world band radio receiver with analog control and led display
Contents
1. 248 Laurentiu Teodorescu Andrei Sorin Gheorghe 4 Hardware design The RF section block diagram is depicted in Fig 3 It contains a S14844 B integrated circuit 3 an FM input circuit an AM input circuit a shortwave RF low noise amplifier and the FM SW RX antenna i4844 B ra TON AMI X ADC gt DAC gt LOUT E d AM anti s DSP f mwl I fi X ADC gt DAC ROUT ANT mmf sw T ey y Tz AMP i EJ Yyy FMI f 4 0190 l Lin ci P XTALI ADC 4 gt TUNE AFC CONTROL INTERFACE 2 0 3 6V VDD1 2 JE XTAL osc z v RST T gt LNA EN IR SCL 4 SDA Fig 3 The block diagram of the RF section 3 The IC 3 Fig 3 contains a CMOS low noise amplifier LNA The LNA inputs are connected to an internal variable capacitor which forms a tuned circuit with the external coils The change of internal capacity is performed in steps by switching of MOS transistors in series with small internal capacitors LNA gain is automatically controlled by the AGC block The internal precision oscillator XTAL OSC uses an external quartz crystal Q The signal from XTAL OSC is applied to an automatic frequency circuit AFC which monitors the high frequency sinusoidal oscillator A double mixer block takes the signals from the LNA and from the high frequency oscillator The resulted low2. S1I4844 B 3 an ultralow voltage stereo audio power amplifier Texas Instruments TPA6100A2DR 6 an 8 bit microcontroller with an integrated 24 bit ADC Silicon Laboratories C805 1F350 4 a keyboard and a 7 segment LED display ANTENNA E EERE Lin SW RF AMP EANA AENEA AEA c1 33p PO ANAMA AM Coil L FM Coil POT SI4844 B Ti Audio L SPK CMOS IC i i Amplifier i Receiver Ri TPA6100 ir RSPK Keyboard BATTERY lt lt 3V t Power ON OFF i 100u is il Fig 1 The block diagram of the radio receiver The electric power is supplied from batteries A stick external antenna is connected for shortwave SW or frequency modulation FM reception World band radio receiver with analog control and LED display 247 3 Principle of operation If the power switch S1 Fig 1 is in the closed ON position the supply voltage 3V is applied to the microcontroller 4 Then the unit peripherals are initialized the display is turned on and the analog to digital converter ADC monitors the local keyboard status The receiver IC 3 is automatically put in off state waiting for external commands The microcontroller acts as the master device on the 4 wire data bus Reset RST I C clock SCL C data SDA interrupt IRQ and S14844 B 3 ATDD Analog Tune Digital Display 7 is the slave device Q li 32KHz SS IRQ 4 digit c8051F350 SDA
3. code from ADC is processed by a tuning configuration function and transmitted over the bus to be executed by the Slave 6 Results The RF SI4844 module 8 is connected by a 4 wires interface to the microcontroller design kit Fig 12 A keyboard is then attached to allow the receiver settings to be modified 4 os 8 ine eee f a Se a FRR Sie Hi x me Fig 12 The layout of S14844 RF section After writing compiling and debugging the C source code the microcontroller is programmed through the Silicon Labs integrated development environment tool IDE After connecting the stick antenna the receiver is turned World band radio receiver with analog control and LED display 255 on from the keyboard and then it is tuned on Romanian radio broadcasting station frequency Rom nia Actualit i f 105 3MHz Fig 12 Fig 13 Receiving National Romanian radio station frequency The unit is capable of receiving channels in the AM SW1 SW8 and FM bands with high sensitivity and selectivity The audio low voltage amplifier provides enough volume for an audition in headphones 7 Conclusions The built prototype has been tested and proved fully functional for all ranges of medium short and ultrashort waves The information on the display may be seen at great distances The adopted design techniques and the complete analog control of receiver functions allow both use of a small number of connections to the microcontrolle
4. 44 E Fig 10 The block of commands World band radio receiver with analog control and LED display 253 The keyboard Fig 11 is also powered from batteries The connection with the ADC is performed by 2 wires By using this method the number of connections with the microcontroller is reduced to a minimum value R5 R6 R7 R8 10k 10k 10k s a lt agi a a a a a ON OFF BAND j VOL o VOL oO MUTE BASS ji BASS j TREB TREB Fig 11 Keyboard connections to ADC 5 Software development The microcontroller Master communicates with the ATDD Slave on the data bus I C 12 by sending commands and receiving information The received information significant to the user is shown later on the 7 segment display The communication is activated only when a key is pressed or the ATDD changed its status The bus is left open after all relevant information has been received from the ATDD This allows short messages between Master and Slave and an improvement of the reception quality the ATDD sensitivity is increased when there is no data transfer on the bus The system uses 3 interrupts the first one is for C bus timing interrupt 1 the second activates Timer 2 interrupt 5 and the last is used by the analog to digital converter interrupt 10 The 24 bit ADC monitors the keyboard with a sampling rate of 10 samples per second being configured in unipolar mode with its internal input buffer disa
5. ST4844 B P 7 segment E Microcontroller SCL ATDD TUNE display DS Master RST Save RO RI R2 Rnt 1 Vref sw1 qd swa SWn Fig 2 The communication between the microcontroller and peripherals When the POWER ON key SW1 Fig 2 is pressed the microcontroller 4 starts the communication with S14844 B 3 Fig 1 2 and it puts the receiver in on state it turns on the 32KHz slave crystal oscillator it selects the RF band type and its properties and finally it adjusts the volume or tone values By default the FM band is selected after the first power up The band and the frequency information are sent periodically to the master device for updating them The microcontroller 4 computes and then converts this information to be released to the 4 digit 7 segment display The microcontroller and the display are connected through 8 wires SS which select the segments 7 wires for the digits 1 wire for the dot and through 4 wires which address the four digits If the band key is pressed the modified band type followed by the corresponding frequency values are displayed The frequency is adjusted by changing the cursor position of the potentiometer P There are also some keys to increase or decrease the volume value or to simply mute the system The same power key is used to power off the unit In the off mode most of the slave internal blocks including the oscillator are stopped to save battery power
6. U P B Sci Bull Series C Vol 77 Iss 4 2015 ISSN 2286 3540 WORLD BAND RADIO RECEIVER WITH ANALOG CONTROL AND LED DISPLAY Lauren iu TEODORESCU Andrei Sorin GHEORGHE This work focuses on the design of a digital world band radio receiver The system control functions are handled by an 8 bit microcontroller with an internal analog to digital converter ADC The unit uses a 7 segment light emitting diodes LED display to allow the information to be visible from a distance and a local keyboard for programming its functions All keyboard buttons are connected to the ADC inputs The tuning operation is analog by using a rotary potentiometer Keywords receiver ADC 7 segment LED display I C bus digital radio analog control 8 bit microcontroller interrupt 1 Introduction Today we are celebrating more than 60 years since the first commercially manufactured transistor radio was sold 1 Since then outstanding technical advances have resulted in increased performance and a reduced size of the receivers The last achievement of the semiconductor industry in the audio field is the development of some digital Complementary Metal Oxide Semiconductor CMOS Integrated Circuits IC s 2 intended to be used as a complete solution for the radiofrequency RF section inside an amplitude modulation AM frequency modulation FM radio receiver These ICs have both low power consumption and high performance making them the right ch
7. bled The debounce function is performed by comparing two successive samples which contain the most significant 8 bits of the output code when a key is pressed by the user If the output code maintains its value it is considered that the corresponding key has been pressed The ADC output code is immune to supply voltage modification since both the ADC reference and the keyboard are directly connected to the batteries Timer 2 is used to command the display segments with a refresh rate of 300Hz A 2MHz clock signal is its time base The segments of the 4 digits are lit one by one by using time division multiplexing and switching the active digit at each moment when this timer overflows 254 Laurentiu Teodorescu Andrei Sorin Gheorghe Timer 0 works as a 16 bit counter in Mode 1 for bus communication It sets the C clock signal SCL at a 500Hz frequency by generating interrupts with arate of 2ms In the moment when the keyboard power key is pressed by the user the microcontroller initializes the serial communication by resetting the chip and by putting the bus in wait condition If an interrupt is received from the ATDD the Master interrogates the Slave about its status The received data from the Slave band frequency volume is processed and put on the display The data that was read from the Slave on the I C bus is sent to the display by a special function which parses the ATDD status and decodes the information on the bus The output
8. esistance and its parameters Band nin MHz na MHz Omin um max um Ramin Q Ramax Q FM 87 108 12 239 13 597 0 124 0 138 SW 2 3 28 5 23 8 83 8 0 0202 0 0712 The antenna efficiency is 10 Rr 1 eee 6 It may be observed that the efficiency is poor for the lower range of SW band especially when the antenna has a minimum length less than 3 If the antenna is fully extended the efficiency is much higher Table 3 Table 3 The antenna efficienc Band Jnin MHz Jna MHz L cm Nmin i max FM 87 108 0 86 0 89 SW 2 3 28 5 15 0 024 0 53 FM 87 108 0 990 0 992 Sw 23 28 5 60 0 29 0 94 World band radio receiver with analog control and LED display 251 The SW amplifier Fig 6 is formed by the L2 R4 Ro Ti Rs Cis circuit T is a high gain low voltage RF common emitter amplifier ANTENNA LV Lin L2 120nH 2 5Kohm 100MHz 1801 Fig 6 The SW amplifier circuit Lz is a chip ferrite bead 11 with variable impedance depending on frequency Fig 7 It is mounted to increase the amplifier input impedance at very high frequency 100MHz By using this technique the SW amplifier input is isolated when working in FM band 3000 2500 2000 Impedance 2 a So o 1000 500 1 10 100 1000 2000 Frequency MHz Fig 7 L ferrite bead impedance 10 Compared to the circuit shown in Fig 6 t
9. he simulated circuit Fig 8 includes additional items as antenna model the Lz impedance in SW band and the low noise amplifier LNA input impedance R10 C17 Fig 8 The SW amplifier simulated circuit 252 Laurentiu Teodorescu Andrei Sorin Gheorghe The amplification frequency characteristic is presented in Fig 9 It can be seen that the amplification is stable in SW band and has a small variation with temperature 6 6 5 8 r r r r r r 2MHzZ GMHZ 12MHz 18MHz 24MHZ 30MHz 36MHZ 40MHz A Frequency Fig 9 Amplification frequency characteristic for SW amplifier The microcontroller 4 Port1 Fig 10 outputs are connected to the display segments while half of Port2 P0 0 P0 1 P0 4 P0 5 Fig 10 addresses the digits through a bipolar current amplifier AMP The I C communication 12 with ATDD IC 3 is carried out with the other half of Port2 P0 2 P0 3 P0 6 P0 7 An internal oscillator OSC provides the 24MHz clock signal for the timers CPU and the ADC The ADC voltage reference is directly taken from battery without being stabilized c80516350 Aa i s Osc Port 1 Vref SEGMENTS VBAT D i ADC Timer Timer CPU i H 0 2 Keyboard f o o o o MEMORY Port 0 Port 0 i P0 2 P0 3 P0 0 P0 1 Li AMP E P0 6 P0 7 P0 4 P0 5 DIGITS Sc SMBUS SI48
10. intermediated frequency low IF signals are sent to analog to digital converters ADC blocks to be translated in digital format A digital signal processor DSP controlled by the internal digital interface performs all audio signal adjustments Two digital to analog converters DAC transform the digital audio signal in analog signal An external potentiometer P connected to an ADC is used for tuning the high frequency oscillator In this way the desired radio station can be received by changing the frequency with the potentiometer The FM input circuit 8 Fig 4 is formed by a monopole antenna in 1 4 whip stick antenna and Dj Lin C1 L3 elements The antenna has variable length World band radio receiver with analog control and LED display 249 18cm 60cm D is a high speed switching antiparallel diode pair with low internal capacitance 5pF mounted for electrostatic discharge ESD protection Lin is an inductor load to change the electrical length of the antenna It compensates the short length of the stick antenna by keeping it in resonance with the FM bandwidth ANTENNA Fie ac le kk a a EE a ee i J FMI ST4844 B ae BAV99 Control Circuit Fig 4 The FM input circuit The output impedance of the antenna is 9 Z R j X 36 5 j 21 5 Q 1 The imaginary term from expression 1 is capacitive The antenna output capacitance is between 20pF 36pF in FM band 88 108MHz at its maximu
11. m length 60cm The simplified equivalent circuit Fig 5 of the stick antenna includes two resistors which model the radiation R and the dissipation Ra resistances Fig 5 The antenna equivalent circuit The radiation resistance is defined by equation 2 10 L2 R 401 Ga 2 In the equation 2 L represents the antenna variable length and is the wavelength of the received signal A is described by a i 6 where c 3 10 m s represents the speed of light and f is the frequency of the received signal The antenna works in both FM and SW bands The R and its parameters at the edges of these bands are determined in Table 1 250 Laurentiu Teodorescu Andrei Sorin Gheorghe Table 1 The radiation resistance and its parameters Band Smin MHz Snax MHz Ainin m Amax M Lmin cm Lmax cM R min Q Rmax Q FM 87 108 2 7 3 4 15 60 0 767 19 47 SW 2 3 28 5 10 5 130 4 15 60 0 0005 1 287 SW 2 3 28 5 10 5 130 4 L 60cm 0 0083 1 287 The dissipation resistance is 10 1 LTT 4 In the equation 4 d is the antenna diameter 4mm o is the metal conductivity 1 566 10 S m and is the skin depth 10 p 5 TfHolr where p 0 638 107Q m is the brass electrical resistivity 4g 4 1077H m is the permeability constant and u 1 is the relative permittivity The results are depicted in Table 2 Table 2 The dissipation r
12. oice for a competitive digital receiver The purpose of this paper is to present the design technique of a modern receiver using CMOS technology The unit is made up of an analog tuned digital CMOS AM FM SW IC 3 that integrates the complete digital receiver function from the antenna input connector to the audio output jack This IC is controlled on a serial bus by a programmable analog intensive 8 bit microcontroller 4 A 7 segment LED display allows the information to be clearly visible at night or during storms at large distances 1 5m from the receiver The keyboard and the tuning circuits are connected through a few analog interfaces to the 8 bit microcontroller Some special techniques are applied to obtain a minimum Ph D Dept of Devices Circuits and Electronic Architectures University POLITEHNICA of Bucharest Romania e mail lteodorescu arh pub ro Eng Infineon Technologies Romania SCS e mail andrei gheorghe infineon com 246 Laurentiu Teodorescu Andrei Sorin Gheorghe number of external components The adjustment procedures are missing since there are no tuning coils or trimmer capacitors The power consumption is small allowing the system to be supplied from only 2 IEC LR6 5 batteries 2 The receiver block diagram The block diagram of the receiver is shown in Fig 1 The system consists of an RF input stage Lin Ci FM Coil AM coil SW RF amplifier a CMOS receiver integrated circuit Silicon Laboratories
13. r and an easy operation Some efficient algorithms were applied to achieve the debounce function for keys and to compensate the supply voltage variations concerning the analog to digital converter reference yielding a stable code at the output of the converter A control algorithm for the display has been implemented by utilizing the time multiplexing The source code has been written and verified to be integrated into more complex projects Acknowledgement The work has been funded by the Sectorial Operational Program Human Resources Development 2007 2013 of the Ministry of European Funds through the Financial Agreement POSDRU 159 1 5 S 134398 256 Laurentiu Teodorescu Andrei Sorin Gheorghe REFERENCES 1 Regency Div I D E A Inc TR 1 The First Transistor Radio Receiver Technical Data And Service Notes Indianapolis 26 Ind USA 1955 2 D Weisman Silicon Labs Introduces the First Single Chip Digital Radio Receivers for Consumer Electronics http www reuters com article 2013 04 22 tx silicon labs idUSnBw225190a 100 BSW20130422 3 Silicon Laboratories Inc SI4844 B20 Broadcast Analog Tuning Digital Display AM FM SW Radio Receiver Austin Texas USA 2013 4 Silicon Laboratories Inc C8051F350 1 2 3 8 k ISP Flash MCU Family Austin Texas USA 2007 5 International Electrotechnical Commission Storage amp Communications May 2012 Geneva Switzerland 6 Texas Instrumen
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