Quad Encoder Problem

[RossWaddell]

This doesn't seem to be my week ... I had problems earlier with converting code from a PIC12F683 to a PIC12F1840 which thankfully was resolved yesterday (thanks Henrik!) but when I come back to something I thought was working fine, it's not.

I found examples of determining the direction of turn of a mechanical quadrature encoder. Darrel helped way back with some of it and all was well until late last night when I thought I'd better retest this after working on other parts of the project. Lo and behold, the MotorRPM variable isn't going up or down steadily but rather goes up by one or two but could just as easily go down (when turning the knob in the same direction). I did spend the first part of the year converting from using PBP's HPWM on CCP1/2 (which are ECCP modules on the 16F1825) to CCP3/4 (regular CCP modules) but at the time I'm fairly certain I tested the quadrature part and it worked OK.

Here's my code (edited for clarity):

' ***************************************************************
' 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
' RC0                       -> Stbd motor direction signal (motor 1)
' RC1/CCP4                  -> Port motor PWM output (motor 2)
' RC2                       -> Port motor direction signal (motor 2)
' RC4/Tx                    -> Serial LCD output
' RC5/Rx                    -> Serial input
      
DEFINE OSC 16               ; Set oscillator 16Mhz

' ***************************************************************
' Device Fuses
' ***************************************************************

#CONFIG
   __config _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _CPD_OFF
   __config _CONFIG2, _PLLEN_OFF & _STVREN_ON & _BORV_LO & _LVP_OFF
#ENDCONFIG

' ***************************************************************
' Initialization
' ***************************************************************

OSCCON   = %01111000        ' 16MHz internal osc

pause 100                   ' As advised by Darrel Taylor for EEPROM issue

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               ' Make all PORTC pins output

' The INTEDG bit of the OPTION_REG register determines on which edge the 
' interrupt will occur. When the INTEDG bit is set, the rising edge will 
' cause the interrupt. When the INTEDG bit is clear, the falling edge will 
' cause the interrupt. 
OPTION_REG.6 = 1             ' 1=Rising edge (default) or button "PRESS";
                             ' 0=Falling edge or button "RELEASE"

Old_Bits       VAR BYTE
New_Bits       VAR BYTE
RotEncDir      VAR BIT       ' 1=CW, 0=CCW
                             ' Rot Enc pin A connected to PortA.1;
                             ' Rot Enc pin B connected to PortA.0
Old_RPM        VAR BYTE
i              VAR BYTE

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

CCP3CON = %00001100         ; Use CCP3 in PWM mode
CCP4CON = %00001100         ; Use CCP4 in PWM mode
                             
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 VAR BYTE        ; Pause during motor spin up
SpinUpPause = 17
#IFDEF USE_LCD_FOR_DEBUG
    SpinUpPause = 12        ; Subtract 5ms pause when outputting to LCD
#ENDIF

MaxDuty     VAR WORD        ; According to Darrel:
                            ;   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

TimeCnt     VAR Word      

' ***************************************************************
' Includes
' ***************************************************************

INCLUDE "DT_INTS-14.bas"    ' Base Interrupt System
INCLUDE "ReEnterPBP.bas"    ' Include if using PBP interrupts
                            ' --> copy both files to PBP main folder 
                            ' (i.e. c:\pbp3)

' ***************************************************************
' EEPROM Variables
' ***************************************************************

MotorRPM_Default   CON  177
EE_MotorRPM        DATA MotorRPM_Default
MotorRPM           VAR  BYTE
READ EE_MotorRPM, MotorRPM

PortEngDir_Default CON  0
EE_PortEngDir      DATA PortEngDir_Default
PortEngDir         VAR  BYTE
READ EE_PortEngDir, PortEngDir
                                                                  
' ***************************************************************
' ASM Interrupt Definitions
' ***************************************************************
                                                                  
ASM
INT_LIST  macro    ; IntSource,            Label,  Type, ResetFlag?
        INT_Handler    IOC_INT,    _RotEncAdjust,   PBP,  yes
    endm
    INT_CREATE     ; Creates the interrupt processor
ENDASM

' ***************************************************************
' Set default values
' ***************************************************************

Old_RPM = MotorRPM
Old_Bits = PORTA & (%00000011)

' Enable interrupts on RPM control now that motors are fully spun up
INTCON   = %10001000        ' Global int enabled, IOCI enabled, 
                            ' INTF flag bit 0 clr, IOCI flag bit 0 clr
IOCAP.0  = 1                ' Enable positive (rising edge) change
IOCAP.1  = 1                ' Enable positive (rising edge) change
IOCAN.0  = 1                ' Enable negative (falling edge) change
IOCAN.1  = 1                ' Enable negative (falling edge) change
IOCAF.0  = 0                ' Clear interupt-on-change flag
IOCAF.1  = 0                ' Clear interupt-on-change flag

@ INT_ENABLE   IOC_INT      ; Interrupt-on-Change interrupt

Main:
    ' Check if motor RPM has changed
    IF MotorRPM <> Old_RPM Then
        Old_RPM = MotorRPM
        GOSUB ChngMotorHPWM
    EndIF   
   
    TimeCnt = 0
	While ButtonPress = 0
	    TimeCnt = TimeCnt + 1
	    Pause 10
	    If TimeCnt > 500 Then BtnAction
	Wend
 
    BtnAction:
        If TimeCnt > 0 and TimeCnt < 200 Then
            PortEngDir = PortEngDir + 1
            If PortEngDir > 1 Then PortEngDir = 0
    
            WRITE EE_PortEngDir, PortEngDir
            #IFDEF USE_LCD_FOR_DEBUG
                HSEROUT [LCD_INST, LCD_CLR]
                pause 5
                HSEROUT ["PortEngDir=", DEC PortEngDir, "  ", 13, 10] ' Send text followed by carriage return and linefeed
            #ENDIF

            GOSUB ReversePortEng
        ElseIf TimeCnt >= 200 Then
            WRITE EE_MotorRPM, MotorRPM_Default  ; restore Default value
        
            MotorRPM = MotorRPM_Default
        EndIf
 
    GOTO Main


' ***************************************************************
' [IOC - interrupt handler]
' ***************************************************************
RotEncAdjust:
    New_Bits = PORTA & (%00000011)
    IF (New_Bits & %00000011) = (Old_Bits & %00000011) Then DoneRotEnc

    RotEncDir = New_Bits.1 ^ Old_Bits.0
    IF RotEncDir = 1 Then
        ; CW rotation - increase speed but only to a max of 'MaxDuty'
        IF MotorRPM < MaxDuty then MotorRPM = MotorRPM + 1
    Else
        ' CCW rotation - decrease speed to a min of 0
        IF MotorRPM > 0 Then MotorRPM = MotorRPM - 1
    EndIF

    WRITE EE_MotorRPM, MotorRPM
    pause 100

DoneRotEnc:
    Old_Bits = New_Bits
    
    IOCAF.0 = 0      ' Clear interrupt flags
    IOCAF.1 = 0

@ INT_RETURN

Here's a video which shows the problem (I hope):

Here's my schematic:



Again, AFAIK nothing has changed in the two months since I last worked on this code and all was well.

Does anyone see where I'm going wrong? Here's what I've tried:

• Swapped out the quad encoder with a spare one (same model)
• Swapped out the PIC and programmed another one
• Replaced the 10k resistors that tie the encoder's A/B outputs to +5V
• Double-checked the connections

Something to do with Timer2 & PWM on CCP3/4? Bad IOC interrupt config? What's strange is that the quad encoder has a pushbutton knob and that's working just fine (although it's not using an interrupt).

[HenrikOlsson]

Hi,
First order of business, remove the Pause 100 from the interrupt service routine.

Also, is the intention really to write the MotorRPM variable to EEPROM on every interrupt? I see two possible issues with that, the first is that the write operation takes a while and the second is that you may wear out the EEPROM. Finally, not related to the actual problem but still

IF (New_Bits & %00000011) = (Old_Bits & %00000011) Then DoneRotEnc

Since you're assigning the value of New_Bits by ANDing PortA with 3 and then, at the end setting Old_Bits = New_Bits there's no need to AND New_Bits or Old_Bits with 3 here as well. Neither of those variables will ever have bits 2-7 set anyway, you've already taken care of that. (As long as you don't use them anywhere else in your program of course).

/Henrik.

[RossWaddell]

It doesn't work with or without the 'Pause 100' in the interrupt service routine - I actually only added that based on some sample interrupt code from DT (I thought it made sense if there's some latency to saving to EEPROM you might want to wait a tiny bit).

Other than saving the new MotorRPM to EEPROM everytime it changes, I don't know what else I can do. Users won't be modifying the motor speed very often (once they find the speed they like, they'll just leave it). I suppose I could set up a timer to save the value to EEPROM if it's changed, but I'm open to suggestions

For the above code line, are you saying I could just use this instead?

IF New_Bits = Old_Bits THEN DoneRotEnc

[HenrikOlsson]

Hi,
According to the manual the WRITE command "is self-timed and may take up to 10 milliseconds to execute on a PIC MCU".
I suspect that's the issue, most encoders produce a full quadrature cycle, ie 4 edges (4 interrupts) per click/detent. IF the WRITE operation takes 10ms (and/or you have that Pause 100 in there) it's likely that it will miss pulses/edges and get confused.

Try commenting out the Write operation and see if that fixes it.

Yes, that's what's I'm saying regarding New_Bits = Old_Bits.
At the beginning of the ISR you do New_Bits = PortA & %00000011 so the top 6 bits of New_Bits are cleared. At the end of the ISR you assign the value in New_Bits to Old_Bits so the top 6 bits in Old_Bits will also be zero. Therefor the second AND operation is unnecessary, but it doesn't have anything to do with the actual problem....

/Henrik.

[RossWaddell]

I'll try this out tonight, Henrik. Thanks so much for your help here and on my other thread from this week.

If the WRITE operation in the interrupt service routine is the cause, then I'll move that to the check in the Main loop.

[HenrikOlsson]

Hi,
Just realised I misunderstood you a bit. I thought you were trying to use the 12F1840 with this code, then I realised you're actually using the 16F1825 that's in the schematic...duh...

Anyway, I've breadboarded a 12F1840 (don't have any 18F1825) and now have an encoder counting properly, sending the count over the USART. I simulated the EEPROM write by adding a PAUSEUS xxx in the handler and found that the limit for correct response - in my case - is around 500us. Anything above that it starts missing edges, coutning the wrong way etc.

So, if the EEPROM write takes even remotely as long as 10ms then that is most likely the issue.

/Henrik.