agc.cpp

// soft AGC and S meter display by Loftur E. Jónasson TF3LJ/VE2LJX 6/14
//

#include <Metro.h>
#include <Audio.h>

#include <Adafruit_GFX.h>        // LCD Core graphics library
//#include <Adafruit_QDTech.h>     // 1.8" TFT Module using Samsung S6D02A1 chip
#include <Adafruit_ST7735.h> // Hardware-specific library

//extern Adafruit_QDTech tft;
extern Adafruit_ST7735 tft;

extern AudioMixer4     Audioselector_I;      // Summer (add inputs)
extern AudioMixer4     Audioselector_Q;      // Summer (add inputs)
extern AudioAnalyzePeak       AGCpeak;  // Measure Audio Peak for AGC use
extern AudioAnalyzePeak       Smeter;   // Measure Audio Peak for S meter

Metro l_ms =   Metro(1);         // Set up a 1ms Metro
Metro lcd_upd2=Metro(500);       // Set up a Metro for S-meter display

float       sample[10];        // A ringbuffer of samples (has to be larger than AGCattack)

float        AGCgain=1;         // Initial AGC gain. 1 = unity gain, 32768.0 max, 0.00004 min
#define       AGCMAX  2
float AGCnomVal = 0.5; // Nominal Output (32768 max)
const int32_t AGCattack = 2;     // AGC Hang time (milliseconds) before reducing gain
const int32_t AGChang   = 30;   // AGC Hang time before increasing gain
const double  AGCslope  = 1.05;   // Relative gain change


//
// Automatic Gain Control function
//
void agc(void)
{
  static uint8_t i;
  static uint16_t hangtimer;
  uint8_t j,k;
  float s_sample;  // Raw signal strength (max per 1ms)
  float samp;      // AGC feedback loop sample strength (max per 1ms)
  float temp;      // yeah, just a temp value
  float uv, dbuv, s, v, dbm;// microvolts, db-microvolts, s-units, volts, dbm, sold = old S-meter value, deltas = abs difference between sold and s
  char string[80];   // print format stuff
  
  if (l_ms.check() == 1)
  {
    // R this code is probably broken with the new audio library
    // Collect S-meter data
    if (Smeter.available()) s_sample = Smeter.read(); // Highest sample within 1 millisecond
    // AGC: Collect current 1ms peak at output and feed to a ringbuffer
    sample[i++] = samp = AGCpeak.read();

    if (i >= AGCattack) i=0;
    
    // Check if we need to reduce gain
    for(j=0,k=0;j<AGCattack;j++)
    {
      if (sample[j] > AGCnomVal) k++;
    }
    
    // We need to reduce gain
    if ((k == AGCattack) || ((k>0) && (hangtimer>=AGChang)))  // Activate AGCattack
    {
      // find largest value
      temp = 0;
      for(j=0;j<AGCattack;j++)
      {
        if (sample[j]> temp) temp = sample[j];
      }
      
      // Instant reduction to appropriate value
      AGCgain = AGCgain * AGCnomVal/temp;
      // Reset hang timer
      hangtimer = 0;
    }
    
    // Increment hangtimer while level is lower than nominal
    else if(samp < AGCnomVal) hangtimer++; 
      
    if (hangtimer >= AGChang)  // We need to ramp up the gain
    {
      Audioselector_I.gain(0, AGCgain * AGCslope);
      Audioselector_Q.gain(0, AGCgain * AGCslope);
    }
    
    if (AGCgain > AGCMAX) AGCgain=AGCMAX; // limit the gain  
    
    Audioselector_I.gain(0,AGCgain);       // Adjust AGC gain
    Audioselector_Q.gain(0,AGCgain);       // Adjust AGC gain   
    //
    // Print stuff to LCD 
    //
    if (lcd_upd2.check() == 1) 
    {
      // Calculate S units. 50uV = S9
     
      uv = s_sample*1000;        // microvolts, roughly calibrated
      v = s_sample / 1000;
      dbm = 10 * log10 (v*v*20); 
      if (v==0) {dbm=-143;};
      dbuv = 20.0*log10(uv);
      s = 1.0 + (14.0 + dbuv)/6.0;
      
      if (s <0.0) s=0.0;
      if (s>9.0)
      {
        dbuv = dbuv - 34.0;
        s = 9.0;
      }
      else dbuv = 0;
      // Print S units
      tft.fillRect(0, 105, 70, 7,ST7735_BLACK);
      tft.setCursor(0, 105);
      if (dbuv == 0) sprintf(string,"S:%1.0f",s);
      else {
        sprintf(string,"S:9+%02.0f dB",dbuv);
        
        }
      tft.print(string);
      tft.fillRect(100,105, 50, 7,ST7735_BLACK);
      tft.setCursor(100,105);
      sprintf(string,"%04.0f dBm",dbm);
      tft.print(string);
 
      if(0)  // Debug stuff
      {
        // Print AGC loop parameters
        tft.fillRect(0, 105, 159, 7,ST7735_BLACK);
        tft.setCursor(0, 105);
        sprintf(string,"pk:%f g:%f",Smeter.read(), AGCgain);
        tft.print(string);
      }
    }
  }  
}