EE100 Spring 2005 Bharath Muthuswamy EE100 Final Project Guide Before I begin many thanks to the EE40 team Prof White Michael Case Abhijit Davare Matthew Leslie Cheuk Chi Lo Marghoob and Bruno from Fall 2004 for designing this project They wrote an excellent guide for this project This guide for EE100 is based on part 1 and part 2 of their guide 1 Objective In this project you get to design a stereo tone controller In other words the circuit will amplify the base and or treble for a two channel stereo system 2 Prelab 1 Please bring a real audio source a discman walkman iPod MP3 player laptop etc to the lab so you can test your design Try to place as many components on the breadboard BEFORE coming to lab 2 Read the material on Active Filters from the reader 3 WORD OF ADVICE BUILD CLEAN NEAT CIRCUITS Use the shortest wire possible use the power rails on your board instead of stringing 12 V and ground everywhere and be methodical when you wire so that you and your GSI can make sense of it For instance use red for power black for ground and blue for signal Figure 1 shows one half of my tone controller Notice how all the wires are almost parallel to the breadboard Also notice how I have added user interface elements the switch and LED Figure 1 One half right speaker of my tone controller circuit EE100 Spring 2005 Bharath Muthuswamy 3 System Block Diagram A block diagram of your tone controller is shown in figure 2 Figure 2 System block diagram The power supply for your system is a 9 V battery than you can buy from any electronics store supermarket The power supply system is to provide a constant 5 V supply to the electronics This is because a real 9 V battery does not provide a steady 9 V supply The regulator tries to make sure the 5 V supply is constant Of course as time goes on the battery starts dying and the regulator cannot maintain the voltage In my case when the LED starts dimming that means I need a new battery A non mathematical explanation of how the regulator works is given in section 4 The tone controller is the heart of the above circuit The left tone controller is the exact same circuit as the right The tone controller is an op amp voltage follower followed by an op amp active filter that can filter the base or the treble regions of the frequency spectrum A non mathematical explanation of how this circuit works is given in section 5 Why do you need the power amplifier stage The answer your op amp tone controller cannot provide enough current to drive any speaker Speaker resistances are usually 8 or 32 ohms Your op amps may be able to provide 10 mA of current on a good day This is not enough to drive the speakers at all and you will end up blowing your op amps This is where the power amplifier comes in The power amplifier simply transfers the input from the op amp tone controller to the speakers but it can generate a lot of current for driving the speakers Overall the cost of the above system is around 10 You can find the datasheets for all the chips ICs in your reader EE100 Spring 2005 Bharath Muthuswamy 4 Block Diagram Component 1 Power Supply Figure 3 The LM2940CT 5 0 9 0 V to 5 0 V voltage regulator The 5 0 V suffix indicates the regulator outputs 5 V Figure 3 shows the top view of the voltage regulator you will be using A linear voltage regulator can be thought of as two variable resistors Vout is obtained from Vin through a voltage divider Refer to figure 4 Figure 4 A simple voltage divider between Vout and Vin However the regulator adjusts Vout when Vin changes using internal feedback 5 Block Diagram Component 2 Tone Controller The tone control circuitry is shown in figure 5 NOTE I HAVE NOT INCLUDED THE VOLTAGE FOLLOWER IN FIGURE 5 The input from your male headphone jack should go to the voltage follower The output of the voltage follower should go to the tone controller Details can be found in section 7 Important parts of the circuit are highlighted source http sound westhost com dwopa2 htm EE100 Spring 2005 Bharath Muthuswamy Figure 5 The tone controller You will be using the LMC6482 opamp the pinout is given in figure 6 for your convenience Figure 6 The LMC6482 pinout top view The tone control circuitry is rather complicated However a feel for the circuit is more than enough As a rule of thumb it is always a good idea to have a feel for anything before you build it This gives you an intuition for what to look at if something goes wrong and you need to debug It also makes the whole process much more fun The positive input to the LMC6482 is simply half the power supply due to the 11k resistors The 10 uF capacitor seen at the positive input merely keeps the node stable free of AC variations The purpose of the 1 uF capacitor at the input is to block any DC component of the audio signal DC voltages do not contain any information about sound and therefore are unnecessary The rest of the passive components are involved in the feedback path The key to understanding the bass and treble gains lie in the potentiometers EE100 Spring 2005 Bharath Muthuswamy If our input signal is very low in frequency bass the top potentiometer controls the gain because the 22 nF capacitor appears as an open use the impedence formula for a capacitor to verify this Therefore our input signal simply divides inside the potentiometer Note that for low frequencies the 560 pF capacitor is effectively an open and does not feed the signal through to the bottom potentiometer If our input signal is very high in frequency treble no voltage appears across the top potentiometer because the 22 nF capacitor appears as a short However the bottom potentiometer divides the input signal and feeds it through the 560 pF capacitor which now appears as a short to the input So for high frequencies the gain is controlled by the bottom potentiometer 6 Block Diagram Component 3 Amplifier Stage Figure 7 The gain stage power amplifier Before the signal goes to the power amplifier we add an extra gain stage This is basically your volume control knob The block diagram of the power amplifier is shown in figure 8 The pinout top view is shown in figure 9 Values for the components in the power amplifier are Ci 20 uF Rf Ri 20 k Cb 0 1 uF Co 220 uF If you are interested in knowing why we chose these values please talk to your TA EE100 Spring 2005 Bharath Muthuswamy Figure 8 A block diagram view of the power amplifier 7 Building the Circuit Figure 9 Power amplifier pinout a Guidelines i As said earlier build clean neat
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