New State machine tutorial

IHi,

I have just finished a 3 parts State machine tutorial.

You can find it here.

Let me know what you think about it.

Jacques

Bit of a leap of faith to think that someone new to FSMs will know what an enum is.

What is a state machine?
It is a way to describe what a system is designed to do (output) depending of the state is presently in. As an example, we could use an LED. An LED can only be in one of two states: {ON, OFF}. Each state is mutually exclusive of the other. An LED cannot be simultaneously ON and OFF. There has to be one of the states that have to be declared as the start state. We will also have to remember in which state the machine currently is (the current state).
enum LedStates{ON, OFF}; //The names of all states
LedStates ledState = ON; //The start state (and the current state after that)

I believe that those two lines, along with the the paragraph above them is simple enough to understand.

Someone new to the state machine concept are not necessarily new to programming. This tutorial is not about C++. It is about implanting a state machine in Arduino's environment which happens to be written in C++.

I my mind, using a "switch" construct is not easier than using enum, since I have met on this site, a few persons that only uses "if" constructs, "since you can to everything with that construct" and won't have anything to do with "switch". But I insist in using it because the "switch" construct is , IMHO, ideal to describe a state machine's behaviour.

So, yes, it is a (double) leap of faith.

Jacques

Just finished Part 1. This is great, thank you so much!

I'm using an Arduino Uno and had to ground my push button with a 10k ohm resistor:

I am glad if it helps.

Jacques

Thanks this is just what i was looking for to translate a growing messy project into something reasonable.

I haven't done the exercises leading up to the elevator problem. I just started trying to solve it but it is tougher than I expected. Esp. the part of taking button presses and responding to them as the elevator is moving in the same direction as the request. Sounds like a queue needs to be used but I will go through the tutorials.

In the TwoStateMachines.ino of Part1 tutorial this routine:

void switchMachine() {
byte pinIs = digitalRead(switchPin);
if (switchMode == PULLUP) pinIs = !pinIs;
switch (switchState) {
case IS_OPEN: { if(pinIs == HIGH) switchState = IS_RISING; break; }
case IS_RISING: { switchState = IS_CLOSED; break; }
case IS_CLOSED: { if(pinIs == LOW) switchState = IS_FALLING; break; }
case IS_FALLING: { toggleMachine(); switchState = IS_OPEN; break; }
}

Turns the led off but how does the Led get turned on again ?

Hi,

In fact, it is toggleMachine() that turns the LED on and/or off.

Jacques

Hello Jacques,

Just finished part 2, vending machine & traffic light. I am getting a good handle on state machines. This is

something I have meaning to spend some time learning. Thank you.

I was thinking the led should represent the switch state ie. be on when the switch is closed and off when the switch is open. or visa versa depending on pullups.

The way it is now each time the switch state enters IS_FALLING it is toggled. So for the same state it is on then the next time it enters it is off.

Is that what you intended ?

Hello Jacques
I like Your documentation. I am teaching Electronics/IOT/Network on a 2 year programme, so I would like to hear if You will allow me to use your material. I have allready done a bit of writing and the contents looks much like what you have done. My examples are : the blinkmachine, the vending machine, the elevator, and I also like the "two hand safety machine" illustrated in this video :

You have some excellent videos. I subscribed. Thanks

kajnorman:
Hello Jacques
I like Your documentation. I am teaching Electronics/IOT/Network on a 2 year programme, so I would like to hear if You will allow me to use your material. I have allready done a bit of writing and the contents looks much like what you have done. My examples are : the blinkmachine, the vending machine, the elevator, and I also like the “two hand safety machine” illustrated in this video :
Two-hand Controls - YouTube

Hi kajnorman,

I would love to see your documentation.

Jacques

Good Day Jacques,

I just dove into state machines and while i am limited to programming i have some latter logic from the 80-90s of GE fanuc PLC. I think this type of "thinking" suites my personal way of creating arduino code. I am currently reviewing and trying to understand the part 1 state tutorial but got stuck.

The switch machine (Notice the change in the IS_FALLING state):
void switchMachine() {
byte pinIs = digitalRead(switchPin);
if (switchMode == PULLUP) pinIs = !pinIs;
switch (switchState) {
case IS_OPEN: { if(pinIs == HIGH) switchState = IS_RISING; break; }
case IS_RISING: { switchState = IS_CLOSED; break; }
case IS_CLOSED: { if(pinIs == LOW) switchState = IS_FALLING; break; }
case IS_FALLING: { toggleMachine(); switchState = IS_OPEN; break; }
}
}
START
FALLING
OPEN
RISING
CLOSED
digitalRead(pin) == HIGH
digitalRead(pin) == LOW
TRUE
TRUE
OFF
ON
START
TRUE
TRUE
The setup:
void setup() {
pinMode(ledPin, OUTPUT);
digitalWrite(ledPin, HIGH);
if (switchMode == PULLDOWN) pinMode(switchPin, INPUT);
else pinMode(switchPin, INPUT_PULLUP);
}

I understand that you are giving the code the option to swtich modes dependent on pullup or pulldown but i cannot rap my head around what is occuring at each case. Can you help me understand this part of the logic?

Thanks Art, i appreciate the time to make the tutorial it has open my eyes to much simple and cleaner arduino projects.

Hello Jacques,
first of all your tutorial is great. For the last two weeks I am trying to find a way for a project, I discovered State Machine and I saw that there is a solution there but now, with your tutorial I am sure that I have to walk in this direction.
I would ask you please for a clue. How I should manage the state machine statement if I have more control devices, in my case I have a motor and its behavior depends of one sensor and two buttons. Sensor always start and stop, and the buttons change direction.
Any suggestion will be very welcome and thank you again for the tutorial

edgardo

Hi @echigard,

Then you have a motor with 3 states : running CW, stopped and running CCW
You would probably want to rember the last direction your motor was running before it was stopped. (last running state)

The sensor changes the state of the motor's state as:

  • if the state is (runningCW or running CCW) then {last running state = motor's state; motor's state = stopped}
  • else: the motor's state is the last running state.

button1 state falling -> motor state : running CW
button2 state falling -> motor state : running CCW

Jacques

Hi @cyrut2,

Read this first.

PullUp is just the exact opposite of PullDown. hence:if (switchMode == PULLUP) pinIs = !pinIs;
If the mode is pullup, pinIs = not pinIs

Jacques

Hello,

Thanks for the tutorial sir, its very helpfull.

Btw, i want to ask you on Part 1 files > TwoStateMachines

enum LedStates{ON, OFF};

*what is [enum] function?

Hi,
its was great!
Thanks for sharing :slight_smile:

I have enjoyed reading the example PDF’s. Very helpful!
I think that there is an error in Part 1, p. 9. The case IS_FALLING should start with a call to toggleMachine() as shown in the c++ files. Without this it is not different from the previous example.