Object oriented state machine

Educational toy project to show how to write a simple object oriented state machine with your own class hierarchy.

Feb 24, 2018

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object oriented

state machine

Components and supplies

Arduino Uno Rev3

Breadboard (generic)

Resistor 221 ohm

LED (generic)

Apps and platforms

Arduino IDE

Project description

Code

OO State Machine

c_cpp

Simple example of an object oriented state machine with two states.

1
2class State {
3  public:
4  virtual ~State(){}
5  virtual void   enter(){};
6  virtual State* run() = 0;
7};
8
9class White: public State   {
10  public:
11  virtual void enter() override;
12  virtual State* run() override;
13};
14
15class   Green: public State {
16  public:
17  virtual void enter() override;
18  virtual   State* run() override;
19};
20
21static White white;
22static Green green;
23unsigned   long lastMillis = 0;
24
25void flash(int pin) {
26   for(int i = 0; i<20; ++i)   {
27    digitalWrite(pin,!digitalRead(pin));
28    delay(30);
29  } 
30}
31
32State*   White::run() {
33  if (millis() < lastMillis + 1000) {
34    digitalWrite(13,HIGH);
35     return this;      
36  }
37  else {
38    lastMillis = millis();
39    digitalWrite(13,LOW);
40     return &green;  
41  }
42}
43
44void White::enter() {
45  flash(13);
46   // update the timer
47  lastMillis = millis();
48}
49
50State* Green::run()   {
51  if (millis() < lastMillis + 2000) {
52    digitalWrite(12,HIGH);
53    return   this;      
54  }
55  else {
56    lastMillis = millis();
57    digitalWrite(12,LOW);
58     return &white;  
59  }
60}
61
62void Green::enter() {
63  flash(12);
64   // update the timer
65  lastMillis = millis();
66}
67
68void setup() {
69   pinMode(13,OUTPUT);
70  pinMode(12,OUTPUT);
71}
72
73bool isChanged = false;
74State*   state = &white;
75State* lastState = state;
76void loop() {
77  // if state changed   last time, call enter
78  if (isChanged)
79    lastState->enter();
80  // call   run repeatedly
81  state = lastState->run();
82  // if state changed, record it;
83   isChanged = (state != lastState);
84  // reset lastState to current
85  lastState   = state;
86}
87
88

class State {
  public:
  virtual ~State(){}
  virtual void   enter(){};
  virtual State* run() = 0;
};

class White: public State   {
  public:
  virtual void enter() override;
  virtual State* run() override;
};

class   Green: public State {
  public:
  virtual void enter() override;
  virtual   State* run() override;
};

static White white;
static Green green;
unsigned   long lastMillis = 0;

void flash(int pin) {
   for(int i = 0; i<20; ++i)   {
    digitalWrite(pin,!digitalRead(pin));
    delay(30);
  } 
}

State*   White::run() {
  if (millis() < lastMillis + 1000) {
    digitalWrite(13,HIGH);
     return this;      
  }
  else {
    lastMillis = millis();
    digitalWrite(13,LOW);
     return &green;  
  }
}

void White::enter() {
  flash(13);
   // update the timer
  lastMillis = millis();
}

State* Green::run()   {
  if (millis() < lastMillis + 2000) {
    digitalWrite(12,HIGH);
    return   this;      
  }
  else {
    lastMillis = millis();
    digitalWrite(12,LOW);
     return &white;  
  }
}

void Green::enter() {
  flash(12);
   // update the timer
  lastMillis = millis();
}

void setup() {
   pinMode(13,OUTPUT);
  pinMode(12,OUTPUT);
}

bool isChanged = false;
State*   state = &white;
State* lastState = state;
void loop() {
  // if state changed   last time, call enter
  if (isChanged)
    lastState->enter();
  // call   run repeatedly
  state = lastState->run();
  // if state changed, record it;
   isChanged = (state != lastState);
  // reset lastState to current
  lastState   = state;
}

OO State Machine

c_cpp

Simple example of an object oriented state machine with two states.

1
2class State {
3  public:
4  virtual ~State(){}
5  virtual void  enter(){};
6  virtual State* run() = 0;
7};
8
9class White: public State  {
10  public:
11  virtual void enter() override;
12  virtual State* run() override;
13};
14
15class  Green: public State {
16  public:
17  virtual void enter() override;
18  virtual  State* run() override;
19};
20
21static White white;
22static Green green;
23unsigned  long lastMillis = 0;
24
25void flash(int pin) {
26   for(int i = 0; i<20; ++i)  {
27    digitalWrite(pin,!digitalRead(pin));
28    delay(30);
29  } 
30}
31
32State*  White::run() {
33  if (millis() < lastMillis + 1000) {
34    digitalWrite(13,HIGH);
35    return this;      
36  }
37  else {
38    lastMillis = millis();
39    digitalWrite(13,LOW);
40    return &green;  
41  }
42}
43
44void White::enter() {
45  flash(13);
46  // update the timer
47  lastMillis = millis();
48}
49
50State* Green::run()  {
51  if (millis() < lastMillis + 2000) {
52    digitalWrite(12,HIGH);
53    return  this;      
54  }
55  else {
56    lastMillis = millis();
57    digitalWrite(12,LOW);
58    return &white;  
59  }
60}
61
62void Green::enter() {
63  flash(12);
64  // update the timer
65  lastMillis = millis();
66}
67
68void setup() {
69  pinMode(13,OUTPUT);
70  pinMode(12,OUTPUT);
71}
72
73bool isChanged = false;
74State*  state = &white;
75State* lastState = state;
76void loop() {
77  // if state changed  last time, call enter
78  if (isChanged)
79    lastState->enter();
80  // call  run repeatedly
81  state = lastState->run();
82  // if state changed, record it;
83  isChanged = (state != lastState);
84  // reset lastState to current
85  lastState  = state;
86}
87
88

class State {
  public:
  virtual ~State(){}
  virtual void  enter(){};
  virtual State* run() = 0;
};

class White: public State  {
  public:
  virtual void enter() override;
  virtual State* run() override;
};

class  Green: public State {
  public:
  virtual void enter() override;
  virtual  State* run() override;
};

static White white;
static Green green;
unsigned  long lastMillis = 0;

void flash(int pin) {
   for(int i = 0; i<20; ++i)  {
    digitalWrite(pin,!digitalRead(pin));
    delay(30);
  } 
}

State*  White::run() {
  if (millis() < lastMillis + 1000) {
    digitalWrite(13,HIGH);
    return this;      
  }
  else {
    lastMillis = millis();
    digitalWrite(13,LOW);
    return &green;  
  }
}

void White::enter() {
  flash(13);
  // update the timer
  lastMillis = millis();
}

State* Green::run()  {
  if (millis() < lastMillis + 2000) {
    digitalWrite(12,HIGH);
    return  this;      
  }
  else {
    lastMillis = millis();
    digitalWrite(12,LOW);
    return &white;  
  }
}

void Green::enter() {
  flash(12);
  // update the timer
  lastMillis = millis();
}

void setup() {
  pinMode(13,OUTPUT);
  pinMode(12,OUTPUT);
}

bool isChanged = false;
State*  state = &white;
State* lastState = state;
void loop() {
  // if state changed  last time, call enter
  if (isChanged)
    lastState->enter();
  // call  run repeatedly
  state = lastState->run();
  // if state changed, record it;
  isChanged = (state != lastState);
  // reset lastState to current
  lastState  = state;
}

Downloadable files

Fritzing diagram of state machine

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