6 01 Spring Semester 2008 Assignment 7 Issued Tuesday Mar 18 1 MASSACHVSETTS INSTITVTE OF TECHNOLOGY Department of Electrical Engineering and Computer Science 6 01 Introduction to EECS I Spring Semester 2008 Assignment 7 Issued Tuesday Mar 18 Overview of this week s work In software lab Work through part 1 of this lab Before the start of your design lab on Mar 20 or 21 Midterm In design lab Work through part 2 of this lab There will be no nanoquiz or homework write up due but we will assign credit for both parts of this lab based on check off sheets 6 01 Spring Semester 2008 Assignment 7 Issued Tuesday Mar 18 2 ABCDE connected together in rows Power Supply and Ground rails Figure 1 Protoboard Circuit Lab Part 1 There are several exercises here to be done in the two lab sessions this week Please be sure to have done Exercise 6 before you leave the software lab of the week the one on Tuesday or Wednesday that is 1 5 hours long The first thing you must do is become familiar with the prototyping board You will be building your circuits on this card an exemplar of which is shown in Figure 1 The protoboard provides for easy and rapid prototyping of circuits you can just plug in component parts and connect wires Under each of the holes in the card are springy connectors This particular card which is just like the ones you will be using has 63 rows of connections Five holes on one side of a separator and five holes on the other side are connected together The separator is there because we can plug in electronic components such as operational amplifiers straddling the separator You will notice the rows are numbered and the columns are labeled A E and F J a little bit like airplane seating There are two columns of holes on either side of the board generally used for power supply and ground and those holes are connected together along the red and blue lines CAUTION for some reason that none of us on the staff understand the connection is broken between rows 31 and 33 Typical use of this thing requires that you jumper connect a wire between the two ends of the power supply rails and between the two ends of the ground rails at those two rows Failure to do this leads almost everyone to wonder why their circuit is not working If you look carefully at the bottom of figure 9 you can see an example of these two jumpers as they should appear on your protoboard We will also be making use of a multimeter used to measure voltage current and resistance Although some multimeters can measure frequency temperature and other things we will make use of only the elementary functions You will also find it convenient to find a pair of clip leads 6 01 Spring Semester 2008 Assignment 7 Issued Tuesday Mar 18 3 Figure 2 Voltage divider schematic colorful wires with alligator clips at each end The multimeters all have two leads One of them the black lead is plugged into a ground or common jack and the other red is usually plugged into a jack marked something like V mA If you need to measure current higher than 100 or 200 mA the red lead goes into another jack that is marked for that higher current The meters all have a control dial that selects what you are measuring AC voltage is measured by setting the dial to one of the stops that have little tilde s representing a sine wave DC voltage is measured by setting the dial to one of the stops marked by a solid line over a dashed line Resistance settings are marked by k Most multimeters also have an off position Many but not all multimeters will turn themselves off after being unused for some period of time but it is best to set the dial to off after you have made a measurement to avoid exhausting the battery You will need to identify resistors Almost all of the resistors we will be using are color coded and some of us find those codes hard to read so it is always best to verify the value of a resistor with a multimeter before using it However the color code consists of three bands around the resistor you have to figure out which end is the first band The first two are two digits of the value The third band is a power of ten The colors have meaning 0 black 1 brown 2 red 3 orange 4 yellow 5 green 6 blue 7 violet 8 gray 9 white 6 01 Spring Semester 2008 Assignment 7 Issued Tuesday Mar 18 Figure 3 Voltage divider on protoboard 4 6 01 Spring Semester 2008 Assignment 7 Issued Tuesday Mar 18 5 Thus a 1 000 resistor is marked by brown black red meaning 1 0 2 or 10 times 102 4 7 k is marked yellow violet red Most of the resistors you will encounter in the lab are rated for 1 4 watt meaning you can dissipate 250 mW under normal circumstances If you dissipate much more than this the resistor will overheat and you may destroy it Question 1 Measure Resistances Find a few resistors of values of say 1k 1000 ohms or 4 7k 4 700 ohms and verify their resistance by using the multimeter It is most convenient to connect clipleads to the probes of the multimeter and use the other end of the clipleads to grab the wires coming from the resistor You will find that the resistors don t necessarily have exactly their stated value but they are generally within a few percent Question 2 Voltage Divider Build up the circuit whose schematic is shown in figure 2 on your protoboard The result might look something like the what is shown in figure 3 What is built here is a simple voltage divider made up of two 4 7 k ohm resistors Note the green wires that connect the right hand lead of one resistor to the power supply rail and the left hand lead of the other resistor to the ground rail The green and yellow leads that go off the edge of the photograph are to be connected to ground and 12 volts respectively The two brown wires are a convenient way of connecting the clipleads from your multimeter to the resistive divider Note that you will be using plastic insulated wires and to make connection with the protoboard the power supply or almost anything else you need to strip about a quarter of an inch of that plastic insulation from the end of the wire We have tools that do this conveniently Take care to take only the insulation and not cut off the end of the wire Question 3 Adjust the power supply Get out a power supply plug it in turn it on and adjust the positive supply to 12 volts Measure the power supply voltage with your multimeter Then connect your voltage divider to the power …
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