Light led 1-4 based on two buttons, how...?

Projects Programming
1

Hi again Arduino forum :slight_smile:

I have the following diagram: (I know it isn't all right wired up, but you get the idea of how it should be)

in case the image doesn't show:

As you can see I have two buttons and four LEDS, and if the following conditions are met, i want this to happen:

button1 + button2 are both low = red led high
button1 + button2 are both high = yellow led high
button1 high + button 2 low = green led high
button 1 low + button 2 high = blue led high

I think this is very basic knowledge, but I am still not very good at this. I've looked through the Arduino page, and I think that I have to use: ifstatement or booleans but I don't know how to accomplish it. I hope you guys are willing to help me, that would be great!

Thank you very much :slight_smile:

best regards
JohannesTN

2

There's multiple ways of doing this - short and efficient, or long and understandable :wink:

What you have there is a simple binary value:

 2 | 1 | L
-----------
 L | L | 0
 L | H | 1
 H | L | 2
 H | H | 3

The efficient way would be to use bitshifting and OR to create a numeric value between 0 and 3 and use that to select an LED's pin number from an array.

The long-winded way would be to have 4 if() statements examining both buttons in different combinations and turning on/off LEDs accordingly.

3

I really have no idea of how much space such sketches for both ways of doing it would take up. I hope it's not too much to ask for, but do you have some examples on how it would look like?

I would like it to be as simple as possible as I could use it later on too

4

Both, on the scale of the amount of flash the Arduino has, are incredibly tiny.

The long-winded way would have 4 blocks of:

if ((digitalRead(button1) == LOW) && (digitalRead(button2) == LOW)) {
  digitalWrite(led1, HIGH);
  digitalWrite(led2, LOW);
  digitalWrite(led3, LOW);
  digitalWrite(led4, LOW);
}

but with each one having a different combination of LOWs and HIGHs.

The efficient, but somewhat cryptic way, would have an array of LED pins:

byte leds[4] = {3, 4, 5, 6};

and then a routine to select the LED:

byte lednum = digitalRead(button1) | (digitalRead(button2) << 1);
for (int i = 0; i < 4; i++) {
  digitalWrite(leds[i], i == lednum ? HIGH : LOW);
}

I'll just quickly describe what is going on there. First, the array is just a simple list of pins. Not mystery there.
Then there's the lednum bit. digitalRead returns either a 1 for HIGH or 0 for LOW. In binary these are 0b00000001 and 0b00000000 respecitvely. So, digitalRead(button1) and digitalRead(button2) would both return either 0b00000001 or 0b00000000. We shift the result of the second digitalRead 1 place to the left, though, so instead of 1 or 0 it returns 2 or 0 - in binary 0b00000010 or 0b00000000.

We then OR those together, which basically superimposes one over the other, which will give us 4 possible combinations:

0b00000000 - no buttons pressed
0b00000001 - button 1 pressed
0b00000010 - button 2 pressed
0b00000011 - both buttons pressed

These binary values, in decimal are 0 to 3. So we then have a little loop going from 0 to 3. In that loop we are turning each of the LEDs either on or off. The little bit of code

i == lednum ? HIGH : LOW

is a short-hand embedded if statememt. It's saying "Is i equal to lednum ? If so use the value HIGH : otherwise use the value LOW. So that is turning off all the LEDs that aren't the selected one, and turning on the one that is.

5

Thank you very much! - I'll go with the

if ((digitalRead(button1) == LOW) && (digitalRead(button2) == LOW)) {
  digitalWrite(led1, HIGH);
  digitalWrite(led2, LOW);
  digitalWrite(led3, LOW);
  digitalWrite(led4, LOW);
}

way of doing it :slight_smile:

I wan't to set the state on one of the buttons (true or false) and then read the state in one of the if-statements, and if "false" do this, if "true" do something other. What would be the easiest way of doing that?

  • my own thought was using Boolian or INT, but what would be the best for reading and writing these states?

thank you
best regards JohannesTN

6

I wan't to set the state on one of the buttons (true or false)

You can't set the state of an INPUT pin. You can only read it's state.

7

Sorry for making me unclear.. I meant set the state of a boolean (or an integer) I don't know which is the best?

8

JohannesTN:
Sorry for making me unclear.. I meant set the state of a boolean (or an integer) I don't know which is the best?

No difference between a boolean and a byte (or char), but an int takes twice as much memory, so don't use that.

9

So I guess I have to go with the boolean for that then? :slight_smile:

10

Thank you very much to all of you for helping me out on this one :slight_smile: