. Vmax = ___________________

If R1 and R2 are connected in parallel instead of in series: • • • •

What is the parallel equivalent of R1 and R2? What is the expected current through each resistor? What is the voltage across each resistor? How would you verify this through measurements? 2/7/2019

ECE 2054/2074 Lab 1 Page 5 of 6

•

How would you measure IR1 and IR2 without blowing the meter fuse? Think about how current is measured! Be careful here or the meter fuse will blow!

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