Bit Angle Modulation (BAM) in a PIC

[Mike, K8LH]

Unfortunately varying duty cycle incrementally does not produce linear changes in brightness.

I use brightness level correction in the form of a "gamma" array which contains a smaller set of duty cycle values, which produce linear changes in brightness, spanning the larger PWM duty cycle range. For example, the C program below for a 12F1822 uses the PWM module for a very smooth fading output with 64 brightness corrected levels using duty cycle values in the 64 element "gamma" array which span the 256 step PWM duty cycle range. Unfortunately, I'm not sure how you would implement something like this in PBP.

Good luck on your project... Cheerful regards, Mike

   #include <system.h>

   #pragma DATA _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _MCLRE_ON
   #pragma DATA _CONFIG2, _LVP_OFF & _PLLEN_OFF

   #pragma CLOCK_FREQ 8000000   // 8-MHz INTOSC

   #define r08 const rom unsigned char


   r08 gamma[] = {  0,  1,  2,  2,  2,  2,  3,  3,  3,  4,
                    4,  5,  5,  6,  6,  7,  8,  8,  9, 10,
                   11, 12, 13, 14, 15, 17, 18, 20, 21, 23,
                   25, 27, 29, 31, 34, 36, 39, 42, 45, 49,
                   53, 57, 61, 65, 70, 75, 81, 87, 93,100,
                  107,114,123,131,140,150,161,172,183,196,
                  209,224,239,255 };

   void main()
   { ansela = 0;                // make pins digital
     trisa = 0b00000000;        // porta all outputs
     porta = 0;                 // all output latches low
     osccon = 0b01110010;       // initialize 8-MHz INTOSC
     while(!oscstat.HFIOFS);    // wait until OSC stable

     ccp1con = 0b00001100;      // pwm mode, p1a active hi
     ccpr1l = 0;                // 0% duty cycle initially
     pr2 = 255;                 //
     t2con = 1<<TMR2ON;         // pre 1, post 1, 7812.5 Hz

     while(1)                   //
     { static char duty = 32;   // start at ~50% brightness
       while(duty < 63)         // fade up to 100%
       { ccpr1l = gamma[duty++];
         delay_ms(30);          // over period of ~1 sec
       }                        //

       while(duty > 32)         // fade down to ~50%
       { ccpr1l = gamma[duty--];
         delay_ms(30);          // over period of ~1 sec
       }                        //
       delay_ms(100);           // pause at 50% brightness
     }                          //
   }

Here's another example using 64 brightness level steps on a 20 LED Charlieplexed matrix with 8-bit (256 level) BAM modulation. While only one LED is being faded in the video, all twenty LEDs could be faded at the same time.