pin code for Quadrature Motor Encoder

Kris Cardoen · 2012-12-29 14:06

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

Harprit · 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 · 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 · 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?

pin code for Quadrature Motor Encoder

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