During a wait in an airport lounge I decided to knock up a new module. Its for those rotary encoders used in place of a pot.

These devices work by giving a 2 bit encoder output and requires the CPU to decode the signals to tell you of the direction of rotation. Being able to monitor the movement as a count is one thing but its better if you can do that over time to establish how fast your rotating the dial.

This modules does that, by setting up a 100hz interrupt it will monitor the inputs and when there has been a change it will note the direction and increment or decrement a counter. Then every 2 hz will convert that to a figure that can be used as a speed indication.

How to use

1 Include the module
Include "DialEncoder.Bas"
2 Tell it what the A and B pins are
(Hash)option EncoderA = PORTB.0
(Hash)option EncoderB = PORTB.1
3 Before you use it Initialise the module
4 Read the current speed and the direction (byte & bit)
RotationSpeed = DialEncoder.Speed
RotationDirection = DialEncoder.Direction

Thats it.

BTW the Code was written for an Grayhill Optical Encoder (Series 62) and debugged/sim'ed all in ISIS by LabCenter Electronics

First is a demo prog followed by the module

    #option EncoderA = PORTB.0
    #option EncoderB = PORTB.1

    Include "Usart.bas"
    Include "convert.bas"
    Include "DialEncoder.bas"

        USART.Write (DecToStr (DialEncoder.Speed),32,DecToStr (DialEncoder.Direction),13,10)
    Until 1 = 2    
Module DialEncoder 

    #option EncoderA= PORTB.0   
    #option EncoderB = PORTB.1

    // validate pin...
    #if IsOption(EncoderA) And Not IsValidPortPin(EncoderA) 
       #error EncoderA, "Invalid option. EncoderA must be a valid port pin."

    // validate pin...
    #if IsOption(EncoderB) And Not IsValidPortPin(EncoderB) 
       #error EncoderB, "Invalid option. EncoderB must be a valid port pin."

    Dim EncoderPinA As EncoderA.EncoderA@
    Dim EncoderPinB As EncoderB.EncoderB@

    Dim EncoderNew As Byte
    Dim EncoderOld As Byte
    Dim TimerCounter As Byte
    Dim EncoderCounter As Byte
    Public Dim Speed As Byte
    Public Dim Direction As Bit
    Dim Timer1Reg As TMR1L.asWord
    Const FudgeFactor = 5
    Const Tmr1Val =((65536)-(_clock*2500))+FudgeFactor

    interrupt Encoder ()  
        T1CON.0 = 0  
        Timer1Reg = Timer1Reg + Word(Tmr1Val)
        T1CON.0 = 1                                
        EncoderNew.0 = EncoderPinA
        EncoderNew.1 = EncoderPinB        
        If EncoderNew <> EncoderOld Then  
            EncoderOld = EncoderOld >> 1 
            EncoderNew = EncoderNew Xor EncoderOld
            If EncoderNew.0 = 1 Then 
                Inc (EncoderCounter)
                Dec (EncoderCounter)
            EncoderOld.0 = EncoderPinA
            EncoderOld.1 = EncoderPinB 
        If TimerCounter > 0 Then
            Dec (TimerCounter)
            TimerCounter = 49
            If EncoderCounter.7 = 0 Then
               Speed = EncoderCounter
               Direction = 1
               EncoderCounter.7 = 0     
               Speed = 128 - EncoderCounter
               Direction = 0
            EncoderCounter = 0
        PIR1.0 = 0     
    End interrupt 

    Public Sub IntialiseDialEncoder()
        EncoderOld = 0
        EncoderNew = 0
        Timer1Reg = Tmr1Val
        T1CON = 0
        PIR1.0 = 0
        INTCON.6 = 1
        PIE1.0 = 1  
        T1CON.0 = 1
        Enable (Encoder)
    End Sub