NRF Scanner

nrfscanner.ino

#include <SPI.h>

// Poor Man's Wireless 2.4GHz Scanner
//
// uses an nRF24L01p connected to an Arduino
// 
// Cables are:
//     MOSI     -> 11
//     MISO     -> 12
//     SCK      -> 13
//     CSN      -> 7
//     CE       -> 8
// 
//
// created March 2011 by Rolf Henkel
//

#define CE  8

// Array to hold Channel data
#define CHANNELS  128
int channel[CHANNELS];

// greyscale mapping 
int  line;
char grey[] = " .:-=+*aRW";

// 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

// get the value of a nRF24L01p register
byte getRegister(byte r)
{
  byte c;
  
  PORTB &=~_BV(2);
  c = SPI.transfer(r&0x1F);
  c = SPI.transfer(0);  
  PORTB |= _BV(2);

  return(c);
}

// set the value of a nRF24L01p register
void setRegister(byte r, byte v)
{
  PORTB &=~_BV(2);
  SPI.transfer((r&0x1F)|0x20);
  SPI.transfer(v);
  PORTB |= _BV(2);
}
  
// 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)
{
    PORTB |= _BV(1);
}

// disable RX
void disable(void)
{
    PORTB &=~_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<200  ; 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]++;
    }
  }
}

// outputs channel data as a simple grey map
void outputChannels(void)
{
  int norm = 0;
  
  // find the maximal count in channel array
  for( int i=0 ; i<CHANNELS ; i++)
    if( channel[i]>norm ) norm = channel[i];
    
  // now output the data
  Serial.print('|');
  for( int i=0 ; i<CHANNELS ; i++)
  {
    int pos;
    
    // calculate grey value position
    if( norm!=0 ) pos = (channel[i]*10)/norm;
    else          pos = 0;
    
    // boost low values
    if( pos==0 && channel[i]>0 ) pos++;
    
    // clamp large values
    if( pos>9 ) pos = 9;
   
    // print it out
    Serial.print(grey[pos]);
    channel[i] = 0;
  }
  
  // indicate overall power
  Serial.print("| ");
  Serial.println(norm);
}

// give a visual reference between WLAN-channels and displayed data
void printChannels(void)
{
  // output approximate positions of WLAN-channels
  Serial.println("                                                                                                     1         1         1");
  Serial.println(" 0         1         2         3         4         5         6         7         8         9         0         1         2");
  Serial.println(" 01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567");
  Serial.println(">      1 2  3 4  5  6 7 8  9 10 11 12 13  14                     <");
}

void setup()
{
  Serial.begin(57600);
  
  Serial.println("Starting Poor Man's Wireless 2.4GHz Scanner ...");
  Serial.println();

  // Channel Layout
  // 0         1         2         3         4         5         6
  // 0123456789012345678901234567890123456789012345678901234567890123
  //       1 2  3 4  5  6 7 8  9 10 11 12 13  14                     | 
  //
  Serial.println("Channel Layout");
  printChannels();
  
  // 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); 
  
  // reset line counter
  line = 0;
}

void loop() 
{ 
  // do the scan
  scanChannels();
  
  // output the result
  outputChannels();
  
  // output WLAN-channel reference every 12th line
  if( line++>12 )
  {
    printChannels();
    line = 0;
  }
}