LAB2 Resistors, Simple Resistive Circuits in Series and Parallel Objective:

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1 LAB2 Resistors, Simple Resistive Circuits in Series and Parallel Objective: In this lab, you will become familiar with resistors and potentiometers and will learn how to measure resistance. You will also familiarize yourself with series and parallel DC circuits and you will verify fundamental circuit properties. Using simple sensors, you will convert nonelectrical parameters (light intensity) to electrical resistance. You will use the breadboard on the CY3214 evaluation board and your digital multimeter for this lab. Items needed: CY3214 eval board Wire package Digital Multimeter with probes Radio-Shack # *12V battery for digital multimeter Radio-Shack # *Phillips type screwdriver to install battery into multimeter *Test clip adapters for digital multimeter Radio-Shack # B 9-volt battery Radio-Shack # volt battery snap connector Radio-Shack # (has 5 connectors in pkg) Package of resistors Radio-Shack # The Breadboard A breadboard is used for holding logic chips, components, and wires that connect them together in order to realize a desired circuit. Breadboards allow engineers to try out circuits without having to solder them to a printed circuit board. The breadboard on the CY3214-PSoCEval-USB board has 400 pin holes in it. The holes are arranged with 0.1 separation between them in a grid pattern. Note there are 30 rows with columns labeled a-j. For each row, the five holes in columns a-e are connected in common. Likewise, the five holes in columns f-j are connected in common. What is meant by common connections is that a row or column of common pins will have the same voltage as each other (or same logic state). This common connection will allow multiple connections to be made at the same pin on a logic chip or allow a node of a circuit to be made. On each side of the rows are two

2 columns, one with red marking and one with blue marking. All of the pins in each column are commonly connected. These columns are often used for providing supply power and ground to the nodes of a circuit. To show the connectivity between holes that are commonly connected, take two precut and stripped wires (the standard size - #22 or #24 gauge wire) and place them in two holes in the same row of the breadboard. Make certain the wires are placed securely into the holes. Using your multimeter, measure the resistivity between each of the wires. Turn on your multimeter, place the multimeter settings switch to Ohms (Ω), and use the lowest value setting (200); place the red probe of the multimeter to the wired end of one wire and the black probe to the wired end of the other wire. Using the test clips on the ends of the probes allows you to measure the values hands-free. The value should be close to 0.0Ω if the two wires are connected together. If an open circuit is present or if the measured resistance is higher than the range set on the multimeter, OL is shown on the multimeter screen. R common_connection = Repeat the procedure but place one of the wires in a different row. R open_connection = Note: Do NOT place wires with larger diameters into the holes (Do NOT try to force the multimeter probes into the holes) this may damage the connections. Do NOT use stranded wire in the holes. Linear Resistors and Resistance Measurements Resistors limit the amount of flow of electricity to a load preventing overloading. Obtain a two resistors from the resistor package in the lab. Make certain the color bands for the two resistors are not the same. Access a resistor color code chart from the internet and determine the values of the resistors you have chosen. R1 color-bands = R1 expected = R1 tolerance = R2 color-bands = R2 expected = R2 tolerance =

3 Place the resistors in holes that are not commonly connected on the breadboard. Using the multimeter, place the red probe on one end of one resistor and the black probe on the other end. Measure the resistance. Resistors do not have a polarity so it doesn t matter which side of the resistor has the red or black probe. Repeat for the second resistor. Record the resistance of each resistor below. How different in percentage is the expected value from the measured value for each resistor? Is this difference within the specified tolerance for this resistor? R1 measured = R1 %_difference = R2 measured = R2 %_difference = Are these resistors ¼ watt resistors or ½ watt resistors? The power dissipated on a resistor is determined by the equation: P = vi = v 2 /R = i 2 R. Determine the maximum voltage possible to not overpower the smallest resistor you have. P max = R = V max = Resistors in Series When two resistors are placed in series in a circuit, the equivalent resistance is the sum of the individual resistances. Place your two resistors in series on the breadboard by placing one end of each resistor in commonly connected holes, and measure the equivalent resistance by placing the red and black probes on the other two ends of the resistors. R equivalent(expected) = R1 + R2 = R equivalent(measured) =

4 Resistors in Parallel When two resistors are placed in parallel in a circuit, the reciprocal of the equivalent resistance is the sum of the reciprocal of the individual resistances. For two resistors in parallel, the equation is R equivalent = Place your two resistors in parallel on the breadboard by placing both ends of the resistors in commonly connected holes, and measure the equivalent resistance. R equivalent(expected) = R equivalent(measured) = A Series Circuit Create a circuit using a nine-volt battery and the two resistors placed in series. R1 V1 9V V3 V2 R2 0 Attach a nine-volt battery to the circuit and measure each of of the voltages, v1, v2, and v3. To measure the voltages, pl place the multimeter with the volts setting selected across ea each of the resistors. Verify that the three voltages satisfy Ki Kirchoff s voltage law (KVL: The sum of the voltages ar around any closed loop equals zero). V1 measured = V2 measured = V3 measured = Using Ohms Law (V=IR), calculate the expected currents across reach of the resistors. I1 calculated = I2 calculated =

5 Measuring Current When measuring current, the meter MUST be placed in series in the circuit. Do NOT place it in parallel with the components. You will blow the fuse on the meter. Measure the current for each path in the series circuit. Does it verify KCL (KCL:The sum of the currents going into a node equals the sum of the currents going out of the node)? I1 measured = I2 measured = I3 measured = 9V V3 V1 R1 V2 R2 0 Measure the current for each path in the parallel circuit. Does it verify KCL (KCL:The sum of the currents going into a node equals the sum of the currents going out of the node)? I1 measured = I2 measured = I3 measured = Voltage Divider Circuits A common term in circuits is a voltage divider circuit. This type of circuit divides the supply voltage by some ratio by using two resistors in series. It doesn t really change the value of the supply voltage just the value of the voltage across R2 as the final voltage. Using your series resistive circuit above, determine how much you divided the supply voltage. V = V3 x =

6 Lab Report Requirements Copy your results from this portion of the lab into an Excel spreadsheet. Copy the results into your report. Use Orcad Capture CIS (part of the PSpice package) to draw the series circuit. Create a simulation and make a screenshot of the results. Repeat this with the parallel circuit. Do the simulated results compare with the actual or calculated results? If there are differences, explain what has caused the differences.