MultiKey – One Wire Keypad


This is a simple and easy to make serial keypad. The microcontroller will output the number of the push button pressed.

This project can be used for many different purposes. Probably the most used application would be to interface to any electronic project that requires a keypad. There are several ready made keypads on the market, but those work with matrix connections and require 7 pins for a 12 button pad. For new programmers, matrix keypads can be a bit tricky to programMultiKey One Wire Keypad

My circuit can use from 4 up to 12 push buttons with only one wire connection ( plus ground pin ) making possible to use a small microcontroller like an 8 pin to use this keypad. It’s also built in a setup mode where it’s possible to change the key output rate. This setting is saved in the microcontroller’s memory.

Another use for this is to, for example, connect to the computer and use it to control applications or even games.

Using any RS232 to keyboard software it’s possible to assign the input signals and convert them to keystrokes.


The schematic shown bellow is for the 5 button version.Schematic MultiKey One Wire Keypad

Notice that pins 11,12,13,15,16,17 and 18 are connected to ground. For each button added just remove the ground connection and connect the pin to a push button and add the resistor the same way as the first buttons.

Parts List
R1                   10K ohms resistor
R2                   10K ohms resistor
R3                   10K ohms resistor
R4                   10K ohms resistor
R5                   10K ohms resistor
R6                   10K ohms resistor
R7                   1K ohms resistor
C1                   10uF capacitor
Led1                SMD green or red led
IC1                  16F88 microcontroller from Microchip
S1                    Push button
S2                    Push button
S3                    Push button
S4                    Push button
S5                    Push button

READ  How to interface keypad with PIC16F877


DB9 connector
Hex program for the microcontroller

For 12 push button version:

R8                   10K ohms resistor
R9                   10K ohms resistor
R10                 10K ohms resistor
R11                 10K ohms resistor
R12                 10K ohms resistor
R13                 10K ohms resistor
R14                 10K ohms resistor
S6                    Push button
S7                    Push button
S8                    Push button
S9                    Push button
S10                  Push button
S11                  Push button
S12                  Push button

For more detail: MultiKey – One Wire Keypad

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