Sketch that responds to certain commands, how is it done?

Question

Alright I have a half complete Arduino sketch at the moment. Basically the sketch below will blink an LED on a kegboard-mini shield if a string of chars equals *{blink_Flow_A}*

Answer 1

Perhaps something like the 'blink without delay' example in the IDE. You check the time and decide to when and how to change the LED/Digital out.

// Variables will change:
int ledState = LOW;             // ledState used to set the LED
long previousMillis = 0;        // will store last time LED was updated

// the follow variables is a long because the time, measured in miliseconds,
// will quickly become a bigger number than can be stored in an int.
long interval = 1000;           // interval at which to blink (milliseconds)

void setup(){
    // Your stuff here
}


void loop()
{
 // Your stuff here.

 // check to see if it's time to blink the LED; that is, if the 
 // difference between the current time and last time you blinked 
 // the LED is bigger than the interval at which you want to 
 // blink the LED.
 unsigned long currentMillis = millis();

if(currentMillis - previousMillis > interval) {
  // save the last time you blinked the LED 
  previousMillis = currentMillis;   

  // if the LED is off turn it on and vice-versa:
  if (ledState == LOW)
    ledState = HIGH;
  else
    ledState = LOW;

  // set the LED with the ledState of the variable:
  digitalWrite(ledPin, ledState);
}
}

Answer 2

To blink a Led without blocking the program, i suggest you use Timer (and the TimerOne library). I make a quick sample code :

#include "TimerOne.h" //Include the librart, follow the previous link to download and install.

int LED = 4;
const int RELAY_A = A0;  
boolean ledOn;

void setup()
{
    pinMode(LED, OUTPUT)
    Timer1.initialise(500000) // Initialise timer1 with a 1/2 second (500000µs) period
    ledOn = false;
}

void blinkCallback() // Callback function call every 1/2 second when attached to the timer
{
    if(ledOn){
        digitalWrite(LED,LOW);
        ledOn = false;
    }
    else{
        digitalWrite(LED,HIGH);     
        ledOn = true;
    }
}

void open_valve() {

  digitalWrite(RELAY_A, HIGH); // turn RELAY_A on

}

void close_valve() {

  digitalWrite(RELAY_A, LOW); // turn RELAY_A off
}

void serialEvent() {
  while(Serial.available()) {
    char inChar = (char)Serial.read();
    inputString += inChar;
    if (inChar == '\n') {
      stringComplete = true;
    }
  }
}

void loop()
{
    // print the string when newline arrives:
  if (stringComplete) {
    Serial.println(inputString);
    // clear the string:
    inputString = "";
    stringComplete = false;
  }


  if (inputString == "{blink_Flow_A}") {
    Timer1.attachInterupt(blinkCallback); //Start blinking
  }
  if (inputString == "{stop}") {
    Timer1.detachInterrupt(); //Stop blinking
  }
  if (inputString == "{open_valve}") {
    open_valve();
  }
  if (inputString == "{close_valve}") {
    close_valve();
  }
}  

Note :
Consider putting the tag 'c' or 'java' to have syntax highlighting on the code.

Answer 3

Let me offer a suggested sketch with a few changes. Bastyen's idea of using a timer is quite good and makes the code much easier. The approach I would suggest is to have the timer pop forever at a fixed interval (100 milliseconds in my sketch). If the LED should not be blinking it stays off. If the LED should be blinking, it switches from off to on or vice versa each time the timer goes off.

#include "TimerOne.h"
/*
 * kegboard-serial-simple-blink07
 * This code is public domain
 *
 * This sketch sends a receives a multibyte String from the iPhone
 * and performs functions on it.
 *
 * Examples:
 * http://arduino.cc/en/Tutorial/SerialEvent
 * http://arduino.cc/en/Serial/read
 */

 // global variables should be identified with _

 // flow_A LED
 int led = 4;
 // relay_A
 const int RELAY_A = A0;

 // variables from sketch example
 String  inputString = ""; // a string to hold incoming data
 boolean stringComplete = false; // whether the string is complete

 boolean shouldBeBlinking = false;
 boolean ledOn = false;

void setup() {
   Serial.begin(9600); // open serial port, sets data rate to 2400bps
   Serial.println("Power on test");
   inputString.reserve(200);
   pinMode(RELAY_A, OUTPUT);
   pinMode(led, OUTPUT);
   digitalWrite(led, LOW);
   Timer1.initialize(100000);
   Timer1.attachInterrupt(timer1Callback);
}

void loop() {  
  if (!stringComplete)
    return;
  if (inputString == "{blink_Flow_A}") 
    flow_A_blink_start();    
  if (inputString == "{blink_Flow_B}") 
    flow_A_blink_stop();
  inputString = "";
  stringComplete = false;
}

void timer1Callback() {
  /* If we are not in blinking mode, just make sure the LED is off */  
  if (!shouldBeBlinking) {
    digitalWrite(led, LOW);
    ledOn = false;
    return;
  }
  /* Since we are in blinking mode, check the state of the LED. Turn
     it off if it is on and vice versa. */
  ledOn = (ledOn) ? false : true; 
  digitalWrite(led, ledOn);
}  

void flow_A_blink_start() {
  shouldBeBlinking = true;
  open_valve();
}

void flow_A_blink_stop() {
  shouldBeBlinking = false;
  close_valve();  
}

void close_valve() {
  digitalWrite(RELAY_A, LOW); // turn RELAY_A off
}

void open_valve() {
  digitalWrite(RELAY_A, HIGH); // turn RELAY_A on
}


//SerialEvent occurs whenever a new data comes in the
//hardware serial RX.  This routine is run between each
//time loop() runs, so using delay inside loop can delay
//response.  Multiple bytes of data may be available.

void serialEvent() {
  if (stringComplete)
    return;  
  while(Serial.available()) {
    // get the new byte:
    char inChar = (char)Serial.read();
    // add it to the inputString unless it is a newline
    if (inChar != '\n')
      inputString += inChar;
    // if the incoming character is a newline, set a flag
    // so the main loop can do something about it:
    else {
      stringComplete = true;
    }
  }
}

A few notes:

1. The setup function establishes the timer with a 100 millisecond interval and attaches the callback routine. Based on my testing, this only needs to be done once.

2. The main loop just ignores everything unless an input string is complete. If an input string is ready, then the input string is checked for two known values and the appropriate steps are taken. The input string is then discarded.

3. The timer callback routine forces the LED off, if we are not in blinking mode. Otherwise, it just toggles the state of the LED.

4. The flow on and flow off routines set the blinking state as need be and control the valve

5. The serial event routine has two changes. First, input is ignored (and kept in the buffer) if an input string is already complete. This will preserve commands that are being sent to the Arduino while the current command is being processed. Second, the newline character is not added to the input string. This makes checking the input string slightly easier.

Answer 4

A state machine (at it's simplest - it can be lots more complicated) can be just a set of conditional statements (if/else or switch/case) where you do certain behaviors based on the state of a variable, and also change that variable state. So it can be thought of as a way of handling or progressing through a series of conditions.

So you have the state of your LED/valve - it is either blinking (open) or not blinking (closed). In pseudo code here:

boolean LED_state = false;  //init to false/closed

void loop(){

 if (checkForCorrectCommand() == true){ //

   if (LED_State == false){
     open_valve();
     LED_State = true;

   } else {
     close_valve();
     LED_State = false;
   }
 }
}

The blinking LED part should be easy to implement if you get the gist of the code above. The checkForCorrectCommand() bit is a function you write for checking whatever your input is - key, serial, button, etc. It should return a boolean.