How to Access 5 Buttons Through 1 Arduino Input

Using this method, I'll show you how you can access 5 (or even more) inputs through 1 Arduino pin. These buttons will only be read correctly if only one is pushed at any time though.

As we go through it I'll explain whatever background info you need to know, so as long as you can blink a button, read a switch and read an analog input, you'll be fine. If you can't do any of these, I'll point you in the right direction in the relevant steps as well.

Step 1: Parts List

This is pretty simple:

1 x Arduino (Obviously)
1 x 100K Resistor (Brown Black Yellow)
1 x 1K Resistor (Brown Black Red)
1 x 10K Resistor (Brown Black Orange)
1 x 33K Resistor (Orange Orange Orange)
1 x 68K Resistor (Blue Gray Orange)
4 x Push button switches
Some wires to connect it all

You can use any push buttons you might have lying around, and the resistor values are not critical. More on this later.

Step 2: The Theory - How Buttons Are Normally Read.

Lets first look at how you would normally read a button. In its simplest form, you would connect your button like the circuit shown.

As you can see, you need 1 Input pin and 1 resistor per button, and then you can check the state in your Arduino sketch using this:

buttonState = digitalRead(buttonPin);

I'm not showing all the setup etc... Obviously you need to declare everything and set the pin as an input, etc. You can see the full example on the Arduino website.

This is fine if you are only using 1 or 2 buttons, but what if you need 10? That leaves very little IO pins for anything else you might want to do.

Step 3: The Theory - Multiple Buttons on One Pin

So how do you put multiple buttons on one pin?

You cheat! The secret to this is using an analog input pin, not digital.

You can read about how the analog input works by going through this Arduino tutorial. Essentially, what you need to know though is that when there is 0V on the analog pin, analogRead() returns a value of 0 and if there is 5V, analogRead will return a value of 1023. For any voltage between 0V and 5V, analogRead will return a number proportional to the voltage.

We can't actually change the voltage that is supplied to the pin (Not easily at any rate, and I'm lazy, so easy is important), but if you remember from Ohms law, V=IR. The current (I) is fixed, which means that we just need to add a resistor between the supply voltage and the analog pin to change the voltage.

For those of you that were getting excited about all the maths that's necessary to calculate the voltages, I'm going to have to disappoint you... I'm lazy, so I don't need maths.

Let's get a bit more practical, and I'll show you why we don't care about the maths. We know that the analog pin reads voltages and we know that we can change those voltages by adding a resistor between it and the supply voltage. We also know that we've gone this far because we want to be able to read switches, so we should probably toss some switches in too.

Now, for those that are interested, To design this, you start with what you know. I know how to connect a single switch to a single input. I wanted 5 buttons, so I duplicated it 5 times. I then simplified it by having a single pull down resister connected to all the buttons, and then simply put resistors between the buttons and the supply voltage and tied all the inputs together.

If you connect each button to the supply voltage through a different value resistor, depending on which button is pushed, the value returned by analogRead would be different, and you can use a bunch of if statements to see which button was pressed. The reason we don't need maths is because we just connect it all up, push the buttons and print the returned values to the serial port.

Step 4: At Last We Can Breadboard It.

Using the previous circuit, build it on a breadboard. I'll show you how I did it, but this is very dependent on which buttons you use, so you'll need to use your imagination. I used micro buttons from old computer mice. I also only had 4 buttons (that worked properly at any rate), so I decided to only do 4 buttons, but the code is set up to handle a 5th button.

Once the circuit is built, you can hook up the GND and 5V to the Arduino, and connect the buttons to analog pin 0 (You can change it, just remember to change it in the sketch).

Remember that I said we don't need the maths? I prefer trial and error. For your resistor values, you should pick values that are fairly evenly spread between an arbitrary lower and higher range. I found that values spread between about 1K and 100K work best. For my resistors, I happened to have 1K, 10K, 33K and 68K lying around, so I used those. If I had a fifth button, i would add a 47K resistor between 33K and 68K.

After I built it, I realize now that the 1K resistor is probably not needed. One of your buttons could be connected directly to 5V, so you need one resistor less than buttons (and the one pull down resistor shared by all the buttons). If one of your buttons is connected to 5V it should always return a value of 1023. So if you want to save a couple of cents, leave out the resistor on button 1.

Step 5: Testing It

Download the attached sketch and upload it to your Arduino. Once it is uploaded, open the serial monitor as well. to test it, watch the serial monitor and then hold down button 1. You will see that the values returned will fluctuate for a bit before settling down in a small band of numbers. Write down the biggest and smallest numbers.

Using the 1K resistor with my button, I got values ranging between 988 and 1011.

After repeating this for all the buttons, I got the following values:
Using the 1K resistor with my button, I got values ranging between 988 and 1011.
Using the 10K resistor with my button, I got values ranging between 910 and 929.
Using the 33K resistor with my button, I got values ranging between 767 and 768.
Using the 68K resistor with my button, I got values ranging between 400 and 609.

The first thing that is clear is that the range is bigger for some buttons. I retested several times with consistent results. I actually replaced the second button because I was getting all kinds of results. I was getting numbers ranging from about 510 all the way through 910, so if you get a huge range of numbers, try a different button.

Once you have these values, you can create a sketch that will read the state of a specific button.

Step 6: Coding It.

To code it, I simply took the debounced button example and modified that to set a state based on which button was pressed rather than just a simple HIGH or LOW state.

You can download the attached sketch. It is actually quite simple. The first section sets up all the variables and constants we'll use.

const int buttonPin = 0;     // the number of the pushbuttons pin
const int ledPin =  13;      // the number of the LED pin for testing

The above just sets up the pins used. Then you need to set up each button and the range of values for that button:

 const int BUTTON1 = 1;
...
 const int BUTTON1LOW = 970;
 const int BUTTON1HIGH = 1024;
...

In the setup, we simply set the pin states and start the serial port (which button is pressed will be written to the serial output):

pinMode(buttonPin, INPUT);
   pinMode(ledPin, OUTPUT);
   Serial.begin(9600);

Then we get to the interesting part. The first part of the program loop is where the magic actually happens, but it simply checks which button was read based on the value we got from analogRead():

int reading = analogRead(buttonPin);
   int tmpButtonState = LOW;             // the current reading from the input pin

   if(reading>BUTTON5LOW && reading     //Read switch 5
     tmpButtonState = BUTTON5;
   }else if(reading>BUTTON4LOW && reading     //Read switch 4
     tmpButtonState = BUTTON4;
   }else if
....
   }else{
     //No button is pressed;
     tmpButtonState = LOW;
   }

The next part just debounces the button press. Basically, without this, pressing the button once would appear to the code as multiple presses. Usually this would allow you to use the button as a toggle switch as well, but I'm not doing that.

I'm planning on using the buttons as reset buttons, so I just need to detect when they are pushed and reset a specific variable.

   if (tmpButtonState != lastButtonState) {
     lastDebounceTime = millis();
   }

   if ((millis() - lastDebounceTime) > debounceDelay) {
     buttonState = tmpButtonState;
   }
   lastButtonState = tmpButtonState;

The last part of the program is just a switch statement that executes different code based on which button was pressed. For testing, they all just switch on the built in LED on pin 13.

switch(buttonState){
     case LOW:
     digitalWrite(ledPin, LOW);
     break;
     case BUTTON1:
     digitalWrite(ledPin, HIGH);
     break;
...
}

And that is in essence how easy it is to control multiple buttons. I haven't implemented this into my project yet, so I might do a library for it at some stage if I need to.

Step 7: Improving It

As with all projects, as soon as I'm done, I start thinking about how I can improve it... Here's some thoughts I had:

1. The consistency of the value returned by analogRead is determined by a couple of things:
   - The power supply. The value could vary dramatically if your power is not well regulated. On a regulated supply, maybe a capacitor could smooth the supply some more?
   - The button. I'm not sure why this would be. One thing I noticed is that the values jump around most right as the state changes. My best guess is that it could be caused by the back emf generated when the button is pressed / released. Maybe a diode across the button could clean it up a bit.

Of course, you might be wondering why we need to improve it. After all, it works fine.

If you could get the range of values for each button down to a minimum, you would be able to put a lot more buttons on each analog pin.

For example, if you could get the values for each button within about 60 points, you could easily put 12 buttons on a pin and use each value resistor in the E12 range between 10K and 100K (10k, 12k, 15k, 18k, 22k, 27k, 33k, 39k, 47k, 56k, 68k, 82k and 100k)

You would probably need to use more accurate resistors (or just measure them and use the ones that are close enough to the target value), and you might need to pick your buttons carefully, but the fact that my third button is always in a range of 2 points proves that you should be able to do this.

The second reason is to get it to work with multiple buttons.

Why shouldn't it work with multiple buttons? Once again, I'm not actually going to do the maths (Turns out I'm still lazy), but I am pretty sure that by choosing your resistors carefully, you could figure out which buttons were pressed even if it was more than one.

If you look at the circuit, you can see that by pressing 2 buttons at the same time, you are essentially putting their 2 resistors in parallel. By calling on uncle Ohm again, you have a formula for determining the total resistance for parallel resistors.

For example, if I pressed my second and third buttons, you can see that a 10K resistor in parallel with a 33K resistor gives you a total resistance of  7.6744K (Nope, I googled it - still no maths). This would be easy to pick up in the code. If however I pushed button 1 and 2 though, the resistance for a parallel 1K and 10K resistor would be 900 Ohms, so now we are in the same range as for button 1.

Of course, if you left out the 1K resistor, there would be no way to detect if button 1 was pressed with any other button. Since I don't need to detect multiple button presses, I 'm not going into more details (At this stage at any rate).

Step 8: Final Thoughts

Thanks for reading!  I hope you found this useful. It is my first Instructable, so any feedback - or ratings, wink, wink :) would be appreciated.

Please take the time to vote for me in the Arduino contest if you found this helpful.

This is the first part of a pretty big project. Look out for my next instructables on running lots of LED's on a small amount of pins and running lots of 7 segment displays on a few pins. Once that is done I'm going to have to put it all together.

Hint: I'm planning on running 4 buttons, 20 Led's 4 seven segment displays and an RGB orb on one Arduino. Then I'm going to need to write some software to control it all from my laptop.

If anybody wants me to document all of it, please let me know in the comments.