Intelligent FM receiver

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Nowadays  due to the ever growing number of radio stations  in the FM band  (between 88 and 108 mhz) it is more and more difficult to find the radio station you want  to listen .On top of that you want to listen different radio stations  dependig on the time of the day , surprinsingly It is not easy to find a receiver being able to switch automatically from different frequencies according to the time.Thanks to microcontroller and arduino it is not difficult to revamp an old FM receiver to do the job

The schematic of the receiver to revamp toshiba_circuit
You have to locate the IC which is doing the frequency conversion .In our case it was  a TA2003 from Toshiba .You have to cut the trace  as indicatde above so  to be able to control the local frequency from  an oscillator that will be set up .

The  local oscillator  can use one transistor followed by another one which acts as a buffer  .You will have to build as many oscillators as you want to receive radio station .Each oscillator is fed by the microcontroler  2 transistor schematic
The design can be quite compact as shown and it worked .! However to stay on line  with the various integrated circuits available on the market we switched to an integrated oscillator much more compact and which only  need  a coil to produce a signal anywhere in the 50 to 600 mhz range  2 transistor layout

The oscillator  use an integrated circuit from MAXIM , the max 2606 .This circuit is able to operate  from 70 to 150 mhz which is perfect for our case  .The intermediate frequency being around 10 mhz  the oscillator has to work from 78 to 95 mhz  or from98 to 125 mhz .It is up to you to choose  .

You will have to put as many potentiometer s that the number of channel  you want to listen .Let's say you want to listen 3 FM radio stations you put 3 potentiometers .To cover the full range given by Maxim the voltage has to go from 0.4 volt up to 2.4 volts

The control of the various oscillators is done by  the arduino according to the schematic below .It is a complete board being linked to the external world through a standard RS232 interaface (DB9) .an ATMEGA 328 with the Arduino bootloader  is more than enough .The arduino receives time information  from a DS1302 circuit  and it remains 9 pins to  connect as many potentiometers .You will notice the 2nF capacitor and the 10k resistor going on pin 1 of  ATMEG328 this set up enabling the capability to program the arduino using the standard procedure  thanks to the DTR sigal taken the th DB9 connector
arduino control schematic

The real time clock schematic is very standard and use a DS1302 according to  outline below .A lithium battery keep the circuit working when no power is available
ds1302 schematic

Everything is done on  a veroboard circuit  and packed inside the radio receiver  being revamped  as shown on the photo below .There is no problem to find a room in these old reveiver ! .On the left of the image you see the arduino board with the DS1302 real time clock  .In th bottom of the image  the oscillaor board with the MAX2606 appear .The ouput of this circuit is sent directement through a small coax to the Toshiba TA2003
overall arduino ds1302 max2606

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Ok when al is done you will have to  adjust the different channels you want to listen by adjusting the different potentiometers .When this is  done  programming the  arduino is the last thing to do .

AN example of program is shown below  in our case where we wanted to listen 3 channels switching from one to another at various time of the day .Thanks to the possibility of arduino board you can program much more complicated schedule  ! .The program take advantage of the DS1302 library which has to de downloaded from the link indicated  on top of the program

it should be noted that a manual command has been implemented using a potentiomer linked to  pin 0 .Depending on the analog value read the receiver is  tuned on  each of the selected channel and can stay as long as you want  or  switch automatically depending on the action take by the program
/* DS1302_Serial_Easy (C)2010 Henning Karlsen

// I assume you know how to connect the DS1302.
// DS1302:  CE pin    -> Arduino Digital 2
//          I/O pin   -> Arduino Digital 3
//          SCLK pin  -> Arduino Digital 4

// revision  10/12/2010, 16/12/2010 ,17/12/2010,26/12/2010
// 13/3/2011
#include <DS1302.h>

DS1302 rtc(2, 3, 4);    // Init the DS1302
Time t;   // Init a Time-data structure

// variables will change:

// radio channel assignement
#define n_radio_station         4   // number of radio stations
#define france_culture        13    // name of station  , pin number
#define radio_classic           12
#define france_inter        10     // name of station  , pin number
#define bfm                     11

#define first_canal              13   // pin use for first channel

// command buttons
# define analogInPin     0     // pin used for manual control using a  potentiometer

int sector_value=1024/(n_radio_station+1);

// other variables
char* instant;
int xx;
int heure ,minute ;
int sensorValue = 0;        // value read from the pot
int channel_to_activate,previous_channel;

void setup() {
  // Set the clock to run-mode, and disable the write protection
  // set charging supercap
  // Setup Serial connection
  // The following lines can be commented out to use the values already stored in the DS1302
  //rtc.setDOW(FRIDAY);        // Set Day-of-Week to FRIDAY
  //rtc.setTime(12, 0, 0);     // Set the time to 12:00:00 (24hr format)
  //rtc.setDate(6, 8, 2010);   // Set the date to August 6th, 2010

void loop(){

  sensorValue = analogRead(analogInPin); 
  sensorValue=sensorValue/sector_value;  // sensorValue  vary now  from 0 to 3 for 4 radio station

  Serial.print("sensor value=");
  if (sensorValue==0)    // case of atomatic mode
    Serial.println(instant);// Send time

    // Serial.println(heure,DEC);
    //  to be modified depending on radio station to listen
    //check_channel(france_inter,2,0,3,10);   // name of fm radio station ,start hour start minute,min depart , h end minute end

    // ***********************************************************************************
    delay (1000);// Wait one second before repeating :)
  else    // case of manual mode
    select_channel(france_inter,sensorValue);// activate the channel selected by the potentiometer



void check_channel(int canal,int h_depart,int m_depart,int h_fin, int m_fin){
  int hdepart,hfin,hactu;
  hactu=60*heure+minute; //
  if  (hactu>=hdepart  && hactu<=hfin )
    //Serial.println(" actif");
    //Serial.println(" non actif");
 void activate_channel()
 {if (previous_channel!=channel_to_activate)
   digitalWrite(channel_to_activate, HIGH);
   Serial.print(channel_to_activate);    Serial.println(" est actif");

void select_channel(int canal,int i){
  int j;
  //Serial.println("active en manu" );
  //Serial.print("canal /i ");Serial.print(j);Serial.print("/");Serial.println(i);
  if (j==i){
    digitalWrite(canal, HIGH);
    //Serial.println ("canal active "); 
    digitalWrite(canal, LOW); 

  // delay(1000);