6.01, Spring Semester, 2008—Assignment 7, Issued: Tuesday, Mar. 18 1MASSACHVSETTS INSTITVTE OF TECHNOLOGYDepartment of Electrical Engineering and Computer Science6.01—Introduction to EECS ISpring Semester, 2008Assignment 7, Issued: Tuesday, Mar. 18Overview of this week’s workIn software lab• Work through part 1 of this lab.Before the start of your design lab on Mar 20 or 21 MidtermIn 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 partsof this lab based on check-off sheets.6.01, Spring Semester, 2008—Assignment 7, Issued: Tuesday, Mar. 18 2ABCDE connected together in rowsPower Supply and Ground railsFigure 1: ProtoboardCircuit Lab: Part 1There are several exercises here, to be done in the two lab sessions this week. Please be sure to havedone Exercise 6 before you leave the “software lab” of the week: the one on Tuesday or Wednesdaythat is 1.5 hours long.The first thing you must do is become familiar with the prototyping board. You will be buildingyour 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 componentparts and connect wires. Under each of the holes in the card are springy connectors. This particularcard (which is just like the ones you will be using) has 63 rows of connections. Five holes on one sideof a separator and five holes on the other side are connected together. The separator is there becausewe can plug in electronic components such as operational amplifiers, straddling the separator. Youwill notice the rows are numbered and the columns are labeled A-E and F-J (a little bit like airplaneseating). There are two columns of holes on either side of the board, generally used for power supplyand ground, and those holes are connected together along the red and blue lines. CAUTION: forsome reason that none of us on the staff understand, the connection is broken between rows 31 and33. Typical use of this thing requires that you ’jumper’ (connect a wire) between the two ends ofthe power supply ’rails’ and between the two ends of the ground ’rails’ at those two rows. Failureto do this leads almost everyone to wonder why their circuit is not working.If you look carefullyat the bottom of figure 9, you can see an example of these two jumpers as they should appear onyour 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 makeuse 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 3Figure 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-Ω-mA’.If you need to measure current higher than 100 or 200 mA, the red lead goes into another jack thatis marked for that higher current.The meters all have a control dial that selects what you are measuring. AC voltage is measured bysetting the dial to one of the stops that have little tilde’s (representing a sine wave). DC voltageis measured by setting the dial to one of the stops marked by a solid line over a dashed line.Resistance settings are marked by ’kΩ’. Most multimeters also have an ’off’ position. Many, butnot all multimeters will turn themselves off after being unused for some period of time, but it isbest 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, andsome of us find those codes hard to read, so it is always best to verify the value of a resistor witha 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. Thethird band is a power of ten. The colors have meaning:0 black1 brown2 red3 orange4 yellow5 green6 blue7 violet8 gray9 white6.01, Spring Semester, 2008—Assignment 7, Issued: Tuesday, Mar. 18 4Figure 3: Voltage divider on protoboard6.01, Spring Semester, 2008—Assignment 7, Issued: Tuesday, Mar. 18 5Thus a 1,000Ω resistor is marked by brown-black-red, meaning 1,0,2, or 10 times 102. 4.7 kΩ ismarked yellow-violet-red.Most of the resistors you will encounter in the lab are rated for 1/4 watt, meaning you can dissipate250 mW under normal circumstances. If you dissipate much more than this the resistor will overheatand you may destroy it.Question 1: Measure Resistances Find a few resistors of values of, say, 1k (1000 ohms) or4.7k (4,700 ohms) and verify their resistance by using the multimeter. It is most convenientto connect clipleads to the probes of the multimeter and use the other end of the clipleadsto grab the wires coming from the resistor. You will find that the resistors don’t necessarilyhave 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 onyour 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 thegreen wires that connect the right-hand lead of one resistor to the power supply rail and theleft-hand lead of the other resistor to the ground rail. The green and yellow leads that gooff 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 multimeterto the resistive divider. Note that you will be using plastic-insulated wires, and to makeconnection 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 toolsthat do this conveniently. Take care to take only the insulation and not cut off the end ofthe wire.Question 3: Adjust the power supply Get out a power supply, plug it in, turn it on andadjust the positive supply to 12 volts. Measure the power supply voltage with your
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