Button.h

00001 #pragma once
00002 
00003 #include "mbed.h"
00004 
00005 class Button
00006 {
00007 private:
00008     DigitalIn pin;
00009 
00010     volatile bool last_state;
00011     volatile bool pressed;
00012 
00013     volatile bool just_switched_to_pressed;
00014     volatile bool just_got_pressed;
00015 
00016 public:
00017     Button(PinName pin_name):
00018         pin(pin_name) {
00019 
00020         last_state = false;
00021         pressed = false;
00022         
00023         just_switched_to_pressed = false;
00024         just_got_pressed = false;
00025     }
00026     
00027     void poll_pin() {
00028         // We need to poll the pins periodically.
00029         // Normally one would use rise and fall interrupts, so this wouldn't be
00030         // needed. But the buttons we use generate so much chatter that
00031         // sometimes a rising or a falling edge doesn't get registered.
00032         // With all the confusion that accompanies it.
00033         
00034         bool state = !pin;
00035         
00036         // Debounce the button by looking over two periods.
00037         if (last_state && state && !pressed) {
00038             pressed = true;
00039             just_switched_to_pressed = true;
00040         }
00041     
00042         if (!state) {
00043             pressed = false;
00044         }
00045         
00046         last_state = state;
00047     }
00048 
00049     void update() {
00050         if (just_got_pressed) {
00051             just_got_pressed = false;
00052         }
00053         if (just_switched_to_pressed) {
00054             just_got_pressed = true;
00055             just_switched_to_pressed = false;
00056         }
00057     }
00058 
00059     bool is_pressed() {
00060         return pressed;
00061     };
00062     // Only active just after a state change from not pressed to pressed.
00063     // Get's reset after `update()` is called.
00064     bool has_just_been_pressed() {
00065         return just_got_pressed;
00066     };
00067 };