Swordfish Module - PWM2

Download the module: PWM2.bas

Other programs that use this module:

• 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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