/* This program written by Alastair GW0AJU.
 The program application is a an "Impedance SWR active bridge". 
 The application is intended to provide a realtime measurement 
 of the radio transmitter antenna while in operation, with the
 "Impedance SWR active bridge" as an inline SWR meter.  


  Ardunio board used = Ardiuno Uno


  date: 12th January 2016
*/


#include <math.h> // (no semicolon) 


//**********  liquid display setup  *********


#include <Wire.h> 
#include <LCD.h>
#include <LiquidCrystal_I2C.h>


#define I2C_ADDR 0x27 // <<- Add your address here.
#define Rs_pin 0
#define Rw_pin 1
#define En_pin 2
#define BACKLIGHT_PIN 3
#define D4_pin 4
#define D5_pin 5
#define D6_pin 6
#define D7_pin 7
 
LiquidCrystal_I2C lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin);








byte a[8] = {B00000,
             B01110,
             B10001,
             B10001,
             B01010,
             B01010,
             B11011,}; // character of the symbol of "ohm"




byte b[8] = {B00000,
             B00001,
             B00010,
             B00100,
             B01000,
             B10000,
             B11111,}; // character of the symbol of "angle"


byte c[8] = {B01110,
             B10001,
             B10001,
             B01110,
             B00000,
             B00000,
             B00000,}; // character of the symbol of "degrees"             
             


//**************** SWR bridge and antenna load calculations variables ****************


     long swr_forward = 0;
     long swr_reflected = 0;
     float vswr_forward = 0;
     float vswr_reflected = 0;
     float v_forward = 0;
     float v_reflected = 0;
     float swr_impedance = 0;
     float RL = 0;
     float Zin = 0;
     float swr =0;
     float ind = 0;
     float cap = 0;
     float cap_scale = 0;
     float ind_scale = 0;
     float cap_scale_t = 0;
     float ind_scale_t = 0;
     float res = 0;
     float res_load = 0;
     
//*********** transmitter power variables ************
     
     float rx_signal_level = 0;
     float rx_signal_voltage = 0;
     float tx_signal_level = 0;   
     float tx_power_output = 0;


//******** start of program code for the impedance swr active brdige ****** 








void setup()
 { 
  
  // ********* start up display messages ************  
   
   lcd.begin (20,4);
   // LCD Backlight ON
   lcd.setBacklightPin(BACKLIGHT_PIN,POSITIVE);
   lcd.setBacklight(HIGH); 
   lcd.createChar(0,a);  // ohms symbol
   lcd.createChar(1,b);  // angle symbol
   lcd.createChar(2,c);  // degrees symbol
   lcd.clear();
   lcd.home();
   lcd.setCursor(0,0);  // first line of display
   lcd.print(" Impedance SWR");
   lcd.setCursor(0,1);  // second line of display
   lcd.print(" active bridge");
   lcd.setCursor(0,2);  // third line of display 
   lcd.print(" program code by");
   lcd.setCursor(0,3);  // fourth line of display
   lcd.print(" Alastair GW0AJU");
   delay(2000);
   lcd.clear();
   lcd.home();
   lcd.setCursor(0,0);  // first line of display
   lcd.print("Transmitter power");
   lcd.setCursor(0,1);  // second line of display
   lcd.print("Standing wave ratio");
   lcd.setCursor(0,2);  // third line of display
   lcd.print("Impedance vector");
   lcd.setCursor(0,3);  // fourth line of display
   lcd.print("Transmission line");
   delay(2000);
   lcd.clear();
   lcd.home();
   RL = 50;  // start up antenna value
}








//*************  void loop ***********************


void loop()
{ 
       radio_monitor();
       delay(400);  // 400ms delay between display updates to prevent display flickering  
}








//*************** start of program code sub-routines ****************








void radio_monitor()
{
        active_load();
        tx_pwr(); 
}
        
//********** calculation processes for the impedance SWR active bridge ***************


//** calculation of the transmitter power output, SWR value and the impedance vector **








void tx_pwr()
 {
  
// ********** transmitter power output measurement **********
  
     float  tx_power_measure = analogRead(2);  // analog 2 to measure tx power output voltage   
     float  tx_signal_level = 0.0048 * tx_power_measure;
     float  tx_power_output = ((tx_signal_level * tx_signal_level) / 50) * 100;   // tx power = (v * v) / antenna
          
        lcd.home();
        lcd.setCursor(0,0);
        lcd.print("Tx = ");
        lcd.setCursor(5,0);
        lcd.print("       ");
        lcd.setCursor(5,0);
        lcd.print(tx_power_output,1);
        lcd.setCursor(11,0);
        lcd.print("Watts");  


// *** calculation of the antenna impedance match as the SWR value *********
     
        swr_forward = 0;  // reset value to zero
        swr_reflected = 0; // reset value to zero
        
        swr_forward = analogRead(0);    // swr forward voltage from impedance bridge
        swr_reflected = analogRead(1);  // swr reflected voltage from impedance bridge
        
        v_forward = 0.0048 * swr_forward; // forward swr voltage measured value
        v_reflected = 0.0048 * swr_reflected; // reverse swr voltage measured value
        
         float ratio = v_forward / v_reflected;
      // float ratio = v_reflected / v_forward;
       float swr_value = ratio; 
       
            lcd.home();
            lcd.setCursor(0,1);
            lcd.print("Swr= 1:");
            lcd.setCursor(7,1);
            lcd.print(swr_value,4);
            lcd.print("    ");


// **** calculation of the antenna as an impedance vector angle *****


             RL = swr_value * 50;  // calculation of antenna resistance, assume match to a 50ohm co-axial cable reference
       float target = 50;
       float angle = ((double)atan2(RL,target))*(180/PI); // arc tangent of y/x


            lcd.home();
            lcd.setCursor(0,2);
            lcd.print("                    ");
            lcd.setCursor(0,2);
            lcd.print("Vec= 50");
            lcd.write(byte(0));
            lcd.print(" ");
            lcd.setCursor(9,2);
            lcd.write(byte(1));
            lcd.print(" ");
            lcd.print(angle,1);
            lcd.write(byte(2));
 }     
 
//***calculate the active load of the antenna as a transmission line measurement  ***


// calculation of transmission line impedance equivelant value based of 50ohm cable reference
// characteristic impedance = SQR( inductance / capacitance )
// where cable inductance = 300nH/m and the cable capacitance = 120pF/m


void active_load()
{
  float res_load = RL;
  
  //******* capacitive loaded antenna *****
  
  if (res_load < 50)
      {
        cap = 300E-9 / ( res_load * res_load);
        cap_scale = cap * 1E12;  
    if (cap_scale <= 1000)
        {
        cap_scale_t = cap_scale;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,1);
        lcd.write(byte(0));
        lcd.print("-j");
        lcd.print(cap_scale_t,0);
        lcd.print("pF");
        }
    else if (cap_scale > 1E3 && cap_scale <= 1E6)
        { 
        cap_scale_t = cap_scale/1E3;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,1);
        lcd.write(byte(0));
        lcd.print("-j");
        lcd.print(cap_scale_t,1);
        lcd.print("nF");
        } 
      else if (cap_scale > 1E6 && cap_scale <= 1E9)
        { 
        cap_scale_t = cap_scale/1E6;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,2);
        lcd.write(byte(0));
        lcd.print("-j");
        lcd.print(cap_scale_t,2);
        lcd.print("uF");
        }
      else if (cap_scale > 1E9 && cap_scale <= 1E12)
        { 
        cap_scale_t = cap_scale/1E9;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,1);
        lcd.write(byte(0));
        lcd.print("-j");
        lcd.print(cap_scale_t,1);
        lcd.print("mF");
        }
      else if (cap_scale > 1E12)
        { 
        cap_scale_t = cap_scale/1E12;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,1);
        lcd.write(byte(0));
        lcd.print("-j");
        lcd.print(cap_scale_t,1);
        lcd.print("F");
        }
      }
      
  ///***** inductive loaded antenna ******
  
  if (res_load > 50)
     {
        ind = (res_load * res_load) * 120E-12;
        ind_scale = ind * 1E12;    
     if (ind_scale <= 1000)
        {
        ind_scale_t = ind_scale;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,1);
        lcd.write(byte(0));
        lcd.print("+j");
        lcd.print(ind_scale_t,0);
        lcd.print("pH");
        }
    else if (ind_scale > 1E3 && ind_scale <= 1E6)
        {
        ind_scale_t = ind_scale/1000;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,1);
        lcd.write(byte(0));
        lcd.print("+j");
        lcd.print(ind_scale_t,0);
        lcd.print("nH");
        }
     else if (ind_scale > 1E6 && ind_scale <= 1E9)
        {
        ind_scale_t = ind_scale/1E6;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,0);
        lcd.write(byte(0));
        lcd.print("+j");
        lcd.print(ind_scale_t,1);
        lcd.print("uH");
        }
      else if (ind_scale > 1E9 && ind_scale <= 1E12)
        {
        ind_scale_t = ind_scale/1E9;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,0);
        lcd.write(byte(0));
        lcd.print("+j");
        lcd.print(ind_scale_t,2);
        lcd.print("mH");
        }
       else if (ind_scale > 1E12)
        {
        ind_scale_t = ind_scale/1E12;
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,0);
        lcd.write(byte(0));
        lcd.print("+j");
        lcd.print(ind_scale_t,1);
        lcd.print("H");
        } 
     }
     
  if ( res_load == 50)
      {
        lcd.setCursor(0,3);  // bottom line of the display
        lcd.print("                    ");
        lcd.setCursor(0,3);
        lcd.print("Imp= ");
        lcd.print(res_load,0);
        lcd.write(byte(0));
        lcd.print(" antenna ");
      }  
 } 


//****************************  end of program code ****************************