Add Example Code for 4x4 Keypad with Raspberry Pi Pico

CMakeLists.txt

@@ -87,3 +87,4 @@ add_subdirectory(usb)
 add_subdirectory(watchdog)
 add_subdirectory(sha)
 add_subdirectory(freertos)
+add_subdirectory(keypad)

README.md

@@ -107,6 +107,7 @@ App|Description
 [hello_7segment](gpio/hello_7segment) | Use the GPIOs to drive a seven segment LED display.
 [hello_gpio_irq](gpio/hello_gpio_irq) | Register an interrupt handler to run when a GPIO is toggled.
 [dht_sensor](gpio/dht_sensor) | Use GPIO to bitbang the serial protocol for a DHT temperature/humidity sensor.
+[keypad](keypad) | Use GPIO to get key pressed on a 4x4 Keypad.
 
 See also: [blink](blink), blinking an LED attached to a GPIO.
 

keypad/CMakeLists.txt

@@ -0,0 +1,21 @@
+set(TARGET_NAME keypad)
+add_executable(${TARGET_NAME}
+    keypad.c
+    )
+
+# pull in common dependencies
+target_link_libraries(keypad pico_stdlib)
+
+if (PICO_CYW43_SUPPORTED)
+	target_link_libraries(${TARGET_NAME} pico_cyw43_arch_none)
+endif()
+
+# Enable printing via USB serial
+pico_enable_stdio_usb(${TARGET_NAME} 1)
+pico_enable_stdio_uart(${TARGET_NAME} 0)
+
+# create map/bin/hex file etc.
+pico_add_extra_outputs(${TARGET_NAME})
+
+# add url via pico_set_program_url
+example_auto_set_url(${TARGET_NAME})

keypad/keypad.c

@@ -0,0 +1,96 @@
+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include "pico/stdlib.h"
+
+
+#define KEYPAD_NUM_ROWS           4
+#define KEYPAD_NUM_COLUMNS        4
+#define NO_KEY_PRESSED         '\0'  // Just a character that unlikely be
+                                     // present in keyboards, so it can by used
+                                     // to determine if no key is pressed.
+#define READ_MS_DELAY            10  // Delay between lectures to avoid noise
+
+
+const uint8_t keypad_rows_pins[KEYPAD_NUM_ROWS] = {
+    10,
+    11, 
+    12,
+    13,
+};
+
+
+const uint8_t keypad_columns_pins[KEYPAD_NUM_COLUMNS] = {
+    18,  // GP18
+    19,  // GP19
+    20,  // GP20
+    21,  // GP21
+};
+
+
+const char keypad_keys[KEYPAD_NUM_ROWS][KEYPAD_NUM_COLUMNS] = {
+    {'1', '2', '3', 'A'},
+    {'4', '5', '6', 'B'},
+    {'7', '8', '9', 'C'},
+    {'*', '0', '#', 'D'},
+};
+
+
+void pico_keypad_init(void){
+    // Initialize GPIOs
+    //Initialize row pins as GPIO_OUT
+    for (int i=0; i < KEYPAD_NUM_ROWS; i++){
+        uint8_t pin_number = keypad_rows_pins[i];
+        gpio_init(pin_number);
+        gpio_set_dir(pin_number, GPIO_OUT);
+        gpio_put(pin_number, 0);  // Make sure GPIO_OUT is LOW
+    }
+    //Initialize column pins as GPIO_IN
+    for (int i=0; i < KEYPAD_NUM_COLUMNS; i++){
+        uint8_t pin_number = keypad_columns_pins[i];
+        gpio_init(pin_number);
+        gpio_set_dir(pin_number, GPIO_IN);
+    }
+}
+
+
+char get_keypad_value(void){
+    // Iterate over key and rows to identify which key is pressed.
+    // When iterating rows, the GPIO_OUT associted to the row needs to be set
+    // to HIGH, and then iterate the columns to determine the GPIO_IN.
+    for (int row=0; row < KEYPAD_NUM_ROWS; row++){
+        gpio_put(keypad_rows_pins[row], 1);
+        for (int column=0; column < KEYPAD_NUM_COLUMNS; column++){
+            sleep_ms(READ_MS_DELAY);
+            if(gpio_get(keypad_columns_pins[column])){
+                // If the pin is HIGH, this means this is a matching row and
+                // column, so we put the row pin to LOW and return the pressed
+                // key by using the bidimensional array keypad_keys.
+                gpio_put(keypad_rows_pins[row], 0);
+                return keypad_keys[row][column];
+            }
+        }
+        gpio_put(keypad_rows_pins[row], 0);
+    }
+    return NO_KEY_PRESSED;
+}
+
+
+int main() {
+    stdio_init_all();
+    pico_keypad_init();
+    while (true) {
+        char key = get_keypad_value();
+        if (key == NO_KEY_PRESSED){
+            printf("No key pressed\n");
+        }
+        else{
+            printf("Key '%c' pressed\n", key);
+        }
+        sleep_ms(500);
+    }
+}