Robostix quadrature decode

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Overview

It is often desirable to use some type of rotary sensor for detecting wheel position. One of the more common techniques involves the use of a quadrature encoder/decoder. This is basically two channels (commonly called A and B) which contain square waves which are 90 degrees out of phase. This is also the simplest form of Gray code.

Some further background is available on the Digital encoders page.

Computer mice (the kind with the balls in them) use quadrature for the X and Y axis: How Computer Mice Work

Source Files

The QD.h and QD.c files (found in the robostix/Common directory) implement polled quadrature. I generally prefer polled quadrature over interrupt driven quadrature since the polled method will automatically compensate for noise.

To track an encoder called Dial, you would add the following definitions to your file (as shown in the QD-Test.c file):

#define  Dial_A_PIN  PINC
#define  Dial_B_PIN  PINC
#define  Dial_A_BIT  1
#define  Dial_B_BIT  0

volatile QD_Counter_t  Dial_Count;
         QD_State_t    Dial_PrevState;

The type of QD_Counter_t defaults to uint16_t and can be set using the CFG_QD_COUNTER_TYPE define in your Config.h file.

You can change the direction of the counting, by swapping the A and B channels.