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Control Software

The following example programs are available to demonstrate the basic principles for using the PWM module on the PIC18F4620 to possibly drive DC Motors, Lamps etc. at analog output voltages:

 ex1_pwm_led_simple.c

Example program that uses the PWM1 output to set the brightness of an LED to 12.5% duty cycle ((12.5% high pulse and 87.5% low pulse). An arbitrary PWM frequency of 25Khz was selected for this example to simplify the calculations.

 ex2_pwm_led_sw.c

Example program that uses the PWM1 output to change the brightness of an LED according to the input from 8 switches.  Sometimes a lower PWM frequency is required to control motors, lamps, etc.  So for this example we chose a PWM frequency of 4Khz.  The switches will be used as follows to set the duty cycle of the LED:

All switches OFF ->   0%

SW0 = ON         ->   12.5%

SW1 = ON         ->   25%

SW2 = ON         ->   37.5%

SW3 = ON         ->   50%

SW4 = ON         ->   62.5%

SW5 = ON         ->   75%

SW6 = ON         ->   87.5%

SW7 = ON         ->   100%

(As you can see it will be in 12.5% increments)

SW0 has the lowest priority and SW7 has the highest, i.e. if SW0 and SW3 is both ON, SW3 will take priority.

 ex3_pwm_led_analog.c

Example program that uses the PWM1 output to change the brightness of an LED according to the input from an analog input.  We chose a PWM frequency of 4Khz.  The brightness of the LED will be based on the following scaling of the input value:

ANALOG VAL  Duty Cycle %   SetDCPWM1 value

==========  ============   ===============

1023        100%           624 (see ex_pwm_led_sw.c to see how 624 was calcualted to be 100% duty cycle for a 4Khz PWM signal)

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512         50%            312

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0           0              0