Friday, June 27, 2014

A simple 2.4GHZ spectrum analyser with nrf24l01,character lcd and an arduino

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Arduino nrf24l01 ghz spectrum scanner

In this weekend i planned to make a simple scanner for the 2.4ghz ism band to search for interesting findings. So a simple poormans spectrum analyser was hooked up with an lcd shield (for displaying characters) and a popular nrf24l01+ module from nordic semiconductor.

This is basically a portable version of the poor mans  scanner based on nrf24l01. I added an lcd display and used the custom charecters to draw a simple bar graphs to show the signal intensities. it was a bit tricky to use the spi pins with the dfrobot keypad shield (some fuzz with the digital pin 10 which is messsed up in the shield). Using a software spi with the nrf24l01 module didn't work as expected. So i ended up bending the D10 pin on the shield :) and using hardware spi with the nrf module.

A simple video is shown below. The bars shows my wifi router. The entire spectrum is fitted in to 16 possible bars (made by custom chars) in the character lcd. Turning on a bluetooth device shows random spots over the entire channels (hopping) and microwaves ovens appears all over the spectrum at lunchtimes!

end

Source code and wiring

Connect the nrf module to the spi pins (10,11,12,13)  and A1 (for CE) and an lcd to pin 8,9,4,5,6,7 

 #include <SPI.h>  
 #include <LiquidCrystal.h>  
 // The LCD is conected to pins 8, 9, 4, 5, 6, 7  
 LiquidCrystal lcd(8, 9, 4, 5, 6, 7);  
 byte minibars[8][8];  
 //credits to Poor Man's Wireless 2.4GHz Scanner  
 // credits to all others  
 // uses an nRF24L01p connected to an Arduino  
 //   
 // Cables are:  
 //   SS    -> 10  
 //   MOSI   -> 11  
 //   MISO   -> 12  
 //   SCK   -> 13  
 //   
 // and CE    -> A1  
 //  
 // created March 2011 by Rolf Henkel  
 //  
 #define CE A1  
 // Array to hold Channel data  
 #define CHANNELS 64  
 int channel[CHANNELS];  
 // nRF24L01P registers we need  
 #define _NRF24_CONFIG   0x00  
 #define _NRF24_EN_AA    0x01  
 #define _NRF24_RF_CH    0x05  
 #define _NRF24_RF_SETUP  0x06  
 #define _NRF24_RPD     0x09  
 //SoftSPI<SOFT_SPI_MISO_PIN, SOFT_SPI_MOSI_PIN, SOFT_SPI_SCK_PIN, SPI_MODE> spi;  
 // get the value of a nRF24L01p register  
 byte getRegister(byte r)  
 {  
  byte c;  
  PORTB &=~_BV(2); //D10  
  //PORTC &=~_BV(1); //analogue 1 as SS  
  c = SPI.transfer(r&0x1F);  
  c = SPI.transfer(0);   
  PORTB |= _BV(2);  
  //PORTC |= _BV(1); //analogue 1 as SS  
  return(c);  
 }  
 // set the value of a nRF24L01p register  
 void setRegister(byte r, byte v)  
 {  
  PORTB &=~_BV(2);  
  //PORTC &=~_BV(1);  
  SPI.transfer((r&0x1F)|0x20);  
  SPI.transfer(v);  
  PORTB |= _BV(2);  
  //PORTC |= _BV(1);  
 }  
 // power up the nRF24L01p chip  
 void powerUp(void)  
 {  
  setRegister(_NRF24_CONFIG,getRegister(_NRF24_CONFIG)|0x02);  
  delayMicroseconds(130);  
 }  
 // switch nRF24L01p off  
 void powerDown(void)  
 {  
  setRegister(_NRF24_CONFIG,getRegister(_NRF24_CONFIG)&~0x02);  
 }  
 // enable RX   
 void enable(void)  
 {  
   PORTC |= _BV(1);  
 }  
 // disable RX  
 void disable(void)  
 {  
   PORTC &=~_BV(1);  
 }  
 // setup RX-Mode of nRF24L01p  
 void setRX(void)  
 {  
  setRegister(_NRF24_CONFIG,getRegister(_NRF24_CONFIG)|0x01);  
  enable();  
  // this is slightly shorter than  
  // the recommended delay of 130 usec  
  // - but it works for me and speeds things up a little...  
  delayMicroseconds(100);  
 }  
 // scanning all channels in the 2.4GHz band  
 void scanChannels(void)  
 {  
  disable();  
  for( int j=0 ; j<100 ; j++)  
  {  
   for( int i=0 ; i<CHANNELS ; i++)  
   {  
    // select a new channel  
    setRegister(_NRF24_RF_CH,(128*i)/CHANNELS);  
    // switch on RX  
    setRX();  
    // wait enough for RX-things to settle  
    delayMicroseconds(40);  
    // this is actually the point where the RPD-flag  
    // is set, when CE goes low  
    disable();  
    // read out RPD flag; set to 1 if   
    // received power > -64dBm  
    if( getRegister(_NRF24_RPD)>0 )  channel[i]++;  
   }  
  }  
 }  
 void outputChannels(void)  
 {  
  int norm = 0;  
  for( int i=0 ; i<CHANNELS ; i++)  
   if( channel[i]>norm ) norm = channel[i];  
  for( int i=0 ; i<CHANNELS ; i++)  
  {  
   int pos;  
   if( norm!=0 ) pos = (channel[i]*10)/norm;  
   else     pos = 0;  
   if( pos==0 && channel[i]>0 ) pos++;  
   if( pos>8 ) pos = 8;  
   plot_minibars(i/4, pos*2);  
   channel[i] = 0;  
  }  
 }  
 void setup()  
 {  
   // Built the characters for bars.  
  for (int j=0; j<=7; j++)   
  {  
   for (int i=0; i<=7; i++)  
   {  
    if (i<=j)  
    { minibars[j][7-i] = B01110;}    
    else  
    { minibars[j][7-i] = 0;}  
   }  
  }   
  for (int i=0; i<=7;i++)  
  {  
   lcd.createChar(i, minibars[i]);  
  }  
  lcd.begin(16, 2);     
  for (int j=0; j<=7;j++)  
  {  
   lcd.setCursor(j, 0);  
   lcd.write(j);  
   lcd.setCursor(j, 1);  
   lcd.write(7);   
  }  
  // Setup SPI  
  SPI.begin();  
  SPI.setDataMode(SPI_MODE0);  
  SPI.setClockDivider(SPI_CLOCK_DIV2);  
  SPI.setBitOrder(MSBFIRST);  
  // Activate Chip Enable  
  pinMode(CE,OUTPUT);  
  disable();  
  // now start receiver  
  powerUp();  
  // switch off Shockburst  
  setRegister(_NRF24_EN_AA,0x0);  
  // make sure RF-section is set properly   
  // - just write default value...   
  setRegister(_NRF24_RF_SETUP,0x0F);   
  }  
 void loop()   
 {   
  scanChannels();   
  outputChannels();   
 }  
 void plot_minibars(int location, int strngth)  
 {  
  if (strngth>7)  
  {  
   lcd.setCursor(location, 1);  
   lcd.write(7);  
   lcd.setCursor(location, 0);  
   lcd.write(strngth-8);    
  }  
  else  
  {  
   lcd.setCursor(location, 1);  
   lcd.write(strngth);  
   lcd.setCursor(location, 0);  
   lcd.write(32);    
  }  
 }  

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