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Download the library: PWM2.bas

Other programs that use this library:

• Large LED Array & Brightness Control via PWM
• Digital to Analogue Conversion (DAC) via PWM
• Infrared (IR) Modulated UART

Variable Frequency PWM Example

The SetFreqByTable() function uses a constants table of PR2 and Timer2 Prescaler load values so the user can switch easily between optimum frequencies and duty cycle resolution. A small utility program has been created to simplify the creation of this array of constants which can be downloaded from HERE. A screenshot of this utility is provided below.

Here is example code that uses some of the newly added functions. This example uses an 18F2550 @ 48MHz. Potentiometers are connected to AN2 and AN3 which create the variable duty-cycle for PWM1 and PWM2 outputs. A pushbutton connected to GND and PORTB.0 is used to toggle between PWM frequencies of 11.75KHz and 5.8KHz which have resolutions of 1024 and 512, respectively. These frequencies were determined from a constants table created with the PWM_Writer Utility. The EasyPIC3 PIC development board was used for this test.

Device = 18F2550
Clock = 48
 
' set up config for 8MHz crystal and USB
Config USBDIV = 2
Config CPUDIV = OSC1_PLL2
Config PLLDIV = 2
Config FOSC   = HSPLL_HS
 
Include "pwm2.bas"
Include "adc.bas"
 
Dim adc0,adc1 As Word
Dim tt As Byte
 
   TRISA = 15
   TRISB = 1
   tt = 0
   ADCON1 = 11                   // AN0..AN3 active ADC's
   INTCON2.7 = 0                 // RBPU active
   PWM.SetFreqByTable(tt)
   PWM.Start1
   PWM.Start2
   While true
      adc0 = ADC.Read(2)
      adc1 = ADC.Read(3)
      If tt = 0 Then
         PWM.SetDuty1(adc0)
         PWM.SetDuty2(adc1)
      Else
         PWM.SetDuty1(adc0 >> 1)
         PWM.SetDuty2(adc1 >> 1)
      End If
      If (PORTB And 1) = 0 Then
         Inc(tt)
         tt = tt And 1
         PWM.SetFreqByTable(tt)
         Repeat
           DelayMS(5)
         Until (PORTB And 1)  0
      EndIf    
   Wend 

Link: What is a Swordfish Library?

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Comments (2)

• 2009-05-13 09:31:56 | L. Gabrielson

  All of these articles are very good, and present a nice library to learn SF Basic! A simple schematic would be nice, and really complete the lesson.

  Thanks for all of these great articles!

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• 2009-10-02 03:17:59 | Graham

  Thanks for the feedback L. Gabrielson!

  
  I've updated the links to included different projects/tutorials that use the PWM2 module - which offer variations of use.

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