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[on:]

Hi all. I've been having some difficulties with this issue and I can't find a good source to explain me what to do in this situation, so I decided to post it here as it has solved some other problems that I had in the past.

What I'm trying to do here is to make work a DC motor by pressing one of the keys of the computer keyboard (number 1), and turning it off with the same key. To do that, what I do is create a variable, and when I press the key, add 1 to that variable.
Now the variable is equal to 1.
Once I press again the same key on the pc computer, the variable should reset to 0 so the motor stops, but this is where I fail to program.

I know there's various options, like when the variable surpases a certain number reset it back to 0 (what I tried), but It doesn't seem to work.

I use Arduino UNO and Motor shield R3 if that helps. If you need anything else, just ask. Thank you!
Here's the code:

Code:

void setup()
{
  Serial.begin(9600);
 
  pinMode(12, OUTPUT); //Initiates Motor Channel A pin
  pinMode(9, OUTPUT); //Initiates Brake Channel A pin
 
  Serial.println("apreta 1 per anar endavant");
  Serial.println("apreta 2 per anar endarrere");
}
   
void loop()
{
  char a = 0;
    if (Serial.available() > 0)
  {
    a = Serial.read();
    if (a == '1')
       {(a++);
       if(a=2){
       a = 0;}
     }
       
  if (a=1) {     
       digitalWrite(12, LOW); //Establishes forward direction of Channel A
       digitalWrite(9, LOW);   //Disengage the Brake for Channel A
       analogWrite(3, 123);   //Spins the motor on Channel A at half speed
  }
  if (a=0) {
        digitalWrite(9, HIGH);
  }}}

[Reply #1 on:]

Code:

if(a=2){

You got the first one right, but not this comparison

[Reply #2 on:]

Code:

if(a=2){

You got the first one right, but not this comparison

If I had a dollar for every time I made that mistake.........

[Reply #3 on:]

Or the next two. The quickest way to swap between 0 and 1 is to use

a=1-a; So if a == 0 you get 1 and if a == 1 you get 0.

Mark

[Reply #4 on:]

Well I use

Code:

a = (a + 1) & 1;

the variable a will alternate between 0 and 1 every time this is executed
as it will if a is initially 0 or 1 with this code

Code:

a = a^1;

[Reply #5 on:]

Code:

if (a == '1')
{
  (a++);
  if(a=2)
  {
     a = 0;
  }
}

There are a few things wrong with this part aside from the previously mentioned errors with the if statement. '1' and 1 are the not the same as far as the micro controller goes, so it would be best not to mix them like you've done here. If a is '1', then you increment it (you don't need the parenthesis surrounding a++ by the way) to '2'. Now you are comparing it to 2. 2 and '2' are not the same. So say that issue is also fixed, you then run into a logical error of what happens the next time you hit the button after your reset a to '0'?

[Reply #6 on:]

If I had a dollar for every time I made that mistake...

If I had a pound for every time I had to point it out...

[Reply #7 on:]

Nothing, the motor keeps going. Sorry for being such a noob, I'm still learning
How should the code look then?

[Reply #8 on:]

Nothing,

So you changed the code and it won't work. So post what you have changed it to and we can see where you haven't understood what was said.

[Reply #9 on:]

Okay, this is what I changed, but I'm not sure what you meant by caomparing the 2 and '2'

Code:

void loop()
{
  char a = 0;
    if (Serial.available() > 0)
  {
    a = Serial.read();
    if (a == '1')
    {a++;}     
    if (a > 1)
    {a == 0;
    }

[Reply #10 on:]

Okay, this is what I changed, but I'm not sure what you meant by caomparing the 2 and '2'

First off, your coding style makes this very difficult to read. Use the Tools > Auto Format before posting your code to save our sanity.

2 and '2' are not equal. '2' is a character representation of 2 and has the equivalent decimal value of 50. When you fix the later mentioned error, you'll notice that if (a > 1) will always be true because anything you type into the serial monitor will have a binary value greater than 1. http://www.asciitable.com/

Code:

   a = Serial.read();
    if (a == '1')
    {
      a++;
    }      
    if (a > 1)
    {
      a == 0;
    }

You're mixing = and == again. If you want to set the value of the left side variable, use =. If you want to compare the value on the left side to the value on the right side, use ==.

[Reply #11 on:]

Or the next two. The quickest way to swap between 0 and 1 is to use

a=1-a; So if a == 0 you get 1 and if a == 1 you get 0.

Mark

I prefer

Code:

a = !a;