LED PWM with High Frequencies?

[RossWaddell]

I've set up a PIC16F1825 to do PWM on CCP3/4 for motor control as follows:

' ***************************************************************
' Set up registers for PWM on CCP3, CCP4
' ***************************************************************

CCP3CON = %00001100         ; Use CCP3 in PWM mode (Motor 1)
CCP4CON = %00001100         ; Use CCP4 in PWM mode (Motor 2)


CCPTMRS = %00000000         ; Use Timer2
                             
T2CON   = %00000101         ; Timer2 on with 1:4 prescaler
PR2     = 62                ; For 16Mhz OSC the desired output freq of 15,873Hz is
                            ; achieved with this PR2 value (8-bit resolution
                            ; with 1:4 prescaler)
                            
                            ; PWM freq must be ~ 16-20kHz to reduce noise

I need to use a relatively high frequency value for the motors. My question is this: would it hurt the LEDs or otherwise be a bad idea to use the same frequency for LED PWM? I want to set up CCP1 with the same timer, prescaler & resolution as the motors so that I can include the LEDs in this loop to 'ramp up' the motors:

' Spin up motors to saved value of _MotorRPM
' (Below a value of 'MinDuty', the motors don't move at all)
FOR i = (MinDuty - PreSpinVal) to MotorRPM
    DutyVar3  = i

    IF PortEngDir = 0 THEN
        DutyVar4 = i              ' Port engine (CCP4), fwd (CCW)
    ELSE
        DutyVar4 = (MaxDuty - I)  ' Port engine (CCP4), rev (CW)
    ENDIF

    CCP3CON.4 = DutyVar3.0
    CCP3CON.5 = DutyVar3.1
    CCPR3L    = DutyVar3 >> 2

    CCP4CON.4 = DutyVar4.0
    CCP4CON.5 = DutyVar4.1
    CCPR4L    = DutyVar4 >> 2 
            
    pause SpinUpPause

    #IFDEF USE_LCD_FOR_DEBUG
        HSEROUT [LCD_INST, LCD_CLR]
        pause 5
        HSEROUT ["RPM=", DEC i, "       ", 13, 10] ' Send text followed by carriage return and linefeed
    #ENDIF
NEXT i

I know of the SPWM_INT.bas include file from Darrel (which allows you to use 200Hz, high enough so no flicker is seen) but I don't know if I need to use that here instead of sharing Timer2 with the same high frequency as with the motors.

[wdmagic]

no it wont hurt the leds

[RossWaddell]

Thanks wdmagic.

Seems like trying to add PWM on ECCP1 is throwing a wrench into the existing motor speed control - the motor just turns 'on' (without ramping up) and the LEDs connect to RC5 are unlit. Is it because ECCP1 is taking control of some pins I'm already using? I think maybe there are additional registers/config I need to set in order to get a single PWM output on RC5.

' ***************************************************************
' Pin Connections
' ***************************************************************

' RA0                       -> B pin of rotary encoder
' RA1                       -> A pin of rotary encoder
' RA2/CCP3                  -> Stbd motor PWM output (motor 1)
' RA3/MCLR                  -> Button switch pin of rotary encoder

' RA5/CCP2                  -> PWM for flashing LEDs ?

' RC0                       -> Stbd motor direction signal (motor 1)
' RC1/CCP4                  -> Port motor PWM output (motor 2)
' RC2                       -> Port motor direction signal (motor 2)
' RC4                       -> Serial output (Tx)
' RC5/CCP1                  -> PWM for steady-on amber LEDs
                            ; This is also the only available Rx pin, so this might not work
                            ; with plan to have 1 knob to control them all
                            
DEFINE OSC 16               ; Set oscillator 16Mhz

OSCCON   = %01111000        ' 16MHz internal osc

ANSELA    = 0               ; Digital only for all PortA pins
ANSELC    = 0               ; Diginal only for all PortC pins

TRISA     = %00001011       ' Make PORTA pins 0-1 input for rotary encoder,
                            ' pin 3 for rotary button
TRISC     = 0

i              VAR BYTE

MOTOR_1_DIR    VAR PORTC.0   ' Alias PORTC.0 as "MOTOR_1_DIR"
MOTOR_1_PWM    VAR PORTA.2   ' Alias PORTQ.2 as "MOTOR_1_PWM"
MOTOR_2_DIR    VAR PORTC.2   ' Alias PORTC.2 as "MOTOR_2_DIR"
MOTOR_2_PWM    VAR PORTC.1   ' Alias PORTC.1 as "MOTOR_2_PWM"

ButtonPress    VAR PORTA.3   ' Alias PORTA.3 as "ButtonPress"

' ***************************************************************
' Set up registers for PWM on CCP3, CCP4 & CCP1, CCP2
' ***************************************************************

CCP3CON = %00001100         ; Use CCP3 in PWM mode (Motor 1)
CCP4CON = %00001100         ; Use CCP4 in PWM mode (Motor 2)
CCP1CON = %00001111         ; Use CCP1 in PWM mode (PWM for steady-on engine LEDs)
;CCP2CON = %00001100         ; Use CCP2 in PWM mode (PWM for blinking engine LEDs)

CCPTMRS = %00000000         ; Use Timer2 for all CCPs
                             
T2CON   = %00000101         ; Timer2 on with 1:4 prescaler
PR2     = 62                ; For 16Mhz OSC the desired output freq of 15,873Hz is
                            ; achieved with this PR2 value (8-bit resolution
                            ; with 1:4 prescaler)
                            
                            ; PWM freq must be ~ 16-20kHz to reduce noise

PreSpinVal  CON 17          ; Value to subtract from MinDuty for motor spin up 
MinDuty     CON 75          ; 75 when max duty = 250 (8-bit resolution)
;SpinUpPause CON 17          ; Pause during motor spin up
SpinUpPause CON 7           ; Pause during motor spin up
MaxDuty     VAR WORD        ; According to Darrel Taylor:
                            ;   MaxDuty = (PR2 + 1) * 4

MaxDuty = (PR2 + 1) * 4     ; 252 but with prescaler resolution it's actually 250

DutyVar3    VAR WORD        ; temp variable to store duty variable for CCP3
DutyVar4    VAR WORD        ; temp variable to store duty variable for CCP4
DutyVar1    VAR WORD        ; temp variable to story duty variable for CCP1

FOR i = 0 to MaxDuty
    IF i <= MotorRPM THEN
        ; Spin up motors but only until saved value of MotorRPM is reached
        DutyVar3  = i
    
        IF PortEngDir = 0 THEN
            DutyVar4 = i              ' Port engine (CCP4), fwd (CCW)
        ELSE
            DutyVar4 = (MaxDuty - I)  ' Port engine (CCP4), rev (CW)
        ENDIF
    
        CCP3CON.4 = DutyVar3.0
        CCP3CON.5 = DutyVar3.1
        CCPR3L    = DutyVar3 >> 2
    
        CCP4CON.4 = DutyVar4.0
        CCP4CON.5 = DutyVar4.1
        CCPR4L    = DutyVar4 >> 2 
    ENDIF

    IF i <= StdyOnLEDs THEN
        ; Fade in steady-on LEDs but only until saved value of StdyOnLEDs is reached
        DutyVar1 = i
       
        CCP1CON.4 = DutyVar1.0
        CCP1CON.5 = DutyVar1.1
        CCPR1L    = DutyVar1 >> 2       
    ENDIF

    pause SpinUpPause
NEXT i

How do I get just a single PWM on RC5 without affecting any other port pins?

[wdmagic]

Sorry I cant help you with that, I dont use that particular chip, and your using a bit of code that im unfamiliar with. Im used to only having 2 pwms, and using the hpwm command to output my signal.