It can be observed from the figure that there is a difference between the ideal and actual waveform. The real signal shows some jitter at the moment the button is pressed or released. This jitter typically lasts for about 5 to 10 milliseconds, depending on the mechanical properties of the switch. When we manually press and release a button, it usually takes more than 20 milliseconds for the contact to stabilize. Therefore, when detecting whether a key is pressed, the MCU should implement a debouncing mechanism. There are dedicated hardware circuits and specialized chips available for this purpose, but in most cases, a software-based delay method is used to eliminate the jitter.
Here’s an example of a simple software debounce implementation:
```c
if (0 == K1) // Check if a key is pressed
{
Delay_ms(8); // Introduce a short delay
if (0 == K1) // Confirm the key is still pressed after delay
{
// Perform the action when the key is pressed
}
while (!K1); // Wait until the key is released
}
```
Although software debouncing effectively ensures accurate key detection, one might wonder if it's truly necessary. Jitter occurs during the pressing of the button, but does it also appear when the button is not pressed? In reality, jitter can also be present on the I/O pin even when no button is pressed, which could lead to false readings. That’s why it's important to have a reliable debouncing method in place.
The main issue arises when the system detects a key press, but the jitter hasn’t fully settled. If the microcontroller proceeds to execute a function immediately, and that function runs faster than the jitter duration, it may trigger multiple actions unintentionally. So the goal of debouncing isn't just to detect a press—it's to prevent the same button press from being interpreted as multiple presses.
This is a common challenge in embedded systems, and while there are various techniques to handle it—such as using state machines or tracking the time since the last valid press—it requires careful consideration. The key is to ensure that once a key is pressed, the system recognizes it only once, regardless of the internal noise or instability. It's all about making sure the user experience remains smooth and consistent.
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