Linearizing an LED for 800 pwm steps'?

[HankMcSpank]

Hiya,

Long time no code!

I'm wanting to use Mike, K8LH 'Just Basic' code to generate values towards linerarizing an LED for PWM ...what Mike has done is great & & more or less ideal for my needs, but to save a bit of post editing for use with my PIC of choice, I ideally seek a way of having the code place a DW on the front of every line.

Mike wrote it in standard basic, but I'm not familiar with syntax (besides I'm very rusty with coding now!) & hoped that someone could quickly edit the code to place a DW at the front of all the outputted lines.

Here's Mike's code that I've modified a little already...

'  Maxim Gamma Correction Algorithm
'
'  JustBASIC (free) interpreter
'
Input "Gamma array size: "; arraysize
Input " Total PWM steps: "; width
Input "Gamma correction: "; gamma       ' maxim uses 2.5

FOR index = 0 to arraysize-1
  dcyval = INT(width*(((width/arraysize*(index+1))/width)^gamma))
  if(index = 0) then
    PRINT
  else
    if(index MOD 34 = 0) then 'this dictates how many values per line
      PRINT " " 'this puts no comma at the end of the line
    else
      PRINT ","; 'this puts commas in between the values
    end if
  end if
  if(dcyval < 100) then print " ";
  if(dcyval < 10) then print " ";
  PRINT dcyval;
NEXT index
PRINT

REM CLOSE

The above gernerates output like this

Gamma array size: 255
 Total PWM steps: 1023
Gamma correction: 2

  0,  0,  0,  0,  0,  0,  0,  1,  1,  1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  8,  9,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18
 19, 20, 21, 22, 23, 25, 26, 27, 29, 30, 31, 33, 34, 36, 37, 39, 40, 42, 44, 45, 47, 49, 51, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72
 74, 77, 79, 81, 83, 86, 88, 90, 93, 95, 98,100,103,105,108,111,113,116,119,121,124,127,130,133,136,139,141,144,148,151,154,157,160,163
166,170,173,176,180,183,186,190,193,197,200,204,208,211,215,219,222,226,230,234,238,241,245,249,253,257,261,265,269,274,278,282,286,290
295,299,303,308,312,317,321,326,330,335,339,344,349,353,358,363,368,373,377,382,387,392,397,402,407,412,417,423,428,433,438,444,449,454
460,465,470,476,481,487,492,498,504,509,515,521,526,532,538,544,550,556,561,567,573,579,586,592,598,604,610,616,623,629,635,641,648,654
661,667,674,680,687,693,700,707,713,720,727,734,740,747,754,761,768,775,782,789,796,803,810,817,825,832,839,846,854,861,868,876,883,891
898,906,913,921,928,936,944,952,959,967,975,983,991,999,1007,1014,1023

whereas what I seek is a DW at the front of each line like thus...

Gamma array size: 255
 Total PWM steps: 1023
Gamma correction: 2

DW  0,  0,  0,  0,  0,  0,  0,  1,  1,  1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  8,  9,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18
DW 19, 20, 21, 22, 23, 25, 26, 27, 29, 30, 31, 33, 34, 36, 37, 39, 40, 42, 44, 45, 47, 49, 51, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72
DW 74, 77, 79, 81, 83, 86, 88, 90, 93, 95, 98,100,103,105,108,111,113,116,119,121,124,127,130,133,136,139,141,144,148,151,154,157,160,163
DW 166,170,173,176,180,183,186,190,193,197,200,204,208,211,215,219,222,226,230,234,238,241,245,249,253,257,261,265,269,274,278,282,286,290
DW 295,299,303,308,312,317,321,326,330,335,339,344,349,353,358,363,368,373,377,382,387,392,397,402,407,412,417,423,428,433,438,444,449,454
DW 460,465,470,476,481,487,492,498,504,509,515,521,526,532,538,544,550,556,561,567,573,579,586,592,598,604,610,616,623,629,635,641,648,654
DW 661,667,674,680,687,693,700,707,713,720,727,734,740,747,754,761,768,775,782,789,796,803,810,817,825,832,839,846,854,861,868,876,883,891
DW 898,906,913,921,928,936,944,952,959,967,975,983,991,999,1007,1014,1023

Can anyone help me out here?

(the code runs with this http://www.justbasic.com/download.html )

[Demon]

Try this modification (untested):

...
  if(index = 0) then
    PRINT
    PRINT "DW ";
  else
    if(index MOD 34 = 0) then 'this dictates how many values per line
      PRINT " " 'this puts no comma at the end of the line
      PRINT "DW ";
    else
...

Robert

[HankMcSpank]

Hi, that worked a treat, here's the output after modifying with your snippets...

Gamma array size: 255
 Total PWM steps: 1023
Gamma correction: 2

DW   0,  0,  0,  0,  0,  0,  0,  1,  1,  1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  8,  9,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18
DW  19, 20, 21, 22, 23, 25, 26, 27, 29, 30, 31, 33, 34, 36, 37, 39, 40, 42, 44, 45, 47, 49, 51, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72
DW  74, 77, 79, 81, 83, 86, 88, 90, 93, 95, 98,100,103,105,108,111,113,116,119,121,124,127,130,133,136,139,141,144,148,151,154,157,160,163
DW 166,170,173,176,180,183,186,190,193,197,200,204,208,211,215,219,222,226,230,234,238,241,245,249,253,257,261,265,269,274,278,282,286,290
DW 295,299,303,308,312,317,321,326,330,335,339,344,349,353,358,363,368,373,377,382,387,392,397,402,407,412,417,423,428,433,438,444,449,454
DW 460,465,470,476,481,487,492,498,504,509,515,521,526,532,538,544,550,556,561,567,573,579,586,592,598,604,610,616,623,629,635,641,648,654
DW 661,667,674,680,687,693,700,707,713,720,727,734,740,747,754,761,768,775,782,789,796,803,810,817,825,832,839,846,854,861,868,876,883,891
DW 898,906,913,921,928,936,944,952,959,967,975,983,991,999,1007,1014,1023

Many thanks....this will save me a lot of time experimenting with different gamma values with the LUT going into the PIC

[Mike, K8LH]

Hi Hank,

Sorry for the late reply. Glad you figured it out. Another slightly more recent version of that Gamma Table program is listed below.

Gamma values of 1.7 to 1.9 worked good for me but it's very much dependent on your LEDs, voltage, hardware, etc..

Cheerful regards, Mike

 '  Leo Bodnar's 'antilogarithmic'
 '  gamma correction algorithm (Mike, K8LH)
 '
 '  JustBASIC (free) interpreter
 '
 Input "Gamma array size: "; arraysize
 Input " Total PWM steps: "; width
 Input "Gamma correction: "; gamma       ' try 0.5 to 1.0
 Input "Entries per line: "; entries     '

 FOR index = 0 to arraysize-1
    dcyval = INT(width^(((index+1)/arraysize)^gamma)+.3)
    if(index MOD entries = 0) then
      PRINT
      PRINT "  DW ";
    else
      PRINT ",";
    end if

    if(dcyval < 100) then print " ";
    if(dcyval < 10) then print " ";
    PRINT dcyval;
 NEXT index
 PRINT
 PRINT
 REM CLOSE

[RossWaddell]

Hi Hank,

Sorry for the late reply. Glad you figured it out. Another slightly more recent version of that Gamma Table program is listed below.

Gamma values of 1.7 to 1.9 worked good for me but it's very much dependent on your LEDs, voltage, hardware, etc..

Cheerful regards, Mike

 '  Leo Bodnar's 'antilogarithmic'
 '  gamma correction algorithm (Mike, K8LH)
 '
 '  JustBASIC (free) interpreter
 '
 Input "Gamma array size: "; arraysize
 Input " Total PWM steps: "; width
 Input "Gamma correction: "; gamma       ' try 0.5 to 1.0
 Input "Entries per line: "; entries     '

 FOR index = 0 to arraysize-1
    dcyval = INT(width^(((index+1)/arraysize)^gamma)+.3)
    if(index MOD entries = 0) then
      PRINT
      PRINT "  DW ";
    else
      PRINT ",";
    end if

    if(dcyval < 100) then print " ";
    if(dcyval < 10) then print " ";
    PRINT dcyval;
 NEXT index
 PRINT
 PRINT
 REM CLOSE

Hi Mike,

I'm implementing a LED dimmer using Darrel Taylor's MIBAM library (see http://www.picbasic.co.uk/forum/cont...-Modulation%29) which accepts values from 0 - 255 for the duty cycle. I also want to smoothly fade the LEDs so I believe I need to include something similar to your Gamma correction algorithm, but I'm having trouble understanding what you mean by 'Gamma array size'. On another thread I see you posted a chart where you used 100 for that value (and 512 for pwm steps) - is that analogous to saying, 'My brightness can go from 0 (fully off) -100% (fully on, max LED brightness) with 512 steps'? Would I use Gamma array size = 100 and pwm steps = 256?

[Mike, K8LH]

Would I use Gamma array size = 100 and pwm steps = 256?

Yes... Good luck with your project...

Cheerful regards, Mike

[RossWaddell]

Thanks Mike!