make an LED flash once with a switch

Using Arduino Programming Questions
#1

Hi everyone,
Experience has showed me that sometimes its easier just to ask knowledeable people a question if you hit a brick wall.
This is probably the easiest question that will ever be answered, i've only had the arduino leonardo for about 2 days so im pretty fresh with it.
In the interest of learning, i decided to try and make a program that will make an led flash once when a switch is turned HIGH. I have been messing around with the code for a while now, and have managed to make the led turn off when the switch is turned off, but when turned on, the switch will continuely flash. I want the switch to only flash once.

const int led = 13;
int switchOne = 2;
int buttonLog = 0;

void setup() 
{
  pinMode(led, OUTPUT);
  pinMode(switchOne, INPUT);
  Serial.begin(9600);
}

void loop()

{

int buttonState = digitalRead(switchOne);

if (buttonState != buttonLog);
 {
 if (buttonState == HIGH)
   {
      digitalWrite(led, HIGH);
      delay(250);
      digitalWrite(led, LOW);
      delay(250);
      buttonLog = buttonState;
   }
 else 
   {
     digitalWrite(led, LOW);
     delay(30);
     buttonLog = buttonState;
   }
   
   
}



Serial.println(digitalRead(switchOne));
}

Any help you can provide would be greatly appreciated!
Thanks
Paul

#2

It is blinking continuously because your code is in a never ending loop.

#3

Ok, so im assuming that by setting buttonLog = buttonState, it doesnt actually carry the value over on the next iteration of the loop?

I thought the "if buttonState = HIGH" statement would only run if buttonState didnt equal buttonLog.

Any ideas how to get it to actually work?

Paul

#4

How have you wired up the switch?

#5

chromesphere:
Ok, so im assuming that by setting buttonLog = buttonState, it doesnt actually carry the value over on the next iteration of the loop?

It will carry over.

#6

Hi Nick! Thanks for the reply!

Thats what i thought! (value carries over)

I've wired up the switch like this arduino tutorial:

Cheers,
Paul

#7 
if (buttonState != buttonLog);

Lose the semicolon.

#8

Thanks Nick, i missed that mistake.

There is a difference between the circuit diagram i linked to and mine actually, replace the momentary with a toggle switch. Which i thought would still work. Once its on, it should only flash once...Either that or im picking up random noise on the switch pin...

Paul

#9

It will work, once the "if" does something useful.

#10

Nick, you nailed it the first time...the switch...

I had the 10k to ground, and not 10k to +5v...The switch pin was floating!

That was a good learning experience! Dont let input pins float!

Working beautifully now, thanks for your help mate!

Paul

#11

That extra semicolon is a problem.

With that extra semicolon there, the first if() statement will do nothing.

Which means the second inner if() statement will be executed every time through the loop(),
rather than just when the state has changed.

The effect of this, is that the blink operation will occur whenever the switch is "high", not just once, when it goes high for the first time.

The other thing I would change, is the very last line, where you text the button state to the PC ( presumably ).
Don't read the pin again, send the state which you already read at the top of the function.

#12

Good advice michinyon! Thanks for your reply, i have changed the serial monitor to buttonState. That makes perfectly good sense to me, thanks!
Paul

#13

....and if that Serial.println( ) at the end is to be of much use for debugging your switch wiring issues, it would probably be a good
idea to send it to the PC immediately after you read it, rather than after a half a second delay, which would just be confusing.

#14

Thanks michinyon, this is very good info for me as im new to programming! I have changed the location of Serial.println() to directly after where buttonState is checked, thanks!

If theres anything other advice you have please feel free to share it!

Paul

#15