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149 lines
4.9 KiB
C++
149 lines
4.9 KiB
C++
/* Rotary encoder handler for arduino. v1.1
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*
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* Copyright 2011 Ben Buxton. Licenced under the GNU GPL Version 3.
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* Contact: bb@cactii.net
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*
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* A typical mechanical rotary encoder emits a two bit gray code
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* on 3 output pins. Every step in the output (often accompanied
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* by a physical 'click') generates a specific sequence of output
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* codes on the pins.
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*
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* There are 3 pins used for the rotary encoding - one common and
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* two 'bit' pins.
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*
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* The following is the typical sequence of code on the output when
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* moving from one step to the next:
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*
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* Position Bit1 Bit2
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* ----------------------
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* Step1 0 0
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* 1/4 1 0
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* 1/2 1 1
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* 3/4 0 1
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* Step2 0 0
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*
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* From this table, we can see that when moving from one 'click' to
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* the next, there are 4 changes in the output code.
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*
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* - From an initial 0 - 0, Bit1 goes high, Bit0 stays low.
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* - Then both bits are high, halfway through the step.
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* - Then Bit1 goes low, but Bit2 stays high.
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* - Finally at the end of the step, both bits return to 0.
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*
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* Detecting the direction is easy - the table simply goes in the other
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* direction (read up instead of down).
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*
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* To decode this, we use a simple state machine. Every time the output
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* code changes, it follows state, until finally a full steps worth of
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* code is received (in the correct order). At the final 0-0, it returns
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* a value indicating a step in one direction or the other.
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*
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* It's also possible to use 'half-step' mode. This just emits an event
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* at both the 0-0 and 1-1 positions. This might be useful for some
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* encoders where you want to detect all positions.
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*
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* If an invalid state happens (for example we go from '0-1' straight
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* to '1-0'), the state machine resets to the start until 0-0 and the
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* next valid codes occur.
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*
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* The biggest advantage of using a state machine over other algorithms
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* is that this has inherent debounce built in. Other algorithms emit spurious
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* output with switch bounce, but this one will simply flip between
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* sub-states until the bounce settles, then continue along the state
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* machine.
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* A side effect of debounce is that fast rotations can cause steps to
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* be skipped. By not requiring debounce, fast rotations can be accurately
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* measured.
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* Another advantage is the ability to properly handle bad state, such
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* as due to EMI, etc.
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* It is also a lot simpler than others - a static state table and less
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* than 10 lines of logic.
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*/
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#include "Arduino.h"
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#include "Rotary.h"
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/*
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* The below state table has, for each state (row), the new state
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* to set based on the next encoder output. From left to right in,
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* the table, the encoder outputs are 00, 01, 10, 11, and the value
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* in that position is the new state to set.
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*/
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#define R_START 0x0
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#ifdef HALF_STEP
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// Use the half-step state table (emits a code at 00 and 11)
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#define R_CCW_BEGIN 0x1
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#define R_CW_BEGIN 0x2
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#define R_START_M 0x3
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#define R_CW_BEGIN_M 0x4
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#define R_CCW_BEGIN_M 0x5
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const unsigned char ttable[6][4] = {
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// R_START (00)
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{R_START_M, R_CW_BEGIN, R_CCW_BEGIN, R_START},
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// R_CCW_BEGIN
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{R_START_M | DIR_CCW, R_START, R_CCW_BEGIN, R_START},
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// R_CW_BEGIN
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{R_START_M | DIR_CW, R_CW_BEGIN, R_START, R_START},
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// R_START_M (11)
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{R_START_M, R_CCW_BEGIN_M, R_CW_BEGIN_M, R_START},
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// R_CW_BEGIN_M
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{R_START_M, R_START_M, R_CW_BEGIN_M, R_START | DIR_CW},
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// R_CCW_BEGIN_M
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{R_START_M, R_CCW_BEGIN_M, R_START_M, R_START | DIR_CCW},
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};
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#else
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// Use the full-step state table (emits a code at 00 only)
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#define R_CW_FINAL 0x1
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#define R_CW_BEGIN 0x2
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#define R_CW_NEXT 0x3
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#define R_CCW_BEGIN 0x4
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#define R_CCW_FINAL 0x5
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#define R_CCW_NEXT 0x6
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const unsigned char ttable[7][4] = {
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// R_START
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{R_START, R_CW_BEGIN, R_CCW_BEGIN, R_START},
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// R_CW_FINAL
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{R_CW_NEXT, R_START, R_CW_FINAL, R_START | DIR_CW},
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// R_CW_BEGIN
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{R_CW_NEXT, R_CW_BEGIN, R_START, R_START},
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// R_CW_NEXT
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{R_CW_NEXT, R_CW_BEGIN, R_CW_FINAL, R_START},
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// R_CCW_BEGIN
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{R_CCW_NEXT, R_START, R_CCW_BEGIN, R_START},
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// R_CCW_FINAL
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{R_CCW_NEXT, R_CCW_FINAL, R_START, R_START | DIR_CCW},
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// R_CCW_NEXT
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{R_CCW_NEXT, R_CCW_FINAL, R_CCW_BEGIN, R_START},
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};
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#endif
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/*
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* Constructor. Each arg is the pin number for each encoder contact.
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*/
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Rotary::Rotary(char _pin1, char _pin2) {
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// Assign variables.
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pin1 = _pin1;
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pin2 = _pin2;
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// Set pins to input.
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pinMode(pin1, INPUT);
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pinMode(pin2, INPUT);
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#ifdef ENABLE_PULLUPS
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digitalWrite(pin1, HIGH);
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digitalWrite(pin2, HIGH);
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#endif
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// Initialise state.
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state = R_START;
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}
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unsigned char Rotary::process() {
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// Grab state of input pins.
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unsigned char pinstate = (digitalRead(pin2) << 1) | digitalRead(pin1);
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// Determine new state from the pins and state table.
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state = ttable[state & 0xf][pinstate];
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// Return emit bits, ie the generated event.
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return state & 0x30;
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}
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