Massachusetts Institute of TechnologyDepartment of Electrical Engineering and Computer Science6.002 – Circuits and ElectronicsSpring 2003Handout S03-059 - Lab #4: Audio Playback SystemIntroductionIn this lab, you will construct, test and demonstrate the audio playback system that you designedin Homework #11. The lab consists of two parts: pre-lab exercises and in-lab exercises; thereare no post-lab exercises. You should complete the pre-lab exercises in your lab notebook beforecoming to lab. Then, carry out the in-lab exercises on your assigned lab day between May 5 andMay 9. After completing the in-lab exercises, have a TA or LA check your work and sign your labnotebook. You may hand in your lab notebook to your TA for grading at that time, or any othertime before the week of final exams.During the in-lab exercises, you are welcome to work with a partner. In this case, it is best ifone person constructs the clock and digital-to-analog converter, while the other person constructsthe low-pass filter and power amplifier. These blocks can be constructed on separate protoboards.Signal and ground connections may then be made between protoboards to complete the constructionof the audio playback system. The point of working with a partner is to speed up construction, butnot to miss out on testing all four blocks. If you do work with a partner, make sure to participatein testing the two blocks constructed by your partner so that you see how they work.Pre-Lab Exercises(4-1) Copy your design for the clock from Problem 1 of Homework #11 into your lab notebook.Label all resistor and capacitor names and values.(4-2) Next to your design for the clock, copy the graph from Part (E) of Problem 1 of Homework#11 into your lab notebook. You will use this information to determine whether the clockyou construct during In-Lab Exercise 4-2 works correctly.(4-3) Copy your design for the digital-to-analog converter from Problem 2 of Homework #11into your lab notebook. Label all resistor names and values.(4-4) Next to your design for the digital-to-analog converter, make a table showing the expectedconverter output vDACwhen each of the data-bit input voltages is 5 V and the others areall 0 V. Base the table on the actual resistor values used in your design. Also, note theexpected value of the offset voltage vOFFrequired to center the converter. You will use thisinformation to determine whether the converter you construct during In-Lab Exercise 4-4works correctly.(4-5) Copy your design for the low-pass filter from Problem 3 of Homework #11 into your labnotebook. Label all resistor and capacitor names and values.(4-6) Next to your design for the low-pass filter, copy the graph from Part (F) of Problem 3of Homework #11 into your lab notebook. Also, make a table showing the expectedmagnitude and phase of the filter output vLPFgiven a 2-V peak-to-peak sinusoidal inputwith a frequency of 4 kHz, 8 kHz and 16 kHz. Base the table on the actual resistor andcapacitor values used in your design. You will use this information to determine whetherthe filter you construct during In-Lab Exercise 4-6 works correctly.(4-7) Copy your design for the power amplifier from Problem 4 of Homework #11 into your labnotebook. Label all resistor and capacitor names and values. Include the modificationwhich provides for a variable gain of 1 to 5.(4-8) Next to your design for the power amplifier, make a table showing the expected magnitudeand phase of the power amplifier output vOUTgiven a 2-V peak-to-peak sinusoidal inputwith a frequency of 10 Hz, 100 Hz and 1 kHz. Base the table on the actual resistor andcapacitor values used in your design. You will use this information to determine whetherthe amplifier you construct during In-Lab Exercise 4-8 works correctly.In-lab ExercisesThe in-lab exercises involve constructing and testing the individual functional blocks of the audioplayback system, and then demonstrating the operation of the system as a whole. Before you beginto work on the in-lab exercises, you must obtain from the Instrument Desk in the Lab a plug-inboard with the counter and memory and a piezo-electric speaker. The 74HC14 CMOS inverterchip needed for constructing the clock can be found in your lab kit. You must return the boardand the speaker or headphones after you finish this lab. There are a limited number of parts, andother students will need them.The in-lab exercises are organized so that you will construct and test one functional block ata time. As each block is found to work properly, you will connect it to those which already work.Consequently, you will alternately construct and test various parts of the audio playback system. Asyou develop the system in this manner, it is essential that you turn off the power to the protoboardbefore you make modifications to your system, or begin any new construction. Also, check yourwiring carefully before turning the power back on. This will avoid damaging the components in thesystem, and save you considerable debugging time.Finally, construct the functional blocks as compactly and neatly as possible. In this spirit, youshould find it easiest to use the components to wire themselves together, rather than using extrawires. This will save you considerable construction time, as well as considerable debugging time.(4-1) To minimize wiring in this lab, the counter and memory have already been assembledon a printed-circuit board. On the back of this board are pins that will plug into theprotoboards in the Lab. Plug these pins into the protoboards so that each pin is insertedinto a separate protoboard row. Further, locate the board so that there is considerableprotoboard space on the side with the memory output data bits. This will make connectionto the board easiest. For example, locating the board towards the lower left corner of theprotoboard may prove best. The clock can then be constructed above the board, while thedigital-to-analog converter, the low-pass filter and the power amplifier can be constructedto the right of the board.Figure 1 shows the pin assignments for the printed circuit board. The pins for the eightmemory output data bits are on the right hand side. The pins for power and ground,and the clock input to the counter are on the left hand side. You should connect thepower pin to the 5-V power supply on the protoboard, and the ground pin to groundon the protoboard. There are also four counter and memory control pins which must beconnected to the 5-V power supply and
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