RDS/RBDS decoder with optional FM stereo receiver.

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This project supports both RDS (Europe) and RBDS (USA) Tuner FM band 88..108 MhZ (Europe and USA.)

You can choose between a 4x20 character LCD or a smaller graphical LCD to display data. A simple  RS232 interface can also be used.

A 4x20 character LCD module will display these:

  • 1st row: Station name (PS), Quality, Program Identification (PI), Traffic Program (TP) and Announcement (TA)
  • 2nd row: Time and Date (CT)
  • 3rd row: Radio Text Line A (RT) 64 scrolling characters.
  • 4th row: Radio Text Line A (RT) 64 scrolling characters.

All major parts are available from our online shop.

Schematic & pcb (Eagle 4.11e), hex file available. Last updated on December 12, 2007.

Circuit explanation

The schematic consists of two major subcircuits:

If you want to build this decoder into an existing tuner, then you won't need to rebuild the tuner part of the circuit. All you need to do then is to look for an MPX-signal in your existing tuner. This is usually found before the stereo decoder chip. This MPX signal must then be fed to the TDA7330 through a 47nF capacitor.

The circuit needs a couple of seconds of valid RDS/RBDS data before driving the LCD.

Quality indicator: a stable arrow (first row on the LCD) means the reception is good. Blinking arrows however indicate no valid RDS/RBDS data is being processed (signal too weak or station transmits no RDS/RBDS data.)

Digital tuning and volume control: the joystick gives us to have full control over the circuit. Last values are stored and reloaded on boot.

You'll have to choose a 4x20 character LCD or a smaller graphical LCD to display data. The smaller graphical LCD is best suited for portable applications, whereas the larger 4x20 character LCD is best for fixed receivers (f.e. in your car). Which display is driven can be chosen when booting: joystick-left for the 4x20 and joystick-right for the smaller LCD.

The RS232 interface also shows all decoded data properly (see the screenshot below.)

 

RDS decoder:
TDA7330   RDS/RBDS decoder chip. Needs an MPX input in order to decode RDS/RBDS data.
PIC18F452-I/L PLCC   This Microchip PIC microcontroller does most of the work: it looks for valid RDS data, then drives the LCD.
Graphical LCD   Nice little graphical LCD  LPH7779 (Nokia 3310 LCD) Low power and best for portable use. Contrast adjustment by pressing volume up or volume down whilst booting.
LCD Module 4x20   Standard 4-lines x 20-characters LCD module. Best choice for fixed receivers.
FM stereo tuner:
TDA7021T   FM Tuner with MPX output. Some handmade coils are needed (more info about how to make these below.)
TDA7040T   Philips PLL Stereo decoder. Needs only a couple of external components.
TDA7050T   Low power stereo headphone amplifier. Small package and low power but still good quality.
Controls   With the micro joystick, there are 5 user controls available. Two for volume (up & down) , tuning (left & right) , save preset (push).
MCP41010-I/SN   256-step 10k SPI digital potentiometer for tuning. A multiturn potentiometer is a (more expensive) alternative.
MCP42010-I/P Dual 256-step 10k SPI digital potentiometer for volume control. Replaces a double stereo potentiometer.

 

All coils use 0,5mm diameter coated copper wire and measure 5mm in diameter.

 

Schematics: (eagle-file can be downloaded below.)

Full resolution image (GIF format).

Bill of Materials (Parts List:)

 

Main connections:

 

 
SPI & RDS/RBDS PIC 18F452-I/L   CONTROLS PIC 18F452-I/L  

LCD  4x20

 PIC 18F452-I/L   LCD-LPH7779 PIC 18F452-I/L
                     
 RBDS RDCL  RE0, pin9    Volume Up  RA0, pin3    1 - GND      1 - VDD  
 RBDS RDDA  RE1, pin10    Volume Down  RA1, pin4    2 - VDD      2 - SCLK  RD5, pin31
       Tuning Up (right)  RA2, pin5    3 - contrast      3 - SDA  RD4, pin30
 SI potmeters  RC0, pin16    Tuning Down (left)  RA3, pin6    4 - RS  RB1, pin37    4 - D/C  RD1, pin22
 SCK potmeters  RC1, pin18    Enter  RA4, pin7    5 - RW  RB2, pin38    5 - CS  RD3, pin24
 !CS volume  RC2, pin19          6 - Enable  RB3, pin39    6 - GND  
 !CS tuning  RC3, pin20          11 - D4  RB4, pin41    7 - VOUT  
             12 - D5  RB5, pin42    8 - RES  RD2, pin23
             13 - D6  RB6, pin43      
             14 - D7  RB7, pin44      
                     

 

 

Downloads: right-click & save as

 
  WARNING: may not be duplicated for any commercial use whatsoever without explicit consent from the author (c) Michel Bavin, TechDesign Electronics.
 

 Schematic:

  • 021v05.sch (Eagle 4.11e), May 20, 2006.
  • eagle_lbr3.zip (Important: copy these to your \eagle\lbr directory). Includes these libraries: dig_pot, lph7779, pic18f4x2, tact-smt, tda, varicap.

 
 PCB:

 
 PIC Hex file: (to program the PIC)
  • 021_v21.HEX December 12, 2007. (combined 4x20 Character LCD module and Graphical LCD module version)
 
 Bootloader PIC Hex file: 18F452_hs20.HEX (only needed for development)
 PIC Source Code: not released, but you can buy a license on this Products page.

 

Info & datasheet:
TDA7330 DIL-20.
PIC18F452-I/L PLCC44.
Graphic LCD module type LPH7779 (NOKIA 3310 LCD) 48*84 pixels and its integrated controller PCD8544.
LCD Module 4x20.
TDA7021T SO-8. FM tuner.
TDA7040T SO-8. Stereo decoder.
TDA7050T SO-8. Headphone amp.
MCP41010-I/SN SO-8. Single digital potmeter.
MCP42010-I/P DIL-14. Dual digital potmeter.
 

Screenshots:

RS232 interface

PCB Layout

   Nokia 3310 LCD

 

 

Tools:

Check out our development tools page.

The PIC code was made with the PCWH CCS compiler ($425,-); you can install Microchip's MPLAB IDE (click on the link and you can get it for free) with it to get things running smoothly.

Programming of the PIC was done with the excellent Tiny PIC bootloader, through the RC6 & RC7 pins. However you will need a regular PIC programmer to write the PIC the first time with...

Eagle 4.11e was used for the schematic & PCB layout. 

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