lab3fused.pdfprelab3.pdfSensor InterfacesA very frequent scenario when designing electronic circuits: you need some sensory input, e.g. temperature. Youfound a sensor (e.g. a thermistor) that converts the actual temperature into an electrical voltage. The next step isto interface the sensor to the rest of your system, typically a computer (microcontroller). Figure 1 shows the setup.Usually the output of the sensor is a small voltage in the milli- or micro-Volt range (for a full-scale signal), while therest of the electronic system (e.g. the computer) expects much larger signals, typically around a Volt. For example,the scale we built earlier generated output signals that were only a few milli-Volt. To overcome this mismatchwe need some kind of interface between the sensor and the computer (or whatever we would like to connect thesensor to), as illustrated in Figure 2 on the next page.Sensor interfaces can perform many functions. Here we focus on the task of gaining up the signal to appropriateamplitude. Specifically, we want the interface to perform the functionv2= Avv1(1)where Avis the voltage gain. For example, if Av= and v1= mV, v2=1 pt.0We will build the sensor interface out of operational amplifiers. To test it, we need an input, and something toverify the output. We could use the scale constructed in an earlier lab for the input, but this would require us towire up that circuit again. Moreover, if we encounter problems, we would have to determine if they are due to theinterface or the sensor—not always a trivial issue.A better solution is to synthesize an appropriate input v1with reliable and well characterized (that’s why it’sexpensive) laboratory equipment to test our amplifier circuit. Once we are satisfied with the result we can combinebuilding blocks (and test again). Tackling circuits one-by-one in this fashion significantly simplifies our task andspeeds up our work.We will use the signal generator to simulate the transducer and the oscilloscope to verify the output from oursensor interface.Signal Generator and OscilloscopeDownload the manuals for the oscilloscope and signal generator and read the quick start and overview guides.Program the signal generator to produce a 1 kHz sinewave with Vs= V zero-to-peak amplitude. Connect thesignal generator to the oscilloscope as shown in Figure 3 on the following page. Observe the sinewave on theoscilloscope display. What is the zero-to-peak amplitude?predicted1 pt.1measured1 pt.2If you just cannot get this right, reread the guide for the function generator. Feel free to play in the lab withdifferent settings of the function generator, e.g. higher frequency signals. Even test equipment is not “ideal” whenused outside its specifications (which the manual explains, although in rather technical terms).Figure 1 Sensor connected to an electronic system (e.g. a computer).1 February 2, 2009 LAB3 v591217.22.1UC Berkeley, EECS 100 LabB. BoserNAME 2:SID:NAME 1:SID:LAB3: Sensor InterfaceFigure 2 Sensor interface.Figure 3 Signal generator connected to oscilloscope.Operational AmplifierLet’s check out the operational amplifier before designing a more complex circuit. This way we are sure the partis working and we get all connections right (e.g. supplies!) without wasting a lot of time debugging a complexsetup.Download the datasheet of the LMC6482M/AM operational amplifier. We are using the part in a 8-pin dual-in-linepackage. Find the following specifications from the datasheet:Pin number of the positive supply, V+1 pt.2Maximum supply voltage, V+− V−1 pt.3Minimum supply voltage, V+1 pt.41 pt.5Minimum junction temperature, Tj[C]1 pt.6Maximum junction temperature, Tj[C]1 pt.7Minimum large signal voltage gain Av, sourcinginto RL= 2 kΩ, V+(unitless)1 pt.82 February 2, 2009 LAB3 v591Maximum input current, IKKNow that we know the pinout of the operational amplifier chip, we can connect it to a power supply and an inputabove and below ground. In order to amplify negative signals, the amplifier will need a negative voltage supply,to see how it reacts in various circumstances. The input will come from the function generator, and will have valuesBas the output cannot fall below the minimum supplied voltage. Also, the sum of the supply voltages must not exceedthe chip’s maximum supply voltage. Use 5 volts for Vdd and Vss unless otherwise directed.3 February 2, 2009 LAB3 v591 Most practical opamp circuits use feedback to set the gain to an accurate and reasonable (e.g. 10) value. This works very well – provided that the feedback is connected correctly. Here we compare opamps with positive and negative feedback. Draw the openloop V versus V characteristic of the operational amplifier. different color than the expected result. out in out in82 pt.Draw the expected VLabel the axes (variable, units, ticks) in the graph below and show the measured result in a versus V characteristics on the plot. Turn on the oscilloscope. Change the scope to XY mode by pressing the Main/Delayed button followed by the XY soft key. Set the function generator to sine wave output at 10 Hz with 100mV peak to peak amplitude.Build the negative feedback circuit and generate the XY plot just as you did in WKH ODVW part C opamp OP2 are grounded, a good precautionary measure that prevents the part from accidentally turning on oreven oscillate and interfere with other devices.Signals are often bipolar (i.e. can assume both positive and negative voltage values). Since the amplifier outputcannot possibly swing below the supply, both positive and negative supply voltagesVddand Vssare needed, asindicated in the diagram. To avoid clutter, the supplies are usually omitted from the circuit diagram. Do not forgetto connect them in practice, as the circuit will obviously not work without.Mark the pin numbers for all connections in the diagram and build your circuit on a protoboard. Verify all con-nections before applying power. If the part gets hot, check if the supply is backwards. Choose Vdd= Vss= 5 V,R1= 1 kΩ and R2such that vo/vi= −10.R2=1 pt.9Figure 4 Inverting amplifiercircuit diagram.Which of the two circuits, A or B, is configured for negative feedback? 82 pt.1 pt.8opy your measured results to the plot below. Figure 4 shows the circuit diagram for an inverting amplifier based on the LMC6482. The inputs of the unusedExplain what’s happening and summarize your result in the graph. Repeat all above with a positive feedback
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