The George Washington University School of Engineering and Applied Science Department of Electrical and Computer Engineering Final Design Review (FDR) Report Design of a Wireless Stereo Speakers System By Alshawwa, Nawaf Prepared for EE – 163 Senior Electrical and Computer Engineering Design Project Laboratory Prof. Joseph R. Silverman Sunday, March 06, 2016 ©2000 Nawaf Alshawwa All Rights Reserved Abstract of the Final Design Report Wireless Speakers System By Nawaf Alshawwa This report is a Final Design Review (FDR) to design, build, and test a Wireless Speakers System. The Wireless Speakers will be able to play music from any audio device such as a CD player or TV. The transmitter will transmit audio signals to the receiver up to a distance of 7 meters. The Wireless Speakers system will operate at Radio Frequency (RF) signals. Specifically, it will utilize Frequency Modulation (FM) techniques to transmit the audio signals. The System is designed to transmit and receive the audio signal on a 48MHz frequency, which is a free band for those that are not licensed or commercial. The system will be powered using an AC outlet. In this report all the major aspects of the design will be defined. These definitions will include description of the design in a top-down approach, specifications, block diagrams, schematics, Gantt charts, economic analysis, and various testing techniques. It will also include a comparative product survey as well as a user manual. The project will require 36 weeks to complete and will expend an estimated 588.5 person hours of labor at an estimated total cost of $13,765. As of November 11th the actual person hours has decreased to 552 hours at a cost of $13,077. At this point we are ending the design phase and entering the building and testing phase. Project report # 1 will be on December 2nd. A working prototype will be available by April 27th, 2000. The estimated total cost of the prototype is $46,418, but the actual cost of the prototype stand at $44,116 so far. A preliminary economic analysis has determined that 100,000 units will be sold at a cost to the company of $106 per unit including indirect Administrative and General costs (A&G). This price also includes a 20 % profit to the company. Estimated retail price for the Wireless Speakers System is $190. ©2000 Nawaf Alshawwa All Rights Reserved 1 Acknowledgements It is the author’s pleasure to mention and thank the following persons, without whom this design would have not been possible to complete: - Professor J.R. Silverman, for providing generous amount of criticism, monitoring the progress of the design, and being the driving force in getting it done; - Jimmy Alatishe, for helping me with the background of Frequency Modulation, and in directing me with the purchasing of parts. - Professor Milos Doroslovaki, for his input on some parts of the design and making sure that the design is going in the right direction. - Mohammed Afridi, for his assistance with designing some parts of the project and his expertise in selecting parts for the design. - Hisham Hamed, for his efforts is explaining some theories about Frequency Modulation, oscillators, and demodulation techniques. ©2000 Nawaf Alshawwa All Rights Reserved 2 Table of Contents Section Page Abstract 1 Acknowledgements 2 Table of Contents 3 List of Tables 4 Table of Figures 5 Introduction 6 Specifications 9 Theory & Description of the Design 11 I. Transmitter 12 II. Receiver (L & R speakers) 26 Physical Layout of the design 35 History of the Project 37 Test of Design 39 Gantt Charts 40 Labor cost vs. Time graph 43 Parts List 44 Economic Analysis 45 Comparative Product Survey 47 Conclusion 48 References 49 Appendix A. Module / Matrix 50 B. User Manual 52 C. Data Sheets 59 D. Log Book 60 ©2000 Nawaf Alshawwa All Rights Reserved 3 List of Tables Section Page Table 1: CA3090 pinouts 32 Table 2: Ten Deliverables Gantt Chart 40 Table 3: CDR to FDR Gantt Chart 41 Table 4: FDR to PR#1 Gantt Chart 42 Table 5: Parts List 44 ©2000 Nawaf Alshawwa All Rights Reserved 4 Table of Figures Section Page Figure 1: Layout of Wireless Speakers System Block Diagram 11 Figure 2: Transmitter Block Diagram 12 Figure 3: Low pass filter schematics 13 Figure 4: Output of the low pass filter 13 Figure 5: Pre-Amp Circuit 14 Figure 6: Output simulation of the Pre-Amp 14 Figure 7:Balance control schematics 15 Figure 8: Graphic Equalizer Schematics 17 Figure 9: Graphic Equalizer Spectrum 18 Figure 10: Volume Control Network. 19 Figure 11: FM Stereo Spectrum 20 Figure 12: Mixer Module 21 Figure 13: Sine Wave Oscillator 22 Figure 14: Mixer of left and right channels 23 Figure 15: Voltage Controlled Oscillator 25 Figure 16: Transmitter’s Power Amplifier 26 Figure 17: Receiver Block Diagram 27 Figure 18: RF amplifier (preselector) 28 Figure 19: Receiver Pre-Amp. 29 Figure 20: PLL Block Diagram 29 Figure 21: FM stereo decoder 30 Figure 22: Stereo matrix Decoder 33 Figure 23: Receiver Power amplifier 34 Figure 24: connector Headphone to Y-Adapter 36 Figure 25: Labor cost vs. Time graph 43 ©2000 Nawaf Alshawwa All Rights Reserved 5 Introduction Wireless speakers have been around for a long time. In fact, the first ones were introduced to the public in the 1940’s. Unfortunately though, they were plagued with problems of static, interference and low power. Nowadays, wireless speakers are as clear as any other speaker system that is corded. This comes as no surprise because of the new technological advances in circuitry and wireless products. These types of speakers give the user the freedom to listen to music anywhere he/she favors. In addition, but this new trend of sound systems can also be used with TVs, Stereo receivers, and CD players…etc among others. The design of the project analyzed in these documents pertains to music listeners, especially those who prefer to listen to music in various places without any constraints. The speakers will pick up the music from across walls and can be arranged in many ways around the house. The design in hand utilizes frequency modulation techniques for modulation and demodulation. Frequency modulation (FM) technique is considered to be one of the hardest methods to achieve. It is also favored over amplitude modulation because of its lower sensitivity to noise and interference, as well as its ability to conserve more power in its message. Yet, it requires less power to be transmitted and can travel to much greater distances. There are two types of FM signals: stereophonic and monophonic. Here stereophonic is favored over monophonic, because it offers better sound quality. Therefore, the design in hand utilizes FM stereophonic techniques to combine both the left and right channels of the audio source and then transmits them to the receiver. ©2000 Nawaf Alshawwa All Rights Reserved 6 In this paper, a full design of a wireless stereo speakers system will be discussed and explained in depth. The paper will contain a complete and general theory to describe the design. The description part will include theory of the project, specifications, circuit schematics, and block diagrams. The report will also include some economical analysis explaining the cost of the design as a prototype and a retail product, as well as the person hour labor and its cost. A time management Gantt Chart will show how long it took to design and build each module, along with costs vs. time graph. A user manual was put together for this product to help consumers understand and troubleshoot this electrical device. ©2000 Nawaf Alshawwa All Rights Reserved 7 Wireless Stereo Speakers System Specifications I. Transmitter: 1. Input Level range 0 ~ 50 milli VP-P from an audio source. 10 % 2. Transmitter’s input impedance > 5 K 10 %. 3. Two line level audio inputs at the transmitter (Left/Right). 4. On/Off switch at the transmitter. 5. Volume control at the transmitter. 6. Balance Control at the transmitter. 7. 5 bands Equalizer at the transmitter. a. 100 KHz dB (fl = 20 Hz & fh = 257 Hz) b. 300 KHz dB (fl = 120 Hz & fh = 800 Hz) c. 1 KHz dB (fl = 600 Hz & fh = 1.6 KHz) d. 3 KHz dB (fl = 1.4 KHz & fh = 6 KHz) e. 10 KHz dB (fl = 4 KHz & fh = 25 KHz) 8. Frequency Modulation (FM) Stereo Transmission. 9. Pre –modulation frequency range 20 ~ 53 KHz (I) L + R channel 20 ~ 15 KHz (II) L – R channel 23 ~ 53 KHz. (III) Pilot at 19 KHz 10. Transmission Frequency 48 MHz (carrier). 11. Range of operation 7 meters 23 ft. 10 %. 12. Transmitter’s output power (FCC Regulations < 100 Milli Watts) 13. Transmitter’s output impedance 50 10 %. 14. Size: 9” W x 7” D x 4” H ©2000 Nawaf Alshawwa All Rights Reserved 8 II. Receiver: 1. Right channel & Left channel speakers. 2. Receiver built in each speaker. 3. Output Load 8 speakers. 4. Output power 5 Watts RMS. 5. System’s bandwidth 20Hz – 15KHz. 6. Size: 8” W x 9” D x 9” H III. Miscellaneous: 1. Power supply 12 volts (AC outlet). 2. Operational temperature = Room Temperature 3. Mono-pole Antenna. 4. Antenna’s length (FCC Regulations < 1.5 meters) Nominal = 15 cm. ©2000 Nawaf Alshawwa All Rights Reserved 9 Theory & Description of the Design The Wireless Stereo Speakers System consists of two major modules: Transmitter and Receiver. Each of these modules is composed of various other smaller modules. For instance, the transmitter as shown in Figure 2, consists of a balance control, equalizer, mixer, and modulator modules. The transmitter is the main part of the design. The transmitter will be hooked to an audio source. The signal will then be filtered to limit the frequencies entering the circuit. This signal is then amplified in the pre-amp stage and put thorough to the balance control to adjust the signal path. The equalizer comes in next, which will fine-tune the signal. After the equalizer stage, the volume control stage is paced in order to adjust the level of the signal. After this stage both the left and the right channels will be combined in the mixer stage to produce the stereophonic signal. This stereophonic signal will be modulated in the modulator module and passed to the power amplifier. At the end, the power amplifier will transmit the signal through the antenna at a power level that complies with the FCC regulation. The receiver’s task is to detect the transmitted signal and pass it through to the speaker. The process requires the following: the signal is picked up at the receiver’s antenna. The antenna is then connected to an RF amplifier, which will emphasize on selected frequencies around the carrier. The output is passed to the pre-amplifier to boost up the level of the signal. Then the demodulator comes in next to recover the information and separate the message from the carrier. Once the message is available, the stereo decoder will separate the left and right channels and then put each to the designated speaker, which will enable the listener to listen to the music. ©2000 Nawaf Alshawwa All Rights Reserved 10 48 MHz CD Player Left Speaker R - Channel Transmitter Right Speaker L - Channel Figure 1: Layout of Wireless Stereo Speakers System I. Transmitter The transmitter’s block diagram is shown in Figure 2 which consists of a balance control, equalizer, mixer, modulator, and an output power amplifier which is connected to the antenna. The transmitter is fed from a CD player, which supplies the audio signal that will be modulated and transmitted. The input impedance of the transmitter is 20 K and has an audio input level (sensitivity) that ranges from 0 ~ 50 milli VP-P. The output signal of the CD player is already stereophonic, which means that the signal is separated into two channels, a left and a right channel. The audio signal is passed through a low pass filter before going to the pre-amp and the balance control network. ©2000 Nawaf Alshawwa All Rights Reserved 11 R Audio Device L Pre-Amp & Filter Balance Control Trans. Amplifier Modulator Equalizer & Volume Mixer Figure 2: Transmitter Block Diagram The low pass filter will be set to roll off the signal at around 15 KHz before entering the transmitter. This is necessary to eliminate beat frequencies that would be caused by combining the 19 KHz from the audio source with the stereophonic pilot signal. The stereo pilot is a signal at 19 KHz used to activate the receiver’s stereo decoder circuit and also to identify the L+R from the L-R signals as shown in Figure 11. The low pass filter will also insure that any unwanted frequencies beyond 15 KHz will not be modulated and transmitted, since the bandwidth of the system is 20 Hz ~ 15 KHz. This bandwidth is set to achieve high fidelity of the stereophonic system. A two-pole sallenkey low pass filter, which is a second order filter, is used in the design as shown in Figure 3. The output of the low pass is fed into the pre-amp, which will boost up the level of the signal in order to equalize it. A printout of the simulation of the output of the filter is provided in Figure 4. ©2000 Nawaf Alshawwa All Rights Reserved 12 0 C4 710p R4 R5 U2 3 10k + V+ 7 V+ 10k 5 OS2 6 OUT V6 2 0 - LM741 V- 1 OS1 4 V- C5 1500p Figure 3: Low Pass Filter Schematics 600mV Vmax = (499.977m) (15.388K,353.600m) 400mV 200mV 0V 1.0Hz V(U2:-) 10Hz 100Hz 1.0KHz 10KHz 100KHz Frequency Figure 4: Output of the low pass filter. ©2000 Nawaf Alshawwa All Rights Reserved 13 The Pre-amp to the transmitter is shown in Figure 5. This Pre-amp is built using a wide band low noise operational amplifier, and designed to have a gain of 10 V/V. This pre-amp has an input impedance greater than 5K, in order to shield and avoid any loading from the pre-amp onto the input source (i.e. CD player). The output of the preamp is fed to the balance control and then to the graphic equalizer. ROUT1 45k RIN1 2 5k V- 4 VSS - OS1 OUT 5 OS2 LF347 VCC 7 + U6 6 V+ 3 0 1 VINPUT3 0 Figure 5: Pre-amp Circuit 2.0V (25.152u,0.9957) Gain = 9.957 V/V 1.0V (25.152u,100.061m) 0V -1.0V 0s 20us 40us 60us V(U6:+) V(U6:OUT) 80us 100us 120us 140us 160us 180us 200us Time Figure 6: output simulation of the Pre-Amp ©2000 Nawaf Alshawwa All Rights Reserved 14 The balance control network will be controlling the input to the transmitter. The balance control circuit is basically a switched circuit that allows specific inputs to pass through a specific path as the user selects. It will balance control the left and the right channels coming from the CD player. When the user selects the right channel for instance, the balance control network will only allow the signal coming from the right channel source to pass through. At the same time it will suppress the left channel signal and ground it. The balance network consists of two potentiometers wired in a center-tapped manner as shown in Figure 7. This configuration will allow balance in the middle and will also ground the unwanted signal by setting each of potentiometers to the desired location. The network has high input impedance, in order not to overload the input source. After the balancing module the signal is passed to the equalizer module. Vleft 0 FREQ = 1k VAMPL = 500m VOFF = 0 Rleft 50k 0 Rright 50k Vright 0 FREQ = 1k VAMPL = 500m VOFF = 0 Figure 7: Balance Control schematic ©2000 Nawaf Alshawwa All Rights Reserved 15 The graphic equalizer module is used to fine-tune the sound system. Equalizers are used to flatten a system’s frequency response (making the levels the same at all frequencies). In this design a graphic equalizer is used to fine-tune the sound signals. The frequency range that the graphic equalizer operates at is 20Hz ~ 15KHz and it is divided into 5 bands. These bands are chosen according to the center frequencies of the design, which are 100Hz, 300Hz, 1KHz, 3KHz, and 10KHz. Each band will have a specific bandwidth, the 3dB points which defines each bandwidth is listed below: 1. 100 KHz dB (fl = 20 Hz & fh = 257 Hz) 2. 300 KHz dB (fl = 120 Hz & fh = 800 Hz) 3. 1 KHz dB (fl = 600 Hz & fh = 1.6 KHz) 4. 3 KHz dB (fl = 1.4 KHz & fh = 6 KHz) 5. 10 KHz dB (fl = 4 KHz & fh = 25 KHz) The first two bands and the last band are designed with quality factor (Q) of 0.5 to cover a wide range of frequencies at beginning and end. The middle bands have Q = 1 which will be more narrow by definition than the earlier bands. By doing so, all the bands will cover the entire bandwidth of the system as shown in Figure 9. In addition, each band represents a set of sounds and instruments. The lower bands are for the bass, the middle ones are for the human voice, and the higher bands are for the treble. The five controls of the equalizer have a range of 10dB at each center frequency. The layout of the graphic equalizer will be typically sliding controls arranged by frequencies. Since the design is in stereo, the equalizer will have two inputs and two outputs. The stereo equalizer controls the whole system (both the left and right channel). Typically frequency bands of a graphic equalizer overlaps. This overlapping ensures better sound quality. ©2000 Nawaf Alshawwa All Rights Reserved 16 10k - OS1 10k 1Vac 0Vdc OUT 3 + 10k V+ R58 OS2 12 V8 10k Vin 5 0 0 U15 7 V7 -12 1 6 Vn uA741 2 Vp 4 0 Vp V- uA741 2 V- R56 4 Vn V6 - Vn 1 OS1 10k 0 6 500 3 10k 500 R65 25k + OS2 5 L1 3 7 Vp 1st Fo =100Hz 4 + OS2 5 L2 10m 3rd Fo =1KHz 3 0 Buffer 500 L3 10m U20 OS1 10k OUT 3 Vp 0 + OS2 U21 6 5 Vin L4 10m Vp uA741 2 4 R81 1 Vn - V- 4 Vn - V- uA741 2 OS1 10k OUT 3 0 + V+ 5 Vin OS2 1 6 5 L5 10m U22 Vp 7 OS2 R80 6 V+ V+ + 500 1 7 OS1 OUT 0 Vp 4 - V- Vn 10k 3 25k + U19 0 0 25k 33u 2nd Fo =300Hz 38 4th Fo =3KHz 0.22u 5th Fo =10KHz 26.7n 1.256k 0 Vn OS1 OUT 10k 7 Vin uA741 2 - 3.3u 69 500 R79 uA741 2 10k Vp 12.57 25k Summer 10k 6 U18 0 220u OS1 OUT 10m U17 0 Vin - 10k 0 1 4 3 6 uA741 2 Vp V- OUT R67 V- 10k 1 V+ OS1 7 - Vn V+ 4 Vn V+ Vin uA741 2 5 OS2 U16 5k V- R66 + 7 25k 7 R61 V+ OUT 220 0 0 Figure 8: Graphic Equalizer Schematic ©2000 Nawaf Alshawwa All Rights Reserved 17 OS2 1 6 5 Vout Fc = 300. 339 6. 0V Fc = 1. 0240K Fc = 3. 0034K Fc = 100. 000 Fc = 10. 089K 4. 0V 2. 0V 0V 1. 0Hz V(R68: 2) 10Hz V(R76: 2) 100Hz 1. 0KHz V(C21: 1) V(R77: 2) V(R67: 1) Frequency 10KHz 100KHz Figure 9: Graphic equalizer spectrum At the output of the equalizer a volume control is designed to adjust the volume of the signal up to +10 dB this network is shown in Figure 10. This network consists of a potentiometer, which controls the level of the signal. When the potentiometer is set to have a maximum resistance, the volume is turned down and when it is set to have a minimum resistance, the volume is turned up. INPUT FROM GRAPHIC EQUALIZER R Volume 50k 0 Figure 10: Volume control network ©2000 Nawaf Alshawwa All Rights Reserved 18 After Equalizing the signals to the selected range of frequency preference, both output of the graphic equalizer (left and right channels) must be combined in order to transmit the signals in FM stereo mode. The mixer is the network that will combine both left and right channels of the signal in a suitable way for stereo transmission. With stereophonic transmission, the information signal is spatially divided into two 20Hz ~ 15 KHz audio channel as mentioned earlier (a left and a right). The spectrum of the stereophonic transmission is shown in Figure 11, which has two channels (1) the left plus right channel (L + R), (2) the left minus right channel (L - R). The L + R stereo channel occupies the 0 - 15 KHz baseband. The L – R channel amplitude modulates a 38 KHz subcarrier and produce the L – R stereo channel, which is a double-sideband suppressed carrier (DSB-SC) that occupies the 23 – 53 KHz passband, used only for FM stereo transmission. A regular mono receiver can demodulate the whole spectrum but only the 20- 15 KHz (L + R) channel is amplified and fed to the speakers. A special stereophonic receiver must be used to listen to the whole FM stereo spectrum, which will be discussed in next few pages of the report. ©2000 Nawaf Alshawwa All Rights Reserved 19 L+R Stereo Channel Stereo Pilot L – R Stereo Channel Subcarrier L+R 0 15 19 23 (LSB) (USB) LR LR 38 53 f (KHz) Figure 11: FM Stereo Spectrum In the mixer module shown in Figure 12, the left (L) and the right (R) channels are combined in a linear matrix network. The linear matrix network will produce the L + R audio signal and the L – R audio signal by inverting the R signal and adding to it the L signal. Now, the L + R and L – R are signals in the audio band and must be separated before modulating the carrier for transmission. This is achieved by translating the L – R audio signal up the spectrum as shown in Figure 11. The translation is done by using the L – R audio signal to modulate a 38KHz subcarrier in a balanced modulator to produce a DSB-SC. Also, for demodulation purposes, a 19 KHz pilot is transmitted rather than the 38 KHz subcarrier because it is more difficult to recover the 38 KHz in the receiver. Dividing the frequency of the subcarrier produces the 19-KHz pilot. This frequency fits between the L + R and DSB-SC L – R signals as shown in Figure 11. To conclude the mixer’s role, all three signals are added together to form the composite stereo band signal, which will be fed to a low pass filter design to roll off at 63-KHz to get rid of the ©2000 Nawaf Alshawwa All Rights Reserved 20 unwanted frequencies. The Composite stereo band signal is then fed to the FM modulator where it modulates the main carrier. R - CH Matrix L - CH L+R LPF Balanced Modulators Composite Baseband Signal to FM Modulator L-R DSB - SC 2 38 KHz 38 – KHz Oscillator Figure 12: Mixer Module The circuit that does all of the above tasks is shown in Figure 14. And as explained earlier, this circuit adds L+R, L-R, and the 19KHz pilot to modulate the carrier signal for transmission. This Mixer circuit consists of three low noise operational amplifiers (SA/NE 5532), and a balanced modulator (LM 1496N) as shown in Figure 11. The main purpose of the Op-Amps is to add, subtract and buffer parts of the signals. The first op-amp inverts the right signal and adds it to the left signals (L-R) as labeled in Figure 14. This output is fed into the (LM 1496N) to amplitude modulate the 38KHz subcarrier. The output on the (LM 1496N) is passed through a low pass filter that has a cut off frequency of 63KHz to get rid of the unwanted RF noise, and then passed through a buffer to shield it from the end stage of the mixer circuit. The end stage is an op-amp that ©2000 Nawaf Alshawwa All Rights Reserved 21 adds all the signals to form the composite stereo signal, which is then fed into the modulator stage to modulate the 48MHz carrier. The mixer circuit required two sine waves to synchronize the operation of the modulator and to help the receiver recover the stereo information. Those signal sine waves are at 38 KHz and 19 KHz, they are produced using the circuit in Figure 13. The oscillator circuit consists of a number of inverters (74HC04), a reset D flip-flop (74HC74), two operational amplifiers (NE/SA U1A 1 U1A 2 1 U1A R2 2 1 3 74 HC0 4 10 0k 1k OS1 5532 OUT + OS2 1 6 5 38 KHz Sine Wave U2 74 HC0 4 VCC 7 74 HC0 4 2 - V+ 2 V- 4 5532), and a 38Khz crystal. 75 - 4 00 pF Trim for Peak 0.00 12u F 10 m 74 HC0 4 22 0pF U1A X1 2 0 0 0 R1 4 +1 2V 14 2 3 56 pF C R S 4 D 6 0 0 Q Q 5 OS1 5532 OUT 1 2 - 3 10 0k 0.00 75u F + OS2 1 6 5 19KHz Sine Wave U2 VCC 7 25 pF 51 0k 74HC74 38 Khz V- 1 V+ 1M 75 - 4 00 pF VCC 10 m Trim for Peak 7 12 0 0 0 Vss V3 -1 2 0 Figure 13: Sine Wave Oscillator ©2000 Nawaf Alshawwa All Rights Reserved 22 V3 0 VCC 12 VSS V2 -12 V3 0 0 R2 10k RIGHT1 2 - 10k LEFT1 OS1 5532 OUT 3 + V+ From Audio LPF V- 4 VSS OS2 1 6 L-R 5 10k 7 VCC 10k 10k 10k 0 2 - OS1 10k Pilot Signal 19Khz Sine wave 5532 OUT 3 100k + V+ VCC V- 4 VSS OS2 Composite Stereo Signal 1 6 L+R+19K+38K 5 7 VCC 1k 5k 10k 0 500 0.1u 8 51 10k 10k 200 51 50k 0 1k 2 3 VCC Balanced 6 10 Modulator 4 12 LM 1496N 1 14 Pin DIP VCC 3.9k 3.9k 20k 0.01u VSS 10m 10m 51 2 0 Carrier Level 6.8k 38Khz Subcarrier Level 4 0 0 0.0012u 0.0024u 0.0012u 0 0 0 V- 0.1u - OS1 5532 OUT 3 + OS2 1 6 5 VCC 7 1k V+ 38Khz Sine Wave 1k VSS (-12V) 0 0.1u D1N5237 0 0 2.2k 0 Figure 14: Mixer of Left and Right Channels ©2000 Nawaf Alshawwa All Rights Reserved 23 Frequency modulation (FM) is used in this design. This modulation is done in the modulation module, which modulates a 48-MHz carrier with composite stereo band signal. Standard FM transmitters use a Voltage-Controlled Oscillator to produce FM signals. A buffer to provide isolation and therefore better oscillator frequency stability follows the VCO. The MC1648 is one suitable IC chip for this modulation. It utilizes a tank circuit to set the frequency of operation as shown in Figure 15. The tank circuit is a parallel combination of a capacitor with an inductor, which both are chosen upon deciding the center frequency of the design. These values can be calculated with f0 = 1 / (2*(LC)^1/2). The bandwidth of this signal can also be calculated from BW = (f0 / Q) where Q is the quality factor. This quality factor determines the 3dB point of the resonant circuit. A varactor diode is incorporated into the tank circuit to provide voltage variable input for the oscillator (VCO). As shown in Figure 15, the 1K resistor is added at the input to protect the varactor during the operation. This resistor is may be removed if the dc input voltage does not cause the diode to become forward biased. Also, 0.1uF capacitors are placed to bypass the VCO input (varactor diode), guaranteeing only dc levels at this point. The FM signal is then amplified up to its final output power by power amplifiers and their driver amplifiers. ©2000 Nawaf Alshawwa All Rights Reserved 24 Vin MC1648 0.1uF 10 0 L 0.15uH 1k 3 12 D MV2106 5 C1 0 Tank Circuit Rvar C2 0.1uF 0 0 Figure 15: Voltage Controlled Oscillator. The transmitter’s output stage is a class AB power amplifier. This power amplifier is designed to transmit the composite signal at a very low power that is set by the FCC regulations (< 100 mWatts). This design is shown in Figure 16, which is a typical class AB, it is characterized over the other classes by having minimal to none cross over distortion. This characteristic is very important in stereo FM transmission, because the receiver will distort and will have problems with decoding the signal. ©2000 Nawaf Alshawwa All Rights Reserved 25 V+ 232 RB1 Q1 TIP31A D5 D1N4002 1 Antenna VINTRANS1 D6 D1N4002 1 ROUTTRANS1 50 TIP32A 0 0 Q3 232 RB2 V- Figure 16: Transmitter’s Power Amplifier II. Receiver (L & R Speakers) An FM waveform carries its information in the form of frequency, so that the amplitude is constant. FM stereo receivers are identical to standard FM receivers up the output of the audio detector stage. There are several methods for demodulating a FM signal such as phase-locked loop (PLL) demodulator, slope detection/FM discriminator, and quadrature detector. In this design, a PLL demodulator is used to recover the audio signals. This particular method is chosen because PLL is the best method conceptually for demodulating a FM signal. The output of the PLL will be put through the decoder to ©2000 Nawaf Alshawwa All Rights Reserved 26 separate the left and right channel. At the end, each channel will be put through to a power amplifier stage to drive the designated speaker. RF Pre-amp Demodulator Stereo Decoder Audio Amplifier Figure 17: Receiver Block Diagram The RF Pre-amp stage is the most important stage of the receiver’s module, since it’s the one that tunes in for the RF signals coming from the transmitter. The antenna picks up signal from the air and passes them to the RF Pre-amp. The RF Pre-amp boosts up the weak signal from the antenna, and tunes to the desired frequency or reception. It also prevents the demodulator’s input from being coupled to the antenna, where it could be radiated into space. The RF Pre-amp usually has tank or a resonator circuit, which is a parallel LCR that is designed to tune in to a specific frequency, this frequency in this design in the carrier frequency, which is at 48MHz. The RF amplifier (preselector) shown is Figure 18 was incorporated from a book called “Secret of RF Circuit Design”. This circuit has a very high sensitivity, which is the ©2000 Nawaf Alshawwa All Rights Reserved 27 ability to pick up weak signals from an antenna. The main job of JFET active preselector circuit is to separate two closely spaced signals, and to reject unwanted signals that are not on or near the desired frequency being tuned. The preselector uses the common gate configuration where the signal is applied to the source and the output is taken from the drain. The tuning will be done using the variable capacitor (Cvar), as shown in Figure 18. The output of the signal will be amplified and fed to the demodulator to recover the information sent by the transmitter. VCC C6 0.01 u 0 R2 27 0 C5 0.01 u 0 L3 10 0u C2 J1 FN43 93 0.00 1u C3 0.00 1u VOFF = 0 VAMPL = 1 0m FREQ = 48meg Vinp ut L1 Cva r 10 uH 36 5p R1 15 0 C4 1n Lo ut 10 uH 0 0 Figure 18: RF amplifier (preselector) A FM demodulator produces an output that is proportional to the instantaneous frequency of the input. As mentioned earlier in the report phase-locked loop demodulation circuitry is used in this design. Phase-locked loop is a feedback circuit, which tries to match a local oscillator to the modulated carrier frequency. A PLL consists of thee major components: a phase detector, a loop filter, and a voltage controlled ©2000 Nawaf Alshawwa All Rights Reserved 28 oscillator (VCO) connected together in the form of a feedback loop as shown in Figure 20. The VCO is a sine-wave generator whose frequency is determined by a voltage applied to it from an external source. The loop is said to be phase locked when the VCO frequency f0 and the loop input signal frequency fi are identical (f0=fi), and only if a phase difference exits between the VCO and the input signal. 90k 490k VSS RIN2 2 OS1 0 + V+ OUT 3 OS2 1 0 10k 6 3 7 VOFF = 0 VAMPL = 100u FREQ = 20k + OS2 5 10k 0 100k VCC 3 100n 5 - OS1 OUT C1 6 LM741 LM741 VCC OUT V+ 10k - OS1 7 2 V- RIN4 - 1 + V+ 2 OS2 1 Vout 6 5 LM741 7 RIN3 4 VSS V- 4 VSS V- 4 390k 100k VCC U6 U7 0 U8 0 V6 VCC 10k VSS V4 12 0 V5 -12 0 0 Figure 19: Receiver. Pre-Amp Input Signal Phase Detector Vd Loop Filter Vo Amp fi,i f0, 0 VCO Free- running frequency Figure 20: PLL Block Diagram ©2000 Nawaf Alshawwa All Rights Reserved 29 After the demodulation stage, the stereo decoder comes in place. Its main job is to process the baseband signal and separate the L and R channels and feed them to the designated speaker. In receiver’s stage the operation of the decoder is opposite to that of the mixer in the transmitter’s stage. The composite baseband signal consists of the L + R audio channel, L –R audio channel, and the 19-KHz pilot. Those channels are separated from the composite baseband signal with filters as shown in Figure 21. The 19 KHz is filtered with a high-quality factor (Q) band-pass filter, multiplied by 2, and fed to the L – R demodulator. The L + R stereo channel is filtered off by a low-pass filter with an upper cutoff frequency of 15 KHz. The L – R double-sideband signal is separated with a broadly tuned band-pass filter and then mixed with the recovered 38 KHz carrier in a balanced modulator to recover the L – R audio information. Frequency Demodulator Composite Low-pass filter Cutoff @ 15KHz 2R Matrix network (Stereo decoder) L+R 2L Baseband signal L-R Band-pass filter 23-53 KHz 19 KHz Band-pass filter L–R Balanced product demodulator Sidebands 19 KHz Pilot Amplifier and (X2) multiplier 38 KHz subcarrier Figure 21: FM stereo decoder ©2000 Nawaf Alshawwa All Rights Reserved 30 VCC GND 11 Divide f by 2 (38KHz) Divide f by 2 (19KHz) Divide f by 2 (19KHz) 13 Power supply regulator 12 L.D . 15 VCO 16 Schmitt trigger 19KHz phase detector P.A 19KHz pilot presence detector 9 Matrix R 14 1 L 10 38KHz (L-R) detector CA 3090 2 3 4 5 6 7 8 L.D = lamp drive P.A = Pre-amp. VCO = voltage controlled oscillator This chip is used to decode the FM stereo signal. It uses a phase-locked loop to achieve subcarrier frequency coherency for demodulation of the L-R signal. It also uses a 76KHz VCO, and a divide by 2 (2) flipflops network to provide a 38KHz subcarrier to synchronize the L-R product detector for demodulation of the DSB-SC. Another (2) flipflop is used to divide the 38KHz down to19KHz for input to the phase detector. The PLL loop gain is high enough here to achive a low phase error. The ouput of the 38KHz L-R detector is combine with the L+R in the matrix netework to produce the left, and right channel seperatly. This proceure is as following: (L+R) – (L-R) = 2R and (L+R) + (L-R) = 2L ©2000 Nawaf Alshawwa All Rights Reserved 31 the number 2 in the (2R) and (2L) indicates only the amplitude of each signal. At the output of each channel there is a deeemphasis network which will recover the preemphasis of the higher frequencies in the transmitter. Input Number Description 1 Composite FM detected signal input 2 Bypass 3 Ground 4 Ground 5 Ground 6 RC Network 7 19KHz Pilot lamp 8 Sensitivity network 9 Left output Channel 10 Right Output Channel 11 + Vcc 12 Lamp Drive circuit 13 Ground 14 Phase lock loop filter network 15 Capacitor network 76KH Network 16 Indicator input 76KHz Table 1: CA3090 Pinouts ©2000 Nawaf Alshawwa All Rights Reserved 32 The matrix network combines the L + R and L – R signals in such a way as to separate the L and R audio information signals. Which are then fed to their respective Deemphasis networks and speakers as shown in Figure 22. LR Matrix Network L+R 2L Deemphasis Network Audio Amp 2R Deemphasis Network Audio Amp Left Speaker Right Speaker Figure 22: Stereo matrix network Decoder The Receiver’s output stage is a class AB power amplifier. This power amplifier is designed to drive an 8-ohm speaker load and produce 5-Wattsrms. This design is shown in Figure 23, which is a typical class AB, it is characterized over the other classes by having minimal to none cross over distortion. The output of this power amplifier will have a voltage swing of about 9 Vp, this will ensure that we are getting the full range and maximizing the sound quality of the speaker. The speakers following this stage are of the full range type with an outer diameter of 120X60 (mm). ©2000 Nawaf Alshawwa All Rights Reserved 33 VCC R1 54 Q2 TIP31A D1 D1N4002 RE1 0.5 RE2 0.5 D3 D1N4002 ROUTREC1 8 TIP32A 0 Q4 R7 54 Vss Figure 23: Receiver Power amplifier. ©2000 Nawaf Alshawwa All Rights Reserved 34 Physical Layout of the Project I. Transmitter: Front & Side View + 10 dB Balance 4” L Volume R 0 Power +10dB - 10 dB 7” 9” Rear View Audio Plug in L R ©2000 Nawaf Alshawwa All Rights Reserved 35 II. Receiver: (Left & Right Speakers) Front & Side View 9” Tune 9” 8” Input Connector: L. Ch To Transmitter From CD Player R. Ch Figure 24: Connector Headphone to Y- Adapter ©2000 Nawaf Alshawwa All Rights Reserved 36 History of the Project The project has gone through some changes in the designing phase. These changes came about when a problem was faced or when an enhancement was considered necessary in some parts of the design. In the beginning, infrared techniques were considered for use in modulation and transmission of the information. After careful review and study of the infrared, many drawbacks were noticed, such as, direct line of sight, short propagation distance, and susceptible to light interference. For that the design took a different route. This route was to use frequency modulation techniques to modulate the carrier signal and transmit the information to the receiver. In the proposal phase, all the efforts were put into figuring out the whole design and integrating the ideas together. On the other hand from an economical point of view, the hours of labor were standing at 576.5 hrs, and the actual cost of the prototype was equal to the estimated prototype cost Between the proposal and the preliminary design review, minor changes were done to the design. The distance of operation was increased from 3 meters to 7 meters. The economical picture of this phase was relatively good, because the hours of labor were reduced by 18.5 hours, which eventually brought down the actual prototype cost by $1626. After the preliminary design review the project entered the critical phase. In this phase, not many changes were done to the design. This phase was being used to figure out and order the parts that were going to be used in the project, such as the, modulator, ©2000 Nawaf Alshawwa All Rights Reserved 37 demodulator, and stereo decoder. At this stage, the hours of labor were cut down slightly by 8 hours. This reduction brought down the actual prototype cost by $112. In the final design review, some changes were made to the design. After simulating and building the graphic equalizer, it was verified that this design was no good for this project because it was not working according to the specification. Therefore, a new design was established to replace the old graphic equalizer. The new design was simulated to verify its right operation, and make sure that it complies with the specifications. From an economical prospective, the hours of labor were cut down by 10 hours from the last critical design review phase, and in total they were reduced by 36.5 hours. Eventually, this has brought down the total cost of the prototype by $2,302. ©2000 Nawaf Alshawwa All Rights Reserved 38 Test of Design The Design consists of two major modules: transmitter and a receiver. Those modules include smaller modules within them, such as modulator, demodulator, filters, and mixers. To test the overall performance of the Wireless Stereo Speakers System, various things are needed such as a CD player, headphone jack Y-adapter, and an AC outlet (110 VACr.m.s @ 60 Hz). The user will plug one end of the adapter into the CD player, and the other end into the transmitter. Each device requires a single AC outlet to power it up. When all of the above are ready then the transmitter will be enabled and it will transmit the information from the CD player to the speakers. Testing the project during design and building periods, a couple of equipment are needed such as a Lambda source power supply to power up the circuits, an oscilloscope to view the signals, and a function generator to supply the circuits with a defined sinusoidal signal. A spectrum analyzer is also needed here to view the fundamental frequencies of the transmitter and the receiver. This will enable the test engineer to check the operation of each module and make sure they work accordingly to the specification defined earlier in the report. The lab equipment are sufficient enough to enable any design, test engineer to make any measurement on a specific circuit ©2000 Nawaf Alshawwa All Rights Reserved 39 Parts List Part Name OR Number SA 5532A CA3090 LM1496N Resistor 47 uF (10V) 10 uF (10V) TO-92 N-CH JFET Toroids Capacitor UA741CN Crystal Choke LF347 MC1648 Tip31A Tip32A NE568AD Choke Casing Speakers Skirted round knob potentiometers Description Dual low noise Op-Amp. Stereo Decoder Balanced Modulator 1/4 Watt (Various Values) Capacitor (Aluminum Electrolytic) Capacitor (Aluminum Electrolytic) N-Channel JFET Toroids Ceramic Disc (Various Values) General Purpose Amp 8-Dip Overtone (Various Values) RF choke 1000uH Wide bandwidth JFET OP-Amp Voltage Controlled Oscillator Meduim Power Amplifier-NPN Meduim Power Amplifier-PNP Phase-Locked Loop RF Choke 10uH Shielded Boxes Oval Magnetic Shielded Speakers Instrumentation Knobs 12mmDual Potntiometers Manu- Vendor facturer Phillips Arrow RCA NTE National NTE Mouser Mouser Mouser Mouser DigiKey Mouser Newark DigiKey DigiKey National DigiKey Motorola mouser mouser Phillips Newark Mouser Sescom DigiKey Keystone DigiKey Panasonic DigiKey Vendor Part number NE5532An NTE789 NTE973D 29SJ250-(value) 75-515D10V47 75-515D10V10 526-NTE312 M5701-ND 140-CD302U9-xxxM UA741CN CTX***-ND M5258-ND LF347M-ND 511-TIP31A 511-TIP32A NE568A M5258-ND TBD P10187-ND 8554K-ND P2B6503-ND TOTAL Price Q Cost @ (quantity) $0.86 @(1+) 6 $5.16 $11.35 @(1+) 1 $11.35 $3.20 @(1+) 1 $3.20 $0.009 @(200) 200 $1.80 $0.05 @(250) 10 $0.50 $0.05 @(250) 10 $0.50 $1.34 2 $2.68 $3.50 3 $4.02 $0.36 @(200) 40 $14.40 $0.26 @(500) 10 $2.60 $3.41 3 $10.23 $3.27 2 $6.54 $0.96 @(100) 2 $1.92 $4.48 1 $4.48 $0.46 @(100) 2 $0.92 $0.46 @(100) 2 $0.92 $1.41 1 $1.41 $3.27 2 $6.54 TBD TBD $6.05 2 $12.10 $3.38 $13.52 $1.99 5 $9.95 $105.60 IP = In Possession, OO = On Order, NO = Not Ordered Table # 5: Parts List ©2000 Nawaf Alshawwa All Rights Reserved 40 Status IP IP IP IP IP IP OO OO IP IP OO IP IP NO IP IP NO IP NO NO NO IP Conclusion As of today the project is on track. The projected completion date is still April 29, 2000. Phase one of the project, described as the design, is coming to a close with the final design review (FDR). The new phase, which requires actually building the project, is scheduled to begin with Project Report # 1 on December 2nd, 1999. Problems were faced in the graphic equalizer’s design, were solved by designing a new equalizer shown in Figure 8. Presently, efforts are being made in order to conduct early building and testing procedures, so that the final design may be ensured. Most of the designs have been completed and verified using OrCAD; the ones not yet completed are not verifiable because of the lack of parts found in OrCAD. To date, almost all the parts have been ordered and are on their way. Starting next week the building phase should begin as projected in the Gantt charts. At this time the retail price of the project is still standing at $ 190. Labor hours have been reduced by 36.5 hours from the initial estimated hours (from 588.5 to 552 hours). In addition, the total cost of the prototype has been reduced by $2302 from the original estimated price (from $46,418 to $44,116). ©2000 Nawaf Alshawwa All Rights Reserved 41 References Young, Paul H. Electronic Communication Techniques, 4th Edition. New Jersey: Prentice-Hall, Inc. 1999. Carr, Joseph J. Secret of RF Circuit Design, 2nd Edition. Washington, D.C: TAB Books, 1997. Roddy, Dennis and Coolen, John. Electronic Communication, 3rd Edition. Virginia: Reston Publishing Company, Inc. 1977. Sedra, Adel and Smith, Kenneth. Microelectronic Circuits, 3rd Edition. New York: Oxford University Press, 1989. Haykin, Simon. Communication Systems, 2nd Edition. New York: John Wiley and Sons, 1978. Motorola, Website: http://www.motorola.com Minicircuits, Website: http://www.minicircuits.com Phillips semiconductor, Website http://www-us.semiconductors.philips.com/ Silverman, Joseph R. The George Washington University. School of Electrical and Computer Engineering. Doroslovacki, Milos. The George Washington University. School of Electrical and Computer Engineering. ©2000 Nawaf Alshawwa All Rights Reserved 42 Appendix - B (User Manual) + B 10 4 Lal RdB ” a n ce 10 dB V 0ol u m e P o w er T u ne ©2000 Nawaf Alshawwa All Rights Reserved 43 User Manual I. Description of the Product: The Wireless Stereo Speakers System is a luxury piece of equipment that can be used in the house, office and outdoors too. This system consists of three modules: transmitter, right speaker, and left speaker. Each of these modules operates from an AC outlet using an AC to DC power transformer. This devise will let the listener enjoy his or her favorite music in many parts of the house, office, or outdoors without having string of wires hanging all around the place. The Wireless Stereo Speakers System connects to the CD player, and transmits the music in the form of RF signals. These signals will be picked up at each receiver and put to the speakers so that everyone around will be able to listen to the music without having to be constrained to the length of wires and messiness. The transmission frequency for the wireless stereo speakers is 48 MHz. The stereo speakers will pick up the transmitted signal up to 23 feet (10 %) away. ©2000 Nawaf Alshawwa All Rights Reserved 44 II. List of Specification of the Product: 1. Transmitter: 1. Input from an audio source. 2. Input Level range 0 ~ 50 milli VP-P. 3. Transmitter’s input impedance > 5 K 10 %. 4. Two line level audio inputs at the transmitter (Left/Right). 5. On/Off switch at the transmitter. 6. Volume control at the transmitter. 7. Balance Control at the transmitter. 8. 5 bands Equalizer at the transmitter. a. 100 KHz dB b. 300 KHz dB c. 1 KHz dB d. 3 KHz dB e. 10 KHz dB 9. Frequency Modulation (FM) Stereo Transmission. 10. Pre –modulation frequency range 20 ~ 53 KHz I. L + R channel 20 ~ 15 KHz. II. L – R channel 23 ~ 53 KHz. III. Pilot at 19 KHz. 11. Transmission Frequency 48 MHz (carrier). 12. Range of operation 7 meters 23 ft. 10 %. 13. Transmitter’s output power (FCC Regulations < 100 Milli Watts) Nominal = 10 Milli Watts. ©2000 Nawaf Alshawwa All Rights Reserved 45 14. Transmitter’s output impedance 50 10 %. 15. Size: 9” W x 7” D x 4” H 2. Receiver: 1. Right channel & Left channel speakers. 2. Receiver built in each speaker. 3. Output Load 8 speakers. 4. Output power 5 Watts RMS. 5. System’s bandwidth 20Hz – 15KHz. 6. Size: 8” W x 9” D x 9” H 3. Miscellaneous: 1. Power supply 12 volts (AC outlet). 2. Operational temperature = Room Temperature 3. Mono-pole Antenna. 4. Antenna’s length (FCC Regulations < 1.5 meters) Nominal = 15 cm. ©2000 Nawaf Alshawwa All Rights Reserved 46 III. How to use the Product: The wireless stereo speakers system is a very simple device to operate. Simple connect all the device: the transmitter, left and right speakers to an AC power outlet using the AC to DC power transformer provided in your purchase. Then connect the CD player to the transmitter-using headphone to Y-adapter. Each end of the Y-adapter connects the rear of the transmitter, in the order shown in the Figure below. L. Ch To Transmitter From CD Player R. Ch Figure: Headphone to Y-adapter connection. The Speakers can be placed within the range given in the specification. Make sure to put the right speaker on the right and left speaker in the left to get the maximum sound fidelity and quality. After all that, you can turn the transmitter ON/OFF using the power button on the front of the transmitter. You can also, adjust the volume and the level of signals using the volume control and the graphic equalizer controls on the front of the transmitter too. Incase the signal is not clear, there is a tune knob on each speaker that enable you to adjust the reception of each receiver until the signal becomes audible. ©2000 Nawaf Alshawwa All Rights Reserved 47 VI. Maintenance Procedures: The wireless stereo speakers system is made of very sensitive devices and should be treated with good care. They should not be applied to extreme temperature or pressure. To ensure a long life for your system, you must follow these instructions: Before connecting any inputs to the transmitter be sure to turn the device off first. Do not put a flower vase filled with water or any small metal objects on the transmitter and the receiver. Exterior influences such as lightning and static electricity can affect the normal operation of your wireless stereo system. If this occurs, turn the transmitter off and on again using the power button on the front panel of the transmitter. Or disconnect and then reconnect the AC power cord to the AC power outlet. For safety precautions: - The units are to be used only where the power supply is AC 120 V, 50 – 60Hz, it cannot be used anywhere else. - To prevent electric shock, match the wide blade of the AC power plug to the wide slot, and fully insert. - When opening the cabinet, be sure to disconnect the AC power plug from the AC outlet. - Wipe the cabinet with a soft cloth when cleaning. IV. Trouble-Shooting Procedures: ©2000 Nawaf Alshawwa All Rights Reserved 48 The wireless stereo speakers system is sensitive to harmful interference. It interference is detected, then it is from a nearby source. In a case of interference bring the units as far as possible from the source of interference. Sources of interference’s can be other transmitters nearby, or high voltage transmission lines. In the case of malfunctioning, reset the system by turning the devices off and back on to check their operation status. If the problem persist, unplug the AC power cord from the AC power outlet. Open the cabinet of the transmitter and check for any lose components, if any found close the cabinet again and send your product back to us and we will gladly fix it for you. In case of unclear sound at any of speakers. You may solve the by tuning the devices using the tune knob on the front panel of the speaker. If the problem did not go away, try getting the speakers closer to the transmitter. If this problem persist send your product back to us and we will gladly fix it for you. ©2000 Nawaf Alshawwa All Rights Reserved 49 Appendix - C (Data Sheets) ©2000 Nawaf Alshawwa All Rights Reserved 50 Appendix - D (Log Book) ©2000 Nawaf Alshawwa All Rights Reserved 51