No surface is perfectly smooth and inelastic. When two surfaces of pushbutton comes together with any force, there is kinetic energy that makes ringing. In one older article we talked about different types of switches. That basic idea and terminogies required to be known for this article on the phenomenon contact bounce of pushbuttons and counteracting with software library.
Contact bounce is a common problem with switches and relay as contacts are usually made of spring. When the contacts strike together, their momentum and elasticity cause them to bounce apart one or more times before making steady contact resulting a rapidly pulsed electric current instead of a clean transition from zero to full current. This is enough to misinterpret the on‑off pulses as a data stream.
It happens with all switches; sliding, pushbutton, relay, etc. It also happens upon opening the switch, not just on closing. Some are better than others – you can get some awful ones that will bounce for tens of ms, and some good ones that settle within <5ms. To add more on the opening of the switch, it’s due to the irregular surfaces opening in a not perfectly perpendicular manner. When pressure is released, one part of the contact may disengage, but another part may briefly obtain a lower resistance than it had previously, the more irregular the surface and the more of an angular force between the contacts, the more pronounced this effect is likely to be.
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Among the mechanical ways of fixes, bounce can be eliminated by use of mercury-wetted contacts, but has the hazard of mercury. Bounce in SPDT switch contacts signals can be filtered out using a SR flip-flop or Schmitt trigger. Schmitt trigger is an active circuit which converts an analog input signal to a digital output signal. All of these methods are referred to as ‘debouncing’. The term “debounce” has arisen in the software development industry to describe the same end result.
Arduino ESP32 Debounce Library
There are many libraries. This library is quite popular and works nicely with ESP32 :
1 | https://github.com/evert-arias/EasyButton |
An easy example from there :
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | #include <EasyButton.h> // Arduino pin where the button is connected to. #define BUTTON_PIN 26 // Instance of the button. EasyButton button(BUTTON_PIN); // Callback function to be called when the button is pressed. void onPressed() { Serial.println("Button has been pressed!"); } void setup() { // Initialize Serial for debuging purposes. Serial.begin(115200); // Initialize the button. button.begin(); // Add the callback function to be called when the button is pressed. button.onPressed(onPressed); } void loop() { // Continuously read the status of the button. button.read(); } |
