pin code for Quadrature Motor Encoder

Comments

• Harprit Posts: 539

  2012-12-29 17:09 edited 2012-12-29 17:09

  The
  Quadrature Encoder
  Object in the object exchange will give you the encoder count when ever you ask for it.
  Hook the encoder up to lines 0 and 1
  Turn the motor
  Read the position in encoder counts
  It is painless.
  If you need more , ask.
• Mickster Posts: 2,901

  2012-12-29 19:14 edited 2012-12-29 19:14

  Kris Cardoen wrote: »

  Hi,
  
  I have a robot with the following type of encoder
  
  
  
  Quadrature Motor Encoder
  Encoder = 100 cycles per revolution
  Encoder = 400 quadrature counts per revolution
  Frequency = up to 30khz
  
  two questions:
  
  
  
  
  
  1. I guess the specs mean that 100 cycles are equal to one complete rotation of the wheel. And that the pulses changes for one rotation are 400, is that correct?
  
  2. I guess I will have to count the state changes on the encoders outputs. I was thinking on using
  
  if pin.In(5) == 1
  
  Is that the right way to do this? How do I have to set my frequency to check the state change?
  
  Any help would be much appreciated
  
  
  
  
  
  
  
  

  Yes, you have at least two pulse-generating "channels" which are typically 90 degrees out of phase. Between the two channels you have four change-of-states occurring which can be decoded to provide 4X multiplication and an indication of the direction of rotation.
  
  True, there are quad-decode objects available in the OBEX but their function is not very straight-forward to me at least.
  
  The logic is VERY simple and I decided to create my own quad-decoder using PropBASIC. Just working simply with the very transitions that we are concerned with.
  
  This is actual functioning code. However, the counter value WILL need to be written to HUB memory which slows things down a bit but on the whole, this code executes faster than any pure PASM that I have found in the OBEX...albeit limited to one encoder (easily expandable but I require > 1.5M quadrature counts/sec).
  

  DEVICE P8X32A, XTAL1, PLL16X
  FREQ 80_000_000
  
  
  Chan_A PIN 18 INPUT
  Chan_B PIN 17 INPUT
  Chan_Z PIN 16 INPUT
  
  Counter VAR LONG = 0
  
  PROGRAM Start
  
  Start:
  
  'Decide where to start
  If Chan_A = 1 And
      Chan_B = 1 Then
      Goto A1B1
  Endif
  
  If Chan_A = 0 And
      Chan_B = 0 Then
      Goto A0B0
  Endif
  
  If Chan_A = 1 And
      Chan_B = 0 Then
      Goto A1B0
  Endif
  
  If Chan_A = 0 And
      Chan_B = 1 Then
      Goto A0B1
  Endif
  
  'This is the main loop
  'The only possible conditions are clearly spelled-out...no masking, no shifting, no rotating
    
   A1B1:
   If Chan_A = 0 Then   
     Dec Counter
     Goto A0B1
   Elseif Chan_B = 0 Then 
     Inc Counter
     Goto A1B0
   Endif
   Goto A1B1
   
  A0B0:
  If Chan_A = 1 Then
     Dec Counter
     Goto A1B0
  Elseif Chan_B = 1 Then
     Inc Counter
     Goto A0B1
  Endif
  Goto A0B0
   
   A1B0:
   If Chan_A = 0 Then
     Inc Counter
     Goto A0B0
   Elseif Chan_B = 1 Then
     Dec Counter
     Goto A1B1
   Endif
   Goto A1B0
   
   A0B1:
   If Chan_A = 1 Then
     Inc Counter
     Goto A1B1
   Elseif Chan_B = 0 Then
     Dec Counter
     Goto A0B0
   Endif
   Goto A0B1
  
  End
  
  
  
  

  
  P.S. My application is not battery powered and so this approach is not at all power efficient. The code could easily be modified to include the waitpne function to reduce the power consumption when no encoder transitions happen to be occurring.
  
  Mickster
• Kris Cardoen Posts: 46

  2013-01-27 12:02 edited 2013-01-27 12:02

  Thanks for the help, my encoders are up and running.
  
  One more question :-)
  
  When I make a full rotation I get value 20.000 reverse -20.000.
  Where does this number come from?