![]() ![]() I have detailed this in the following sub sections. We could use two approach when working with keypad wherein we could use Polling or Interrupt in reading the keypress. ![]() Wiring/Schematic – Keypad to Raspberry Pi Keypad Raspberry Pi R1 GPIO17 R2 GPIO27 R3 GPIO22 R4 GPIO5 C1 GPIO23 C2 GPIO24 C3 GPIO25 C4 GPIO16 Code You will see this in action in the Code section of this post. We can actually switch or invert the Column and Row values by pulling down the column to Low and then sending a Pulse of High in each row.You can disregard the 10K ohm resistor symbol there as I just put it there to avoid shorting our GPIO directly to the ground source and act as a load.Kindly note of these things in the diagram. After looping each row, we reset it back to High.Then we pulse the next Row and check each columns until the end which is R4 in this case.Then it proceeds to the next column until the end. In the case above, if the key “1” was pressed then the column (C1) is like being “ shorted” to the ground causing a read value of “LOW”.We then check each switch in each column to verify if anything has been pulled low. For each row (R1,R2,R3,R4), we send a pulse of LOW like connecting it to GND pin.The columns (C1, C2, C3, C4) are pulled up HIGH by default when no keypress is initiated.As I have mentioned, the membrane switches are arranged in a matrix manner. The image above will show the logic on how we are going to read our keypad keypress. How do we read the Keypad input with our Raspberry pi? You don’t need external power to connect to this component as any microcontroller GPIO could sufficiently drive this component. They are arranged in a matrix like manner to limit the number of pins and uses a membrane switch under the hood. The pinouts above shows a 4×4 keypad membrane with the first 4 pins allotted to its rows and the next 4 to the columns. Membrane keypads comes in different dimensions such as a 4×3 or 4×4 (e.g number of rows X number of columns). Connecting Wires Components Keypad Membrane.Raspberry Pi ( I used Raspberry Pi Zero W).The following components or materials are needed to follow along with this post. ![]()
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