Rotary Encoder Interface Code

[sleazyd]

Just wanted to share my admittedly garbage rotary encoder code. If someone has anything better, please feel free to share:

Symbol ENC_A = Input7
Symbol ENC_B = Input6
Symbol ENC_INT_PIN = %10000000
Symbol ENC_INT_PASK = ENC_INT_PIN ^ $FF
Symbol Val = b1
Symbol ENC_UP = 2
Symbol ENC_DOWN = 1
Symbol ENC_OOPS = 0
Symbol LED = 0

Start:
    Val = 127
    SetFreq m8
    ' Chosen because 0-100% = 0 - 1023
    pwmout 3 , 255, 512
   
    ' Set the interrupt for the oposite edge
    b0 = ENC_A * ENC_INT_PIN
    b0 = b0 ^ ENC_INT_PIN
    SetInt b0, ENC_INT_PIN
   
MainLoop:
    Pause 50
    GoTo MainLoop

interrupt:   
    High LED
    If ENC_A = 1 Then
        if ENC_B = 1 Then
            Val = Val - 1
        Else
            Val = Val + 1
        EndIf
        SetInt 0, ENC_INT_PIN
    Else
        if ENC_B = 0 Then
            Val = Val - 1
        Else
            Val = Val + 1
        EndIf
        SetInt ENC_INT_PIN, ENC_INT_PIN
    EndIf
    W1 = 0
    b2 = Val
    W1 = W1 * 4
    pwmout 3 , 255, W1
    Low LED
    Return

I'm using an encoder that has a common and 2 pins that use a Gray code to pulse out the direction. Sparkfun has a similar one at http://www.sparkfun.com/commerce/product_info.php?products_id=9117. It's expecting the A/B inputs of the encoder on Input6 and Input7. This uses the pseudo Interrupts to get the data, setting them to goff a change on the 'A' pin. This means you're only getting 1/4 the resolution available, but the Picaxe was having a hell of a time keeping up when I tried a full quadrature decode.

 

[westaust55]

Welcome to the PICAXE forum.

I assume that you have an 18X or 18M PICAXE chip ?

Others with a different PICAXE chip will need to change the pin used for the PWMOUT command.

 

[sleazyd]

Yes, it's an 18x. The PWMOut command was just so that I had some feedback that it was working. The general principle should work fine for anything that supports the StInt command.

 

[boriz]

This was my first attempt. Seems to work ok, but I can't help thinking there is a better way. (I seem to remember reading something about XOR).

#picaxe 14m
'quadrature encoding on pin0 and pin1
do
	do
		bit2=bit0:bit3=bit1
		bit0=pin0:bit1=pin1		
	loop until bit0<>bit2
	if b0=11 or b0=4 then
		inc b1
	elseif b0=1 or b0=14 then
		dec b1
	endif
	gosub update_display
loop