Bit Angle Modulation (BAM) in a PIC

[JimAvanti]

I notice this is an old thread (Starting in 2009 with the last post in 2011). I downloaded Darrel Taylor's BIBAM ver 1.1 and had it working great with a 16f690.
I am now trying it on a 18f14k22 and I can't get it working at all. From what I am reading it should work with the 18F's. I am trying to control 9 outputs (3 RGB LEDs). The 16f690 is too slow @8MHz

Does anyone know if there are any issues using this with the 18f14k22 or if there is an updated BIBAM available?
I am getting assembly errors when I try to compile: Symbol not previously defines (_VarIn), Missing arguments.

Jim

[Darrel Taylor]

Hi Jim,

It should work with the 14K22.

That error can only be generated by a BAM_PIN statement.

Make sure it looks something like this ...

BAM_PIN (PORTB,0, Duty1)

Note the comma between PORTB and 0.
Duty1 should be a BYTE var.

Make sure the designated pins are available.
The 14K22 only has RA0-RA5, RB4-RB7 and RC0-RC7

[JimAvanti]

Darrel,
I don't know what I did, but I got it to work. The code was working on the 16f690. The ports are the same on the 18f14k22 so that error should not have been there.

Anyway, I swiched to the 18f14k22 because I am trying to control 9 ports (3 RGB LEDs) and the Ramps up/down were not smooth at all on the 16f690. I was hoping the speed from 8MHz to 16MHz would fix the problem, but it didn't.

I just made a copy of the program and removed all the BIBAM code and replaced it with PWM statements (One for each of the 9 ports with a cycle of 1 and no pause). It works smooth and looks good, except the LED's are not quite as bright since they are actally taking turns being on, but they show no visible flicker.

If I could just get the BIBAM to work as smoothly. I must be doing something wrong. I am controling all 9 LED ports directly from the micro. I did try using transistors, but it made no difference.

I will keep trying, but I am running out of ideas.

Jim

[Darrel Taylor]

What does the BAM_INFO report?

Are you using the Cylon example, or something you wrote?

[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.

[JimAvanti]

It is something I am writing. I was assuming that the duty in the BIBAM routine was directly related to the brightness level so that a loop from 0 to 255 should be a smooth increase in brightness. All I am doing right now is fading colors up and down to smoothly blend colors together. I will play with it a bit more next week.
Thanks,
Jim