I needed a simple debounce for a push button wired directly to a digital input on an ATMega. I’m sure there are more advanced techniques but this is working well for me.
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int ButtonPressed() { /* the button is pressed when BUTTON_BIT is clear */ if (bit_is_clear(BUTTON_PIN, BUTTON_BIT)) { delay_ms(DEBOUNCE_TIME); if (bit_is_clear(BUTTON_PIN, BUTTON_BIT)) return 1; } return 0; } |
Where bit_is_clear is defined in AVR-LIBC IO.H as
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#define bit_is_clear ( sfr, bit ) (!(_SFR_BYTE(sfr) & _BV(bit))) |
and when I actually use this to detect a press I incorporate a timer to prevent another detection (double press). The timer is started and a blocking flag cleared upon completion, which will then allow a second detection.
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BOOL buttonWaiting = FALSE; int buttonCounter = 0; void ProcessCurrentState() { // Check buttons here if (!buttonWaiting && ButtonPressed()) { buttonWaiting = TRUE; buttonCounter = 0; timerAttach(TIMER2OVERFLOW_INT, ClearButtonWait); // Process button press // or take appropiate action } } void ClearButtonWait() { buttonCounter++; if(buttonCounter > BUTTON_OVERFLOW_COUNT) { buttonWaiting = FALSE; timerDetach(TIMER2OVERFLOW_INT); } } |