Keypad 3*4

Membrane keypads are made of a thin, flexible membrane material. They do come in may sizes 4×3, 4×4, 4×1 etc. Regardless of their size, they all work in the same way.

One of the great thing about them is that they come with an adhesive backing so you can attach it to nearly anything. You just have to peel the paper backing off.

Let’s take 4×4 keypad as an example. It has total 16 keys. Beneath each key is a special membrane switch.

All these membrane switches are connected to each other with conductive trace underneath the pad forming a matrix of 4×4 grid.

If you had used 16 individual push buttons, you would have required 17 input pins (one for each key and a ground pin) in order to make them work. However, with matrix arrangement, you only need 8 microcontroller pins (4-columns and 4-rows) to scan through the pad.

Pinout of 4×3 & 4×4 Membrane Keypad

The pinout of 4×3 & 4×4 membrane keypad is as follows.

How keypad works & How to scan them?

The working principle is very simple. Pressing a button shorts one of the row lines to one of the column lines, allowing current to flow between them. For example, when key ‘4’ is pressed, column 1 and row 2 are shorted.

A microcontroller can scan these lines for a button-pressed state. To do this, it follows below procedure.

1. Microcontroller sets all the column and row lines to input.
2. Then, it picks a row and sets it HIGH.
3. After that, it checks the column lines one at a time.
4. If the column connection stays LOW, the button on the row has not been pressed.
5. If it goes HIGH, the microcontroller knows which row was set HIGH, and which column was detected HIGH when checked.
6. Finally, it knows which button was pressed that corresponds to detected row & column.

Wiring 4×3 & 4×4 Membrane Keypad with Arduino

Now that we know everything about the membrane keypad, we can begin hooking it up with Arduino.

The connections are pretty straightforward. Start by connecting pin 1 of keypad to digital pin 9 on Arduino. Now keep on connecting the pins leftwards like 2 with 8, 3 with 7 etc.