20pcs TB371 4 Key MCU Keyboard Button Board Compatible UNO MEGA2560 Pro Mini Nano Due for Raspberry Pi Teensy++ Geekcreit for Arduino – products that work with official for Arduino boards

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Description
1. 4-button Common Cathode key module(When pressed output low level).
2. GND K1 K2 K3 K4′ 4 PIN OUT 2.54mm
3. Working voltage:DC 0-48V
4. Size:12.7 x 33mm
5. It can be inserted directly into Arduiuo uno3 mega2560 due, for linking up to your Arduiuo uno3 Mini Nano Mega2560 Breadboard for raspberry pi banana pi etc,or others MCU PLD CPU ( AVR STM32 ARM PIC C51 NRF24LE1 CC2530 MSP430 STM8 FPGA CPLD etc.)
Circuit schematics
Arduiuo uno3/mega2560 Code
//******************************************************//
/*
Arduiuo_4key_uart
This example code is in the public domain.
*/
// Define key pin
int K1 = 13;
int K2 = 12;
int K3 = 11;
int K4 = 10;
// variables will change
int buttonState = 0; // variable for reading the pushbutton
// the setup routine runs once when you press reset
void setup()
// the loop routine runs over and over again forever
void loop()
while(!buttonState);//Wait button release
buttonState = digitalRead(K2);
if(!buttonState)Serial.print(‘k2 n’ );
do
while(!buttonState);//Wait button release
buttonState = digitalRead(K3);
if(!buttonState)Serial.print(‘k3 n’ );
do
while(!buttonState);//Wait button release
buttonState = digitalRead(K4);
if(!buttonState)Serial.print(‘k4 n’ );
do
while(!buttonState);//Wait button release
delay(100);
}
//******************************************************//
Package Included
20 x 4 Key MCU Keyboard Matrix Button Board

Additional information