Arduino keypad with 1 Analog pin

Here is my circuit design for Arduino keypad, using only 1 analog pin (instead of 7 serial pins), 6 resistors (can be reduced to 5) and 1 capacitor:

keypad_bb

And now for the full story:

I decided it’s time to add a keypad to my Arduino playground. Usually, those simple keypads come with 7 pins (actually 9, but 2 are not connected to anything on 3×4 keypads) which are connected to Arduino like this:

I wanted to use less pins as possible, so I thought of getting 74hc165, but then I decided it’s time for a new challenge – resistors, and I went with something more like this:

As you can see it this diagram (and others found on the web), one can connect his keypad via 1 analog pin, using all kind of resistors schemes. I decided to build my own with the resistors I already have at home. My 1st setup worked fine, but resistors differentiation wasn’t enough and 2 keys (1 and 5) were showing same value when pressed. So I went along and fixed that, and the working result is the 1st diagram you saw in this post. Final shopping list follows:

Shopping List

Amount Part Type Properties
1 Ceramic Capacitor package 100 mil [THT, multilayer]; capacitance 0.01µF; voltage 5V
3 330 Ω Resistor package THT; tolerance ±5%; bands 4; resistance 330Ω; pin spacing 400 mil
2 2.2k Ω Resistor package THT; tolerance ±5%; bands 4; resistance 2.2kΩ; pin spacing 400 mil
1 4.7k Ω Resistor package THT; tolerance ±5%; bands 4; resistance 4.7kΩ; pin spacing 400 mil

Here is the Arduino code I’m using for my keypad. Check values to meet your own:

/*
 * keypad example.
 */

// analog pin connected to keypad
#define KEYPAD_PIN 0

// milliseconds to wait, to make sure key is pressed
#define TIME_TO_WAIT 50

void setup()
{
	Serial.begin(9600);
}

void loop()
{
	// reading once
	int r1 = analogRead(KEYPAD_PIN) / 10 * 10;
	// waiting
	delay(TIME_TO_WAIT);
	// reading 2nd time - to make sure key is pressed for at least TIME_TO_WAIT milliseconds
	int r2 = analogRead(KEYPAD_PIN) / 10 * 10;
	if (r1 == r2) {
		switch (r1) {
		case 350: Serial.println("0"); break;
		case 270: Serial.println("1"); break;
		case 360: Serial.println("2"); break;
		case 120: Serial.println("3"); break;
		case 210: Serial.println("4"); break;
		case 330: Serial.println("5"); break;
		case 0  : Serial.println("6"); break;
		case 240: Serial.println("7"); break;
		case 340: Serial.println("8"); break;
		case 50 : Serial.println("9"); break;
		case 250: Serial.println("*"); break;
		case 80 : Serial.println("#"); break;
		}
	}
}
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8 thoughts on “Arduino keypad with 1 Analog pin

  1. Hi, i would like to know how i do to put the right values in the cases, in my project just the number 4 worked.
    Thnks already.

    1. If you understand the logic, I recommend start playing with what you already got and see if you can create your own version – all you need is to create different resistance in the wires. If nothing works, then you’ll have to get capacitors like the ones I’ve used. G’luck.

  2. hello, please i’m doing my degree in physics technology and would like to know if this kind of idea would work because i want to use an arduino UNO a keypad for password, SD card Reader and a relay.
    because when i connected them with the SD card reader sharing some pins with the keypad it failed to work.
    thanks and hope to hear from you soon

    1. I can guarantee it worked for me.. 😉
      You can also extend your pins with shift registers and other combos. just keep that in mind.

      good luck with your degree.

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