debounce

Button signal processing and debouncing.

Buttons are mapped to handler functions which are called when the button has reliably transitioned to the down (pressed) or up (released) positions. Glitches are filtered out by this debouncing library.

Button inputs may be read directly from GPIO, over PCF8574 I2C bus (via libi2cparallel: https://github.com/kimballa/i2cparallel), or any other method. You should monitor the hardware signals in a polling loop. Each time you receive a new signal input sample, use Button::update(signalValue) to transmit the new sample. The Button class itself does not directly monitor a hardware signal input. The update() method will fire your handler method (of type buttonHandler_t) when a clear state change has been monitored:

void pollButtons() {
  myButton.update(digitalRead(MY_BTN_PIN));
  pcfButton.update(myI2CParallel.read() & 0x01); // update from lsb of I2C 8-bit bus.
}

void loop() {
  pollButtons();
  // Do other stuff
  delay(25); // wait 25 ms.
}

Each button is assigned a unique id (which can e.g. be the same as its index within a vector<Button> array), which is passed to the handler function along with the button state (BTN_OPEN or BTN_PRESSED):

// myBtnHandler is a fn ptr of type buttonHandler_t with this signature:
void myBtnHandler(uint8_t btnId, uint8_t btnState) {
  if (btnState == BTN_PRESSED) {
    // Handle keypress of the particular button.
  }
}

Button wiring diagram

This library assumes that the GPIO input is pulled high (to Vcc) when the switch is open, and sunk low when the switch is closed. You can accomplish this by configuring the GPIO as INPUT_PULLUP and attaching an SPST switch between the GPIO pin and GND, or by configuring the GPIO pin as INPUT, attaching a 10 kOhm resistor to Vcc, and then wiring the SPST to GND, like so:

                         Vcc+
                 10k      ^
(MCU pin) ---+--/\/\/\----|
             |
             \
              \   SW1 (SPST-NO)
               \
             |
             |
           (GND)

You can wire a switch in the reverse as well, but you should then reverse your usage of the BTN_OPEN and BTN_PRESSED constants in code that uses this library.

Compiling

Find the debounce library in the Arduino IDE and add it to your project; make sure to #include <debounce.h>.

Alternatively, I build this with my Arduino makefile:

• Clone the makefile project such that arduino-makefile/ is a sibling of this project directory.
• Create ~/arduino_mk.conf from the template in that directory and customize it to your board and local environment. See other one-time setup instructions in that project's README.md and/or the comment header of arduino.mk.
• Build this library with make install
• For other arduino-makefile-based projects, add this to your project's dependencies with libs := debounce

License

This project is licensed under the BSD 3-Clause license. See LICENSE.txt for complete details.